RESEARCH DIVERIS MANUAL by Lee H. Somers COLLEGE OF ENGINEERING Department of Meteorology and Oceanography Lee H. Somers Jack L. Hough Project Directors Underwater Operations Project Technical Report No. 4 Supported by: UNIVERSITY OF MICHIGAN SEA GRANT PROGRAM NATIONAL SCIENCE FOUNDATION: GRANTS NO. GH-50 and GH-98 NOAA: U. S. DEPARTMENT OF COMMERCE 1971

This report, or any part thereof, may be reproduced with proper credit to the author and the University of Michigan Sea Grant Program,

TABLE OF CONTENTS Page LIST OF FIGURES........................... x LIST OF TABLES... * *.......................... xii CHAPTER I. INTRODUCTION HISTORY OF DIVING...................... 5 DIVER TRAINING........................... * *.. 10 MEDICAL QUALIFICATIONS....................... 11 PHYSICAL FITNESS...................... * 12 UNDER WATER AND PRESSURE: DIVING PHYSICS.............. 13 Pressure............................** 13 Water............. 14 Air..................... 15 Light and Vision Underwater...*......... 19 Propagation of Sound.................... 20 Additional Information..................... 20 DIVING WITHOUT BREATHING APPARATUS................. 21 Donning Face Mask, Swim Fins, Snorkel and Lifejacket.... 22 Swimming with Fins ***....................... 24 Surface Diving Techniques................. 24 Using the Snorkel...................... 25 Entries.......................... 26 CHAPTER II. PHYSIOLOGICAL AND MEDICAL ASPECTS OF DIVING INTRODUCTION.................... * 29 BAROTRAUMA........ *............. a... 30 Dysbaric Cerebral Air (Gas) Embolism and Associated Complications...................... 39 IMPAIRED CONSCIOUSNESS DURING BREATHHOLD DIVING........... 44 iii

Page BREATHING MEDIA CONTAMINATION...................48 Carbon Monoxide Poisoning...,............. *48 Oil-Vapor Contamination of Air Supply............ 51 Carbon Dioxide Excess............ 51 GAS NARCOSIS AND TaCICITY................. 54 Inert Gas Narcosis, O. I*. *. 00 * 00... 0, 0. *54 Oxygen Toxicity........... *... *. * 57 DECOMPRESSION SICKNESS: AIR DIVING............... 58 OTHER COMPLICATIONS......... ~.....~.... ~ ~. 69 Lung Infection.. e **. * *. * ** * ** * 69 Extena Ear Infection................. 69 External Ear Infection...........,..,.... 69 Hyperventilation Syndrome................ 70 ADDITIONAL INFORMATION 0 *.0........ 71 BASIC FIRST AID PROCEDURES................... 71 General......................71 Control of Heavy Bleeding...............,..... 72 Artificial Respiration.,................... 72 Prevention of Shock................... 73 Minor Wound............... 74 Burns;.. * *. * *,,,, 74 Head Injury....................... 75 Convulsions. *....................*. * 75 Injury to Spine or ekNeck...........,,,.. 75 Fractures...,....,........... 76 Heat Exhaustion......................76 Heat Stroke........................ 76 Frostbite. x..................... 77 Snak e Bite......................77 DIVING ACCIDENTS: RECOGNITION AND FIRST AID........... 79 RECOMPRESSION..................... 83 Recompression Chambers........... *.... * * 87 iv

Page CHAPTER III. DIVING PROCEDURES PERSONNEL........................... 91 Diving Supervisor........................ * 91 Diving Teams............ 92 PRELIMINARY DIVE PLANNING................... 93 Survey of Mission or Task...................... 94 Evaluation of Environmental Conditions.......... 94 Selection of Diving Techniques........... 100 Selection of Divers and Assignment of Jobs....... *100 Selection of Equipment................. * 100 Fulfillment of Safety Precautions........., 101 Establish Procedures and Brief Personnel........ **101 Diving Vessel.................... 102 DECOMPRESSON PROCEDURES......................10 Automatic Decompression Meter......... 105 Repetitive Dives................... *.. 112 Interrupted or Omitted Decompression............ * 115 Decompression for Dives at High Altitude........ * 116 Surface Decompression ****..................... 119 Diver's Log Book............ * 120 DIVING IN COLD WATER...................... 122 Wet Suit....................... 123 Dry-Wet Suit...................... 130 Wet Suit Buoyancy...................... 130 Dry Suit: Standard.................. *.. 133 Dry Suit: Variable-Volume............... 35 Dry Suit: Constant Volume................. 137 Diving Suit: Open-Circuit Hot Water System.......... 138 Diving in Cold Water.................. 138 Diving Under Ice................. * 141 OVEREXERTION AND EXHAUSTION................... 143 CHAPTER IV. SELF-CONTAINED DIVING INTRODUCTION................. 145

Page OPEN-CIRCUIT SCUBA...............147 Demand Type SCUBA Regulator......... *..... 147 One Stage Demand Regulator. *...........*... 149 Two Stage Demand Regulator.. *.... ** *.. 149 Exhaust Valves *..... * * *. * * * * * * * * * *. 155 Thermal Reaction................. * 156 Compressed Air Cylinder................... 157 Cylinder Valve Assembly.... *..... *. * * *,, * *. 159 Low Pressure Warning Device (Reserve)....... 159 Auxiliary Breathing Systems.................. * * 165 Harness.. *.. *.... *. 0*. 0 * * * * 165 PREVENTIVE MAINTENANCE: SCUBA.................. 166 Periodic Inspection and Overhaul: Regulators *le......... 169 Prevention of Lung Infection......... * *. * *. * 169 Maintenance of High Pressure Cylinders....... *.... 170 AIR COMPRESSORS AND BREATHING MEDIA *a......... g....... 175 AIR REQUIREMENTS......................... 181 CALCULATION OF AIR VOLUME AT VARIOUS CYLINDER PRESSURES...... 186 ACCESSORY EQUIPMENT..................... 187 Face Mask................. * 187 Swim Fins.......................... 190 Snorkel. l....................... 193 Lifejacket........................ * 194 Knife -.......................... 197 Weight Belt....... * * * * *.197 Watch Bl............... 1200 Depth Indicator. O. *. O............... *. 203 Safety Line and Reel..................... 205 Underwater Lights................... 208 Observation Boards.. *........... 210 Slate...........*... 210 Instrumented Observation Board........... *. 212 Whist0 l.e................. *.. 213 Flare MK-13......................... 213 Rescue Light: ACR-4F..................... 214 Wireless Communications Systems.................... 214 Equipment Bags and Boxes.......... l** *.........e *.. *, 219 Surface Floats................. 219 Net Sample Bags,...................,. 220 vi

Page SCUBA DIVING PROCEDURES................ ** 221 Personnel * * *.. *... * * 221 Minimum Equipment...~..... ~ ~ ~ ~ 221 The Buddy System *..... *..*. *.. * * * * 222 Hand (Visual) Signals........... * 222 Preliminary Preparation............ * 224 The Dive * * * *. *. *...... 224 Post Dive.. *.................. ~ 226 Underwater Navigation.*... *...... *. 226 EMERGENCY PROCEDURES..,............... 230 Exhaustion of Air Supply......... *. * 230 Loss or Flooding of Face Mask. ~............ *...... 230 Purging Water from the Breathing System ~... ~.. ~... 231 Recovery of Lost Mouthpiece 0 ~*...... ~... 232 Entanglement................ *.. ~ ~ 232 The Role of the "Buddy" in Underwater Emergencies *. * * 233 Emergency Ascent. * * ****** ** * * 234 At the Surface. *......... *. 236 Drowning *. * * * * * * * * * *.... 236 LIFESAVING PROCEDURES......... *......... 237 Trouble Situation.............. 238 Panic Situation. *. *....... 238 Approach *. *.............* *.....* 239 Equipment Aids...... *........... 239 Towing...* * * *..........*. *.... 240 Assist.............. * * * 240 Releases................. * * * * * * * * * * 241 Releases.......................... 241 After Rescue......................... 242 Lifesaving and Water Safety Training..... * 242 CHAPTER V. SURFACE-SUPPLIED DIVING SURFACE AIR SUPPLY SYSTEM........ a..............246 Sources of Compressed Air... ****. ****** *....... 248 Air Control System...... *.... 250 FREE-FLOW/DEMAND MASK..................... 252 Dive Preparation Procedures............ 256 Purging a Flooded Mask................... 257 Emergency Ascent................... 257 vii

Page Post Dive Procedures and Preventive Maintenance... 257 LIGHTWEIGHT HELMETS...................... 259 General Aquadyne Lightweight Helmet. *.......... * 261 Dive Preparation Procedures **... 262 Dress-in Procedures....~ ~~~ ~.. *.. ~ ~ * * 262 UMBILICALS...................... *263 Gas Supply Hose...... *...... 264 Communications Wire.... * **........ 265 "Kluge" or "Pneumo' Hose................ 266 Hot Water Supply Hose..** le** *.............. 266 Assembly of Umbilical... **................ *.. 267 Use and Storage of Umbilical................ 268 268 HARDWIRE COMMUNICATIOS SYSTEM l............... * 268 ACCESSORY EQUIPMENT................. ** *..273 Coveralls... @-0 * *************...** *273 Weight Belt 2,, * * * *,,,.*. 273 Shoes and Leg Weights.............,.... 273 Harness., 0........................ e 274 Emergency Gas Supply System............* 274 Head Protectors. ~*~** 0 * ~g 0 0 le t~~ 0 ~ ~ ~ * ~~~275 Knife.0.............*.*.... 275 DIVING PROCEDURES....................... 275 Preliminary Preparations................ 276 Calculating Air Requirements........*.... 276 Dressing Procedures...........279 The Dive o.............................. 280 Tending the Diver........ * * 281 Fouling................. 284 Blowup.............,,285 Ascent.. 0 **** *****************286 Post Dive,... *,, ~.. ~ ~~ 287 REFERENCES......... ~ ~ ~ ~ ~ ~ ~ ~.....289 APPENDICES I. DIVING DUTY MEDICAL EXAMINATION FORM..........299 viii

Page II. BASIC AND ADVANCED RESEARCH DIVER TRAINING COURSES... 305 III. TABLES FROM U.S. NAVY DIVING MANUAL (1970)........ 317 Table 1-9 Decompression procedures............. 319 1-10 U.S. Navy standard air decompression table.. 320 1-11 No-decompression limits and repetitive group designation table for no-decompression air dives.................. 324 1-12 Surface interval credit table for air decompression dives............ 325 1-13 Repetitive dive timetable for air dives..... 326 1-14 U.S. Navy standard air decompression table for exceptional exposures............ 327 1-26 Surface decompression table using oxygen.... 331 1-27 Surface decompression table using air...... 333 1-29 Treatment of an unconscious diver.......* 336 1-30 Treatment of decompression sickness and air embolism................ 337 1-31 Minimal recompression, oxygen breathing method for treatment of decompression sickness and air embolism................. 338 1-32 Notes on recompression.............. 339 1-34 Precautions in use of recompression chamber... 343 IV. EMERGENCY PROCEDURES FOR DIVING ACCIDENTS IN MICHIGAN AREA 345 V. CONVERSION FACTORS..................... 351 VI. DIVING EQUIPMENT CHECKLIST............... 357 ix

LIST OF FIGURES Figure Page 1-1 Research diver equipped with surface-supplied free-flow/ demand mask and variable-volume suit installing a current meter for study of water circulation in Grand Traverse Bay................ 2 1-2 The relationship between depth, pressure and volume.... 17 2-1 Anatomy of the ear and nasal accessory sinuses..... 32 2-2 Rupture of lung tissue and possible avenues of gas dissemination....... *...... 41 2-3 Recompression chambers.................. 88 3-1 Automatic decompression meter (computer)..,.. 106 3-2 Repetitive dive worksheet............... 113 3-3 Repetitive dive worksheet with example of computation for a repetitive dive................... 114 3-4 Protective suits for divers............... 124 3-5 Buoyancy of foamed neoprene wet type suit relative to compression at various depths........... 132 3-6 Opne-circuit hot water diving system........ 139 4-1 Diver equipped with open-circuit self-contained underwater breathing apparatus........... 146 4-2 Cross section of common double hose regulators..... 48 4-3 Cross section of single hose demand regulators.... 150 4-4 Cross section of piston type first stage...... 151 4-5 Spring-loaded low pressure air warning mechanism..... 160 4-6 Open-circuit SCUBA components............. 163 4-7 Open-circuit SCUBA components.... *.... 164 4-8 Portable high pressure air compressor for filling SCUBA cylinders ~ ~ ~ ~ ~ ~ ~ ~. ~.........176 x

Figure Page 4-9 Accessory equipment for skin and SCUBA diving....* * 188 4-10 Accessory equipment for skin and SCUBA diving...... 191 4-11 Lifejackets and buoyancy compensators...... *... 195 4-12 Diver's knife and tool.... o........ * 198 4-13 Weight belts for skin and SCUBA divers......... 199 4-14 Accessory equipment for skin and SCUBA divers: decompression meter, depth indicator, and underwater watch.. 201 4-15 Accessory equipment for skin and SCUBA divers...... 202 4-16 Safety line and reel..........,... 206 4-17 Underwater hand lights.......... 207 4-18 Accessory equipment for skin and SCUBA divers.... 211 4-19 Wireless underwater communications systems..... 217 4-20 Hand signals for SCUBA divers as recommended by the Underwater Society of America............. 223 5-1 Surface-supplied divers wearing free-flow/demand mask and hot water suit (left) and lightweight helmet and cold water wet suit (right).............. 244 5-2 Air supply systems................ 247 5-3 Air control panel.*. * * * * * *.. * 251 5-4 Free-flow/demand mask.......... 253 5-5 Surface-supplied diving components........... 258 5-6 Surface-supplied diving helmet and umbilical.* * *.... 260 5-7 Hardwire communications system and stop watches for timing dives.......... *.......... 269 5-8 Surface-supplied diving components * * * * * * * *. * * * 272 xi

LIST OF TABLES Table Page 2-1 Frequency of symptoms occurring in decompression sickness *..................... 67 2-2 Frequency of combination of symptoms.......... 67 2-3 Interval between surfacing and onset of initial symptoms. ~ ~ ~ ~. ~ *... ~ ~ ~ ~ ~ 67 3-1 Theoretical depth at altitude for given actual diving depth in fresh water............... 117 3-2 Theoretical depth of decompression stop at altitude... 117 4-1 Theoretical duration of air supply in a standard single open-circuit SCUBA cylinder at various depths for five levels of exertion. "No-decompression" limits are included for convenient comparison....... 182 xii

CHAPTER I INTRODUCTION During the last two decades, diving with self-contained underwater breathing apparatus (SCUBA) has become an important method of scientific investigation. The underwater scientist (Figure 1-1) does not have to depend on conventional surface sampling techniques and "educated guesses" for shallow water studies. He can work directly in the underwater environment to observe, sample, photograph, and make complete field studies in much the same manner as his dry-land colleagues. Working underwater, the scientist may record evidence which might be completely missued using conventional surface sampling and remote recording techniques. The underwater scientist does, however, have many disadvantages compared to his dry-land counterpart. He is limited in depth and duration by physiological and physical factors. Weather conditions and underwater visibility are also important factors affecting underwater work. For the non-diver, Tanner (1959, p. 566) explains his impression of working underwater: "It is like doing ordinary dry-land fieldwork, on a cold January night, without a moon, during a dust storm, by the light of a flashlight of variable power. The vehicle in the exploration would have to be a helicopter, restricted to flying largely out of sight of the land surface. It lowers the geologist (by rope ladder, perhaps) to the ground, at each sampling location. He can only see those materials within the range of his flashlight beam. This might be as much as 60 or 70 feet, or as little as six or seven inches. In the latter instance he would have to work with his face to the ground; fortunately that is a convenient 1

3 position for a diver.t Certainly all research dives are not as difficult as one might conclude from the above explanation. However, physiologically man possesses few natural adaptations for existing in a liquid medium and for the conservation of body heat, Despite the disadvantages and limitations, the research diver quickly learns to adapt himself to the underwater environment. Recent developments in diving suits and life support equipment have increased the diver's underwater capabilities. Mixed gases, saturation diving, and the use of underwater habitats offer solutions to the depth and duration limitations for those fortunate enough to have the proper equipment. The application of modern surface-supplied diving techniques and equipment has been shown to increase the efficiency of research diving operations at the University of Michigan by a factor of four for most underwater scientific projects when compared to conventional open-circuit SCUBA. Underwater work is difficult, time-consuming, and expensive. Generally, diving investigations are used to supplement, verify, or complete data acquired by other methods of study. For example, research divers may be required to identify bottom features encountered during bathymetric, sub-bottom seismic, or sidescanning sonar surveys. A geological investigation of an underwater construction site made totally by divers would probably be considered inadequate for determining details of the area unless other methods of investigation were also used. On the other hand, basic field research on fish behavior might be completely undertaken using diving techniques. Regardless of the project or the role that the diver plays in a study, it is the general consensus of those scientistjwho participate and benefit from

4 underwater studies that research diving techniques are of considerable importance and, in some instances, invaluable to the study of our lakes and oceans. The basic principles of air diving with SCUBA and surface-supplied equipment are discussed in this technical report. Emphasis is primarily on diving in the Great Lakes. Forthcoming publications will cover ocean diving, biological and geological research techniques, underwater photography, light salvage, underwater research procedures, mixed gases and other specialized diving techniques.

5 HISTORY OF DIVING The accumulation of sea shell artifacts at prehistoric living sites possibly indicates that food was taken from the sea by divers long before references in recorded history. The earliest records are of Cretan sponge divers (3000 B.C.) and recovery of oyster pearls in China (2200 B.C.). Military divers were used during the Trojan Wars (1194 B.C.). Reference to military diving activities is made by Herodotus (5th century B.C.) and in Homer's Iliad (pre-700 B.C.). Alexander the Great deployed frogmen against the defenSes of Tyre (333 B.C.) and was supposed to have descended in a diving bell himself. Records indicate paid salvors and diving regulatory laws in the 3rd century, B.C. Aristotle (4th century B.C.) writes of the diving bell. Prior to this time all diving was probably done by breathholding to depths not exceeding much over 100 ft. The diving bell was the dominant diving apparatus for the next 22 centuries, until about 1800. In the late 1600's the bell was refined and in 1691 a sizable and sophisticated bell was patented by Edmond Halley. This bell was ventilated by lowering barrels of fresh air, and dives were made to 60 ft for 1.5 hr; divers made breathholding excursions from the bell. By 1770 the elementary hand operated air compressor provided the next major advancement in diving. This enabled LeHavre (1774) to develop a moderately successful helmet-hose diving apparatus. Surface-supplied compressed air diving developed as the prevalent diving technique by 1800 and was to maintain a virtually unchallenged position until the mid-1950ts. A boosting factor to diving in the 1800's was the salvage of HMS Royal George. For this operation Augustus Siebe developed and perfected the

6 diving helmet and "closed dress" in 1837. The Siebe helmet and "closed dress" have been the primary diving apparatus for the working diver from 1837 to the 1960's. The present U.S. Navy Mark V Deep Sea Diving Outfit is only a modification of the 1837 Siebe outfit. Progress in diving, from 1837 to present, was dependent on two factors: improvement of the air compressor and the study of hyperbaric physiology. The compressor improved rapidly during and following the industrial revolution; however, the study of diving physiology was slow to progress. Paul Bert, in 1878, started to untangle the complexities of nitrogen absorption and elimination or the "bends." The first recompression chamber for treatment of bends was installed to support the cassion workers during construction of the first Hudson River Tunnel in New York (1893). In 1907, based much on Paul Bert's work, John S. Haldane published the first decompression tables for divers. The development of self-contained underwater breathing apparatus (SCUBA) did not begin with Cousteau. Borelli, in 1680, developed a SCUBA based on the theory that the diver's hot, exhaled breath could be rejuvenated by cooling and condensing. Needless to say, this unit was not successful; however, this represents a movement toward "freeing" the diver. Borelli also experimented with the "fin" and bouyancy compensating devices. In 1835 Condert published the design of a free-flow SCUBA which consisted of a helmet, flexible dress and a compressed air reservoir fitted around the diver's waist. This was to have significant influence on the design of future diving apparatus. Rouquayrol (1865) developed a "demand" regulator system. Although this unit was basically surface-supplied by a hose, it also had significant influence on the development of SCUBA. In 1878, Fleuss

7 and Davis designed the closed-circuit oxygen SCUBA which utilized a chemical carbon dioxide absorbent. This was the beginning of a long list of closed-circuit oxygen SCUBA with the eventual development of the semiclosed circuit mixed-gas SCUBA by Lambertsen. Yves le Prieur, in 1924, introduced a manually valved self-contained compressed air breathing apparatus. In 1942 Cousteau and Gagnan developed the demand type SCUBA which is the basic compressed air SCUBA used throughout the world today. Sport diving and spearfishing were being practiced in many European countries during the 1920's and were introduced into the United States in the late 1920's. It wasn't until the early 1950's, with the ready availability of compressed air SCUBA, that the popularity of sport diving started to accelerate to its present popular status. Factors contributing to the growth of sport diving include availability, improvement and simplification of diving apparatus; an increased number of training programs; publication of the exploits of naval diving groups such as those of the Underwater Demolition Teams (UDT) and SEAL Teams; an increased layman's interest in ecology, oceanography and related disciplines; and the general increase in need for leisure time or recreational activities. According to Dugan (1956) the first recorded scientific dives were made by Professor H. Milne-Edward (Sicily) in 1844. Over the years many dives of a scientific nature have probably been made by breathholding and with helmet or bell type diving apparatus. Engineering survey dives were also made in the 1800's. Geologists, during the late 1940's, used deep sea and shallow water surface-supplied diving apparatus for limited underwater observations. It wasn't, however, until 1949 that modern scientific diving

8 had its true beginning in the United States. Conrad Limbaugh introduced self-contained scientific diving at Scripps Institution of Oceanography. Since 1949 Scripps and the Navy Undersea Warfare Center (formally, U.S. Navy Electronics Laboratory) at LaJolla, California have housed the largest and most active group of diving scientists in the world. Currently, nearly all research groups studying the fresh water and marine environment utilize divers to various degrees. The beginning of the U.S. Navy diving program is not actually known; however, official records indicate that George Stillson began developing the Navyts program in about 1912. The F-4 Submarine disaster of 1915 that somewhat paralleled the more recent Thresher incident in terms of government and public reaction apparently stimulated interest in diving. The first U.S. Navy diving school was opened in 1915 and the Navy's famous Experimental Diving Unit originated in 1927. Navy helium-oxygen diving experiments began in the 1930's and were used extensively in the salvage of the submarine Squalus (1939), During World War II the great potential of military diving became evident. The famous U.S.N. Underwater Demolition Team had its beginning in 1943. The U.S. Navy's diving program is ranked "first" in the world by most authorities. Experimentation in living in a hyperbaric environment began in the early 1960's. The concept of saturation diving and living in underwater habitats was introduced by Dr. G. Bond, a U.S. Navy submarine medical officer. In 1964 the first U.S. underwater living experiment, SEA LAB I, was conducted off Bermuda at a depth of 192 ft. SEA LAB II and other projects followed as part of a continuous Man-in-the Sea Program.

9 Concurrently, Cousteau (France) conducted the CONSHELF series of underwater living and work programs with a successful 28 day- 330 ft submergence. More recently, the TEKTITE program has provided an opportunity for scientists to utilize saturation diving techniques. Man is now pushing to greater depths and staying for longer durations, Working dives have been made to depths exceeding 500 ft and experimental chamber dives have tested man's ability to function in excess of 1700 ft. New self-contained closed-circuit mixed-gas breathing apparatus is capable of sustaining a diver at depths beyond 1000 ft for up to 6 hours. The increasing demand for the working diver in the oil industry and offshore construction has opened a new era of diving. During the last decade the diving industry has made tremendous advancements via "commercial" rather that "military" influences. The immediate future holds many advancements in diving apparatus, techniques, and physiology which will influence the expansion of research, commercial, sport and military diving activities. For further information on the history of diving consult Dugan (1956, 1965), Searle (1966), Davis (1962), Fane and Moore (1956), Cousteau (1953), and U.S. Navy (1970).

10 DIVER TRAIN ING All research divers must successfully complete a diver training program prior to participating in underwater research activities, Generally, initial training is acquired in a basic skin and SCUBA diving course conducted under the auspices of an instructor certified by the National Association of Underwater Instructors, Young Mens Christian Association, Professional Association of Diving Instructors or equivalent organizations. The basic course includes training in basic skin and SCUBA diving skills, emergency procedures for open-circuit SCUBA, equipment use and maintenance, an introduction to the underwater environment, and basic diving theory. Most of these courses, through adequate for sport diving enthusiasts, are inadequate for training research personnel or "working" divers. Generally, the basic sport diving course must be supplemented with more emphasis on equipment, procedures, advanced techniques, and supervised open water diving. A few universities and governmental agencies conduct specialized research diver training programs. Advanced training in research techniques and surface-supplied diving is recommended. Basic and advanced research diver course outlines are included in Appendix II. Diver training qualification tests given in Somers (1971) are also included in Appendix II of this manual.

11 MEDICAL QUALIFICATIONS Applicants for diver training and all active divers are required to pass an annual physical examination. The medical requirements for diving are summarized as follows by Lanphier (1957): "One of the primary considerations is that diving involves heavy exertion. Even if a man does not intend to engage in spearfishing or other activities which are obviously demanding, he will sooner or later find himself in situations which tax his strength aid endurance, Even the best breathing apparatus increases the work of breathing, and this adds to the problem of exertion underwater. Lifting and carrying the heavy equipment on dry land is also hard work. The necessity for freedom from cardiovascular and respiratory disease is evident. Individuals who are sound but sedentary should be encouraged to improve their exercise tolerance gradually by other means before taking up diving. The influence of exertion on conditions such as diabetes should be considered carefully. It is not reasonable to apply a fixed age limit to sport divers, but men over 40 deserve special scrutiny. An absolute physical requirement for diving is the ability of the middle ear and sinuses to equalize pressure changes. The Navy applies a standard "pressure test" in a recompression chamber to assess this ability since usual methods of examination have insufficient predictive value unless obvious pathology is present. However, even going to the bottom of a swimming pool will generally tell a man whether his Eustachian tubes and sinus ostia will transmit air readily or not. In the case of middle ear equalization, part of the problem is learning the technique of "popping your ears." Presence of otitus or sinusitis is a definite contraindication for diving, even in a man who can normally equalize pressure. A history of disorders of this sort suggests that diving is unwise; but as in the case of frequent colds or allergic rhinitis, prohibition of diving is not invariably justified. Here, much depends on the individual's common sense and ability to forego diving if he has trouble. A perforated tympanic membrane should rule out diving because of the near-certainty of water entering the middle ear. The use of ear plugs presents no solution to any of these problems and is, in fact, strongly contraindicated. Any organic neurological disorder, or a history of epileptic episodes or losses of consciousness from any cause, makes diving highly inadvisable. A more difficult problem for the physician to evaluate and handle adroitly arises in the psychiatric area. The motivation and general attitude of some aspirants make safe diving unlikely from the outset; and those individuals who tend to panic in emergencies may well find occasion for doing so in diving. Recklessness or emotional instability in a diver is a serious liability for his

12 companions as well as for himself, Claustrophobic tendencies are clearly incompatible with diving." Further information regarding the diver's physical examination and qualifications is available in U.S. Navy (1970), Miles (1966) and Dueker (1970). A medical examination form is included in Appendix I. PHYSICAL FITNESS Flexibility, strength, and endurance are necessary for underwater swimming and diving. Good physical condition may prove to be the most important aspect of diving safety. The physically fit individual is able to withstand fatigue for longer periods and is better equipped to tolerate physical stress. Diving, particularly for novices, places severe stress on the entire body, especially the cardiovascular and respiratory systems. Anxiety, lack of skill (inefficiency), non-conditioned heart, hyperventilation, overweight, equipment restrictions, breathing resistance, and cold water are among the factors which cause increased heart rate and the onset of fatigue. As a general rule, average participation in diving activities is not sufficient in itself to develop and maintain a high level of physical fitness. Diving must be supplemented by a regular exercise program. This is especially true forpersons who do not dive on a regular basis. Persons who participate only on a seasonal basis should exercise regularly when not diving, or at least initiate a conditioning program 6 to 8 weeks prior to the diving season. Jogging is an excellent conditioner for divers. Consult Cooper (1970), President's Council on Physical Fitness (1965) or other publications recommended by your physician or instructor for exercise programs.

13 UNDER WATER AND PRESSURE: DIVING PHYSICS Nearly all new experiences, both pleasant and unpleasant, encountered in diving stem directly from the great differences in physical properties and characteristics which exist between the gaseous and liquid media. Some apparent differences include: 1. Water has an increased density and viscosity. 2. Optical and acoustical properties differ. 3. Water has a higher degree of heat conductivity than air. 4. Gases breathed under increased pressure have varient physiological effects. In order to understand the basic principles of diving, the diver must be familiar with certain aspects of physics which deal with pressure and density relative to liquids and gases. Pressure Pressure is the amount of force applied per unit area. In diving, pressure units commonly used are millimeters of mercury (mm Hg), pounds per square inch (lbs/in2 or psi), and atmospheres (atm). One atmosphere is the amount of pressure or force exerted by the earth's atmosphere at sea level and is equal to 14.7 lbs/in' or 760 mm Hg. Terms frequently used when referring to pressure include gauge pressure, absolute pressure, and ambient pressure. Gauge pressure referes to the difference between the pressure being measured and the surrounding pressure. Most gauges are calibrated to read "zero" at normal atmospheric pressure. Absolute pressure is gauge pressure plus atmospheric pressure (14.7 lbs/in2) or total pressure being exerted. Ambient pressure refers to absolute pressure surrounding or encompassing an object,

14 Water Water, in its purest form, is a colorless, odorless, tasteless, and transparent liquid. Taste and color are due to the presence of substances dissolved or suspended in the water. Pure water weighs 62.4 lbs/St t (STP) while sea water weighs approximately 64 lbs/ I depending on the amount of total dissolved solids. For all practical purposes, within the normal range of diving, water can be considered as incompressible and density variations due to temperature changes insignificant. Consequently, the pressure exerted by water will be directly proportional to the depth. For every 33 ft in sea water (34 ft in fresh) the diver descends, there is a pressure increase of 1 atm or 14.7 lbs/in2; pressure increases.445 lbs/in2 per foot of descent. An object placed in water will sink or float depending on the density and volume of the object. Archimede's Princie states that any object wholly or partially immersed in a liquid is buoyed up by a force equal to the weight of the liquid displaced. For example, a fully equipped diver weighing 192 lbs may displace 3.16 ft3 or 202 lbs of sea water. Consequently, he is considered to have 10 lbs of positive buoyancy. If the same diver was outfitted with a 20 lb weight belt, he would be 10 lbs negatively buoyant. Neutral buoyancy or a state of hydrostatic balance is achieved when the weight of the water displaced equals the weight of the object when totally submerged. Sea water increases an individual's buoyancy by approximately 1/30th his body weight over what it is in fresh water. Water conducts heat more rapidly than any other liquid. In water below 700 F. body heat is lost faster than it can be replenished.

15 Air This manual deals primarily with diving using air as a breathing medium. Air is composed of nitrogen (78.1%), oxygen (20.9%), carbon dioxide (0.033%) and various inert and rare or trace gases. It may also contain water vapor and suspended and dissolved solids. Nitrogen, the main component of air, is colorless, odorless, tasteless, and inert (in its free state). Under increased pressures it is selectively soluble in various body tissues and acts as an intoxicant or anesthetic on the central nervous system. xygen, the only gas capable of supporting life, is colorless, odorless, and tasteless in its free state. Under high pressures oxygen has toxic effects on the body. Carbon dioxide, a natural waste product of metabolism, is colorless, and tasteless in normal concentration. It is the princip' respiratory process stimulate. High concentrations are toxic to the human and will produce unconsciousness with subsequent death (higher concentrations). Other gases important to the diver are carbon monoxide and helium. Carbon monoxide is highly poisonous, and all possible measures must be taken to avoid contamination of the diver's air supply. It is the product of incomplete combustion of fossil fuels. Helium is colorless, odorless, tasteless, inert, lightweight, non-toxic, and non-explosive. During the last two decades helium has become the major inert gas substituted for nitrogen in deep diving breathing media. Narcotic effects of helium are relatively insufficient (to 800 ft) and breathing resistance due to lower density is reduced. However, helium does conduct heat about 5 times as rapidly as air.

16 In comparison to a liquid or solid, air, as any gas, has a very low density, is compressible, and its behavior is governed by simpler laws of physics. Air weighs only about 0.081 lbs/ft3. The temperature, pressure and volume relationships are more conveniently expressed in terms of an imaginary substance balled an "ideal gas." If the temperature of a fixed mass of gas is kept constant, the relationship between the volume and pressure will vary in such a way that the product of the pressure and volume will remain essentially constant. Mathematically, pV - constant where the symbol p is pressure (absolute) and V is volume. The temperature and mass are constant. In other words, at a constant temperature and mass the volume of a gas is inversely proportional to the pressure exerted on that gas, p < V-, thus when the pressure is doubled, the volume is reduced to 1/2 of the original volume. This relationship is Boyles Law and is graphically illustrated in Figure 1-2. Two different states of a gas at the same temperature may be denoted by subscripts 1 and 2 and Boyle's Law may also be written, PlV1 - P2V2. Charles's Law states that if the pressure of a fixed mass of gas is kept constant, the volume of the gas will vary directly with the absolute temperature. By combining Boyle's and Charles's Laws the pressure, temperature, and volume relationships of an ideal gas can be expressed as, - "- constant. T

17 0 VOL a I OR 100% 100% Dia SEA LEVEL I ATM ABS OR 14.7 PSIA 0N VOL * /2 OR 50% 73% Dia 2 AT MS OR 29.4 PSIA 33 FT -- o VOL I/3 OR 33 R % 69.3% 63.3% 66FT | S 3ATMS OR 44.1 PSIA Da VOL - /4 OR 25% 99FT 4 ATMS OR 58.8 PSIA 0 VOL- VY OR 20% 332FT I 5ATMS OR 73.5 PSIA.-... VOL-'lo OR l10O/ 297 FT 10 ATMS OR 147.0 PSIA FIGURE 1-2. The relationship between depth, pressure, and volume.

18 Two states of the gas may be denoted with subscripts. P1Vl - P2V2 T1 T2 In diving one generally works with a mixture of gases rather than a single pure gas. The concept of partial pressure is explained by Dalton's Law which states that the total pressure exerted by a mixture of gases is the sum of the pressures that would be exerted by each gas if it were present and occuppied the total volume. Partial pressure computations are useful for understanding diving physiology and necessary for mixed-gas diving. The partial pressure (pX) of a given gas in a mixture may be calculated by the formula, pX - PtX%, where Pt is the total pressure of the gas mixture (absolute) and X% is the percent of gas X by volume in the mixture. Hence, the partial pressure of oxygen in the atmosphere at sea level is, p02 - 14.7 (.21) or 3.1 lbs/in2. Gas is soluble in a liquid. Gas absorption is governed by Henry's Law which states that the amount of a gas that will be dissolved in a liquid at a given temperature is almost directly proportional to the partial pressure of that gas. The term "amount" refers to number of molecules or mass of the gas. When gas is in solution, its actual volume is negligible and there is no volumetric increase in the amount of liquid. Henry's Law simply expresses the effect of partial pressure on the amount of gas that will dissolve in a liquid. Solubility is also dependent on the type of liquid and temperature. For example, the solubility of nitrogen in oil or fat is about five times its solubility in water at

19 the same pressure. The lower the temperature, the higher the solubility. This explains why a warm bottle of carbonated beverage forms bubbles more actively than does a cold one. Gas diffusion refers to the intermingling of gas molecules. In diving, Henry's and Dalton's Laws are considered when dealing with the diffusion of gas in the human body under pressure. The difference between the partial pressure (or tension) of a gas inside of a liquid (or container) and its outside partial pressure will cause the gas to diffuse in or out of the liquid and control the rate of diffusion. This pressure differential is frequently called the gradient. If a gas free liquid is exposed to a gas, the inward gradient is high and the rate at which gas molecules will migrate into the liquid is high. As the gas tension in the liquid increases, the rate of diffusion decreases and eventually an equilibirum is reached where the gas tensions in the liquid and outside the liquid are equal. The liquid is then considered saturated for a given pressure and gas. The subjects of gas solubility and diffusion are important in the study of decompression sickness and nitrogen narcosis. Light and Vision Underwater The penetration of light is an important factor for divers, particularly when taking underwater ambient light photographs. The luminous energy of sunlight diminishes underwater with increased depth. Basically, in clear water the luminous energy (or ambient light) is reduced to 1/4 surface value at 16 ft, 1/8 surface value at 50 ft, and 1/13 surface value at 130 ft. Solar light probably does not penetrate beyond 1650 ft even under the most ideal conditions of transparency. Many factors control

20 light penetration* When a light ray enters the water, it is reflected, refracted, transformed to heat, absorbed and diffused by the water and materials in the water. The colors of the solar spectrum are absorbed with practically all red colors gone at a depth of 30 ft and only blues and greens visible at 100 ft. Underwater refraction is never greater than 48.5~, the critical angle of refraction. This corresponds to a grazing incident ray in air (at sunset and sunrise). A ray of light directed upward (underwater) at an angle greater than 48.5~ is totally reflected back into the water instead of being partially refracted into the air. This makes the surface appear as a mirror when the diver is in the proper position. Due to the refraction of light rays passing from water to air, objects viewed underwater through a face plate appear 1/4 closer and 1/4 larger. Light travels at 3/4 the speed in water as it does in air, Propagation of Sound The average speed of sound underwater is about 4,900 ft/sec as compared to a speed of less than 1,100 ft/sec in air. Various types of sonic and ultra-sonic equipment are used for depth sounding, location of submerged objects and wireless communications. Large sonar transponders (on military vessels) and underwater explosions are a serious hazard to divers. Additional Information The above has been only a brief review of the basic physical principles necessary for the study of diving theory, For additional information on diving physics refer to US. Navy (1970). Diving instructor candidates must

21 thoroughly understand the various aspects of diving physics as given in the U.S. Navy (1970). DIVING WITHOUT BREATHING APPARATUS Emphasis on diving with SCUBA should not obscure the importance of diving without respiratory equipment. Frequently the research diver will be required to recover specimens, photograph or make observations in shallow water without the aid of SCUBA. A physically fit, veteran diver will generally be capable of breathhold dives to depths of 40 ft or more. Conditioned spearfishermen or persons who make breathhold dives frequently may dive to depths exceeding 90 ft. The current record breathhold dive is to a depth in excess of 240 ft. Breathhold diving or skin diving is a necessary part of training for diving with SCUBA. Proper use of mask, fins, and snorkel, surface swimming, surface dives, underwater swimming, pressure equalization, and rescue techniques are all necessary skills required for mastering SCUBA diving. Furthermore, skin diving on shallow coral reefs can provide endless hours of pleasure. Breathhold diving is not without hazard. The diver must be an excellent swimmer and in reasonably good physical condition. An enthusiastic skin diver will frequently expose himself to more adverse conditions and greater physical strain than the casual swimmer. He will venture farther from shore under more hazardous environmental conditions for longer durations. The skin diver is subject to barotrauma of the ears and sinuses as any other diver. Air embolism and related complications are only a problem if the diver breathes air while underwater from SCUBA, a habitat, an air

22 pocket under a rock ledge, or the like, Breathholding itself can cause serious problems and the diver must thoroughly understand the potential hazards of prolonged breathholding under pressure. Physiological aspects of breathholding and submergence are discussed in Chapter II. The basic equipment for breathhold diving includes a mask, a snorkel, a pair of swim fins and a lifejacket. These items are discussed in the section on "Accessory Equipment" in Chapter IV, The diver may use a weight belt to achieve a state of near neutral buoyancy on the surface. Actually the diver should have slight positive buoyancy at the surface. Never wear sufficient weight to cause the diver to sink. Information on skin diver training and skills is given by Empleton (1968). Donnin Face Mask Swim Fins Snorkel and Life acket The face mask should fit the diver's face comfortably and hold its position on the face when the diver evacuates air from inside the mask by inhaling through his nose. If during inhalation, air leaks into the mask or the mask fails to hold to the diver's face, it either does not fit or there is some material such as hair, wet suit hood or mask strap preventing the entire edge of the mask from sealing. Prior to diving the face plate should be coated with an anti-fog compound such as saliva, dishwashing soap, or a commercial preparation. Fogging underwater may be removed by admitting a small quantity of water into the mask, rinsing the face plate and purging the water from the mask. Some divers even retain a small volume of water in their masks for this purpose throughout the dive. The mask strap should be periodically inspected for signs of wear and adjusted so that the mask fits comfortably and snug, but not tight, A tight fitting mask may cause discomfort or a headache, and a loose fitting

23 mask may easily be lost. Prior to donning the mask, the diver should wet both the mask and his face to improve the sealing action. Then the mask is grasped by the face plate retainer, positioned on the face, and secured by placing the strap behind the head. Generally the diver uses both hands for this procedure; however, donning the mask completely with only one hand must also be mastered. Test the seal by inhaling through the nose. Always hold the mask to the face when jumping into the water. The selection of swim fins is based on fit, physical condition and mission requirements. Prior to each dive the fins, particularly the adjustable heel straps, are checked for signs of wear or damage. Adjustable straps and buckles must be secure. To facilitate donning, wet both the fin and foot. Grasp the fin by the side rib at the instep and slide onto foot. Then position the heel strap. Don't don fins by pulling on the heel strap or back of the foot pocket on shoe-type fins; this frequently damages the strap or foot pocket. Shoe-type fins may be more easily donned by turning the back of the foot pocket under the fin (inside out), sliding the fin onto the foot, and flipping the back of the pocket into place. For breathhold diving, the snorkel is generally secured to the mask strap by a small rubber retainer. Prior to use the snorkel should be inspected and cleared of foreign material (insects, sand, etc.), if necessary. To don, insert the mouthpiece into the mouth with the flange between the teeth. Adjust the retainer so that the snorkel is comfortable in your mouth, and the tube points slightly to the rear when the face in in the water in swimming position (looking down and slightly forward). The life jacket should be inspected prior to each dive to insure that

24 the gas cylinder is full, the activator is functioning properly, and that there are no tears or leaks, Don the lifejacket and secure with the straps. The straps should be snug and comfortable, but not tight enough to induce restriction when breathing deeply. Swimming with Fins The kick used almost exclusively by skin and SCUBA divers is a modification of the standard flutter type kick used by swimmers. Since swim fins greatly increase the efficiency of the flutter kick, the diver's version of this kick is much slower and the feet travel through a wider arc. The kick action is from the hip with pointed toes and slight flexure in the knees. When used on the surface, the fins should not break the surface of the water throughout the entire motion. The body should stay relatively straight. If the hips tend to buoy up the legs resulting in the feet breaking the water surface continuously or if there exists a necessity of bending at the hips to keep the feet under, the diver should swim with his body straight but tilted downward at a slight angle to the water surface, A weight belt may be required to overcome hip buoyancy. Underwater the diver should relax and may increase the arc of the kick. The legs may have to be spread slightly to avoid fins touching. Do not stiffen the knees and avoid excessive body roll. Maintain a slow, steady rhythm. Avoid excessive use of hands when swimming on the surface or underwater; trail them in a relaxed fashion at your side. Surface Diving Techniques The breathhold diver or skin diver swims on the surface and breathes through a snorkel until he is ready to submerge. At this time he ventilates

25 his lungs a few times, takes a full breath of air and executes a head or feet first surface dive. The head first (jack-knife) surface dive is performed by bending the body at the waist, thrusting the trunk well down, and bringing the legs out of the water into a vertical upward position. The weight of the legs above water should be sufficient to thrust the body downward; no other movement should be necessary until the fins are fully submerged. Then continue downward motion by kicking. As soon as the diver submerges he should start equalizing pressure in his ears as explained in Chapter II. Some divers prefer the feet first surface dive. The diver prepares for the dive as above; however, to execute the dive he drops his feet and assumes an upright vertical position with his head above the water. He then kicks strongly with his fins and at the same time brings his hands sharply to his sides. This action raises part of the diver's upper body above water. Now the toes are pointed, the diver relaxes, and drops vertically underwater. When submerged, turn on face or side and kick downward. Using the Snorkel The snorkel is positioned on the mask strap so that it is comfortable and not submerged during surface swimming. A normal breathing rhythm and volume exchange should be maintained. Avoid repeated hyperventilation or "skip" breathing (holding breath for long periods between inhalations). When the diver submerges the snorkel will partially fill with water; however, the entrapped air and pressure equalization will keep water from entering the diver's mouth in most cases.

26 During ascent, look up toward the surface and rotate the body 360~ to check for overhead obstructions. Keep the face pointed upward so that the top of the snorkel is slanted downward. Gently expel air into the snorkel while coming up. Because of the downward slant, the air will remain trapped in the tube and displace all the water. Start exhalation approximately 2 ft from the surface. When you reach the surface, simply roll into a swimming position and resume breathing. Since you exhaled underwater, cautious inhalation will bring fresh air upon reaching the surface. Entries Whenever possible skin and SCUBA divers should enter the water from a diving ladder or by jumping feet first from a low platform. A basic factor to remember when performing all jump or roll type entries is to hold the face mask to your face to prevent loss. Some divers prefer to hold the bottom of a SCUBA cylinder against the back to minimize the possibility of hitting the head with the regulator. This is generally not necessary if the SCUBA is designed and fitted properly. The following entries should be mastered by skin divers (without SCUBA); they will later be used for SCUBA diving. An excellent method of entering the water from a low platform is to simply sit on the platform with the feet in the water, hold the mask to the face, tuck chin, and roll forward in a somersault fashion. The shoulder or SCUBA cylinder will hit the water first. The step-in or stride entry is used from a dock, platform, or boat dock. Hold the mask firmly against the face and look straight ahead. In a smooth

27 motion, bend slightly forward at the waist and step off with a wide stride; do not look down. As the body strikes the water and starts to submerge, make a sharp scissor type kick and sweep free arm downward. This entry resembles the standard feet first lifesaver's entry. When working from small boats, it is generally desirable to sit on the gunnel with the back to the water and feet in the boat. To enter, simply press the mask to the face, tuck chin, and fall backwards. The SCUBA cylinder will strike the water first.

CHAPTER II PHYSIOLOGICAL AND MEDICAL ASPECTS OF DIVING INTRODUCTION The human body is designed to function in a gaseous atmosphere of approximately 20% oxygen and 807. nitrogen at a pressure of about 15 lbs/in2. Significantly decreasing or increasing the pressure exerted on the body or changing the partial pressure of the breathing medium can induce radical physiological changes. Low level gas contaminants such as carbon monoxide and carbon dioxide have serious implications at the higher pressures encountered while diving and may cause unconsciousness with subsequent drowning. Prolonged breathholding while subjecting the body to significant pressure changes, as during skin diving, can result in unconsciousness without significant signs to indicate the onset of complications. Subsequently, the diver may drown. The human's normal atmosphere, oxygen and nitrogen, produces both toxic and narcotic effects when breathed at high pressure. In addition, the inert gas is absorbed during pressurization and must be eliminated from the body at a prescribed rate to avoid complications, One must also consider the direct physical effects of pressure. The human body has been exposed to pressure equivalents exceeding 1700 ft during experimental chamber dives without apparent residual damage. Exactly how much pressure the human body can endure is still unknown. The body contains several rigid or semirigid gas-containing spaces (middle ear, paranasal sinuses, lungs and airways, and gastrointestinal tract) which, because of restricted openings, are subject to mechanical damage when pressure differen29

30 tials exist between the internal space and the external environment. The effects of high pressure on the human body and breathing media must be fully understood by the diver, If physiological reactions to high pressure are not recognized by the diver and properly controlled, injury or death may occur. For discussion purposes, the physiological and medical aspects of diving will be classified into the following categories: 1, Barotrauma 2, Impairment of consciousness during breathhold diving 3. Breathing media contamination 4, Gas narcosis and toxicity 5. Decompression BAROTRAUMA Living tissue can be exposed to relatively high pressures without damage or changes attributable to the pressure itself, Behnke (1944) remarks on man's tolerance to rapid and extreme alterations in barometric pressure "1without physiologic effects" relative to diving to a maximum of 500 feet, Recently, Brauer (1968) suggests a physiological depth barrier, using the gas mixture tested so far, as a result of a series of experimental chamber dives reaching a aximum of 1,189 feet. More recently, chamber dives have been successfully completed to over 1700 feet. However, central nervous system (CNS) Pnvolvement appears as the limiting factor and not necessarily mechanical tissue damage. At pressures above 1000 atmospheres, well beyond oridnary diving pressures, Fenn (1967 ) indicates coagulation of proteins, inactivation of enzymes, disintegration of red blood cells and blood coagulation0 At the present state of hyperbaric research there

31 is no definite answer to the question, "How much pressure can the human body endure?" The human body contains several rigid or semirigid air-containing spaces which, because of restricted openings, are subject to mechanical damage when unequalized pressure differences exist. The air-containing structures of the body are the middle-ear spaces, the paranasal sinuses, the lungs and airways, and the gastrointestinal tract. With the exception of these air-containing spaces the entire body consists of fluids and solids which for all practical purposes within the limits of diving are incompressible. The middle ear and sinuses are lined with membranes containing blood vessels. As the external pressure being exerted on the body is changed, this pressure is transmitted via its blood vessels to the membrane lining of these air spaces. Unless the pressure in these spaces is equal to the ambient pressure, a pressure differential exists causing barotrauma or pressure injury. The middle ear (Figure 2-1) is connected with the throat by the Eustachian tube which functions to drain and ventilate the middle ear. When Eustachian tube blockage (mucus or congestion, tissue overgrowth, local inflamation and swelling) prevents pressure equalization in the middle ear, painful aerotitis media or "middle ear squeeze" with possible tympanic perforation (rupture of the eardrum) may occur. The diver will experience discomfort and pain in the first few feet of descent. Further descent will result in increasing pain, with stretching of the eardrum and dilation and eventual rupture-of the blood vessels in both the tympanic membrane and the lining of the middle ear. Actual rupture of the eardrum may occur with a pressure differential of as little as 5 lbs/in2, at about

32 EXTERNAL INTERNAL EAR EAR CANAL EAR SPACE S/ INUSS- OPENING OF EUSTACHIAN EUSTACHIAN TUBE TUBE LEADING TO THE THROAT I ANATOMY OF THE EAR ETNENOIDA - "P S AX"ILLA1Y11,r tlJ I^il SINU~ IS D FIGURE 2-1. Anatomy of the ear (Courtesy of U.S. Divers Co.) and nasal accessory sinuses (Reproduced from U.S. Navy 1970). SPNNOI ~ nasal accessory sinuses (Replroduced from U.S. Navy 1970).

33 10 feet deep (Lanphier 1957, p. 122), Generally a slight blockage of the Eustachian tube by mucus or swelling can be overcome by maneuvers for "clearing the ears" such as swallowing, yawning, or exhaling against closed mouth and nostrils (Valsalva maneuver). Variations in ability to ventilate the Eustachian tube may in some instances be an anatomical factor of the individual's tube size (Taylor 1959). The diver is cautioned to use the Valsalva maneuver with discretion. Increased intrathoracic pressure produced during the maneuver will result in hypotension in the normal individual. This is primarily due to impairment of venous return to the heart and the potential of pulmonary stretch reflexes inducing certain cardiac arrhythmias. Duvoisin and associates (1962) suggest that the combination of these two influences is probably responsible for the syncope (fainting) which has been demonstrated frequently upon doing the Valsalva maneuver. Davison (1962) indicates that the Valsalva maneuver could result in a catastrophic outcome and further suggests that these factors led Armstrong (1961) to state that any prolonged Valsalva maneuver should be avoided during airplane flights (particularly by pilots). In fact, the cardiovascular response to this maneuver has been implicated in aircraft accidents (Lamb and associates, 1958). The implications relative to SCUBA diving are evident. A prolonged and intensive Valsalva maneuver could possibly result in unconsciousness and subsequent drowning. Hyperplastic lympoid tissue in or about the Eustachian tube may inhibit pressure equalization. Radium treatments to reduce the size of this tissue obstruction or enlarge the pharyngeal orifice of the Eustachian tube have been proposed by some physicians (Haines and Harris 1946;

34 Duffner 1958). Haines and Harris report 90% success with radium treatment methods, Taylor (1959) emphasi;es that radium should not be used without a full understaadi of ita potential dangers. When a diver surfaces after experiencing ear squeeze, he may spit blood which drains to the throat through the Eustachian tube. If drainage and/or discomfort persist, a physician should examine the injury and prescribe treatment, Local treatment of ear squeeze is ordinarily contraindicated, The diver should not re-enter the water until healing is complete, Antibiotics may be indicated to combat infection. Schilling and Everley (1942) and Haines and Harris (1946) indicate that the most frequent and most serious complication of aerotitis media is temporary or permanent impairment of auditory acuity based on the evaluation of thousands of submarine personnel subjected to pressure tests. These findings are summarized by Taylor (1959), Haines and Harris contend that although capable of equalizing pressure in the middle ear, many subjects develop complications by letting the increasing pressure "get ahead" of them one or more times and then would equalize only after some damage had been done, It should be emphasized that a diver should not wait for pain as a signal to equalize pressure in his ears. The equalization maneuvers should start immediately when the diver begins his descent or at least at the first "sensation of pressure change" on the ear, Pain is an indication that barotrauma already is present, When the eardrum ruptures, a sudden relief in pain may be experienced, If the diver's ears are exposed directly to the water, the entry of cold water into the middle ear may cause a violent upset of the sense of balance, The diver may experience extreme vertigo (dizziness) because of thermal effect

35 on the inner ear and semicircular canal and may also become nauseated and vomit. This reaction usually subsides in a minute or so as soon as the water in the ear warms to body temperature. Blood is generally present in the external auditory canal. Except in the presence of infection, healing takes place in a few days to a few weeks depending on the severity of the injury. During this time diving is prohibited and water should not be allowed to enter the external auditory canal, Antibiotics may be necessary, especially if the diver has been in polluted water. Blockage of the sinus ostia results in aerosinusitis, or sinus squeeze, with painful edema and hemorrhage in the sinus cavities. These cavities are located within the skull bones and are lined with mucus membrane continuous with that of the nasal cavity (Figure 2-1), The mechanism is much the same as that described for aerotitis media. With normal gas pressure within the sinus cavity and an excess pressure applied to the membrane lining via the blood, a vacuum effect is created within the cavity. Unless the pressure is equalized, severe pain and damage to the membrane will occur, A diver who has experienced sinus squeeze will often surface with blood in his mask or will notice a small amount of blood and mucus discharge from his nose following the dive. Sinus squeeze can be avoided by refraining from diving when there is nasal congestion as a result of an allergy, cold, or infection. If discomfort develops in the sinus areas during descent, it may be relieved by the Valsalva maneuver; if not relieved, terminate the dive. Following aerosinusitis infection may develop, as indicated by persistant pain and discharge; medical attention and systemic antibiotics are generally necessary,

36 In som instances the use of a long-acting nasal vasoconstrictor (decongestant) prior to diving may be beneficial (U.S. Navy 1963), Hubner and Slhnert (1963) surveyed a large group of divers instructors, and physicians and found that, as the occasion demanded, 56 percent of the divers had used an oral-nasal decongestant, 75,1 percent had used nasal drops or a spray, and 19,5 percent had used an inhaler. An oral decongestant containing phenylpropanolamine HCl, phenaramine maleate, and pyrilamine maleate was most frequently prescribed, and phenylephrine hydrochloride (neosynephrine) was the most commonly mentioned local decongestant. The vasoconstrictive action of this oral decongestant used as a pre-dive prophylactic agent tends to keep the nasal passages, sinuses and Eustachian tubes clear by shrinkage of the nasopharyngeal mucus membrane, Sme discretion must be exercised in the use of decongestants due to possible individual associative reactions. [~n ascent, the ears and sinuses generally vent the expanding gas without much difficulty. However, occasionally blockage may result from mucus or swelling of tissue injured during descent and result in a reverse earr o sinus sueez In the event of symptomatic developments during ascent, slowly descend to facilitate pressure equalization. The after effects of vasoconstrictors used prior to descent may produce tissue swelling in individual cases, and consequent Eustachian tube or sinus ostia restriction. As a diver descends while holding his breath, the flexible portion of the thorax is compressed and the diaphragm elevated. Consequently the air within the lungs and airways is compressed and the system assumes a more

37 "expiratory" position. Until recently it was indicated in the literature that no difficulty is experienced until the position of maximal expiration is reached; then the volume of air equals the residual volume of the lungs plus the volume of the airways. Beyond this point, further descent while breathholding may result in pulmonary congestion, edema, and hemorrhage in the lungs. The diver may experience a sensation of chest compression, breathing difficulties and possible chest pain. This condition is generally called thoracic squeeze. Rahn (1965), however, suggested that during breathhold dives to greater depths blood is forced into the thorax, replacing air and resulting in a significant decrease in residual volume. Schaefer and associates (1968) made measurements of thoracic blood volume displacements during breathhold dives to depths of 130 ft using the impedance plethysmograph. These measurements confirmed that a significant shift in blood volume into the thorax does take place. Furthermore Robert Croft, a U.S. Navy diver, and Jacques Mayol successfully dived to a depth of 240 ft and 231 ft respectively. These are considerably greater depths than could be predicted on the basis of total lung volume/ residual volume ratios. Based on total lung volume/ residual volume ratios, Mayol's depth threshold would have been 90 ft. Theoretically, a blood shift of 980 ml into the thorax was necessary with a corresponding replacement of air and reduction of his residual volume to approximately one-half that measured. Underwater photographs taken during the 240 ft dive show pronounced caving in of the thorax, compression of the abdoment and skinfolds flapping around the chest. The details of these experiments are summarized by Schaefer and associates (1968).

38 Gas-containing structures attached to the surface of the body are potential sources of locaX "squeeze." Failure to equalize pressure during descent uider the diver s face mask can result in damage to the skin and particularly to the eyes. The mechanism of damage is similar to that of middle ear or sinus squeeze, The most easily damaged tissues are those covering the eyeball and lining of the eyelids and the spaces around the eyeball. Excessive pressure differential may cause conjunctival and even retrobulbar hemorrhage with tension on the optic nerve and possible loss of vision. Subcutaneous hemorrhage and swelling of the facial tissue under the mask may be evident. The condition is avoided by the diver simply admitting air into his mask through his nose. The classical form of'divers sueeze" may be encountered in helmetclosed suit (i.e., conventional deep-sea rig) diving when the pressure within the helmet suddenly drops below that of ambient. The condition results either from the loss of pressure within the supply line with subsequent venting to a lower pressure or by sudden increase in the depth of the diver, as in a fall, without compensation by increasing gas supply pressure. The helmet itself constitutes the nonequalized rigid space, and the external pressure of the water acts to force the diverts body into it. For the same reasons, a similar condition can occur when the diver is using a surfacesupplied full face mask, The resulting injury has already been discussed above, It is because of these possibilities that a non-return valve in the supply line at the helmet or mask is so essential in all surface-supplied diving equipment. Proper diving procedures and tending are necessary to prevent falls, etc.

39 A closed watertight diving dress (suit) can also produce squeeze unless gas is admitted into the dress by some means during descent. The squeeze is usually noted as a pinching sensation in the area of suit folds and ridges; welts and ecchymoses may be produced in the skin. External ear squeeze can also result. The mechanism and consequences are essentially like those of middle ear squeeze. Damage to the tympanic membrane may be equally severe, though the force is applied in the opposite direction. Hemorrhagic blebs may form close to the eardrum and blood drains from the external auditory canal. The common foamed neoprene wet type suit generally eliminates these hazards; however, there -is potential hazard with thin tight fitting hoods. Ear plugs are contraindicated in diving not only because of the potentiality of external ear squeeze, but also because the unequalized pressure may force the ear plugs deep into the external auditory canal. Gas pockets in the gastrointestinal tract do not produce difficulty during descent since the walls are nonrigid and equalization is accomplished by compression of the gas. However, expanding gas in the gastrointestinal tract during ascent may produce difficulties. Expansion of gas swallowed during the dive or formed as a result of eating gas producing foods just prior to the dive can cause severe pain and is capable of producing manifestations including fainting, respiratory embarrassment and reflex circulatory collapse. Dysbaric Cerebral Air (Gas) Embolism and Associated Complications Dysbaric cerebral air embolism is an acute, serious occupational hazard associated with diving, submarine escape training, and explosive

40 decompression in aerospace work. The condition is not to be confused with decompression sickness>, which in the average case tends to be less acute. The connotation dysbarica Is proposed by Waite and associates (1967s, p. 205) to differentiate this form of air embolism incurred in a diminishing ambient pressure from the accidental variety occurring at one atmosphere in a hospital setting. Since air is probably the most common breathing medium for divers, the term "air" embolism is most frequently used; however, with the advent of extensive mixed-gas diving, "gas" embolism is also correct terminology. According to the U.S. Navy (1970) air embolism is probably second only to drowning as a cause of SCUBA diving fatalities. Waite and associates (1967) suggest that a e'fairl" number of the estimated 60 SCUBA diving deaths reported by the National Research Council for 1965 were due to air embolism. Smith (1967) suspects air embolism as a prime cause of SCUBA fatalities, The incidence of air embolism in relation to submarine escape training is summarized by Waite and associates and Miles (1962). In a diminishing pressure situation, as a diver ascending from depth, the air in the lungs is expanded because of the decreasing external pressures, If the normal exhalation route of the expanding gas is interrupted either voluntarily, as in breathholding, or involuntarily, from local respiratory tract obstruction, the intrapulmonary pressure progressively distends alveoli and rupture of alveoli ensues. Localized partial or complete bronchial obstructions include "ball-valving" bronchial lesions, mucus, broncho-spasms and so forth (Linaweaver, 1963). Walter (Smith 1967, pe 19) suggests that bronchial mucus and irritants, particularly tobacco, are prime offenders, From the point of rupture (Figure 2-2), the gas may dissect along bronchi and enter the mediastinum to create a mediastinal ehpvsema, A diver with a icdiastinal emphysema may experience manifesta

41 0' \ d l CEREBRAL AIR EMBOLISM.: t \. ~'Sr' ik'^> AIR PASSES VIA CAROTID ARTERIES TO BRAIN;r\ <t < c D^^^Vr 1 ir A S T I N A;?:=:^^ ^ -- - MEDIASTINAL EMPHYSEMA | I f^t^ P ^0 - ^ - AIR PASSES ALONG BRONCHI TO MEDIASTINUM ALVEOLI RUPTURED BLOOD VESSEL:, \.~ ~ AIR ENTERS PLEURAL CAVITY (PNEUMOTHORAX) FIGURE 2-2. Rupture of lung tissue and possible avenues of gas dissemination (Courtesy of U.S. Divers Co.).

42 tions including substernal pain, breathing difficulties, and even collapse due to direct pressure on the heart and great vessels. Cyanosis may be evident. From the mediastinum the gas frequently migrates into the subcutaneous tissues (subcutaneous emphysema), most often in the neck and supraclavicular region, This will add manifestations evident by enlargement of the neck, voice changes, breathing difficulties, and crepitation (cracking sensation) upon palpation of the neck and supraclavicular region. If there is a weakened area on the surface of the lung, such as alveoli emphysematous blebs, rupture may take place into the pleural space with the development of a pneumothorax. Pneumothorax is an infrequent but serious complication of diving. This may result in partial or total collapse of the lung on the side involved. As the diver continues ascent, the air entrapped in the pleural space expands at the expense of the collapsing lung and may eventually cause displacement of the heart, This is a serious complication because both breathing and circulation are impaired. Manifestations include chest pressure and pain, breathing difficulties and cyanosis. The most serious consequence of alveolar rupture is the release of gas into the pulmonary circulation, and via the pulmonary vein, left heart, aorta and carotids, into the cerebral circulation. The cerebral area is most frequently offected since the diver is usually in an erect or head up position, and the bubbles tend to rise. Any bubble too large to pass through an artery will lodge and obstruct circulation to adjacent area or organs. This obstruction is the embolus. The wide clinical spectrum of symptoms and signs associated with cerebral air embolism include headache, vertigo, cranial nerve involvement, visual,

43 auditory, and speech disturbances, loss of consciousness, coma, paralysis, convulsions, loss of vital signs, and death (Waite and associates 1967). Death results from coronary and/or cerebral occlusions with cardiac arrhythmias, respiratory failure, circulatory collapse and irreversible shock (Linaweaver 1963, p. 519). The symptoms are dramatic and sudden in onset, usually occurring within seconds of surfacing or may even occur prior to surfacing. Many cases occur without development of any symptoms prior to unconsciousness; the diver may or may not experience discomfort or pain in the chest prior to or during alveoli rupture. The tearing of lung tissue often results in bloody froth at the mouth; however, the absence of bloody froth does not preclude the possibility of air embolism (U.S. Navy 1970). Dysbaric cerebral air embolism and its related conditions are best prevented by observing the following procedures or rules established by the U.S. Navy (1963, p. 134) and supplemented by the author: 1. Careful selection of personnel: All candidates for diving duty or training must undergo a complete medical examination including an evaluation of his medical history. History of tuberculosis, asthma, or chronic pulmonary disease may be disqualifying; the lungs shall be normal as determined by physical and X-ray examination (chest roentgenograms taken at full inspiration and full expiration). The daily condition of the diver must also be considered; a severe cold (especially with respiratory complications) is temporarily disqualifying. 2. Proper, intensive training of every diver in the physics and physiology involved in diving: Many cases of air embolism have occurred simply because the diver did not understand Boyle's Law and its application to diving. A thorough understanding of diving physiology and an awareness of the consequences of air embolism promotes a positive attitude toward the observance of basic diving procedures and safety standards. 3. Proper, intensive training of every diver in the use of diving equipment and diving and safety procedures: This is especially important in the use of SCUBA. When an improperly trained diver loses his gas supply underwater, his first overwhelming instinct is to hold his breath and surface immediately. Training and proper indoctrination give the individual confidence which is so

44 important during times of danger so that intelligent and proper action will be t:aken, thus avoiding panic, 4, Never hold -your breath during ascent from a dive in which a breathingaaratus was used: Breathe regularly during ascent. When the apparatus fails or gas supply is exhausted and a free ascent in unavoidable, exhale continuously during ascent to prevent overexpans ion of the lungs, 5. Diver should avoid smo:ki There is sufficient evidence to indicate that smoking causes serious irregularities in the lung tissue and excessive bronchial mucus. Subsequent blockage of airways and weakened tissue can result in rupture of lung tissue. The only recognized standard and effective treatment of cerebral air embolism is the recompression method. Complete and authoritative discussions of this topic are available in U.S. Navy (1970). Recompression procedures and principles are given in the section on Recompression. IMPAIRED CONSCIOUSNESS DURING BREATHHOLD DIVING Prolonged voluntary breathholding while swimming underwater can result in loss of consciousness and subsequent drowning. Craig (1961, 1961a) studied cases of near drownings and deaths resulting from loss of consciousness while swimming underwater and found that during such circumstances diving accidents were explainable by loss of consciousness due to hypoxia, Hyperventilation is a common practice among underwater swimmers, i.e., skin divers, sponge and pearl divers, etc. By hyperventilation the swimmer can significantly deplete the carbon dioxide (C02) stores of the body. The partial pressure of CO2 (pCO2) in the nerve tissue regulating respiration appears to be the primary stimulus to respiration, with comparatively little stimulus derived from low oxygen partial pressures (pO2). While swimming underwater the diver uses 02 and produces C02; however, since the C02 is used for repletion of the subnormal body CO2 stores, there is insufficient CO2 stimulus for respiration. When the oxygen consumption is increased, as in

45 the first few seconds of exercise, the p02 may decrease to a degree incompatible with cerebral function before the rise in pCO2 commands the diver to surface for air. Loss of consciousness can result from hypoxia (or anoxia, which has about the same meaning) with little specific warning. The victim may actually continue his activity between the time of loss of consciousness and final collapse. This condition is further complicated by increased ambient pressure and ascent from depth. Paulev (1968) and Paulev and Naeraa (1967) conducted controlled experiments to study the mechanism of hypoxia and carbon dioxide retention during and following breathholding dives. During these dives the alveolar oxygen tension (pAO2) decreases linearly, but remains high enough to reoxygenate the blood quite completely during most of the dive. However, staying on the bottom longer than 90 sec yielded significantly low pAO2 and arterial 02 tension (paO2). The low pAO2 and the Bohr effect (the lower the hemoglobin 02 saturation is, the greater the paC02) has in fact resulted in a significant fall in 02 saturation; thus the blood cannot carry as much 02 from the lungs to the tissue as before. Some divers have been reported to have lost consciousness at the bottom, and they possibly have contracted the dangerous combination of a low pAO2 and a very high pACO2. Shortly after reaching the bottom a diver may experience a subjective "breaking point" approach sensation due to increased paC02 stimulus plus stimuli elicited from smaller lung volume. This sensation is easily overcome by the willpower of trained breathhold divers. The expert skin diver can actually "condition" himself to voluntarily or involuntarily ignore the breaking-point sensation (or urge to breathe) and over a period of time becomes inured to the subsequent PCO2 buildup that would drive the average

46 person to the surface for air, During ascent, a relief of the breaking-point sensation is experienced because the lung volume increases and the pAC02 falls, even though oxygen may actually diffuse from the alveoli to the blood at a slower rate due to pACO2 decrease, Since the pA02 may fall below the venous pO2, the possibility for 02 transfer from the blood to the lungs is present. Blood oxygen stores may be rapidly depleted. If during ascent blood deprived of oxygen arrives at the cerebral cortex, the diver may lose consciousness with little or no warning before or just as he reaches the surface. Unconsciousness during ascent when the diver is below the "buoyance point" is a potentially fatal condition. Ironically, many competitive skin divers wear lead weight belts which makes them negatively buoyant for effortless diving, Bond (1965) condemns competitive breathholding exercises and contests, even under the auspices of a good organization, and anyone who wears excessive weights. Unfortunately, competitive breathholding contests are a common occurrence in nearly every American swimming pool. Bond cites one such experience involving a 16 year old male in excellent physical condition participating in a contest conducted in a swimming pool. Wearing a face mask and weight belt the young man settled to the bottom of the pool and remained there for 9 minutes in full view of almost 200 spectators. Finally, he was hauled to the surface in a state of unconsciousness and not breathing. His breathing was successfully revived; however, subsequent examination and electro-encephalograms revealed no cortical activity. In other words, this young man was now doomed to lead the life of a vegetable for the rest of his days.

47 Neurological phenomena including unconsciousness as a result of decompression sickness may occur from repeated breathhold dives to great depths (Paulev 1968; 1965). The increase in the paN2 is high at about 20 m depth. Although the volume of N2 absorbed during each dive may be small, the increase in tissue pN2 (ptN2) could account for the occurrence of N2 containing bubbles in the tissue following many repetitive and rapid alterations in ambient pressure. Bond (1965) relates a personal experience in which he was a victim of decompression sickness as a result of 7 hours and 20 minutes of continuous breathhold skin diving to depths of 80 to 100 ft. Fortunately, such cases are rare, probably because most human divers cannot breathhold dive deep enough nor often enough to contract decompression sickness. Cross (1962,1965) discussed the dreaded disease of Tuamotus pearl divers, "taravana." These pearl divers are true skin divers; they use no breathing apparatus or air supply for their underwater work. Yet, many of those stricken with "taravana" exhibit symptoms likened to those of classic decompression sickness - vertigo, paralysis, unconsciousness, and insanity. These divers may make as many as 6 to 14 dives per hour to depths up to 150 feet and stay submerged an average of 1 min and 35 sec. This schedule is continued daily throughout the pearl diving season. On one exceptionally good diving day, good weather and seas, Cross observed that 47 divers were stricken with "taravana," A total of 34 suffered vertigo, nausea, and dizziness. Eleven surfaced paralyzed or unconscious and were rescued. Six of these were partially or completely paralyzed and two were "mentally affected." Two young men died. Cross suggests that anoxia is the principle cause of "taravana", with

48 its effects on the central nervous system and the brain accounting for the many and varied symptoms He points out that Mangareva divers space their dives 15 minutes apart, instead of the 4 to 8 minutes used by the Tuamotus divers, and do not suffer from "taravana," Certainly anoxia or hypoxia explains many of the symptoms, and it should also be stated that continuous daily and seasonal exposure of brain tissue cells to hypoxia conditions could possibly result in cumulative and irreversible brain damage. On the other hand, decompression sickness as discussed by Paulev (1968, 1965) is also an equally significant explanation, especially when considering the cumulative underwater time and depth, Frequently, loss of consciousness while underwater is referred to as shallow water or underwater blackout, The U.S. Navy (1963) defines shallow water blackout as a, "accident in which a diver loses consciousness, presumably from carbon dioxide excess without an adequate respiratory warning." Bond (1965) considers lowering of oxygen levels of vital organs as a primary cause, For a more comprehensive review of breathholding consult DuBois (1955) and Rahn (1965). BREATHING MEDIA CONTAINATION Carbon Monoxidc Po! son in Carbon monoxide (CO) is probably the most serious breathing media contaminant. Carbon monoxide readily combines with the blood hemoglobin (to form COHb) and renders it incapable of transporting sufficient oxygen. Hemoglobin, in fact, combines with CO about 200 times as readily as with oxygen, Shepard and associates (1958) have shown that the diffusion capacity for CO increases progressively with increasing exercise. When this occurs, tissue anoxia develops even though the supply of oxygen to the

49 lungs is ample. At sea level the toxic effect of CO is proportional to the amount of COHb formed; however, at depth a diver may tolerate a considerably higher ratio of COHb because some of the oxygen transport requirements are met by the oxygen in solution (due to increased pO2 at depth). However, since the reconversion of COHb to oxyhemoglobin is relatively slow compared to the time required for COHb to form, the diver may develop symptoms of CO poisoning immediately on ascent (U.S. National Research Council 1956). Consequently, contamination of SCUBA air with even small amounts of carbon monoxide can be very dangerous. At present specifications and purity standards for high pressure compressed diver's breathing air allow for a maximum of 10 (0,001%) ppm carbon monoxide (Anonymous 1964; U.S. Navy 1970). On several occasions the author has analyzed air obtained from "dive shops" and found concentrations of CO beyond the recommended limits. Occupational Health (1963) reports on the examination of 25 SCUBA tanks for presence of CO. Only two tanks showed no CO present and 18 tanks had CO concentrations between 10 and 25 ppm. Five of the samples had concentrations greater than 25 ppm, with one sample of 75 ppm. The diver must be certain that the air supply meets recommended purity standards. SCUBA air supply must be obtained from reliable sources. Periodic air analysis are recommended; organizations conducting diving operations should include CO gas analysis equipment in their diving lockers. Methods of analysis, safe limits and methods of removal are discussed in U.S. Navy (1970). The wide spectrum of symptoms associated with carbon monoxide poisoning include headache, dizziness, nausea, weakness, confusion and other mental changes. The tender or diving partner may note failure to respond, clumsiness, and bad judgement. Frequently no symptoms are evident;

50 the diver may lose consciousness without warning and breathing may cease. In general, the symptoms parallel those of other forms of anoxia with one exception, the victim's coloration is red instead of blue. In spite of the displacement of oxygen, hemoglobin combined with CO has a bright red color. Consequently, a victim who becomes anoxic because of carbon monoxide poisoning often exhibits an unnatural redness of lips, nail beds and sometimes of the skin instead of the characteristic cyanosis (blueness) often associated with other type of anoxia. When carbon monoxide poisoning is indicated, get the victim into fresh air (or non-contaminated area) as soon as possible. If breathing has stopped, start artificial respiration at once. The victim should be given oxygen as soon as possible; administration of oxygen increases the amount of oxygen reaching the tissue inspite of the inactivity of the hemoglobin and it also accelerates the elimination of CO from the blood. A carbon monoxide victim should be treated under medical supervision. The treatment of carbon monoxide victims with oxygen at two atmospheres pressure has been described by many investigators including Smith and associates (1962). Records of rapid and complete recovery are establishing hyperbaric oxygen as a standard method of treatment. Contamination with carbon monoxide can arise from two primary sources: 1, The gas may be present in the intake air from having the compressor intake located too close to or downwind from the exhaust of a gasoline-driven engine or other source of exhaust gas. In large cities and industrial areas CO is a common atmospheric pollutant and may rise, at times, beyond the safe concentration level for diver's air. Consequently, the air supplier must be constantly aware of atmospheric pollution levels and/or take measure to remove excessive CO during the air compression process. 2, Oil-lubricated compressors, particularly when not operated or maintained properly, can develop high cylinder temperatures that cause partial combustion (oil "flashing" or "dieseling") of the

51 lubrication oil. All breathing air compressors must be maintained in accordance with manufacturer's specifications. Oil-Vapor Contamination of Air Supply Oil vapor, from oil-lubricated compressors, is probably the most common contaminator of SCUBA air supply. Oil fumes give an unpleasant taste and odor to the breathing mixture, and under pressure the concentration may be sufficient to cause pulmonary irritation, cough and in extreme cases, pneumonia. Do not use contaminated air; charge SCUBA cylinders at a reliable facility. Avoidance of excessive oil vapor in compressed air requires careful and regular compressor maintenance, water and oil vapor condensors, and an effective filtering system. Carbon Dioxide Excess Carbon dioxide (C02) is a natural by-product of oxidation and metabolism. The C02 tension in the human body increases with the rate of production due to physical exertion and inadequate ventilation of the lungs. Under normal conditions CO2 is the primary respiratory stimulant to the respiratory center in the medulla. Normal concentrations of CO2 in atmospheric air are 0.04% and a pCO2 of 40 mm Hg is the normal alveolar tension. Breathing a mixture of 2% CO2 slightly increases the respiratory rate. The effects of C02 are dependent upon the pCO2. In accordance with Dalton's Law of Partial Pressures, a 2% C02 mixture at the surface ( 1 atmosphere) will at 132 feet (5 atmospheres) have essentially the same effects as a 10% mixture would at the surface. The effects of increased carbon dioxide content in the respired air have been investigated by many researchers. Greenbaum and Hoff (1966) list more than 300 papers on carbon dioxide's effects; special mention is

52 made of the report by the U.S. National Research Council (1956). The effects of increased pCO2 on body functions are extensive and variable, Adequate respiratory ventilation is of considerable importance when considering the design of all diving apparatus, recompression chambers, underwater habitats, submersibles, etc. The following discussion will only include those aspects of carbon dioxide excess relative to operational diving. Miles (1962) indicates that there has been a wide tendency to use carbon dioxide an an underlying cause of many of the accidents and illnesses encountered in diving. It has been blamed for nitrogen narcosis, oxygen poisoning, shallow water blackout, and as contributory to decompression sickness. Accidents with no obvious cause are frequently attributed to carbon dioxide excess. The recent death of a U.S. Navy Sealab III aquanaut was attributed to carbon dioxide poisoning due to failure to fill a breathing apparatus filter canister with'Baralyme" (a C02 absorbent) (Anonymous 1969). As a diver without breathing apparatus descends the alveolar pressure of carbon dioxide does not rise appreciably because of absorption by the circulating blood to maintain a pCO2 of about 40 mm Hg. During a breathhold dive the rise in alveolar CO2 is due to the accumulation of gas from metabolic processes. For all intent and purpose carbon dioxide excess can be considered secondary to anoxia in loss of consciousness while breathhold diving. Voluntary lowering of the normal pCO2 by hyperventilation prior to the dive retards the respiratory response and enhances the development of hypoxia, In diving with breathing apparatus excessive accumulation may result when the carbon dioxide absorbent unit is inefficient or exhausted in closed and semi-closed circuit SCUBA and mixed-gas helmet rigs or when

53 there is an inadequate gas supply to sufficiently ventilate the helmet or mask. The resulting accumulation and subsequent inhalation of carbon dioxide (5% concentration) produces respiratory stimulation (i.e., panting, breathlessness, distress, etc.), cerebral dilation and headache. As the concentrations increase the diver may become confused, irrational and drowsy and if the concentration rises above 10 percent, the diver will generally lose consciousness. Conditions which enhance the retention of CO2 in the body include unusual exertion, inadequate ventilation, high oxygen tensions, increased density of breathing medium and inadequate equipment design. Naturally, a diver must receive adequate gas supply to ventilate the breathing system and remove carbon dioxide; this is extremely important under conditions of heavy exertion. Increased alveolar oxygen pressure effects the carbon dioxide response (Lloyd and associates 1958; Lambertsen and associates 1963). Increased breathing resistance, whether due to apparatus design or gas density, favors CO2 retention and therefore decreases sensitivity to C02 (Lanphier 1958). Lanphier favors abandoning nitrogen-oxygen mixtures in favor of less dense helium-oxygen mixtures for mixed-gas SCUBA diving. Eldridge and Davis (1959) concur with Lanphier in that increased breathing resistance causes pCO2 and exertion levels to rise in parallel, whereas ventilation response remains constant or even decreases. If a diver does not ventilate his lungs sufficiently to eliminate as much CO2 as he is producing, he can, in effect, poison himself (U.S. Navy 1963). A number of accidents in which the diver has loss consciousness for no apparent reason have been explained on this basis, Deliberate reduction in breathing rate to conserve air in the use of open-circuit

54 SCUBA is an extremely dangerous practice, Most authorities consider it better to breathe normally and consume more air than to practice periods of breathholding between inspirations and risk the lethal consequences of CO2 build-up. GAS NARCOSIS AND TOXICITY Inert Gas Narcosis Among the major factors likely to cause performance impairment in divers at increased ambient pressures is inert gas narcosis, Although the common inert gases (nitrogen and helium) associated with diving are physiologically inert under normal conditions, they have distinct anesthetic properties when the partial pressure is sufficiently high. The problem of compressed air "intoxication" has long been recognized by divers and researchers. Behnke and associates were among the first to attribute these effects to high partial pressure of nitrogen. Many theories of compressed air intoxication were advanced by various investigators. Damant (1930) attibuted part of the intoxicating effects to the increased oxygen pressure. Bean (1950) expressed doubt that nitrogen was the responsible agent, and contended that the sole causative factor is a rise in body C02 tension brought about by rised gas density. Manifestations of anxiety (Hill and Greenwood 1906) and claustrophobia, or a combination of all of the aforementioned factors or else by the pressure itself (Shilling and Willgrube 1937) have also been suggested. However, encephalographic studies by Bennett and Glass (1961) leave little doubt that high nitrogen pressure constitutes an important causative factor of compressed air narcosis, Associated causes may include the density and

55 oxygen partial pressure of the respired mixture which, in turn, may cause an increased carbon dioxide tension that synergistically potentiates the narcosis (Bennett 1963). Taylor (1962), on the other hand, finds that CO2 does not contribute to the causation of the narcosis. Bennett (1966) considers the problem of compressed air intoxication in detail and Miller (1963) discusses the theories of inert gas narcosis. Nitrogen narcosis, or compressed air intoxication (U. S. Navy 1963; Lanphier 1957), characterized by symptoms similar to alcohol intoxication, first becomes evident at depths about 100 feet. Beyond this depth, most compressed air divers show some impairment of thought and judgment and of the ability to perform tasks that require mental or motor skill. Such impairment, even if mild, obviously constitutes a potential hazard to the diver's safety. Most divers lose their effectiveness at about 200 feet and at about 250 feet, the average diver is, for all practical purposes, useless and a menace to himself. Like alcohol, the effects of nitrogen vary with the individual person and its hazards can be minimized within certain limits by conscious effort. Miles (1962) tabulates the sequence of events for the average man under the influence of high pressure nitrogen in a breathing medium of air as follows: 100 to 150 feet: Light head, increasing self-confidence, loss of fine discrimination and some euphoria. 150 to 200 feet: Joviality and garrulousness; perhaps some dizziness. 200 to 250 feet: Laughter may be uncontrolled and approach hysteria. Power of communication is lessened and mistakes made in simple practical and mental tasks. May be peripheral numbness and tingling. Less attention paid to personal safety. Delayed response to signals and stimuli. 300 feet: Depression, and loss of clear thinking. Impaired neuromuscular co-ordination.

56 350 feet: May approach unconsciousness but there is the additional danger of oxygen poisoning, Several predisposing factors nay advance the onset of symptoms and ameliorating factors may help to increase the tolerance to nitrogen narcosis (Miles 1962). Alcohol taken prior to pressurization greatly enhances the nitrogen effect, the two being almost additive, Fatigue will increase susceptability as will any circumstance causing retention of carbon dioxide, In the inexperienced diver, anxiety is likely to advance the onset of symptoms, On the other hand, experience, strong will and frequent deep diving all help to increase the tolerance to high nitrogen tensions, Bennett (1963) suggests that certain drugs might lessen the narcotic effects of nitrogen, The principles of prevention lie in common sense and proper diving procedures. Compressed air divers must observe definite depth limitations. The U.S, Navy (1970) considers 300 feet as an absolute limit for surfacesupplied air diving and 130 feet as the maximum air working limit for SCUBA divers, except specially trained personnel, For dives to depths greater than can be reached safely by air divers, helium-oxygenmixtures are employed. Published accounts of "sport" dives, using compressed air SCUBA, to depths of 200 to 300 feet are not uncommon, and one account mentions a "record" dive to 390 feet, Recently another "record' SCUBA dive (air) of 437 feet was reported in a local newspaper (The Grand Rapids Press: January 26, 1969). Need the trained diver be reminded that even 200 feet is well beyond the depth limit deemed reasonable and proper by the Navy for compressed air SCUBA, Not only is the diver subjected to extremely high pN2 and subsequently nitrogen naroesis, but also oxygen poisoning and decompression sickness,

57 U.S. Navy (1970) Standard Air Decompression Tables are calculated to only 300 feet. The publication of such "stunts" tends to lure the unsuspecting novice to depths beyond the capacity of his equipment, knowledge, skill and physiology. The treatment of gas narcosis is no problem. Simply reduce pressure (ascend) and recovery is complete, except in severe cases where some temporary amnesia and, in all cases, tiredness due to pressure exist (Miles 1962, p. 103). Oxygen Toxicity The toxic effects of excess oxygen are of considerable importance in diving and hyperbaric research, and the mechanism of these effects is not yet thoroughly understood. The administration of 100 percent oxygen to humans continuously for 24 hours at normal atmospheric pressures causes substernal distress in 86 percent of subjects and under pressures above 1.0 atmosphere for a sufficiently long time, and at sufficiently high pressure eventually leads to the development of oxygen toxicity characterized by general convulsions (Greenbaum and Hoff 1966). The cause of these convulsions is not yet completely understood in spite of considerable research in this field, Oxygen toxicity is a function of pressure and duration. The safe period of oxygen inhalation is further reduced by immersion, exercise and carbon dioxide inhalation. High pressure oxygen poisoning effecting the brain and causing convulsions can definitely occur at p02 of 2.0 atmospheres and sometimes even lower (U.S. Navy 1970). Oxygen tolerance varies with individual divers and may also vary from day to day. The U.S. Navy has established an "oxygen tolerance test" for divers to detect those with unusual susceptability which requires breathing pure oxygen for 30 minutes at 60 feet in a dry chamber. The U.S. Navy recommends a normal 25 foot

58 depth limit and for exceptional operations a 40 foot limit for pure oxygen breathing during working dives; dive duration is limited in accordance with depths Emerson (1966) recommends an allowed p02 range of 0.2 to 0.4 atmospheres for prolonged mixed-gas diving exposures and suggests that 0.2 to 1.5 atmospheres might be acceptable for short durations. Warning symptoms of oxygen toxicity, in order, are: muscular twitching, nausea, abnormalities of vision and hearing, difficulty in breathing, anxiety and confusion, unusual fatigue, uncoordination and convulsions. Oxygen poisoning is reversible and the convulsions are not in themselves dangerous but may result in physical injury, air embolism (uncontrolled ascent), and drowning (particularly with SCUBA). The convulsions are usually selfterminating with no apparent lasting effects. The mechanism of oxygen poisoning, although presently obscure, may be considered to be a direct effect through interference with enzyme systems. For an authoritative discussion of oxygen toxicity, the reader is referred to the U.S. National Research Council (1966), DECOMPRESSION SICKNESS: AIR DIVING The term "decompression sickness" refers to the "signs, symptoms and basic underlying pathological processes caused by rapid reduction in barometric pressure from high pressure to one atmosphere, or from any higher to any lower level of pressure" (Greenbaum and Hoff 1966, p. 151). The basic underlying pathologic process in decompression sickness is the local formation of bubbles in body tissue, both intravascular and extravascular. The resulting symptoms vary widely in nature and intensity depending on the location and magnitude of bubble formation. When the diver is breathing

59 air, the primary constituent of these bubbles is nitrogen with a small fraction of carbon dioxide. To understand the basic causes of the bubble formation phenomenon, it is necessary to examine what happens to air when breathed under increased ambient pressure. In accordance with the laws of partial pressures, the amount of a given gas that will dissolve in a given liquid is determined by the percentage of that gas in the total mixture and by the ambient pressure. When the pressure of the gas mixture is increased, a pressure gradient exists between the tensions of the dissolved and undissolved phases of the gas. This gradient drives each gas into solution in proportion to its partial pressure until an equilibrium is established between the dissolved and undissolved phases of the gas. If the ambient pressure is then decreased, the tension of the gas in the dissolved phase exceeds that of the gas phase, and the pressure gradient is reversed. The factor of time for equilibrium to be established in either direction is a principal factor in the discussion of decompression sickness. Nitrogen is the only principal component of air that is inert; it therefore is unaltered in the respiratory process and, for all practical purposes, quantitatively obeys purely physical laws. Consequently, at gaseous equilibrium the partial pressure values of nitrogen in the alveolar air, venous and arterial blood and body tissues are identical. Oxygen and carbon dioxide are actively functionable in the metabolic processes and under ordinary diving circumstances, the metabolic cushion renders the tissue tensions of these-two gases of little significance in the mechanism of bubble formation (Dewey 1962).

60 Nitrogen will not dissolve in all body tissue at the same rate or in the same amount, This is because nitrogen is transported from the alveoli to the tissue in solution by the blood. Consequently, tissues rich in blood supply will equilibrate at a faster rate than those having more limited circulation (Jones 1951), Nitrogen is approximately five times more soluble in fat than in water (Vernon 1907); tissues high in lipid content (i.e., spinal cord, bone marrow, and fat deposits) must take up a proportionally greater amount of nitrogen before saturation (equilibrium) is reached (Dewey 1962, p. 761). When the pressure gradient is reversed, the slowest tissues to release all extra nitrogen will again be those with limited circulation or high lipid content. Behnke and associates (1935) determined that, after complete saturation of all tissues, elimination of all excess nitrogen requires approximately 12 hours, About 75 percent of this nitrogen is eliminated in the first 2~ hours. From the diverts point of view, the degree of tissue saturation and, consequently, the amount of time required for tissue desaturation (subsequent decompression time) is dependent upon the depth, or pressure, of the dive and the amount of time at depth, The mechanism of bubble formation is summarized by Dewey (1962, p, 761). Bubbles tend to form in any tissues that are saturated with nitrogen whenever the ambient pressure is reduced to a point where a "steep" pressure gradient is driving the gas out of solution. Haldane and associates (1908) first postulated that when the tissue partial pressure of nitrogen is more than twice that of the ambient partial pressure of nitrogen, symptom-producing bubble formation will occur. Once this 2:1 threshold pressure gradient is exceeded, the number and size of symptom-producing bubbles formed will be

61 directly proportional to the magnitude of the disparity between these two partial pressures. Under these conditions the rate of diffusion of gas from the tissues into the expired air, via the blood and alveolar membrane, is too slow to cope with the volume of nitrogen evolved. Hence, the nitrogen comes out of solution locally in the tissue in the form of bubbles. It is probable that microscopic bubble formation ("silent bubbles") occurs in parts of the body without giving rise to symtomatic manifestations and that these bubbles may cause chronic delayed damage such as aseptic bone necrosis (Greenbaum and Hoff 1966, p. 158). Bateman (1951) indicates that some degree of bubble formation probably occurs whenever the tissue partial pressure of nitrogen even moderately exceeds that of the surrounding atmosphere. Obesity, physiologic aging, excessive physical exertion during the dive and poor physical condition are factors predisposing a diver to decompression sickness (Dewey 1962). As previously point out, fatty tissues constitute a large nitrogen reservoir due to the 5:1 oil-water solubility ratio. During a deep or lengthy dive a considerable amount of nitrogen is dissolved in the body tissues. If the diver is obese, it can be readily seen that during ascent the blood, essentially a watery tissue, will not be capable of transporting in solution the increased volume of gas evolved from the excess fatty tissues. Consequently, the blood will supersaturate and lead to intravascular bubble formation on the capillary level. This will result in subsequent supersaturation and extravascular bubble formation in "blocked" tissue. Aging introduces an increasing proportion of tissue with sluggish circulation and, therefore, the increased

62 possibility of local bubble formation. Excessive physical exertion increases the respiration rate and the rate of circulation of the total blood volume. Consequently, during excess exertion under pressure, larger amounts of nitrogen are transported to the tissue per unit of time than normally. Consider the circumstances where a diver is working hard underwater, i.e., moving heavy objects, swimming against a strong current, etc. This diverts tissues may absorb excessive nitrogen equivalent to ten to twenty minutes extra diving time under normal conditions and if he was on a dive schedule of 60 minutes to 60 feet (the "1no-decompression" limit for that depth), he may suffer decompression sickness if he surfaces without decompression stops. Poor physical condition is a direct extension of the above situation. Harvey and associates (1946) demonstrated that forceful movement of muscles and joints under increased ambient pressure results in an increase in bubble formation at those sites during decompression. Excessive carbon dioxide build-up in tissue has also been empirically and experimentally observed to lower the threshold for bubble formation during ascent (Blinks and associates 1951), SCUBA divers commonly use methods, i.e., skip breathing or controlled breathing, to lower air utilization and increase dive time. These practices can result in excessive carbon dioxide retention in tissue and could possibly be a factor predisposing a diver to decompression sickness. Needless to say, these "modifying factors" cannot be overlooked in operational diving, If all of these factors were accounted for in standard air decompression tables (U.S. Navy 1970), the tables would be impractical

63 for normal diving and divers. Consequently, the discretion of the diving officer, diving supervisor, and the diver himself must be relied upon to take these factors into account when planning the dive schedule. Let's recall the 60 minute dive involving heavy exertion at a depth of 60 feet. The trained and knowledgable diving officer, supervisor or diver will use the 70 or 80 minute schedule to determine the decompression for this dive even though the actual bottom time was 60 minutes. Instead of surfacing directly with "no-decompression", the diver holds at 10 feet for 2 or 7 minutes to rid his body of possible excess nitrogen. Seven minutes is a small price to pay when one considers the possibility of the many hours in a recompression chamber required to treat decompression sickness. The simple one-compartment decompression meter (Anderson 1967; Somers 1970) is increasing in popularity among divers, particularly SCUBA divers. This meter is designed to simulate the physiological processes of nitrogen absorption and elimination by the human body and automatically computes the diver's decompression requirements. Although these meters appear to be very satisfactory for normal diving operations, they do not take into account the diver's physical condition, excessive physical exertion, and other factors affecting individual absorption and elimination of nitrogen. The author is familiar with one case of decompression sickness that is probably a result of these "modifying" factors not being taken into account when using a decompression meter. Following the meter "read-out" the diver suffered a severe case of decompression sickness following his third or fourth repetitive working dive in cold water to depths exceeding 80 feet. Also it should be pointed out that these meters are designed to function

64 relative to the osid-level tissue nitrogen absorption and elimination times and are not recommended- for extremely deep and/or long duration dives on which the higher tissues absorb more nitrogen. The symptoms of decompression sickness are variable in their nature and intensity, depending on the location and size of the bubbles. Localized pain is the most predominant symptom, occurring in about 89 percent of all cases and is the only symptom in roughly 68 percent of cases. The onset of pain, sometimes likened to that of a severe toothache, is often gradual with fairly rapid increase in severity; untreated, it almost invariably progresses to an "unbearable" stage. The location of the pain is usually rather localized at first and extends centrifugally to involve a progressively larger area Generally, the pain is neither aggravated nor alleviated by motion or local palpation. Joints and tendinous structures are the most common location of pain symptoms, Various theories regarding the mechanism of pain production have been postulated, and Dewey finds Nims (1951) theory most acceptable. Nims reasons that a gaseous bubble developing in the tissue must displace and deform adjacent structures which possess var3ng degrees of elasticity and deformation resistance, Furthermore, given the same amount of gas, the deformation pressure in a "tight" tissue, such as tendon, ligament and joint capsule, must be greater than that in "loose" tissue, such as fat. When this deformation pressure exceeds a certain threshold value, nerve fibers are stimulated by the mechanical deformation. On this basis, "tight" tissues are the most probable sites for symptom occurrence. This verified by experience and experimentation (Inman and Saunders 1944), Localized skin rash and itching is experienced fairly often by divers during or immediately following decompression. A peculiarly irregular,

65 modified'rash" is the most common type of skin lesion related to decompression sickness. The distribution tends to be related to subcutaneous fat deposits and is characteristically found, in order of frequency, in the pectoral region, back of shoulders, upper abdomen, forearms and thighs. Recompression causes complete disappearance of the visible lesion; however, tenderness may persist for several days. The underlying pathologic changes and mechanism of skin lesion production in decompression sickness are clear. Individual susceptibility varies. Ferris and Engel (1951) is a major source of information on this subject. Transient blurring of vision and other visual disturbances occasionally accompany more serious manifestation of decompression sickness. Visual disturbances are probably secondary to vasomotor decompensation and shock and are rarely of CNS origin. Central nervous system (CNS) manifestations are probably the most serious consequence of inadequate decompression. The great variety of bubble formation sites yield a comparable variety of disturbances, sometimes bizarre, often multiple and certainly unpredictable. Theoretically, bubble formation can produce just about any symptom. Damage may be extensive or confined to minute structures. Most CNS lesions occur in the spinal cord, particularly in the lower segment; cerebral damage is relatively rare. Quadriplegia, paraplegia and paralysis of a single or several extremities in every combination have been reported. Early vasomotor collapse and shock are associated with the more serious manifestations. Various body organs and functions may be affected. Permanent residual damage may result in loss of bowel and bladder control and/or some degree of residual paresis in one or both of the lower extremities. Gersh and Catchpole (1951)

66 summarize the findings on pathologic changes in the human CNS caused by decompression sickness Other manifestatons include respiratory distress ("chokes"), headaches, nausea and fatigue. The "chokes" is the rare but interesting symptom of delayed development of substernal distress, often described as burning. The condition is aggravated by deep inspiration and subsequent burning pain in all phases of respiration and an uncontrollable urge to cough. As the pain intensifies and spread, respiration becomes difficult, coughing more severe, The victim becomes cyanotic, very apprehensive and progresses into clinical shock with subsequent loss of consciousness on occasion, The condition can be fatal if untreated. Headache, nausea and fatigue generally are considered to be nonspecific reflex phenomena secondary to the conditions previously discussed. Marked fatigue, often out of proportion to the physical exertion expended, is frequently experienced following deep dives, particularly if the decompression has been marginal. The onset of fatigue is generally 2 to 5 hours after surfacing and is characterized by an overpowering urge to sleep. The underlying mechanisms responsible are not known; however, fatigue is frequently considered a minor manifestation. Certain symptom patterns are evident. Study of case histories indicates that certain symptoms and anatomic sites are more frequently involved than others. Table 2-1 summarizes the frequency occurrence of the more common symptoms, Duffner and associates (1947) reported on the frequency of combinations of symptoms (Table 2-2), Symptoms may appear immediately after surfacing or more than 6 hours later (Table 2-3), Treatment for decompression sickness is discussed in the following section on Reoin rse ion,

67 TABLE 2-1. Frequency of symptoms occurring in decompression sickness (modified from Dewey 1962, p. 763). SYMPTOM FREQUENCY (%) Local pain 89.0 Lower extremity (70%) Upper extremity (30%) Skin rash (with itching) 11,0 Visual disturbances 6.0 Motor paralysis or weakness 5.5 Vertigo 5,0 Numbness 4.8 Respiratory distress ("chokes") 2,4 Headache 1,9 Unconsciousness 1,5 Aphasia 1.2 Nausea 0,9 TABLE 2-2. Frequency of combination of symptoms (after Duffner and associates, 1947). COMBINATION FREQUENCY (%) Single symptom only 70.0 2 symptoms 25.6 More than 2 symptoms 4.4 Pain as only symptom 68.0 Localized pain not symptom 5.3 TABLE 2-3. Interval between surfacing and onset of initial symptoms (after U.S. Navy 1956, p. 190), INTERVAL AFTER SURFACING OCCURRENCE OF INITIAL SYMPTOMS (%) Within 30 min 50 Within 1 hr 85 Within 3 hr 95 Within 6 hr 99 Delayed more than 6 hr 1

68 The prevention of decompression sickness is best accomplished by observing the following eas established by the U.S. Navy (1963, p. 128) and supplemented by the author. 1. ~aeful slectn of ersonnel For example, persons not properly trained in diving ad the use of decompression tables and procedures are immediate candidates for a case of the "bends" In addition, persons with old injuries and diseases which could result in abnormally restricted circulation should be rejected; in other words, divers must met certain medical standards, 2, Observation and evaluation of each man before he makes an dive: Alcohol intrxication or "hangover", excessive fatigue, or a general rundown conditicn should be sufficient to temporarily restrict a man from diving activities, All of these conditions may enhance susceptabi ty to decompression sickness. It is the responsibility of the divers, the diving officer or the diving supervisor to restrict a diver when his physical condition is not satisfactory. 3. Careful attention to details of the dive: Establishment of a good dive plan with accurate depth and time determinations is mandatory. Never depend on SCUBA tank volume and air supply duration as a measure of "no decompression" limits. Table 4-1 readily illustrates that a SCUBA (open-circuit) diver can exceed "no decompression" limits even when using a standard single cylinder (72 ft3) All divers working below a depth of 30 feet should be equipped with a watch and depth indicator and/or automatic decompression meters Keep accurate records of all dives, they may be important in diagnosis d treatment of decompression sickness, 4, Strict observance of the decmresson tables or automatic decoipPresslon meter) with due consideration of modif in factors: Adhere to the tables at all times unless there is reason to question the accuracy of depth or time. In this event, decompress the dir for der dive of greater depth or longer duration. Terminate dive if decompression meter malfunction is suspected and undergo conventional stage decompression if the "no decompression" limits have possibly been exceeded. Also, take into account working conditions, ie., physical exertion, water temperature, etc., and lengthen decompression accordingly. When in doubt, always act in the diver's favor by adding to the decompression; never shorten decompression for mere convenience, 5, Re o mptoms or,_sins immediatel: Serious cases of decompression sickness often begin with a slight pain or itch. Failure to treat promptly can result in serious permanent damage or at least prolonged treatment,

69 Dewey (1962) published an excellent paper giving a relatively complete discussion of decompression sickness. This work has been a major source for the above discussion. For additional practical information the reader is referred to the U.S. Navy (1970) and Cross (1968). U.S. Navy Standard Air Decompression and Repetitive Dive Tables are given in Appendix III. OTHER COMPLICATIONS Lung Infection Several cases of lung infection have been traced to a fungus which grows in the hoses of regulators. This fungus is thought to be nourished by human saliva and grows more readily in tropical climates. Divers have been hospitalized, and there are unverified reports of death from acute cases of lung infection. The fungus can be eliminated by soaking the hoses, mouthpiece and non-return valves in a mixture of 2 oz Zephiran Chloride and one gallon water; should metal parts be soaked, add 16 antirust tablets to prevent corrosion. An alternate procedure (U.S. Navy 1970) is to scrub the hoses with surgical soap and rinse with a 100 ppm chlorine solution. A non-corrosive germicidal and fungicidal disinfectant should be used on metal parts; remove disinfectant before using equipment. External Ear Infection Ear infection or "fungus" may be considered an occupational disease of divers. The actual infection is usually contracted in contaminated or warm climate waters due to bacteria similar to those which cause pimples and boils. To prevent infection rinse ears with a 50% to 70% alcohol solution after diving to dry the ear canal. If infection develops, it is necessary to consult a physician for treatment.

70 Hp ervent ilat ion Sndrome Hyperventilation initiated by anxiety and/or physical stress may result in unconsciousness or muscle spasms as possible consequences of excessive depletion of carbon dioxide with subsequent acid-base imbalance in the blood and body, In the water this can result in drowning. Some individuals are more susceptible to low CO2 tension (hypocapnia) than others; however, loss of consciousness and muscle spasms could probably be induced in almost anyone with sufficiently prolonged hyperventilation. Both SCUBA and surface-supplied divers should be aware of the problems associated with hyperventilation. If the diver notices that he is involuntarily hyperventilating, he should take immediate steps to slow his breathing rate, A SCUBA diver should notify his buddy and, if feasible, promptly ascend, When he reaches the surface, he should inflate his lifejacket, Don't attempt to swim to the boat or shore unaided since unconsciousness may be imminent. A tender should continuously monitor his diverts breathing for signs of hyperventilation. If the diver starts to hyperventilate, he should be asked to stop work and rest. Holding his breath for short periods will aid in replenishing low C02 levels and possibly avert further complications. Drowning and the hyperventilation syndrome are discussed in detail by Prasser (1969).

71 ADDITIONAL INFORMATION For further information on the physiology and medical aspects of diving, the reader should consult U.S. Navy (1970), Dueker (1970), Greenbaum and Hoff (1966), Lambertsen (1967), Lambertsen and Greenbaum (1963), Hoff and Greenbaum (1954), Bennett and Elliott (1969), Goff (1955), Miles (1962), and Committee on Hyperbaric Oxygenation (1966). Psychological aspects of diving and living underwater are discussed by Radloff and Helmrelch (1968). BASIC FIRST AID PROCEDURES First aid is the "immediate and temporary care given the victim of an accident or sudden illness until the services of a physician can be obtained (American National Red Cross, 1957)." Proper first aid can make the difference between life and death. Every diver and person related to diving operations should have a good knowledge of first aid. An American National Red Cross first aid course or equivalent is recommended. The following is a brief reminder of some vital aspects of first aid particularly applicable to diving related accidents as given by U.S. Navy (1963, 1970), American Medical Association (1967), and American National Red Cross (1957). General If the nature of the injury is uncertain, immediately check victim to detect respiration, bleeding, head injury or broken bones. The first objective is to save life by: (1) preventing heavy loss of blood, (2) maintaining breathing, (3) preventing further injury or contamination of wounds, (4) preventing shock, and (5) sending for a physician. The first aider must avoid panic, inspire confidence, and do no more than necessary to sustain life until professional help arrives. Obtain the services of a

72 physician in all but minor uncomplicated wounds or burns. Never release a victim that has been tnconscious without first being examined by a physician. Control of Iealt Bleedin If bleeding is heavy from wounds to one or more large blood vesselst this must be stopped- before anything else, Such heavy loss of blood can result in death in 3 to 5 minutes. Immediately apply pressure directly over the wound with dressing, clean cloth, or hand or fingers. Secure dressing with bandage or cloth strips and elevate bleeding part higher tha e est th rs the body unless bones are broken. Keep victim lying down and take shock prevention measures. Administer liquids (water, tea, coffee) if the victim is conscious and can swallow. Do not give alcoholic beverages or any liquid if the victim is unconscious or abdominal injury is suspected, Use a tourniquet only for an amputated, mangled, or crushed limb or profuse bleeding that cannot otherwise be controlled. Use only a wide, strong piece of cloth. Wrap tourniquet around upper part of limb above wound, Tie with an overhand knot, place a short stick on the knot, and secure with a square knot. Twist stick just tight enough to stop bleeding. If there is delay in getting to professional help, cautiously loosen the tourniquet in 20 to 30 minutes. If no bleeding recurs, leave loose; retighten if bleeding resumes. Keep under constant observation and mark TKI" on victim'$ forehead, Do not cover tourniquet, Artif icial Res prationl If the victim is apparently not breathing or the lips, tongue, and fingernail become blues start artificial respiration immediately; seconds

73 count. When in doubt, begin artificial respiration since little or no harm can result from its use and delay may cost the victim's life Mouthto-mouth breathing is generally considered the best method since it can be performed in a number of positions including in the water or in cramped surroundings, requires no special equipment, is not fatiguing for the first aider, and allows the first aider greater control of a procedure. Proceed as follows: 1. Quickly check mouth and throat for obstructions. Remove vomitus, mucus, etc, with a cloth or index finger. Tilting the head and body to the side is helpful. 2. Turn victim on his back. 3, Lift victim's neck with one hand and tilt his head by holding the top of his head with your other hand. If necessary, pull the chin up so the tongue doesn't fall back to block the airway. 4. Close the nose by pinching with fingers. 5. Take a deep breath and place your mouth over the victim's mouth, making an air tight seal. 6. Blow rapidly until the chest rises; forecfully into adults and gently into children. 7. Remove your mouth and let the victim exhale while you take another breath. 8. Repeat inflation of the lungs 12 to 20 times per minute until the victim is pronounced dead or regains breathing. Do not give up. Prevention of Shock Shock is a serious complication in almost any injury, severe illness, or emotional upset. Signs of shock include: (1) cold, moist skin, (2) paleness, (3) chilling, (4) nausea or vomiting, (5) shallow breathing, and (6) weak, rapid pulse. Prevent or treat as follows:

74 1. Keep victim lying down with head slightly lower than the rest of the body (fxcept if head injury is suspected or this position causes breathing difficulties). 2, Keep victim warm by covering, 3, If conscious, able to swallow, not vomiting and has no apparent abdominal injury, give liquids (water, tea, coffee, etc.; never alcoholic beverage), Give shock solution (1 qt water, 1 tsp salt, 1/2 tsp baking soda) if available. 4, Keep victim calm and reassure, Minor Wound Small cuts and abrasions are common for divers. Infection is the principal danger in small wounds, so any break in the skin must be protected, Do not touch a wound with your fingers or allow clothes to touch it. Keep it clean, Do not use an antiseptic on the wound. Immediately cleanse the wound and surrounding area with soap and warm water, wiping away from the wound. Hold a sterile pad firmly over the wound until bleeding stopso Apply a clean dressing and secure with a bandage, Bandaids may be used for small wounds, Burns Burns result from heat or chemicals. Any burn, including sunburn, may be complicated by shock and the victim must be given first aid for shock. Place the cleanest available material over all burned body areas to exclude air. Nonalcoholic liquids are beneficial if possible. Transport victim immediately to hospital for severe burns. All burns, except where skin is reddened in only a small area, should be seen by a physician, Do not apply ointments, grease, baking soda, or other substances to extensive burs,

75 Head Injury It is difficult to discover internal injury to the head. Suspect a brain injury if the person loses consciousness, or has blood or fluid escaping from the ears or nose, slow pulse, headache, convulsions, different size eye pupils, or is vomiting. It is necessary to keep the victim lying down and under close observation. Do not place the head lower than the feet. If the victim is unconscious, remove false teeth or objects that might cause choking. Do not move if there is bleeding from the nose, mouth or ears. Control bleeding from a head wound by applying a pressure dressing. Use common sense in regard to using pressure over a possible skull fracture. Convulsions Do not attempt to restrain or douse victim with water. Remove objects that might injure victim or in close quarters, surround with padding (pillows, air mats, blankets, etc.). Don't place a finger or hard object between the teeth. Injury to Spine or Neck If possible, do not move victim or allow victim to move without proper stretcher and professional assistance. If the victim must be removed from the water and a neck or head injury is suspected, support victim taking care not to move the head, neck or back. Place a stiff, wide board under victim and secure with straps. Keep head level and under slight tension. Do not let it drop forward. Keep victim warm and quiet until professional assistance is available.

76 Fractures Do not move a person with suspected fracture until it has been splinted unless the victim is in imminent danger. Place the limb in as natural a position as possible without causing discomfort. Apply splints which are long enough to extend beyond the joints above and below the fractured area, Any firm material can be used. Inflatable splints are excellent. Secure splint at a minimum of three sites; above the joint above the fracture, below the joint below the fracture, and at the level of the fracture, If the fracture is open, apply a pressure dressing to control bleeding and prevent contamination and splint without trying to straighten the limb or return it to natural position. Heat Exhaustion A person suffering from heat exhaustion has pale and clammy skin, rapid and weak pulse, weakness, headache, nausea, and possibly, cramps in abdomen or limbs. The victim should be kept lying down with the head level or lower than the rest of the body. Move him to a cool place; however, protect him from chilling. Give the victim salt water (1 tsp salt to 1.qt water) if he is conscious. Heat Stroke A heat stroke victim will have flushed, dry, and hot skin, rapid and strong pulses and is often unconscious. Cool the body by sponging with cold water or cold applications and if the victim is conscious, give salt water (1 tsp salt to 1 qt water),

77 Frostbite As frostbite develops the skin changes from a pink color to white or greyish-yellow. Initial pain quickly subsides and the victim will feel cold and numb. Generally he is not aware of frostbite. Cover the frostbitten area with a warm hand or woolen material. If the fingers or hands are frostbitten, have the victim hold his hand next to his body, in his armpits. Get victim to heated area as soon as possible and place frostbitten part in warm water (1080 F). If this is impractical, gently wrap area in blankets. Do not rub with snow or ice; let circulation return naturally. When part is warmed, encourage the victim to exercise fingers and toes. Do not use hot water, hot water bottles or heat lamps on frostbitten area. Snake Bite Poisonous snake bites must be dealt with immediately. With exception of the coral snake, in the United States poisonous snakes can be recognized by the presence of two distinct punctures caused by the fangs. Swelling occurs rapidly and the skin becomes dark purple in color. Lie victim down immediately and apply a constricting band around the arm or leg above the bite if the bite in on a limb. Tighten the band just enough to make veins stand out prominently under the skin without causing the pulse to disappear below the band nor cause a throbbing sensation. Keep the victim absolutely quiet and transport immediately to a physician. Apply ice over the bite if possible. If there is to be considerable delay between occurrence of bite and treatment, make a crosscut (approximately 1/4 in. long and 1/4 in. deep) over each fang mark to encourage free bleeding. Apply

78 suction by mouth or suction device; continue for at least one hour. After the first hour, the band may be loosened for approximately 1 minute in every 30 minutes. The victim may administer first aid to himself.

79 DIVING ACCIDENTS: RECOGNITION AND FIRST AID Probably the most serious mistake in dealing with diving accidents is the failure to recognize air embolism or decompression sickness. In many incidences these may be indistinguishable from each other; however, they both require the same first aid measures and recompression. In the more serious situation, death is generally the consequence of failure to recompress and permanent damage of some degree can be expected in all untreated cases. Regardless, they must at least be considered in diagnosis of almost any abnormal sign or complaint presented by a person who has been underwater with breathing apparatus. Unconsciousness, during or following a dive, presents a particular problem of diagnosis and management; however, one practical rule can be given: an unconscious diver must be considered a victim of air embolism or decompression sickness until proven otherwise by medical personnel. These conditions can coexist with seemingly more obvious causes of unconciousness such as apparent or "technical" drowning (Bond 1965) and injury to the head. Spontaneous recovery doesn't rule them out if neurologic defects remain. Respiratory arrest from any apparent cause must also be managed the same as unconsciousness if the victim has been using underwater breathing apparatus. However, obviously the standing rule for first aid if the diver is not breathing must be to administer artificial respiration immediately and continue while the victim is being transported to a recompression chamber, has regained natural breathing or has been pronounced dead by medical personnel. All divers and personnel connected with diving operations must know how to apply mouth to mouth artificial respiration. Using a

80 lifejacket or float, artificial respiration can be administered while the diver is still in the water and being returned to the base of operation. A mechanical resuscitator has advantages; however, do not wait for the resuscitator, start manual artificial respiration immediately while the resuscitator is being brought to the scene and readied. Neurologic disorders short of unconsciousness must likewise be considered as resulting from air embolism or decompression sickness in almost every case. Nearly the entire spectrum of central or peripheral nervous symptom involvement manifestations can be produced or simulated by these conditions, Air embolism nearly always manifests itself during ascent or within a few minutes after surfacing, and the symptoms are usually major, Decompression sickness, on the other hand, may become evident many hours after the dive and may involve anything from minor local defects to unconsciousness and convulsions, Blody froth, coughed up or seen at the nose or mouth, signifies lung injury. When a diver using underwater breathing apparatus exhibits this symptom, particularly if associated with neurologic disorders, he is probably a victim of air embolism. In breathhold diving, bloody froth generally indicates thoracic squeeze, Unconsciousness, respiratory arrest, neurologic disorders and certain associated manifestations are indicative of air embolism. Symptoms are dramatic and sudden in onset and brain damage or death can result in a matter of minutes; recompression is the only proper treatment. What first aid procedure can possibly benefit the victim? Kruse (Bohmrich 1965) observed dramatic relief from symptoms of air embolism when he placed a victim in a 150 head down position. Atkinson (1963) conducted a series of

81 experiments with laboratory animals in which he injected emboli and tilted the animals in a 15~ head down position. This technique was successful in increasing intravenous pressure, dilation of the venous system and capillary bed of the brain, dislodgement and dispersion of emboli, and restoration of circulation. The tilt table technique is not considered as a substitute for recompression, but as a slight modification of the standard position used in first aid for a victim of shock. The resultant intracranial vascular pressure increase may be paramount in the prevention of permanent brain damage, Atkinson (1963, p. 702) states that, "In view of the serious consequences of the neurologic manifestations of air embolism, the supine Trendelenberg position (150, head down) might be considered as a first aid measure until recompression can be accomplished." The victim is maintained in this position while enroute to a recompression facility and resuscitation may be accomplished in this position if necessary. Based on laboratory experimentation, the 15~ tilt appears preferable. Mediastinal and subcutaneous emphysema and pneumothorax are often associated with air embolism. If symptoms of these conditions are indicated, consider the diver as a victim of air embolism and take appropriate first air measures, Damage to the ears and sinuses can result in local pain, hemorrhage, and subsequent infection. Most submarine medical officers conclude that a strict "hands-off" policy results in fewer complications and more rapid healing. Seek medical attention if drainage, tenderness, and infection persist. The primary first aid procedure for respiratory problems (anoxia, CO2 excess, CO poisoning, near drowning, and oil-vapor inhalation) is breathing fresh air. If breathing has ceased, start artificial respiration

82 immediately. All victims must receive first aid for shock and medical attention, even if the victim is revived without medical assistance. Carbon monoxide victims must be treated with oxygen, preferably under increased pressure (recompression). Oil-vapor inhalation victims may be retained for medical observation. The proper action for almost all diving casualties can be summarized in four simple statements (U.S. Navy 1970): 1. If the diver isn't breathing, start artificial respiration immediately. 2, Acquire medical attention at once (unless the injury is a mild or simple condition). 3. If the diver is injured, give appropriate first aid (combat shock; Trendelenberg position). 4, If there is any possibility of air embolism or decompression sickness, arrange for immediate transportation to a recompression facility,

83 RECOMPRESS ION It is absolutely essential that a victim of decompression sickness or an air embolism be treated by recompression as soon as possible following the appearance of symptoms. In cases of decompression sickness prompt and adequate treatment will generally preclude the development of residual damage. It is well established that the incidence of slow or incomplete response to treatment and the magnitude of residual damage are directly proportional to the length of time between the first appearance of decompression sickness symptoms and the beginning of recompression procedures (Dewey 1962). In cases of air embolism, the brain is frequently involved; when it is, the symptoms are usually extremely serious and unless the victim is recompressed promptly, death or permanent residual damage may follow a delay of 1 or 2 minutes (U.S. Navy 1970). Transportation to the nearest facility equipped with a recompression chamber must be by the most rapid means available. When the distances are great, an ambulance is generally not the most rapid transportation available. Efforts should be made to obtain a helicopter or other airborne conveyance under such circumstances. Flight at a low altitude will not appreciably aggravate the victim's condition and is of minor consequence when the alternative is delay (Dewey 1962, p.818). All the technical and theoretical details of treatment by recompression will not be reiterated here. Complete and authoritative discussions are available in U.S. Navy (1970) and Lanphier (1966). Lanphier points out that the purpose of recompression is to provide prompt and lasting relief from symptoms of decompression sickness and air embolism. Recompression procedures

84 are designed to reduce the bubble to a size at which they become asymptomatic and to insure that no bubble becomes symptomatic upon subsequent decompression. Procedures must be such that no new bubbles form in the process, Proper treatment must be conducted under the auspices of specially trained personnel. Improper or inadequate attempts by untrained personnel to recompress a victim may result in even more severe damage than the initial manifestations. There are a number of important considerations in the application of recompression treatment to decompression sickness. It is important to treat even doubtful cases, since failure to treat can result in serious complications. As previously stated, the recompression must be prompt for delay further complicates treatment and recovery. Recurrence of symptoms is not uncommon, even during or immediately following properly prescribed treatment (Rivera 1964; Goodman 1967). Consequently, the treated victim should remain near a treatment facility for at least 24 hours following treatment. Appendix III contains the various treatment schedules currently used by the USo Navy, It can be readily seen that more serious manifestations require compression to a greater depth and extend the time required for treatment. Oxygen is used at shallower depth to reduce the alveolar pN2 to the lowest possible level, thus creating a "steeper" gradient across the alveolar membrane to enhance the diffusion of gas. Why are victims of decompression sickness or air embolism not compressed to depths greater than 165 feet to even further reduce the size of offending bubbles? The reason becomes clear if one considers the fact that the diameter, not the volume, of the bubble is the critical dimension governing

85 symptom development. Whereas the volume is inversely proportional to the absolute pressure, the diameter is inversely proportional to the cube root of 2 times the pressure. Consequently, recompression to 165 feet reduces the bubble volume to one-sixth of its surface value; however, only decreases the diameter of the same bubble by a factor of 1/3,35. Recompression to a pressure equivalent to 858 feet only reduces the diameter by a factor of as much as 1/5. Clearly, recompression to depths greater than 165 feet offers little more than additional complications. There is an increasing awareness of the incremental frequency with which difficulties are encountered in recompression treatment of severely injured divers and the grossly inadequate decompression now characterizing civilian diver casualties. Current U.S. Navy recompression procedures are, in general, reliable for treatment of "pain only bends" subsequent to exposures conducted in accordance with the U.S. Navy (1970); however, inadequate in the treatment of severe decompression sickness following grossly inadequate decompression from compressed air dives. Goodman and Workman (1965) and Goodman (1967) reviewed this situation and developed and evaluated alternative therapeutic approaches to treatment of decompression sickness. The studies resulted in the development of the "MinimalPressure, Oxygen Recompression Treatment for Decompression Sickness (Appendix III). Goodman and Workman believe that the current U.S. Navy treatment tables should be retained with oxygen recompression procedures alternately available. Goodman (1967) indicates that the new minimalpressure oxygen approach has consistently afforded prompt, complete, and lasting relief in severe decompression sickness. The minimal-pressure oxygen approach is indicated for decompression sickness only; no reference

86 is made to its use in treatment of air embolism. In accordance with U.S. Navy procedures, treatment of air embolism requires between 18 and 38 hours in a recompression chamber, providing there are no complications or recurrence of symptoms. Recently, Waite and associates (1967) conducted experiments with animals to determine if alternate procedures might be feasible. They found that maximum effects of recompression were observed between 2 and 4 atmospheres absolute. However, at present there is insufficient evidence to say that the maximum pressure of 165 feet (6 atmospheres absolute) should be considered as unnecessary. They also found indications that prolonged recompression, as in Tables III and IV of the U.S. Navy Standard Treatment Tables (Appendix III), is not necessary to effectively treat cerebral air embolism. All successful treatment runs in this series of experiments consisted of bounce dives to 165 feet for less than 10 minutes and return to the surface at 60 ft/min with a 2 minute stop at 10 feet (170 foot table). This procedure is not yet prescribed for treatment of air embolism in humans and is not to be used as an alternate to Standard U.S. Navy (1970) procedures. Emergency procedures for handling diving accidents that require recompresion in the Michigan area are given in Appendix IV. A detailed list of recompression chambers has been published by the U.S. Navy (1971). Recompression in the water without a chamber is not recommended because it is extremely hazardous and difficult. Divers have been recompressed using a deep sea diving rig as a substitute for a chamber; however, the U.S. Navy (1970) considers this means only in a "grave emergency." The deep sea rig does offer some protection and a nearly inexhaustible air

87 supply. Any attempt to recompress a diver underwater using SCUBA is invariably dangerous and, almost without exception, futile. Inadequate treatment of air embolism and decompression sickness is frequently worse than none (Lanphier 1957, p. 127). Possibly, future medical research and the development of sophisticated SCUBA will open new avenues of practical field treatment of less complicated cases. However, at present, all suspected victims of air embolism or decompression sickness must be transported to an approved recompression facility without delay. The layman is cautioned against attempting to administer recompression. Such action without supervision by a licensed physician can involve risk not only of harm to the victim but may involve legal complications, both civil.and criminal. Recomnpress ion Chambers A recompression chamber (Figure 2-3) is a chamber in which a diver may be put back under pressure for treatment of decompression sickness or air embolism or for surface decompression procedures. The chamber is generally constructed of metal and has a working pressure of at least 75 lbs/in2, Maximum working pressure capability and size will depend on mission requirements. A double-lock chamber, two separate compartments capable of being pressurized independently, large enough to accomodate two divers and an attendant in the main compartment is recommended, Double-lock chambers generally have an inside diameter of 48 inches or more. The chamber should be equipped with oxygen breathing equipment which is designed to prevent excessive accumulation of oxygen in the chamber. Air and oxygen supply system will depend on the installation, size and type of chamber.

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89 Small portable chambers are not commonly used by the U.S. Navy and the commercial diving industry. However, they may have value when no other chamber is avilable and diving activity is conducted at a great distance from a larger chamber. The U.S. Navy (1970) indicates that even if the chamber is so small that it only accomodates a single victim, it is far better than no chamber at all. The value of the portable chamber is increased if it is designed to facilitate transfer under pressure to the nearest larger chamber. For further information on design specification and operation of recompression chambers consult U.S. Navy (1970). Information on general requirements for materials certification in hyperbaric facilities is given by U.S. Navy (1970a).

CHAPTER III DIVING PROCEDURES Diving procedures is a subject that is frequently ignored in sport diving manuals used for many research diving training programs. Since research diving operations must be conducted at the highest possible level of efficiency and safety, it is necessary that all personnel have a knowledge of standard operational procedures. Basic procedures as given in this chapter are modified from U.S. Navy (1970) for compatibility with research diving operations, Somers (1971) gives the diving operation regulations and procedures used at the University of Michigan, Also Included in this chapter are decompression procedures and cold water diving techniques and equipment, PERSONNEL Diving Supervisor The diving supervisor should hold a diver's certificate valid for the depth at which diving operations are being conducted and be qualified in the use of all equipment used in the diving operation for.which he is supervisor, The diving supervisor is in complete charge of a particular diving operation at the scene. His primary function is to plan, organize and manage the diving operation. He is responsible for maintaining safety standards and must not tolerate violations of accepted diving procedures and standards. On major operations the diving supervisor will generally not enter the water. His usual post is on the surface where he is in full 91

92 command of surface personnel and in a position to direct tenders and stand-by divers in an emergency situation. In order to utilize diving capabilities to maximum efficiency, an individual with proper qualifit cations may temporarily assume diving supervisor responsibilities while that person is working as a diver. However, it is absolutely necessary that a diving supervisor be in charge at the surface during all major diving operations, He should not be burdened with added responsibilities such as tending, timekeeping, communications, etc. On simple and limited diving operations, particularly when using SCUBA, the diving supervisor may also assume responsibilities as a diver and team leader. Diving Teams A SCUBA diving team must consist of no less than two divers, Diving alone should not be permitted, and all team members must hold a valid diving certificate. A leader will be designated for each diving team prior to entering the water, and it will be the responsibility of the other divers to stay in visual or physical contact of the leader, If a diver becomes separated, he should promptly surface or return to a previously designated location, A diving supervisor will be designated for each diving operation. His qualifications and responsibilites are in accordance with those previously described, The tender must be qualified to independently tend divers and operate all surface support equipment. He may be trained in theory and operational aspects by the divers and diving supervisors. Ideally, tenders should be previously trained by instructors and assigned to diving

93 operations by the diving supervisors. A tender-assistant may assume tender responsibilities when under the direct supervision of a fully qualified diving and tending personnel. He may receive instruction in proper tending procedures during field operations. A tender should be assigned as communications man, timekeeper, record keeper and diverts assistant. It is recommended that one qualified person shall be designated as a "stand-by" diver and should be ready to enter the water promptly in the event of an emergency. The stand-by diver may accept tender responsibilities in routine operations; however, in more complicated diving operations the stand-by diver must be free from all other duties, A surface-supplied diving team (deep-sea, lightweight helmet, shallowwater mask, hookah, etc.) should consist of a certified diver and tender. When a surface-supplied diver is required to work under obstacles or when there is a possibility of entanglement, a stand-by should be ready to enter the water promptly in the event of an emergency. For all dives in excess of 60 feet it is highly recommended that a stand-by diver and tender be prepared to commence operations within one minute. PRELIMINARY DIVE PLANNING Preliminary planning is vital for the success of any diving operation. Without adequate preparation the entire diving operation may fail and, even more seriously, the safety and well-being of the divers may be jeopardized. The diver must be placed on the job under optimum conditions including sufficient knowledge, training, experience, equipment and safety. Surface support must be capable and well organized. The diving supervisor is responsi

94 ble for preliminary planning and organization, However, the diving team and ship's crew mst render all possible assistance. The preliminary planning phase of a diving operation is divided into the followingf 1, Survey of mission or task, 2, Evaluation of environmental conditions. 3, Selection of diving techniques, 4. Selection of divers and assignment of job. 5. Selection of equipment, 6, Fulfillment of safety precautions, 7, Establish procedures and brief personnel. SEure of ^Mission or Task The first step in planning a diving operation is to assess the mission or task and to formulate a general approach. It should be determined if th is feale aobd if the proper equipment and personnel are available to undertake the job, All factors that might constitute a specific hazard ahould be noted, Evaluation of Environmental Conditions Diver safety, especially self-contained divers, is influenced considerably by environmental conditions. Careful consideration must be given to both surface and underwater conditions and appropriate arrangements made for diving under these conditions. Surface conditions to be considered include sea state, weather (present and predicted), tides, currents, ship traffic, etc. Underwater conditions include depth, bottom type or condition, visibility, and temperature. Weather conditions will generally be the first factor to consider in planning a dive. When possible, diving operations should be canceled or delayed during bad weather, Generally, rough seas can be expected during

95 storms and high winds. Weather forecasts must be reviewed to determine if proper weather conditions will last for a sufficient amount of time to complete the mission. Critical weather changes and a wind shift can jeopardize safety of personnel and vessels. Conditions must be such that adequate mooring may be maintained for the duration of the operation. Do not attempt self-contained or surface-supplied diving in rough seas (Sea State 4: 5 to 8 ft waves) and, when possible avoid or limit diving in moderate seas (Sea State 3: 3 to 5 ft waves). Naturally sea state limitations will be dependent to a large degree on the type and size of diving vessel. Diving operations may be conducted in rougher seas from properly moored larger vessels or fixed structures. Land based self-contained divers should avoid entering the ocean in heavy surf. Entry through surf will be discussed in a future publication. Current and tidal conditions must be considered before commencing with diving operations. Current direction and magnitude are important considerations when mooring a diving vessel. When currents exceed 1 knot, self-contained diving operations should be avoided unless adequate previsions are made for a diver pick-up boat to operate down current. Divers should carry smoke flares. Heavily weighted surface-supplied divers are frequently required for work in currents. Tidal currents may prohibit diving at some locations except during periods of tidal current direction change. Consult tide tables when necessary and determine magnitude of tidal currents prior to diving. Self-contained diving operations should not be conducted during periods of low visibility (fog, snow, rain, etc.). Self-contained divers are particularly vulnerable during periods of low visibility since they

96 may lose orientation and be unable to relocate the diving vessel or shore base. Also, the diving vessel may be in danger when anchored during periods of limited visibility, Surface-supplied diving is permissible under limited surface visibility conditions providing the diving vessel can safely anchor. ShipBtraffic may constitute a hazard to divers, particularly selfcontained divers, It is necessary to display proper visual signals in a prominent location on the diving vessel during operations in order to notify approaching vessels that divers are in the water. The following signals are appropriate: 1. American Diverts Flag: This is a red flag 4 units wide by 5 units long with a one unit wide white diagonal from the upper left to lower right corners. Sizes are not standardized and will vary with the size of the vessel, 2, International Code of Signals: The two letter signal "H.D." has the meaning, "I am engaged in submarine survey work; you should keep clear," 3. NATO Navies, Flag Numeral 4: This flag (a red flag with a white St. Andrew's Cross) flown alone means, "Divers or friendly underwater demolition personnel down." 4, Underwater Task Shapes: A "red ball - white diamond - red ball" shape display spaced 6 ft apart may denote diving operations. Self-contained divers must tow a float on which a diverts flag is displayed or be accompanied by a chase boat with a diver's flag if they operate out of the immediate vicinity of the support ship. The flag must be 3 ft above the water. Diving personnel must be protected from excessive exposure to adverse weather conditions, When working in tropical areas, the staging area should be shaded to prevent overexposure to sun. During cold weather in northern waters d s and surface personnel must be protected from cold air temperatures and rwind, Divers should not be expected to dress in an open unprotected

97 vessel. When working from small craft, divers should dress prior to leaving shore base. If under ice dives are required, dress in heated shore facilities or heated portable structures on ice. Do not submit divers to excessive exposure prior to the dive. Heated quarters and warm showers should be available immediately after surfacing. The selection of diving dress and equipment will depend on the mission, weather conditions, and type of vessel. For example, even though water temperatures may permit the use of wet type suits, cold air temperature and wind would dictate a variable-volume dry suit (or equivalent) when diving from an open or unheated vessel. In addition, double hose regulators should be used with open-circuit SCUBA for diving in extremely cold weather and water. The type of bottom effects the diver's ability to work and is a factor in determining visibility. Consequently, this must be considered in the preliminary dive plan and certain precautionary measures may be necessary to insure the diver's safety and efficiency. Mud (silt and clay) bottoms are generally the most restrictive for divers. The slightest movement will stir sediment into suspension and restrict the diver's visibility. The diver must orient himself so that the current, if any, will carry the suspended sediment away from the work area and he must use a distance line. Since the self-contained diver is more hampered by the limited visibility, surface-supplied diving techniques should be considered for work. For general survey work self-contained diving techniques have certain advantages. The diver can weight himself to be neutral at survey depth and move about without touching the bottom.

98 Sand bottoms present little problem for divers. Visibility restrictions from suspended sediment are less and footing is firm. In marine areas the diver must be alert for sting rays buried in the sand. Coral reefs are solid with many sharp protrusions, The diver should wear gloves and coveralls or a wet suit for protection if the mission requires considerable contact with the coral. Survey divers and photographers have to be cautious to avoid injury. Learn to identify and avoid corals and any marine organisms that might inflict injury. WatIer deth is a basic consideration in the selection of personnel, equipment, and techniques. When possible, determine the depth accurately prior to diving and plan the dive duration, air requirements, and decompression schedule accordingly. Water temperature is a major factor to be considered in dive planning since it will determine the type of equipment (diving suits) and, in some cases, the practical dive duration. Cold water diving procedures and equipment are discussed later. Underwater visibility depends on locality, water conditions, season, bottom type, weather, and currents, Dark or murky water is a disadvantage in all underwater operations. Self-contained diving should be avoided under limited to zero visibility conditions when possible and surfacesupplied diver used. If self-contained divers must work in limited visibility water, a "buddy"t line is recommended. Self-contained divers are at a considerable disadvantage especially if decompression is required. In addition to a descent (shot) line, a distance line carried on a reel is required. This enables the divers to return to the shot line for controlled ascent. Short distance lines are also desira

99 ble for surface-supplied divers in limited visibility. An alternate method of controlling ascent and decompression is by the use of an inflatable float with a line marked (at 10 ft intervals below the float) which is twice as long as the diving depth. At the end of the dive the diver releases the float and secures the line to an object on the bottom with a releaseable knot. He may then ascend to the appropriate decompression level unreeling the remaining line below him. When he surfaces, the diver simply tugs on the free end of the line to release the knot and to retrieve the line. Self-contained divers must establish a procedure for reunion of separated divers. Generally, the best procedure is to surface or return to a predetermined bottom location if separated. Striking the SCUBA cylinder with a rock or knife has only limited value in reuniting separated divers.

100 Selection of Diving Techni ues The proper diving technique, SCUBA or surface-supplied, is based on the mission requirements, environmental conditions, and available personnel. It is the responsibility of the diving supervisor and divers to review the situation and determine which technique to use. The advantages and limitations of various techniques are discussed in respective chapters. Selection of Diversand Assignment of Jobs The diver must be qualified and designated in accordance with the depth and equipment rating required for the mission. Consult Somers (1971) for diver rating. The diving supervisor is responsible for determining the qualifications of a diver before assigning him to a mission. In addition to the diver, the diving supervisor must designate qualified tenders, timers and stand-by divers, Selection of Equipment The diving supervisor and divers will determine whether to use SCUBA or surface-supplied diving equipment for a particular mission based on a review of the mission requirements, personnel available and environmental conditions. The diver must be outfitted with the proper equipment to complete the mission or task assigned. Minimum equipment requirements for self-contained and surface-supplied divers are in respective sections of this manual. When selecting equipment, the diver should not overburden himself with accessories. Use only the equipment required for safety and completion of the mission or task. When the diver is encumbered with excess equipment, the possibility of entanglement and fatigue increases,

101 Fulfillment of Safety Precautions All personnel associated with the diving operation are responsible for maintaining proper safety standards. Ultimately the diving supervisor (or team leader) must assume responsibility for the safety of the divers. He must evaluate each and every aspect of the operation. Safety is considered in all aspects of preliminary planning. Divers must not be committed to a mission or task which is unreasonably hazardous or for which they are not sufficiently trained or equipped. In evaluating environmental conditions and the dive site, the diving supervisor must train himself to anticipate potential hazards and take appropriate measures to protect the divers from these conditions. Naturally, all hazards can not be eliminated from any diving operation; however, they can be minimized. If a particular hazard is foreseeable, it can usually be eliminated. The diving supervisor may wish to prepare a list of potential hazards including precautionary measures to use when setting up the operation and briefing the personnel, Establish Procedures and Brief Personnel The diving supervisor or team leader, after careful evaluation of the above factors, will establish the operational procedure and brief all personnel. The procedure and briefing should include the following information: 1. Objectives and scope of the operation. 2. Conditions in the diving area. 3. Dive plans and schedules. 4. Assignment of personnel: buddy teams, divers, tenders, and specific tasks for each. 5. Safety precautions. 6. Special considerations,

102 Diving& Vessel Research divers will be required to dive from vessels (or boats) of various sizes and descriptions ranging from small inflatable rubber boats such as the Zodiac to large research vessels 300 to 400 feet in length. The type and magnitude of diving, operation, and environmental conditions will determine the type of vessel. For example, nearshore self-contained diving in relatively calm water may be accomplished without much difficulty from a good quality rubber inflatable boat or small wood, metal or fiberglas boat equipped with a dependable outboard engine. More extensive offshore self-contained diving operations or surface-supplied diving must be undertaken from a large vessel with adequate deck space and seaworthiness. The following factors must be considered relative to the mission requirements: 1. Adequate size to comfortably accommodate divers, surface personnel and equipment, 2, Sufficient stability and seaworthiness to function as a platform for diving operations. 3, Vessel well maintained, in satisfactory operating condition, and equipped with proper safety equipment as required by state and/or federal laws. 4. Large open work area, 5. Provide adequate protection from sun or cold. 6. Mooring capability (3 or 4 point moorings may be required). 7. Sufficient storage space to accommodate diving equipment when not in use. 8, An adequate ladder to facilitate entering and leaving the water. The diving ladder is a very important part of the boat's equipment. Most boats, unless specifically designed and equipped for diving, will not

103 have a ladder that is safe for use by divers. Serious injuries have resulted from the use of inadequate ladders. The ladder should include the following features: 1. Metal construction. 2. Extend 4 to 5 ft below the water line. 3. The rungs should be wide enough to allow comfortable use with bare feet and stability with heavy diverts shoes. 4. A hand rail should extend the full length of the ladder in order to give the diver a "hand hold" until he is completely on deck. 5. The ladder should have about a 10-15~ inclination relative to the side of the vessel. 6, The ladder should be secured to avoid movement when the diver is on it.

104 DECOMPRESS I ON PROCEDURES The necessity for decompression depends upon the depth and duration of the dive, Dives should be planned to avoid decompression when possible, especially by self-contained divers. When decompression is inavoidable, the diving supervisor or team leader must provide adequate arrangements for handling it. The standard method of decompression is to bring the diver to the surface with stops at various depths for times specified by U.S. Navy (1970) Standard Air Decompression Tables (Appendix III). In addition, decompression meters are currently widely used for SCUBA diving decompression. Decompression for self-contained divers is somewhat more complicated than for surface-supplied divers, The dive must be thoroughly planned in advance, Depth, dive duration, and air supply must be properly calculated to insure that the diver is not forced to the surface without adequate decompression, The diver must be equipped with a watch and depth indicator and carry a small slate on which is recorded the decompression schedule. There are four techniques for decompression in self-contained diving: a. Plan the dive so that decompression may be completed on the original SCUBA, b. Switching to a surface-supplied mask or demand regulator at the first decompression stop. c, A second SCUBA attached to a line at the first decompression stop. d. Surface decompression chamber. Most depth indicators are inadequate for determining precise decompression stop depths, A line or chain marked at 10 ft intervals and weighted heavily enough to keep it vertical in a current is adequate. The diver should

105 hold the line just below the proper marker in any comfortable position where the lower part of his body is not above the marker. Decompression is generally simpler and safer for surface-supplied divers. Sufficient air supply for completing decompression is available from the compressor or large air cylinder units. Since the dive duration is timed accurately by surface personnel and depth is determined by sounding or pneumofathometer, the diving supervisor or tender may accurately determine the decompression schedule, The decompression stop depths are indicated by a marked line, pneumofathometer, or markings on the diver's umbilical. Decompression is controlled by the diving supervisor and/or tender. A decompression stage may be used to facilitate decompression. If a stage is not available, the diver may be held securely at a given depth by tension on his umbilical or he may hold himself in place on the descent line. For long decompressions without a stage, a boatswain chair or sling may be rigged and secured to the descent line with a prussik knot. Surface decompression procedures may be used if a chamber is available. Automatic Decompression Meter The decompression meter (Figure 3-1) is increasing in popularity among both sport and research divers. In the research diving field, these meters are used by many organizations including Scripps Institution of Oceanography (personal communication: James Stewart), the University of Washington (personal communication: Charles Birkeland) and the University of Michigan. The decompression meter is designed to simulate the physiological processes of nitrogen absorption and elimination by the human body. The

106 UB[ABE eSiC CAE PLE!6.A StjSS*' -:-i B*!.*...........................................................5 o s F t.......................................................................................................'.'.""*....'.B|0 -''........ ~~~~~~~~~~~~~~~~"-.........../................................................................ 0 R O L B { ~ ~ N 14 ~IV ~ i~t WI0 |U~u I t;f Aflu;tt JIV I run;S~ PilESS ~ ~ ~ VURE V'i*) PORTS* "..'......................................................-*.... 0... - -. 0 s 5.........................D |..................................... " > > ZA ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~....................\ [ {> \~ < 9 a tGCNA~~~~ttPA~A I I,. FI(,IJRL 3.:,I. AutomXati:e d ocompz, a;~.~on mtetwoe: (computt::,.~) o (a) Illust~ratilon oou~:~oay o)f,(:CUBAPRO~ (bs) l:)iag~n f~7om AlldetNoPN (19SI7)R UNI3R.... A......AT.AS.PE...S NO 2A O.........S...... AG.N' S A.................A..I..............................................~~~~~~~~~~t................OUR.ON.18 HO SIN................PRESSURE.EN....PORTS........... FIGUI~h 31110 utomat o doooprosm In motor(compuer), (a X........Io cour. syo..S.UA....(......m.ro.A.drso.(1 6/)

107 meter automatically computes the diver's decompression. Inspite of its remarkable function, the meter is uniquely uncomplicated, It is composed of a rigid watertight housing which contains a sealed Bourdon tube, a flow restricting ceramic filtering element and a distensible gas filled bag, all housed in a stainless steel case. The Bourdon tube is connected to a indicator needle. The distensible gas filled bag is attached to the Bourdon tube housing with the filter element located between the two, The meter starts operating automatically as soon as the diver submerges, allowing water to enter the static pressure ports on the back of the meter. As the diver descends the pressure compresses the gas in the distensible bag, establishing a pressure gradient between the gas bag and the rigid chamber. The contained gas is forced through the element into the Bourdon tube chamber. This filtering or flow-restricting element is a porous ceramic material that has the relatively same diffusion ratio as the mid-level tissue in the human body. The quantity of gas passing through the element is relative to the time/depth factor. The resulting pressure upon the Bourdon tube activates the indicator. During ascent a reverse transference takes place with gas diffusing through the element from the Bourdon tube chamber to the distensible bag. This simulates the rate of nitrogen diffusing from the human body. The diver ascends directly to the depth indicated on the meter dial. At this depth he slows his ascent to correspond with the counter-clockwise movement of the indicator around the dial. (In the red sector of the dial, insert dashes represent 10 ft, 20 ft, etc, while the dots represent 15 ft, 25 ft, etc.). Never ascend to a depth shallower than that indicated on the meter.

108 The meter must be used in conjunction with an accurate depth gauge or a marked shot line, It is not necessary to decompress by 10 foot increments. Actually, decompression is more effective if the diver "follows" the indicator up, rather than decompressing by stages, because he maintains a maximum safe pressure differential which allows the greatest exchange of gas from the body. However, at the 10 ft level, it is advisable to wait until the indicator says to surface because it is often impractical to attempt decompression in less than 10 feet of water. Most SCUBA divers find that the decompression meter is most beneficial for Savo l decompression, The diver simply terminates his dive before the indicator enters the decompression zone and surfaces directly at 60 ft/min. The "no-decompression" limits designated by the meter are dependent on cumulative underwater time in a 6 hour period. The zones are designated as follows: 1 hr - 2 hr: Cumulative underwater time of one to two hours; the "no-decompression" limit is the edge of the first red rectangle indicated by the arrow, 30 min - 1 hr: Cumulative underwater time of 30 min to I hr; the "nosdecompression" limit is the round dot. 0 - 30 min: Underwater time is less than 30 minutes; the "no-decompression" limit is the radial line adjacent to the numeral 10. When the diver surfaces, the indicator will be in the Memory Zone and it will take at least six hours for the meter to clear itself. Obviously another diver can not use the meter for at least six hours. However, the same diver may make repetitive dives within the six hour period and the saturation (residual nitrogen) time shown on the Memory Zone from the previous dives wi ll automatically be added to the time of the next dive, This makes the meter a valuable unit for operations

109 requiring a large number of repetitive dives. The indicator needle normally remains in the small blue zone of the dial. It may wander within this zone in accordance with changes in barometric pressure. However, if the needle is not in the blue zone prior to the initial dive or does not return to this zone 6 hours after termination of diving, it is likely that the meter has been damaged or is faulty. Do not use the meter until it has been inspected, repaired and recalibrated at an authorized repair facility. How good is the automatic decompression meter? If used with good judgement, the meter proves to be a valuable accessory for SCUBA divers, Perhaps the best use of the meter is to avoid the necessity of making decompression stops, i.e., when the meter shows that the diver is approaching the "no-decompression" limit, he can surface. The meter is particularly helpful to SCUBA divers who make many repetitive dives to different depths for variable times at depth. Sometimes it is extremely complicated to maintain proper diving schedules using conventional repetitive dive tables for such dives. A comprehensive comparison of the SCUBAPRO decompression meter and U.S. Navy Standard Air Decompression Tables was made by Mount (1970), Using the U.S. Navy tables as a "reference standard," the meter is more conservative at depths less than 80 feet, whereas the tables are more conservative in excess of 80 feet. In other words, the decompression meter indicates decompression required at less bottom time on shallow dives and the tables require decompression before the meter indicates on deeper dives. On decompression dives the meter tends to give more decompressio on longer duration dives. In general the meter gives satisfactory (by comparison) multiple

110 dive schedules. Based on Mount's study it appears, however, that repetitive dives with a surface interval of over 6 hours and less than 12 hours on the meter are unsafe and should be avoided. Furthermore, since the meter apparently reaches saturation with a bottom time of two hours, it is recommended that it not be used for divers with bottom times exceeding two hours. The meter is not recommended for short duration (bottom time of 5 minutes or less) deep dives, Mount's findings indicate that the meter requires longer total decompression time for longer bottom dives at depths up to 300 ft than equivalent dives in accordance with the tables. For dives to 200 ft or below, the depth of the first decompression stop appears to be shallower by the meter than by the tables. Basically, controlled research data is insufficient and inconclusive to determine the reliability of the meter over depths of 200 ft at this time. However, many dives have been completed to depths in excess of 200 ft using the meter with no apparent complications. Although these meters appear to be satisfactory for normal operations, they do not take into account the diver's physical condition, amount of work, and other factors affecting the individuals absorption and elimination of nitrogen, Like decompression tables, the meter cannot be considered as "complete" protection against the bends. The diver should still keep track of depth/time factors, as well as surface intervals and other data needed to "double" check against the mechanical factor. The experienced diver can generally judge these factors relative to a meter that is malfunctioning. Periodic checks against another meter is one of the best safety checks. Periodic repair and recalibration service is available for a nominal fee from the manufacturer and U S, distributor (SCUBAPRO). This factory check

111 and recalibration is highly recommended at periodic intervals depending on the amount of use and abuse. Some divers carry two meters as a check for accuracy; however, most divers cannot afford this luxury. Although the meter is used on thousands of dives each year without occurrence of bends, it is not infallible. The meter must be used with common sense and good judgement. Do not interpolate or "push" the meter! The meter is extremely susceptible to shock and damage from excessive abuse. If a meter is dropped or otherwise damaged, it should be returned to the factory for repair and recalibration. Also when being transported by air, the meter must be shipped within the pressurized portion of the aircraft or in a pressure-proof container. Most divers carry their meters with them in the airplane cabin. The meter should be rinsed in fresh water, dried, and properly stowed after each use. Do not attempt to disassemble the instrument or clean the static pressure ports under any circumstances. This could result in severe damage and subsequent malfunction. The manufacturer recommends periodic testing of the meter. This test is conducted as follows: 1. Subject the meter to a pressure equivalent to exactly 30 meters sea water (98.425 ft) in a chamber or by immersion in water. 2. Maintain the meter at this depth for exactly 30 minutes. 3. Rapidly return the meter to the surface and check to see if the pointer is in the zone of the second red rectange ( + 1 mm displacement allowable). If the needle doesn't fall within the above range, the meter is malfunctioning and must be returned to an authorized inspection and repair facility,

112 Repetitive Dives A dive performed within 12 hours of surfacing from a previous dive is a repetitive dive, The period between dives is the surface interval, In conventional diving, for all practical purposes, excess nitrogen requires approximately 12 hours to be effectively eliminated from the body, The minimum surface interval requiring repetitive dive computation using the U.S. Navy procedures is 10 minutes, For any interval under 10 minutes, add the bottom time of the previous dives to that of the repetitive dive and choose the decompression schedule for the total bottom time and the deepest dive, Specific instructions are given with the U.S. Navy Standard Air Decompression and Repetitive Dive Tables in Appendix I Ie All divers, both sport and research, must understand and be able to calculate dive schedules using the repetitive dive tables. This is the standard method of determining decompression schedules and of avoiding decompression when planning multiple dives. Regardless of the current upward trend in the use of the decompression meter for repetitive dives, the tables are still the only method for the majority of divers who do not have access to decompression meters, Repetitive dive work sheets are included in Figures 3-2 and 3-3.

113 REPETITIVE DIVE WORKSHEET I. PREVIOUS DIVE: minutes see table 1-10 or 1-11 for Groupfeet repetitive group designation II. SURFACE INTERVAL: _hours minutes on surface see table 1-12 Group Group._ (from I.) for new group j III. RESIDUAL NITROGEN TIME: feet (depth of repetitive dive) see table 4 minutes Group (from II.) 1-13 IV. EQUIVALENT SINGLE DIVE TIME: m.inutes (residual nitrogen time from III.) (add) minutes (actual bottom time of repetitive dive) (sum) minutes V. DECOMPRESSION FOR REPETITIVE DIVE: _ minutes (equivalent single dive see table time from IV.) feet (depth of repetitive dive) J 1-10 or 1-1 LI No decompression required or Decompression stops:__ feet minutes feet minutes feet minutes _feet minutes FIGURE 3-2. Repetitive dive worksheet (U.S. Navy 1970).

114 REPETITIVE DIVE WORKSHEET I. PREVIOUS DIVE: Z_~minutes see table 1-10 or 1-11 for Group.. /_ feet repetitive group designationJ II1. SURFACE INTERVAL: Lhours minutes on surface see table 1-12 Group (from I.) for new group III. RESIDUAL NITROGEN TIME: / feet (depth of repetitive dive) see tableb] x minutes Group'- (from II.) 1-13 IV. EQUIVALENT SINGLE DIVE TIME: fMminutes (residual nitrogen time from Mi.) (add) /,minutes (actual bottom time of repetitive dive) (sum) 7Mminutes V. DECOMPRESSION FOR REPETITIVE DIVE: 2 minutes (equivalent single dive see table time from IV.) /. feet (depth of repetitive dive) J 1-lOor l-11 E No decompression required or Decompression stops:, ffeet minutes feet_ minutes __ feet____ minutes feet _ minutes FIGURE 3-3. Repetitive dive worksheet with example of computation for a repetitive dive (U.S. Navy 1970).

115 Interrupted or Omitted Decompression A diver may be forced to surface prior to completing required decompression, especially when using SCUBA. In this event he must enter a decompression chamber or return to the water to complete his decompression. If a chamber is available, immediately recompress the diver to 100 feet for 30 minutes and bring him up in accordance with Treatment Table 1 or 1A. If a chamber is not available, the diver should be returned to the water and decompressed using the following procedure based on the Standard Air Decompression Tables (U.S. Navy 1970): Repeat any decompression stop deeper than 40 ft. At 40 ft, remain for 1/4 of the 10 ft stop time. At 30 ft, remain for 1/3 of the 10 ft stop time. At 20 ft, remain for 1/2 of the 10 ft stop time. At 10 ft, remain for 1 1/2 times the scheduled 10 ft stop time. Upon completing this procedure the diver should be observed for symptoms of decompression sickness and stand-by arrangements for transport to a chamber should be in effect. The U.S. Navy (1970) suggests that Treatment Table 1 or 1A procedures may be attempted at sea; however, it is unlikely that this procedure would be successful for non-military or non-commerical diving operations as it requires surface-supplied equipment, proper water depth, sufficient air supply, sufficient thermal protection, etc. Inadequate decompression on Treatment Table 1 could seriously injure the diver and be worse than the delay required to transport a diver to a chamber should he exhibit symptoms of decompression sickness.

116 Decoression for Dives at High Altitude Standard U.S. Navy Air Decompression Tables are computed for diving with reference to sea level, Two modifications must be made when these tables are used at high altitude to correct for differences in atmospheric pressure. The diver must compute, or refer to a table, to obtain the theoretical depth of the dive and the theoretical depth of decompression stops for a given altitude. Both the theoretical diving depth and decompression stop depths will vary with altitude. There are various procedures and tables for computing decompression for high altitude diving. The tables are based on theoretical calculations and most have not been thoroughly tested. The procedures and tables given below are those recommended by Cross (1967, 1970). These procedures and tables are given because of prior wide distribution and apparent acceptance by divers. The author does not accept responsibility for accuracy or reliability of these procedures and tables, Theoretical diving depths to 10,000 ft for actual diving depths to 250 ft are given in Table 3-1, To find the theoretical diving depth, enter the table at the exact or the next greater depth than the maximum actual depth attained during the dive. Enter the table horizontally with this depth to the vertical column of the exact or next greater altitude (listed at the top of the column) of the body of water in which the dive is being made. The figure given in the selected altitude column for the actual depth is the theoretical depth of the dive at that altitude, Once the theoretical dive depth has been found, standard U.S. Navy Air Decompression Tables (U.S. Navy, 1970) are used to determine decompression time. Decompression

117 TABLE 3-1. Theoretical depth at altitude for given actual diving depth in fresh water (Cross 1970). Actuarly- Depth Theoretical Depth at Various Altitudes (in feet) 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 0 0 0 0 0 0 0 0 0 0 0 10 10 11 11 12 12 12 13 13 14 15 20 21 21 22 23 24 25 26 27 28 29 30 3.1 32 33 35 36 37 39 40 42 44 40 41 43 45 46 48 50 52 54 56 58 50 52 54 56 58 60 62 65 67 70 73 60 62 64 67 69 72 75 78 81 84 87 70 72 75 78 81 84 87 91 94 98 102 80 83 86 89 92 96 100 103 108 112 116 90 93 97 100 104 108 112 116 121 126 131 100 103 107 111 116 120 124 129 134 140 145 110 114 118 122 127 132 137 142 148 153 160 120 124 129 134 139 144 149 155 161 167 174 130 135 140 145 150 156 162 168 175 181 189 140 145 150 156 162 168 174 181 188 195 203 150 155 161 167 173 180 187 194 202 209 218 160 166 172 178 185 192 199 207 215 223 232 170 176 182 189 196 204 212 220 228 237 247 180 186 193 200 208 216 224 233 242 251 261 190 197 204 212 220 228 237 246 255 265 276 200 207 215 223 231 240 249 259 269 279 290 210 217 225 234 243 252 261 272 282 293 305 220 228 236 245 254 264 274 284 296 307 319 230 238 247 256 266 276 286 297 309 321 334 240 248 258 267 277 288 299 310 323 335 348 250 259 268 278 289 300 311 323 336 349 363 TABLE 3-2. Theoretical depth of decompression stop at altitude (Cross 1970). Prescribed Theoretical Depth of Decompression Stop (in feet) Depth 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 0 0 0 0 0 0 0 0 0 O 0 10 10 9 9 9 8 8 8 7 7 7 20 19 19 18 17 17 16 15 15 14 14 30 29 28 27 26 25 24 23 22 22 21 40 39 37 36 35 33 32 31 30 29 28

118 stop depths are computed using Table 3-2 in a similar fashion. For example, assume that a dive is to be made in a lake at an altitude of 3,860 ft and the actual depth of the dive is 85 ft. By entering Table 3-1 to 90 ft and across to the 4000 ft altitude column, it is found that the theoretical dive depth is 104 ft. This means that an 85 ft dive at 4000 ft is equivalent to a 104 ft dive at sea level. Since the rule of using the exact of next greater depth applies, the theoretical depth used in determining decompression for this dive would be 110 ft. Further assume that the above dive is for a bottom time of 36 minutes. Entering standard air decompression tables for a depth of 110 ft and duration of 40 min (next greater time from 36 min) it will be found that the decompression schedule requires a stop at 20 ft for 2 min and 10 ft for 21 min. The prescribed decompression stop depths must be converted to theoretical decompression stop depths for an altitude of 4000 ft using Table 3-2, Consequently, the diver actually makes decompression stops at 17 ft (instead of 20 ft) and 9 ft (instead of 10 ft). Repetitive dives may be computed using theoretical depth values. Use the repetitive group designator given for the theoretical dive depth at a given altitude, In the Surface Interval Credit Table, no modifications are required since depth is not a function of this table. However, theoretical depth must be used when determining residual nitrogen time using the Repetitive Dive TimeTable. For example, assume that a "no-decompression" repetitive dive is to be made to an actual depth of 60 ft after a surface interval of 2 hr, The initial dive, to a theoretical depth of 104 ft for a bottom time of 36 minutes, indicates a repetitive group "L." Following the 2 hr surface interval the repetitive group designation is "G." The

119 sea level equivalent of a 60 ft dive at 4000 ft altitude is 69 ft (Table 3-1). Consequently, the residual nitrogen time, entering the Repetitive Dive Time Table at repetitive group "G" to a depth of 70 ft, is 37 min. Since the "no-decompression" limit is 50 minutes, this means that the repetitive dive cannot exceed 13 minutes actual bottom time, If for any reason an initial dive is made at altitude and a repetitive dive at a lower altitude or sea level, simply assume that the initial dive was made at the lower altitude. Consult tables for the lower altitude (in the case of an ocean repetitive dive, the actual depth). However, if the initial dive is made at sea level or a lower altitude and the repetitive dive at high altitude, the initial dive must be treated as if it were made at the higher altitude. The repetitive dive would be computed for the higher altitude as previously discussed. For further information on diving at high altitude consult Cross (1967, 1970). Surface Decompression The primary advantages of surface decompression in a chamber are the comfort and security provided to the diver by allowing him to surface in case of extremely cold or rough seas, physical exhaustion, equipment malfunction, etc. If the chamber is equipped with a proper oxygen breathing system, the use of pure oxygen saves an appreciable amount of the total decompression time required as compared to air decompression. In surface decompression procedures, stage decompression in the water is reduced to a minimum or is eliminated and the major portion of the decompression is accomplished in a surface chamber in accordance with U.S. Navy Surface Decompression Tables 1-26 and 1-27 (Appendix III), If decompression is

120 to be on oxygen, use Table 1-26 with an initial ascent rate of 25 ft/min instead of the standard rate of ascent for air diving. For surface decompression on air, use Table 1-27 with an ascent rate of 60 ft/min. Following completion of required water stops, ascend directly to the surface, enter chamber, and pressure down as soon as possible. Do not exceed 3,5 min surface interval. Consult U.S. Navy (1970) for details of surface decompression procedures and chamber operation. Divers LoE Book The Diverts Log Book is a permanent record of his training, experience, and qualifications, A record of diving experience is necessary for advancement in research diver classification and instructor certification. Divers are encouraged to keep accurate records of all diving activities, The following information should be recorded for all dives: 1. Date 2, Geographic location 3. Underwater time 4, Depth 5e Equipment used 6, Swimmer or tender 7. Purpose of the dive and a brief description of work accomplished. In addition the following information is desirable: 1. Diving conditions (underwater and surface) 2. Air source and consumption 3. Exertion level 4. Comments on equipment and diver performance 5, Cumulative record of dives and underwater time Several commercially prepared log books are available; however, these are generally inadequate for research diverts records. A permanently bound notebook (approximately 4 in by 6 in or 5 in by 8 in.) has proven satisfactory. Specially printed log sheets carried in a loose leaf binder

121 are used in the University of Michigan's program. It is recommended that a "rough log" be prepared in the field during operations and information be entered in the permanent log book at the end of each diving day.

122 DIVING IN COLD WATER A survey of civilian diving activities in the United States indicates that 83% of all divers are in water below 60~ F, 60% of all divers are in water between 600 F and 400 F, and 25% of all divers are in water below 40~ F (Frey 1967), Of these dives, 44% have a duration of 90 min or longer and 33% have a duration of 45 to 90 min. In diving, the major cause of physiological depletion is cold stress, Cold is a major limiting factor relative to diver performance, comfort, and safety. Initially, upon submergence in cold water there is a mobilization of the body's heat generation and insulation resources to resist the cold. This response is characterized by immediate cooling of the body's surface layers, vasoconstriction, metabolic rate increase with possible increase in core temperature, respiration increase, and a decrease in heart rate. Continued exposure results in localized cooling with the hands and feet exhibiting the most rapid rate of heat loss. The hands and feet cool rapidly because they have the greatest skin surface area to mass ratio of all body regions and little or no subcutaneous fat, The diver's finger dexterity, tactile desSrimination and kinesthetic sensation diminishes with subsequent reduction in his ability to perform manual skill tasks. Loss of manual skill, even by degrees, results in a deteriorated state of efficiency and safety. The diver's ability to make critical valve adjustments and handle emergency situations is impaired. The diver is, however, still capable of performing certain tasks. For example, a diver may adapt by using the side of his hand to thread a nut onto a bolt instead of his impaired fingers. Also, individual variations in susceptibility to cold and discomfort, skill level, and motivation play a

123 major role in diver performance under cold stress. Cooling of the hands and arms results in a marked decrease in muscle strength. A 50% reduction in grip strength can be expected when an unprotected subject is immersed in 50~ F water for 1 hr. The diver's ability to board a boat or ascend a diving ladder without assistance may be impaired. Tenders and surface personnel must be prepared to render assistance. Cold stress causes deterioration in motor and mental processes. Visual perception, sensory motor coordination and anticipation (purely a mental process) are effected to various degrees. The loss of mental agility (problem solving ability) and memory impairment are symptomatic of severe cold stress. Cold stress may limit the amount of information that one can retain and can also be responsible for erroneous recollection, both vital factors in scientific observations. At this point man is not only useless as a working diver, but he is a hazard to himself and his colleagues. Further exposure can lower core temperature (normal: 98.60 F + 1~) and skin temperature (normal comfort: 91.5~ F to 87.8~ F). When core temperature drops to 970 F, the central nervous system's neuroregulatory capacity is affected, and severe pain followed by nerve damage is indicated when skin temperature drops below 55~ F. Wet Suit The foamed neoprene wet type diving suit (Figure 3-4a) is probably the most widely used suit today. With a properly fitted suit, only a small quantity of water is able to enter and this water is quickly warmed by the body. Heat loss is restricted by the insulating properties of the closed-cell foamed neoprene material. Unfortunately, this material is

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125 subject to compression under pressure and its insulating effectiveness decreases with depth. In contrast, an incompressible wet suit material is currently undergoing development and testing. This material shows promise as an ideal for insulating the diver; however, at present it is rather bulky and heavy, Insulation is primarily dependent on foamed neoprene thickness. Wet suits are commonly available in 1/8 in., 3/16 in., 1/4 in., and 3/8 in, thicknesses. Selection of suit thickness depends on water temperature, mission requirements (continuous swimming or limited underwater activity), dive duration, and individual comfort preference (thicker suits are more restrictive). The following are suit thickness recommendations for various temperature ranges: 700 F and above 1/8 in, jacket 600 F to 700 F 3/16 in, suit (standard) 50~ F to 600 F 1/4 in. suit (standard) The standard wet suit consists of a jacket with zippers in the front and arms, pants with leg zippers, a hood, boots and glove-mitts (3 finger type). Various design modifications and accessories are used to increase thermal comfort and protection. Suspenderntype pants ("bib type" or "Farmer Johntype") which resemble sleeveless coveralls are commonly used to provide added thermal protection to the diver's torso, an area of greatest heat loss. The 1/8 in. or 3/16 in. hooded vest is highly recommended for increasing thermal protection and allowing for seasonal variation. This vest prevents significant water seepage to the chest area (through zipper) and the back of the neck. It is extremely important to protect the head and back of the neck from cold water exposure since these areas are highly sensitive to cold and have significant effects on the body's thermal

126 balance, Added torso protection is afforded by a 3/8 in. shirt body. One-fourth inch sleeves and hood may be used on the 3/8 in. body to provide for minimum arm movement restriction and head comfort. For extremely cold water (28~ F to 35~ F) a 3/8 in. suit or multi-suit arrangement is desirable. Some divers prefer a 1/8 in. or 3/16 in. suit over or under a 1/4 in. suit, Standard suits are equipped with leg, arm, and chest zippers backed with a neoprene overlap strip to minimize water seepage. Zippers facilitate easy and rapid dressing and undressing. Unfortunately they also constitute a weakness in the insulation barrier and allow cold water seepage. Zippers are frequently eliminated from suits designed for extremely cold water diving or are backed with special backing pieces (gussets) glued and sewn to both sides of the zipper opening. If zippers are used, heavy-duty nickel-silver models are currently recommended. Hands and feet exhibit the most rapid cooling rates. In moderate temperature waters and when finger dexterity is required for manual skill performance, divers frequently wear 1/8 in. or 3/16 in. five-finger foamed neoprene gloves. Unfortunately gloves offer only minimal thermal protection. The three-finger glove mitt (3/16 in. or 1/4 in.) is most commonly used in cold water. For extremely cold water a gauntlet type 1/4 in. mitt which is designed to reach to just below the elbowgis recommended. Gloves and mitts must be carefully fitted, for the slightest restriction in the fingers will impair circulation and cause cold and numb fingers. Footwear must be properly fitted to keep the diver's feet warm, yet prevent cramping and circulation restrictions. Foamed noeprene boots with a hard rubber or felt sole are designed to minimize wear (damage to bottom surface) and to protect the diverts feet when walking, Since the

127 bottom is generally constructed of hard rubber with low insulating properties, a neoprene insole is recommended. Recently some manufacturers are improving protection by simply securing a hard sole to the bottom of a specially designed neoprene sock. The neoprene sock, without a hard sole, is designed to fit the foot snugly like a regular sock. Some sort of overboot or shoe is required to protect the foot and soft neoprene when walking on rough surfaces. High top boots reaching to just below the knee are recommended for extremely cold water, Hoods must be designed to give maximum protection to the head, neck and face; however, they should not interfer with proper fitting of the mask and SCUBA mouthpiece. Proper sizing can be extremely important because the skull is rigid and requires more accurate fitting than other suit parts, A poorly fitted hood can cause severe jaw fatigue, a choking sensation, a headache, dizziness, and coldness. An extremely tight fitting hood and suit neck could cause unconsciousness by restricting blood flow to the head. For extremely cold water Neushul (1961) states that no part of the face should be in direct contact with the water if diving is to be continued for extreme periods. This requires special hood design with separate openings for the mouthpiece and mask, Ray and Lavallee (1964) concluded that this is not necessary. The author has noted facial discomfort and numbing of the facial area and lips with possible impairment of ones ability to retain a SCUBA mouthpiece, A full face mask over a standard hood has merits, A special cold water hood which extends well over the shoulder area is available. However, the author suggests that the outer shirt should have an attached hood for cold water diving. This may be worn over a hooded vest, a high neck vest with separate 1/8 in,

128 hood or a vest without a hood, Most wet suits are currently lined with a four way stretch nylon fabric, This nSl i n 1 facilitates dressing and retards tearing, There is a slight reduction in suit flexibility, and some divers claim that thermal protection is reduced, No scientific data is available to support this reduction in thermal protection factor. Nylon lining also serves as a base for sewn seams, The sewn seam is desirable since it virtually eliminates tearing at seams, The advantages of nylon linings appear to outweigh the disadvantages, consequently, nylon lining is recommended, The outer surface of the suit may be smooth or textured rubber or nylon covered, Some manufacturers claim that the textured surface increases flexibility and is more resistant to abrasion. Most suits are currently manufactured with textured surfaces, although distinct advantages of textured surfaces relative to smooth surfaces are not clearly defined. A nylon outer surface significantly increases suit durability. A slight decrease in flexibility is evident; however, the nylon surface is desirable for the working diver. Other factors to consider when selecting a wet suit include color, crotch strap snaps and spine pad. Black rubber is preferable since coloring compounds may tend to weaken material and lower elasticity, Twist lock fasteners are commonly used to secure the crotch, Some manufacturers are now successfully using a specially designed velcro fastener for crotch straps, The shoulder straps of suspender type pants should be secured with large velcro strips. Spine pads are used to reduce the flow of water in the spinal area,

129 Although production model wet suits are available In a wide range of sizes including longs, regulars and shorts, custom tailored suits are recommended. A custom suit is tailored to 20 or 30 personal measurements and various modifications may be specified by the diver. Fit is extremely important. A wet suit should fit snugly; not to tight to restrict circulation yet not too loose to allow excess seepage and accumulation of water, Too tight of a fit in the chest area can result in restriction to breathing with subsequent respiratory fatigue. A good quality suit will fit snug and comfortably, but will stretch with body movement, Most divers wili be fortunate enough to have two or more wer suis to use for various water temperature ranges. Taking into consideration comfort, thermal protection, versatility and cost the following suit and accessories are recommended for the 400 F to 700 F temperature range: Shirt: 1/4 in.; no zippers in arms Pants: 1/4 in.; no zippers Vest: 1/8 in,; hooded Boots: 1/4 in,; hard sole Mitts: 1/4 in.; glove mitts Hood: 3/16 or 1/4 in. Cold water wet suits are discussed by Ray and Lavallee (1964) and Neushul (1961). Current investigations, in general, support the conclusions of these authors with regard to wet suit design. The following wet suit (custom tailored) has proven satisfactory for water temperatures of 40~ F to 50~ F (moderate activity level): Shirt: 3/8 in. body with 1/4 in. sleeves and attached hood; sleeve zippers with gussets and inverted shirt sipper are optional Pants: 1/4 in. suspender-type cut high in neck. Vest: 1/8 in. hooded or turtle neck neoprene Boots: 1/4 in, hard sole Mitts: 3 finger glove-mitts

130 For Arctic diving conditions and in water temperatures of 28~ F to 40~ F the following wet suit (custom tailored) is recommended: Shirts 3/8 in with attached hood; no zippers Pants: 3/8 in, suspender-type Vest: 1/8 in, hooded Boots: 3/8 in, foot with 1/4 in, upper to just below knee Mitts: 1/4 in. or 3/8 in, gauntlet type extending to just below elbow Recently, a foamed neoprene wet type suit has been developed that is virtually watertight. Entry is gained through a water proof/ pressure proof rear zipper, and the cuff, leg and neck seals are specially constructed to minimize water entry. This unit appears to be advantageous in keeping the diver relatively dry and requires less critical fit. However, the same compression is noted with depth as in a standard wet suit and similar insulati rduion reduction is evident. Wet Suit Buo cy The amount of weight required to offset the buoyancy of a foamed neoprene wet suit is primarily determined by the depth of the dive. The small closed gas cells in foamed neoprene rubber are compressed as pressure is increased and, thus, the flotation, or buoyancy, factor is decreased, Several methods may be used to determine the amount of weight necessary to achieve neutral buoyancy. To determine surface buoyancy, the diver must don all of the equipment which he plans to wear during the dive. Wearing a weight belt with clip-on lead weights or carrying weights in a net bag, he enters the water and adds or subtracts weight until he achieves a state

131 of neutral buoyancy. At neutral buoyancy he should sink slightly with exhalation and rise with inhalation. This amount of weight is generally satisfactory for diving in depths of less than 30 ft. Remember that a full standard 71.2 ft3 SCUBA cylinder contains approximately 5 lbs of air; consequently, the diver can expect to be about 5 lbs more buoyant at the end of a dive when his air has been depleted. Minor buoyancy compensations may be made using the diver's lifejacket. This technique is discussed in the section on SCUBA diving equipment. The diver may theoretically determine his weight requirements at depth by using a buoyancy-depth graph for foamed neoprene wet suits (Figure 3-5). For example, a diver wearing a medium size 1/4 in. wet suit will find that the suit has approximately 18 lbs of buoyancy at the surface and 8 lbs of buoyancy at a depth of 100 ft. Consequently, he will need to remove 10 lbs of weight from his belt to maintain the same bouyancy at 100 ft as he had at the surface. The graph is only intended to serve as a general guide. Since various factors, including neoprene rubber quality, suit age and condition, individual body types, and equipment affect buoyancy; only personal experience can ultimately determine weight requirements. The density difference between fresh and salt water has only a slight effect on the suit's buoyancy. Since the graph is for fresh water, the figures may be multiplied by a factor of 1.03 for salt water diving. Remember, however, that the diver must add weight when he makes the transition from fresh water to salt water to compensate for his body's displacement. For example, if a 180 lb individual dressed in a bathing suit is neutrally buoyant in fresh water without the addition of weight, he will displace approximately 2.88 ft3 or 180 lbs of fresh water. This same individual will displace about 184 lbs of salt water. Since he weighs only 180 lbs, approximately 4 Ibs of weight must be added to achieve neutral buoyancy in

132; 5 i, t l,4 i. Li...tuit.:.. +... ~!~..... l-" " I....' 1......... - 1 0 30 20.!i+T i ti:il; *0l,,!;,, K_. "''.i''':.;'' q;... i,.'~:''', r- "'.::, 1 100;7;:*:;.;!!":"'::;i::'.:::.i::i::!!in *!i',ii:!;*j *''::!:": *,:;*. *..'"::::.''~,;r!': i i'i:':i:: ~ -I:::i.::;'i!::'.::- i i:: l.:.,. jL 20,'. i-tt-' i -i 1.5 l. i " t - - - q —'-?t 6 ~ I. 2. 5. 4. BUOYANCY - POUNDS WEIGHT FIGURE 3-5. Buoyancy of foamed neoprene wet type suit relative to compression at various depths (from Dey 1965). 10::, ii illil::iit;'i: ~: l:i~!it:i~i li:ll~~~!l;ii:ll~ ~ ~~.:~~I:i: ~~~.~~:II i:;i~~i:i~iil~ ~'i::::li~l;::;::r.., j!!7, 0.. L -o1 iiif~~~~~~~~~710 1 7 6 _1__21 20 19 M 1 16 15 -T F, -~~~~~~~~~~~~~~~~~!~iiiii iii.: iilii I., 2.'S. 4. BUOYANCY POUNDS WEIGHT~~~~~~~~~~~~~~~~~~~~~~~~~~: FIGURE 3.5. Buoyancy of foamed neoprene wet type suit relative to~~~~~~~~~~~~~~~~~i ~ i compression at various depths (from Dey 1965)o~~~~~~ii

133 salt water. Frequently, novice divers will find that they will reduce their weight belt requirements by 4 to 5 lbs during the first year of diving. Certainly part of this reduction is due to improvement in skill, relaxation, and breathing characteristics. However, about half of this reduction is due to wet suit deterioration through normal usage. A rapid alternate, but less accurate, method of determining the amount of weight required by a diver wearing a wet suit to achieve neutral buoyancy at the surface is the formula of 1 lb of lead for each 10 lbs of body e ight. Dry Suit: Standard The standard dry suit (Figure 3-4b) is generally made of two-ply gum rubber and is worn over one or more layers of thermal or woolen underwear or a foamed neoprene wet suit. Dry suits are commonly classified by type of entry: neck, front, rear, or waist. The front and waist entry models are currently popular. Dry suits were used for most cold water diving prior to introduction of the wet type foamed neoprene suit. Unfortunately, dry suits are subject to leakage if the entry is not properly sealed. Also, a slight tear can result in complete wetting of the undergarments and subsequent loss of thermal insulation properties. The dry suit is frequently uncomfortable at depth due to squeese as the air in the suit is compressed. Since insulation properties depend on the thickness of the air space provided by the undergarments, thermal protection decreases with depth. Air may be introduced into the suit through the face seal from the mask to partially

134 compensate for compression and prevent external ear squeeze. Some divers wear thick porous padding in their hoods to help prevent ear squeeze. The dry/wet suit combination has proven adequate for long term submergence in shallow cold water where the diver must remain relatively immobile, The wet suit is worn as an undergarment; thermal protection is thus retained in the event of leakage, Unfortunately this combination is rather restrictive to movement and may induce fatigue during long underwater swims, After entrance is made into the front or rear entry dry suit, the entrance tunel must be made watertight. The following method of making a watertight seal is recommended: 1, Spread the entry tunnel flat at the open end. 2 Fold once and carefully pleat the entire length. 3, Hold securely and clamp or tie (elastic cord) the pleated material. To seal the waist entry dry suit, the following method is recommended: 1, Fold pants entry chute over hip. 2, Lay shirt entry chute over the pants chute and fold so that the shirt entry is now on the inside and the pants chute is on the outside., 3, Place the rubber tube belt at the top of the entry chutes and roll the chutes downward, (The tube belt is optional: proper seal may be made without a belt) When wearing a dry suit, do not jump into the water. Enter gradually and purge trapped air out of the cuffs or face hole. If attached gloves are used, submrge one at a time while purging air. Extreme caution must be observed when using a dry suit to prevent external ear squeeze or rupture of the eardrum, This problem is eliminated by admitting air from the mask through the face seal.

135 Instead of attaching gloves to the suit, most divers now use heavy foamed neoprene wet type mitts. If dry type mitts or gloves are desired, the best method of attachment is to simply remove the suit cuffs and cement the gloves in place. After using the dry suit, it must be thoroughly dried, powdered and stored in a dry, cool, dark area. Avoid excessive heat. Roberts (1963) discusses the use of dry suits, dry/wet suit combinations and suit entry techniques in detail. Dry Suit: Variable-Volume The variable-volume dry suit (Figure 3-4c) is a flexible, lightweight, one-piece dry type suit with integral boots and hood, and separate glovemitts. It is constructed of 3/16 or 1/4 in. closed-cell neoprene rubber with a nylon lined interior and textured rubber or nylon exterior. The seams are stitched and large kneepads are affixed. The suit is entered through an opening that extends from the breast bone down around the crotch and up to the nape of the neck in back. A waterproof, pressureproof zipper completely seals the opening and permits the diver to dress and undress in approximately five minutes. The suit is designed to be worn with light or heavy underwear and may be used with SCUBA or surfacesupplied lightweight helmet and mask. This suit is fitted with inlet and outlet valves to permit diver control of inflation and deflation of the suit, consequently, permitting control of displacement and buoyancy. Air supply for the suit is taken from the diver's air supply (SCUBA or umbilical) through a hose attached to a low pressure outlet on the regulator or umbilical, or from a small auxiliary cylinder. Controlled inflation produces only limited local

136 ballooning and squeeze is minimized since the elasticity of the suit material facilitates equalisation of pressure differentials over the entire body, While the neoprene rubber is compressed with increasing depth, the insulation properties of the underwear and the air envelope surrounding the diver are relatively unimpaired. The diver may utilize the variable-volume factor to control buoyancy and thus allow a wide range of weight to be used safely. Approximately 25 to 30 lbs of weight are required to neutralize the buoyancy of the suit, In order to allow the diver to swim with neutral buoyancy and work heavy,, 10 to 15 lbs of weight may be added, For work requiring,maximum stability on the bottom and no swimming, up to 40 lbs of weight may be added in the form of a heavy weight belt and diver's shoes and/or leg weights, The suit is also an effective life preserver. Inflation of the suit allows a surfaced SCUBA diver to float on his back above wave action. If the diver were to lose consciousness during ascent, air would automatically vent through the wrist seals, Blowup may be controlled by venting air from the exhaust valve, through wrist seal cuffs, or by unzipping the suit. Currently a variable-volume dry suit is manufactured in Sweden and marketed under the nae UNISUIT. Using heavy "arctic" underwear (a knitted nylon fur suit supplied by the manufacturer) the Swedish Navy has tested the suit in water temperatures of 37~ F to 500 F at depths of 60 to 100 meterso Tests conducted on a recent Arctic expedition in the presence of the author included a 2,5 hr dive in shallow (to 30 feet) water with a temperature of 29~ F to 30~ F. Further testing by the author has indicated

137 satisfactory performance to depths of 200 ft in cold water with lightweight helmet and mask, Specific instructions for use and maintenance of the UNISUIT are supplied by the manufacturer; divers are encouraged to follow these instructions to avoid malfunction and unnecessary suit damage. The zipper requires special handling and maintenance procedures. Dry Suit: Constant Volume The constant volume dry suit was designed primarily for self-contained or surface-supplied diving in extremely cold or contaminated water. It is constructed of rubberized cotton twill similar to that used in conventional deep-sea or lightweight diving dresses (suits). As the diver descends the internal volume of air is kept nearly constant by exhalation of air into the suit through the diver's mouth or nose. Constant automatic exhaust valves located at each ankle of the suit and in the top of the hood automatically maintain pressure balance and vent air during ascent to prevent over-inflation of the suit. The hood is fitted with a hinged lens face mask and a mouthpiece "T" connection for use with a double hose regulator. Entry is through the neck opening; the hood is sealed to the suit with a special metal ring. The constant volume suit is extremely durable. Currently, this suit is used more often with a surface-supplied demand regulator system than SCUBA. The suit is somewhat cumbersome and uncomfortable for long under water swims.

138 Diving Suit:..n-Cilrcuit Hot Water 5s stem The open-circult hot water system (Figure 3-6) consists of a loosely fitted wet suit desined with internal tubing to distribute heated water uniformly over the diver, an insulated hose, a surface water heating unit, and a water pump, The one piece front zipper entry suit is constructed of 3/16 inch foamed neoprae with nylon on both sides. An insulated hose from the heating unit attaches to a control manifold mounted on the side of the suit which enables the diver to control the flow of water. The size of the surface water heating unit used depends on depth, number of divers, and water temperature requirements. A satisfactory unit for 1 to 2 divers is a portable, liquid propane, flame to coil 200,000 BTU water heater similar to a small swiming pool heater, The unit is equipped with a mixing manifold to control water flow rate and temperature, A pump is required to pass water from its source through the heat exchanger and down to the diver, A constant flow of 1.5 to 2 gal/min is required to maintain comfort in cold water, A 40 lb/in2 head is sufficient for most operations and the water temperature is adjusted to reach the diver at his desired comfort level, generally 90~to 100~ F. fDiv in Cold Water Cold water divers must have adequate pre-dive rest and nutrition. At least 6 to 8 hr of sleep and caloric intake of at least 5000 calories and possibly as mech as 7,500 calories per day is recommended (Ray and Lavallee 1964)o This is necessary to establish the reservoir of energy necessary to combat body heat loss,, Onset of cold stress will otherwise be accelerated, In general, divers will perform better in cold water if they are in good

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140 physical condition and have adequate rest and nutrition for a week or so prior to diving operations. Breakfast on diving days should consist of foods with high carbohydrate content but low amounts of residue because deftcation is rather inconvenient for a suited-up divers. Intake of candy and honey may be beneficial; however, avoid foods and eating habits that might produce nausea. Water temperature and dive duration are two important factors in the selection of diving dress. Although specially designed wet suits have been used for SCUBA diving under Arctic conditions, dry type suits are recommended for long duration dives when the water temperature is below 50~ F or if the diver is to remain relatively immobile. A relatively inactive diver in a 3/16 in. wet suit will maintain thermal balance for prolonged periods only if the water temperature is above 700 F. When possible, use surface-supplied hot water circulating suits or variable-volume dr suits. The selection and design of wet suits for various temperature ranges has been discussed previously, The diver must be provided with a warm sheltered area for dressing and should avoid exposure as much as possible prior to the dive. Chilling the diver prior to the dive accelerates the onset of cold stress. If the diver must be transported to the dive site or is to be exposed to surface cold conditions, he must be provided with a heavy parka or insulated exposure suit and insulated overboots. The diver should be protected from exposure between repetitive dives. This is extremely important if he is wearing a wet suit. Never commit a chilled diver to a repetitive dive. Hot water carried in insulated containers is extremely beneficial for self-contained divers using wet suits. Hot water injected into the

141 diverts suit through the neck opening, mitts, and boots prior to the dive warms the diver and delays the onset of chilling. Similar post-dive hot water injection rapidly restores warmth to hands and feet and rewarms the diver. Care must be taken not to scald the diver. Underwater the diver should avoid excessive movements that tend to increase the flushing of water in and out of his wet suit. Maintaining a reasonable level of exercise produces heat and delays the onset of cold stress. Immobility accelerates chilling. For safety purposes, the diver should terminate his dive with the onset of involuntary shivering and/or diminished manual dexterity. When the diver surfaces, remove breathing apparatus, weight belts, and fins. Immediate injections of hot water into wet suit, mitts and gloves are beneficial; do not remove mitts in cold air until hands can be dried and warmed. If there is to be considerable delay in undressing, remove mitts, dry hands and don wool or insulated mittens. Vigorous exercise will promote warming. The diver should dress-out, have a hot shower, and don dry clothing as soon as possible* The use of a variable-volume dry suit is extremely beneficial when periods of surface exposure are necessary, Diving Under Ice Diving under ice is particularly hazardous and should only be undertaken when absolutely necessary. The diver is subjected to severe cold stress, emergency procedures are complicated, and the SCUBA may be adversely affected by severe cold. In fact, the use of open-circuit SCUBA for diving under ice is discouraged, The effects of cold on SCUBA regulators are

142 discussed in Chapter IV, University of Michigan research divers use surface-supplied diving tecmiques for under ice work, In additi to previously discussed procedures the following should be considered when working under ice: 1, Use ple protective clothing and do not commit a chilled diver to an under ice mission, 2, Always have a stand-by diver ready to enter the water immediately. 3, Cut a hole large enough to accommodate 2 or 3 divers even though one diver is under the ice at a time. (Be sure to mark the hole clearly following ice diving to warn fisherman and snowmobile riders of the hazardous opening,) 4, Limit dive furation and provide sufficient facilities for immdiate waming. 5 Never rely o a compass the safety line or umbilical is the only way to insure relocation of the hole, 6, The safety line mst be secured to the diver, not his equipment. A trained tender st handle the safety line or umbilical, 7, Avoid long excursions under the ice. If it is necessary to cover large areas when under the ice, cut several holes 1nd mae a series of dives, 8, Avoid having more than one surface-supplied diver or one SCUBA team in the water at a time, 9 Divers must have considerable open water experience prior to diving under ice, 10, If SCUBA Is used, use only two hose regulators and carry an auxiliary breathing unit, Do not inhale from regulators above water, wait until you submerge. Additional information on diving under ice is given by Ray and Lavallee (1964),

143 OVEREXERTI E AND EXHAUSTION Nearly everyone has experienced the "out of breath" feeling, from working too hard or running too fast. It is possible for a person to exceed his normal working capacity by a considerable margin before the respiratory response to overexertion is apparent. The end result is generally shortness of breath and fatigue. On land this presents little problem. Underwater (under increased ambient pressure) the problem of exertion is modified by several factors and is considerably more serious. Even the fin breathing apparatus offers some resistance t t he flow of air. As the depth increases so does the density of the air and consequently it moves through the body's air ways with greater resistance to flow, When shortness of breath and fatigue are brought on by overexertion, the diver may not be able to get enough air. The feeling of impending suffocation is far from pleasant, and it may lead the inexperienced diver to panic and a serious accident, Man's ability to do hard work underwater has definite limitations, even under the best of conditions. Many situations can lead to exceeding these limits. They include: 1. Working against strong currents, 2. Prolonged heavy exertion. 3. Wasted effort. 4. Breathing resistance, especially with poorly designed and maintained breathing apparatus. 5. Carbon dioxide build up, 6. Insufficient breathing medium, contamination. 7. Excessive cold or inadequate protection. The diver will realize that he has overexerted himself by labored breathing, anxiety, and a tendency towards panic that accompanies the

144 overexert ion feeling. If the diver feels the typical "air hunger" and labored breathing starting to appear, he should do the following: 1. Stop, rest, and ventilate to get a maximum flow of air by holding the SCUBA mouthpiece in place and pushing the purge button on a single hose unit or with a double hose unit, turn on your back to obtain a free flow of air. Breathe deeply. Ventilate helmet or mask with free flow, 2, Inform your "buddy" or tender, 3, Do not shoot to the surface -- terminate dive with a slow, control led ascent, 4, When you reach the surface, inflate your life preserver and return to the boat or shore or if to exhausted, signal for an immediate "pick-up," The "buddy" and surface crew shoulds 1. Render all possible assistance. 2, Watch for signs of panic that might lead to a serious underwater accident. 3, Help diver aboard, 4, Provide rest, warmthe and nourishment. Overexertion can be prevented if the individual knows and observes his limitations, takes into consideration the working conditions and sets up the diving operation accordingly. For example, plan the dive so that you can move with the current and not against it, Diverts should keep themselves in excellent physical condition, The equipment must also be in top working condition. Be alert for signs of fatiguet

CHAPTER IV SELF-CONTAINED DIVING INTRODUCT I ON Self-contained underwater breathing apparatus (SCUBA) (Figure 4-1) was developed to facilitate complete freedom of movement underwater. The diver carries his breathing medium with him thus allowing him to operate independent of surface support and with freedom from the encumbrance of the umbilical required for surface-supplied diving apparatus. Three major categories of SCUBA are currently in use: Open-circuit demand Compressed air Cryogenic (primarily experimental) Semi-closed circuit (mixed-gas application) Closed circuit Pure oxygen Mixed-gas Cryogenic Open-circuit demand type SCUBA is the simplest type and the one most frequently used by divers. Only open-circuit demand type SCUBA will be discussed in detail. The diver must know and appreciate the difference between selfcontained diving (open-circuit: air) and surface-supplied diving so that he can choose the proper equipment for a specific mission. The best way to compare these two types of diving is to consider the advantages and disadvantages of SCUBA. Advantages of SCUBA: 1. Mobility 2. Portability 145

146 I....................................~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~...................~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~'~+~.......... ~ ~ ~ + + +..~ ii~~~~~~~~~~~~~~~~~~~~~~~~~~~~1F ii:? E \~2' \ i. ~~ \ V *. I'b II IaX.~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~..... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~S~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ii N5 ~a I\: 1:sg;:pj)~:U$ (.'hoi:::o by u~l:::7)::.. ZiI: 2:-:-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~.......... a::::~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~..... I::: 1t it 5~$;:I:I: I:::~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~..........::~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~i: ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~............. 1 i:PI~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~...................~~~~~~~~~~~~~~~~I: It~~~~~~~~~s::$I::a:::-:::::i::j:: a~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~.......X X............................................~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~l ikN, Alill~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~l ~~~~:: -::::-~-:i~.:::::: I:: i:::-::l-:::i:' i~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~......... iii~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~im FTC;URF: 4-X, niwar aqu~r~arar i ns~ta~1 open-carcul~ ssl%-cafstr~tr~e~r-1........... br*8~~~~~~~hlrrtr: apf~~~~~~~~~~~~~~~aait~~~~~~~lls (Pho~~~~~~~~~~~~co by wuP~~~~~~~~~~~~ilar).~~~~~~I

147 3. Adaptable to small boat operation (requires minimum support equipment) 4. Training readily available to most research personnel. Disadvantages: 1. Limitations of depth 2. Limitations of duration (air supply) 3. Limitation of exertion 4. Inefficient for most diving missions 5. Limited communications capability 6. Limited thermal protection for self-contained divers 7. Requires a minimum of two divers for safety purposes 8. Relatively unsafe for limited visibility diving conditions Recent field experience has shown that open-circuit SCUBA has definite limitations and that for many missions surface-supplied diving techniques may increase operational efficiency by as much as a factor of four. However, at present, open-circuit SCUBA is still the "standard" diving apparatus for research diver applications. The advantages and disadvantages of surfacesupplied diving will be discussed later, OPEN-CIRCUIT SCUBA Demand Type SCUBA Regulator The demand regulator is a mechanism which reduces the high pressure air in the cylinder to ambient or breathing pressure. The volume of air delivered is regulated by the diver's inspiratory requirements. In open-circuit demand SCUBA, the diver inhales air from the air cylinders and exhales directly into the surrounding water; in a properly designed apparatus no gas is rebreathed. Demand regulators are available in both one and two reduction stage types, In the discussion of regulator valve systems the terms "upstream" and "downstream" are frequently used (Figure 4-2a). Downstream refers to a valve which is forced open by the high pressure air. Consequently a mechanical force such as a spring must counteract the force of the high pressure air. A downstream high pressure valve spring is calibrated to hold

148 OGS PRESSURE HIGH PRESSURE AIR AIR I:' i,, DO0 STREAM VALVE SEAT UP STREAM VALVE SEAT a TWG STAGE REG'ULATOR HIGH PRESSURE INTERMEDIATE PRELSURE -.. MO PUTHPIECE -' SWATER valve seats, (b) Two stage regulator. (Courtesy of U.S. Divers Co.) UOS, Divers Co@)

149 the valve closed against a full cylinder pressure and, consequently, offers greater mechanical resistance to opening at a low cylinder pressure. In the upstream type valve, the opposite is true. The high pressure air closes the high pressure valve and as the cylinder pressure drops, the valve offers less resistance to opening. One Stage Demand Regulator The one stage demand regulator (Figure 4-2a) is designed to reduce air at cylinder to ambient pressure through one reduction stage. Inhalation lowers the pressure in the air chamber and the flexible diaphragm is deflected inward by the higher water pressure. This movement activates the lever system to open the high pressure valve. Air flows from the cylinder until the demand ceases, the pressure in the air chamber is equal to ambient and the high pressure valve closes. This regulator is commonly available in only double hose models. It is rugged, has a limited number of moving parts and is relatively easy to maintain and repair. However, breathing resistance increases with high air flow requirements at greater depths and there is a slight variation in flow with changing cylinder pressure. Two Stage Demand Regulator The two stage demand regulator, available in both single (Figure 4-3 and 4-4) and double hose (Figure 4-2b) models, is designed to reduce the high pressure air from cylinder pressure to ambient pressure through two reduction stages. In double hose models the pressure reduction mechanisms are housed as a single unit which attaches to the cylinder valve. However,

TO SECOND STAGE AIR FROM r 1ST. STAGE IR I-i, PRE —y7. ~.. HIGPREPSSURE TlSUVAIV$BE a j-E: i AIR PRESSUIE~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~I PES R D IAPHRAGM AIR 5 f STANDARD SINGLE HOSE FROM Y *<^^ H-1&,/ 1 FIRST STAGE I ST. STAGE DOWN STREAM VALVE b To d FIGURE 4-3. Cross section of single hose demand regulators. (a) Tilt valve second stage, (b) Downstream valve second stage. (c) Balanced first stage, (d) Standard first stage. (Courtesy of U.S. Divers CO.)

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152 in single hose models the first and second stage reduction mechanisms are separated by a length of hose and the second stage is part of the mouthpiece assembly. The first stage is depth compensated and designed to maintain a constant intermediate pressure of 110 to 130 lbs/in2 above ambient pressure, depending upon the make of regulator. Three types of intermediate pressure reduction valve systems used in SCUBA regulator first stages are described later. The second stage is a demand lever activated unit designed to reduce the intermediate pressure to ambient pressure. Inhalation by the diver causes a pressure reduction within the second stage air chamber with respect to ambient pressure and a flexible low pressure diaphragm is deflected inward. This activates the second stage demand lever which opens the low pressure valve assembly and allows air to enter the second stage chamber until demand ceases and the internal pressure equals ambient pressure. As air is released from the intermediate pressure chamber the high pressure valve opens and allows air to enter the intetriediate pressure chamber from the cylinder. When pressures are balanced, the valves close to stop air flow until the next inhalation. In single hose regulators the low pressure diaphragm may be depressed manually to activate the demand lever and start air flow. First stage reduction valves are available in standard, balanced, and piston types. In the standard first stage assemby (Figure 4-3d) the high pressure cylinder air acts to close the valve. Counteracting the closing force of the cylinder air is a large spring pressong against a high pressure diaphragm which is coupled to the high pressure valve seat assembly. Movement of this diaphragm moves a stem to open or close the

153 valve seat assembly. The heavy spring is manually adjusted to hold the valve seat assembly open until the intermediate pressure increases to a pre-determined level. The first stage is depth compensated by water or air pressure exerted on the high pressure diaphragm. The delivery efficiency of the mechanism varies with cylinder pressure. The small diaphragms used in single hose regulators are extremely sensitive to fluctuations in pressure and, consequently, slight pressure variations can have marked effects on air flow capacity and breathing effort. To reduce the amount of variation caused by cylinder pressure differences, it is necessary to reduce the size of the inlet orifice. Unfortunately, a small orifice adds resistance to air flow and, therefore breathing, when high air flow volume is required. Thus the standard first stage has definite air delivery limitations under high flow requirements, especially at depth. In comparison to the standard first stage, cylinder pressure has no effect on the seating of the high pressure valve assembly in the balanced first stage (Figure 4-3c). In the balanced valve, a valve stem of approximately the same size as the orifice is extended outside the high pressure chamber. Therefore, high pressure is not exerted on the end of the valve stem. With the cylinder air pressure neutralized, only the mechanical forces of the springs affect the operation of the valve. These springs can be set at the exact desired intermediate pressure and do not vary with changes in cylinder pressure. Consequently, large orifice diameters can be used and te breathing resistance produced by moving air through a small orifice is eliminated. This first stage is designed to enclose the entire valve assembly for protection against salt water corrosion and

154 foreign material, yet maintain depth compensation. The balanced first stage is used in most high performance regulators. The isAn tpe first stag (Figure 4-4) is a simple and functional unit with only one moving part - the piston. This is probably the most common first stage currently used in single hose regulators. It is currently not used in double hose regulators. By using a precisionground spring of proper compression, the desired intermediate pressure can be maintained with no further adjustment. As the system is pressurized, air flows through a small hole, located in the side of the piston stem just behind the soft seat, up through a bore in the piston stem and pressurizes the air space between the cap and the large end of the piston (Figure 4-4b), In the balanced flow-through piston model (Figure 4-4a) air enters the open end of the piston and a soft seat is embedded in the case just below the end of the piston. This force acting on the larger area of the piston is greater than the force at the small end due to the differential in surface areas. Consequently, the piston moves toward the small end. The piston is depth compensated through application of hydrostatic pressure to the spring side of the piston by admitting water into spring chamber. In this manner the intermediate pressure always remains at a predetermined level above ambient pressure. When this pressure is reached, the piston moves downward, and the air flow from the cylinder is stopped by the closing of the valve. As the diver inhales, the intermediate air pressure is subsequently reduced, the piston moves upward, and air flows through the regulator until the diver stops inhaling and the predetermined

155 intermediate pressure is again reached, Since the operation of the piston depends on the sea of the two 10" rings, damage to these or the very smooth bores by sand or salt crystals canresult in malfunction. Exhaust Valves In double hose regulators, air is exhaled through a non-return valve located in the mouthpiece assembly into the exhalation hose where it is channeled to the open chamber portion of the regulator case. A non-return valve at the end of the exhalation hose permits air to escape, but prevents water from entering the exhalation hose. The exhaust valve is located in the regulator case in order to minimize exhalation resistance by placing the exhaust valve at a lower pressure than the lungs when the diver is in normal swimming position. High exhalation resistance results in greater respiratory fatigue over long durations than equivalent inhalation resistance. The exhaust valve port in a single hose regulator is located in the lower portion of the second stage air chamber (mouthpiece assembly). A non-return valve prevents water from entering through this port. The exhaled air is deflected away from the diver's face through a special rubber assembly. Until recently, most single hose regulator exhaust valve ports were small enough to cause significant exhalation resistance. Most current models are designed with larger exhalation valve ports in order to minimize this resistance.

156 Thermal Reaction In cold climates and/or cold water internal freezing of regulators may result from moisture mixed with the cylinder air. In this case, cooling of the air due to expansion from high pressure to low pressure, causes moisture in the air to freeze. Consequently, ice crystals may plug the orifices in any regulator and cause malfunction. Piston type first stage regulators appear to be extremely susceptible to ice crystal problems and are not recommended for extremely cold water diving operations. Only moisture free air should be used for cold water diving operations. Extgernal freezi may occur when single hose regulators are used in water at temperatures near freezing (32~ F). Ice crystals have been observed to form around both the first and second stage assemblies. These ice crystals may plug openings and interfer with the movement of regulator parts causing either loss of depth compensation, free flow or restricted breathing. The primary reason for external freein in single hose regulators is the small size of the regulator case exposed to the water. Expansion of cylinder air from high pressure to low pressure absorbs heat from the surrounding metal and, consequently, reduces the temperature of the metal, When it is immersed in water already near the freezing point, the reduction in the temperature of water in contact with the metal causes freezing. The ice crystals may build up rapidly to plug orifices in both the first and second stages of the regulator. In two hose regulators the high pressure reduction mechanism is somewhat protected from contact with the water by the large metal case. Also the larger mass of metal affords a better heat transfer. Two hose

157 regulators are less likely to malfunction from internal and external freezing. Compressed Air Cylinder The compressed air supply for open-circuit SCUBA is contained in steel or aluminum alloy cylinders. Aluminum cylinders, not bearing a Department of Transportation approval stamp, are generally restricted to European countries and United States military applications. U.S. Navy cylinders are constructed of materials which comply with low magnetic effects (i) requirements to facilitate operations around magnetic mines. Cylinders for civilian use generally have a rated working pressure of 2250 lbs/in2 and a normal internal volume of 730 in3 When charged to 2250 lbs/in2 a standard cylinder contains approximately 64.7 ft3 of free air. The 71.2 ft3 capacity is at 10% over working pressure (2475 lbs/in2) allowable under Department of Transportation (DOT) specifications as indicated by a plus (+) symbol adjacent to the initial hydrostatic test date stamped near the cylinder neck. Cylinders with free air capacity (at 10%. over pressure) of 26, 38, 50, 52.8, 75, and 100 ft3 are also available. Open-circuit SCUBA is available in 1, 2 or 3 cylinder assemblies. The exterior of the cylinder is protected against rust and corrosion by galvanized metal, epoxy paint or vinyl plastic coating. Galvanized exteriors are recommended for durability against abrasion. Epoxy paint or plastic over zinc galvanized surfaces prevents electrolytic corrosion of the zinc by salt water. However, with proper preventive maintenance electrolytic corrosion is relatively insufficient. High pressure cylinders are stamped with letters, numbers and symbols near the neck giving certain specifications. The following is an example

158 of the markings found just below the neck of a standard SCUBA cylinder: DOT 3AA2250 K7422 USD 1L 70+ DOT designates that the cylinder is acceptable for interstate transport in accordance with Department of Transportation specifications. Cylinders manufactured prior to January 1970 may read ICC (Interstate Commerce Commission) in lieu of DOT; the change to DOT resulted from governmental reorganization and an amendment to the Hazardous Materials Regulations. The type of metal alloy used in manufacturing is designated by 3AA or 3A indicating chrome Iolybdenum alloy and carbon steel alloy, respectively. The rated working pressure, 2250 lbs/in2, follows the material designation. In the above example K7422 is the cylinder serial number and USD is the distributor's symbol. The hydrostatic test date is indicated by 1L 70+. The ((L) is the registered symbol of the tester and the (+) following the test date designates that the cylinder may be charged to 10% over the rated working pressure. The bottom of SCUBA cylinders is often fitted with a rubber or plastic boot for protection and to facilitate holding the cylinder in an upright position. Boot equipped cylinders should not be left unattended in an upright position, The boot should also be removed periodically to inspect for corrosion; preventive measures may be required.

159 Cylinder Valve Assembly The cylinder valve assembly is primarily a shutoff valve to control the flow of air from the SCUBA cylinder and is designed to facilitate attachment of a demand regulator or cylinder filling device. Most open-circuit valve assemblies have a thin, metallic safety disk which is designed to rupture at 3000 lbs/in2 cylinder pressure as a measure to prevent cylinder damage from excessive pressure. The assembly may also include a spring-loaded low pressure air warning mechanism (Figure 4-5). The shutoff valve may be incorporated into manifold units for use with multiple cylinder SCUBA. Low Pressure Warning Device (Reserve) All open-circuit SCUBA must be equipped with a positive warning system to alert the diver that his gas supply is critically low. The system may be a valve mechanism, an audible signal device, a calibrated orifice or a pressure readout gauge. Warning systems may be incorporated into the regulator assembly or cylinder valve. The most common mechanism is an air reserve valve consisting of a pressure relief valve with a manual override. This type is generally referred to as a spring-loaded reserve (Figure 4-5). This mechanism permits a free flow of air to the regulator until the cylinder pressure 2 falls to a predetermined level (approximately 300 lbs/in for single cylinder SCUBA and regulator; 500 lbs/in2 for two cylinder SCUBA). At this pressure, a spring forces a flow check against the port orifice and restricts the air flow, causing increased breathing resistance. This is followed by total obstruction of air flow.

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161 The remaining air may be released by manually overriding the check valve. The diver activates a reserve lever which advances a plunger pin and pushes the flow check off of the orifice against the action of the spring. The entire reserve air supply is available to the diver. Unfortunately, this reserve lever may be accidentally activated during the dive or the diver may fail to place it in a proper position prior to the dive. In either case the diver may completely exhaust his air supply at depth without warning. The audible low air warning system is probably the most foolproof mechanism used in SCUBA in that it eliminates the human error possibility of neglecting to properly position the reserve mechanism and the possibility of accidental activation. In this system an audible signal automatically sounds when the cylinder pressure reaches a given level. The signal continues during inhalation until the air supply is exhausted or inhalation ceases. This type of warning mechanism is only in limited production at present, probably due to design, manufacturing, and marketing problems. The depth compensating or restricted orifice principle is no longer used on most American SCUBA for low pressure warning mechanisms. This device operates on the principle that a stream of air will flow through an orifice of a given size in direct proportion to the pressure differential existing on both sides of that orifice. The orifice size is calbirated so that there will be insufficient air flow through the orifice for normal inhalation when the pressure differential is approximately 200 to 300 lbs/in2 The restriction to air flow is, therefore, dependent also upon depth. Consequently, near the end of the air supply the diver feels

162 a restriction to air flow during inhalation. Direct ascent increases the pressure differential across the orifice and sufficient air should be available for ormal ascent. Once air pressure has dropped low enough the diver must immediately ascend unless provisions are made in design for by-passing the restrictive orifice, Descent is impossible, If the diver breathes "lightly" and consumption (volume per breath) is limited, he may "breathe past" his reserve supply at shallow depths, In this case air demand is insufficient for the diver to notice significant restriction and he may nearly empty the cylinder(s) before breathing restriction is evident, If under these conditions the demand would suddenly increase, air flow would be insufficient, Also, the restrictive orifice reduces the flow capacity of a regulator even when the pressure differential is high; this greatly reduces the regulator's operational efficiency. Divers are therefore discouraged from using SCUBA equipped with restricted orifice reserve mechanisms. So divers prefer to use two cylinders connected by a yoke (Figure 4The diver opens only one cylinder at the beginning of the dive and upon depletion of that air supply opens the second cylinder. The air equalizes between the cylinders, the reserve cylinder s1 closed and the diver terminates his dive after he has performed this procedure two or three times, Some divers use two single SCUBA cylinders with separate regulators mounted in a double cylinder harness (Figure 4-6c); this method requires switching mouthpieces while underwater. An underate presure a (Figure 4-6a) is recommended for all SCUBA. This gauge may be connected to all single hose regulators, some double hose

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165 regulators or the cylinder valve (not recommended). A special adaptor is available to facilitate use with all double hose regulators. The high pressure gauge is fitted with a length of high pressure hose which allows it to be positioned so that the diver may constantly monitor his cylinder pressure. Auxiliary Breathing Systems Many divers now use regulators with dual second-stage assemblies (Figures 4-6a and 4-6d) to facilitate buddy-breathing. Some single hose regulator first-stage assemblies are designed with two low pressure ports; others require a special adaptor (Figure 4-6b). The auxiliary mouthpiece should be secured to the diver's shoulder harness with a quick-release mechanism. Cave divers often mount a 12 to 40 ft3 air cylinder and single hose regulator on their twin cylinder SCUBA as an emergency air supply in case of regulator malfunction (Figure 4-6e). During one test, a diver safely returned from 200 feet to a reserve air supply at the decompression stop using this emergency SCUBA. The unit should be securely mounted, and the air turned on prior to the dive. Another method of connecting two regulators to a single air source was designed and constructed by James Dell of the University of Michigan. The "Dell-T" (Figure 4-6f) is not available commercially; however, it may be constructed by any competent machinist. Harness The SCUBA cylinder is secured to the diver's back with a harness and/or backpack assembly (Figure 4-7). Currently, most single and double

166 tank assemblies are fitted with a removable metal or plastic contoured backpack assembly, The waist strap is equipped with a quick-release type buckleand one shoulder strap is generally equipped with release snaps to facilitate donning and rapid removal of equipment in an emergency, The backpack must fit the diver comfortably, hold the cylinder securely, and be constructed of corrosive resistant materials, Some backpacks are equipped with a cam-action cylinder release mechanism to facilitate cylinder removal, This mechanism should be adjustable and equipped with a safety mechanism to prevent accidental release of the cylinder. The assembly should be inspected and adjusted, if necessary, prior to each dive. For double tk assemblies, the standard harness (without backpack) is preferred by may divers, PREVENTIVE MAINTENANCE: SCUBA Open-circuit SCUBA regulators are durable, but they can be damaged and malfunction unless given reasonable care. Simple preventive maintenance will insure maximum operating efficiency with minimum repair requirements. SCUBA regulators are built extremely rugged externally but are delicate internally. The clearance between parts is close and foreign material such as rust and salt corrosion can cause inefficient operation and malfunction, Observe the following preventive maintenance procedures for open-circuit SCUBA regulatorst (a) Never stow or transport SCUBA with the regulator attached. (b) Do not allow water or foreign matter to enter the high pressure inlet of the regulator. P and insert the protective cap into the yoke to seal the high pressure inlet immediately after detaching the regulator from the cylinder. When water, salt or fresh, evaporates, it leaves a residue of salts or minerals.

167 This residue can accumulate on internal parts of the regulator resulting in friction, decreased functional efficiency and excessive wear. Chlorinated swimming pool water is nearly as harmful to regulator parts as salt water. Use only plastic or rubber protective caps with a solid core and fitted with an o-ring to insure a more positive seal. Avoid metal protective caps since electrolysis corrosion may result from the reaction of contact between two different metals and salt water. (c) Rinse regulator thoroughly with fresh water following each use. The procedure for rinsing single and double hose regulators is given below: Single hose reagulators: 1. With the dust cap in place, flow fresh water, preferably warm, into all parts; a two minute rinse is recommended to dilute salt water accumulations and remove all foreign matter. This is extremely important for a regulator with the piston type first stage since salt and sand deposits can interfer with the movement of the piston. 2. Wash the second stage assembly by flowing water into the mouthpiece and out the exhaust tee. Do not depress the purge button while washing the second stage assembly. This action opens the second stage valve and will allow salt, foreign matter and water to enter into the valve assembly, hose and possibly the first stage. If there is any possibility of the purge botton being depressed during washing, place the regulator on a SCUBA cylinder and allow air to flow through it. 3. Shake excessive water from the regulator and hang it by the yoke to dry. Double hose regulators: 1. With protective cap securely in place, wash the regulator housing and exterior of hose with fresh water to remove salt water and foreign matter. 2. Hold the mouthpiece in a vertical position with the exhaust downward. Flow water gently into the mouthpiece to avoid dislodging the rubber intake check valve and admitting water into the intake hose. 3. Remove excess water from the exhaust hose corrugations by blowing through the mouthpiece or shaking the regulator while holding the hose where it clamps to the regulator housing with the mouthpiece up and the hose slightly stretched.

168 4, Hang by the yoke to dry, The above procedure is for simple field maintenance of double hose regulators, -It is virtually impossible to keep water from seeping into the intake hose and eventually the air chamber. Periodically the air chamber and intake hoe must be cleaned and dried as follows: (a) Remove hoses from the regulator housing, wash, and hang to dry so the water drains out. (b) Fill air chamber with fresh water, empty and shake out excess water, Repeat three times, (Use distilled water if local water has a high alkaline or mineral content.) (c) Attach regulator to cylinder and position with inlet port pointing downward. (d) Turn on the air and with a long shanked screw driver, or similar device, depress the low pressure diaphragm by inserting the screw driver through a small exhaust port. This will cause air to flow and dry the inside of the air chamber. Continue air flow for one or two minutes, (e) Check condition of and properly position exhaust valve, (f) Reassemble making certain that hoses are properly positioned with respect to exhaust and inlet ports. Regulators may be washed by immersing them in a bucket of fresh water, Single hose regulators may be completely submerged. For two hose regulators submerge the housing and hoses but not the mouthpiece. Only partially submerge the mouthpiece with the exhaust side underwater to allow water to enter the exhalation hose. During storage and transport, protect regulators from abuse, physical damage and exposure to high ozone levels in surrounding air (produces rubber deterioration), A protective container is recommended for carrying.regulators in the field, Careful inspection of the high pressure inlet filter is an excellent

169 indicator of potential type and source of foreign material that may be entering the regulator. This filter is designed to exclude large particles of foreign material; however, it will not prevent all material from entering the regulator. The following indicators are noted: (a) A black wet substance is an indicator of salt water inside the cylinder. (b) A black dust or powder may indicate contamination of the cylinder interior with activated charcoal from the compressor filter. (c) A reddish-brown accumulation indicates fresh water inside the cylinder. (d) A greenish or turquoise colored accumulation indicates that salt water has come into contact with the filter and suggests potential internal contamination of the regulator. This is usually a result of carelessness. Periodic Inspection and Overhaul: Regulators SCUBA regulators should be inspected by a qualified technician annually. In the event of even minor malfunction, immediate repair is indicated. Annual maintenance procedures involve inspection (and possible replacement) of all rubber parts, pressure setting adjustments, and evaluation of the internal condition of the regulator. Periodically, the regulator must be completely overhauled including disassembly, cleaning and replacement of worn or defective parts. If the regulator has been subjected to abuse and physical shock, it should be inspected by a qualified technician prior to use in open water. Prevention of Lung Infection A serious infectious lung condition may result from inhalation of a micro-organism (fungus) which contaminates the interior of SCUBA, particu

170 larly double hose regulator breathing hoses and mouthpiece tees. This fungus growth is more common in tropical areas, The fungus can be eliminated by periodically cleansing the regulator as follows: (a) Disassemble breathing hoses and mouthpiece, (b) Thoroughly scrub the interior of the hoses and mouthpiece components with surgical soap (or Phisohex) using a suitable brush, (c) Rinse in fresh water and immerse all rubber parts in a chlorine solution (1/2 cup chlorox to one gallon water) for at least two minutes, (d) Dry completely and reassemble. The procedure should be repeated every two weeks during periods of use and prior to storage, Maintenance of High Pressure Cylinders Air cylinders and high pressure manifolds should be rinsed thoroughly with fresh water to remove all traces of salt deposits. The exterior of the cylinder should be inspected for abrasion, dents, corrosion and rust. If the cylinder has been subjected to severe damage resulting in deep abrasion or denting, it should be hydrostatically tested before refilling, External rust and corrosion should be removed and a protective coating applied to these areas to prevent further deterioration of the cylinder wall, The tank boot should be removed periodically. The portion of the cylinder under the boot is particularly subject to corrosion and rusting since the boot retains moisture next to the cylinder, Occasional application of protective coatings to this area may be required. Also, periodically inspect the area under the tank harness bands for rust and corrosion.

171 Internal rusting and corrosion are problems that have become more apparent in recent years (Peyser 1970). Some SCUBA repair facilities claim that approximately 80% of all cylinders received for hydrostatic testing have to be tumbled to remove excessive rust from the interior of the cylinder. Care must be taken to prevent moisture accumulations in high pressure cylinders. When a cylinder is completely drained of air while using a single hose regulator, water may enter the cylinder through the regulator if the purge button is depressed allowing the second stage valve to open. The obvious solution to this problem is never to allow the cylinder to be completely drained of air, Always terminate the dive with a small amount of air remaining in the cylinder (approximately 300 psi is sufficient to keep water from entering the cylinder). Never depress the purge button underwater when the cylinder is empty. Moisture may enter the cylinder during charging. The cylinder should never be completely submerged prior to attachment of the filler assembly. Small amounts of water may be trapped in the valve orifice and injected into the cylinder. Inadequate removal of moisture from air by high pressure compressor filter systems is another source of internal moisture. Be certain that the compressed air filter system has an adequate moisture separator. All SCUBA cylinders should be internally inspected at least once a year for rust and corrosion. A special rod type light that illuminates the entire inside of the cylinder should be used for this visual inspection. Most diving equipment suppliers and repair facilities provide this service.

172 Rust chips may be detected by rocking the cylinder through its horizontal axis while pressing it next to the ear and listening for foreign matter. Also gently tapping an empty cylinder with a hammer may reveal internal rust and corrosion. A clean cylinder will have a clear metallic ring and a corroded or structurally weak cylinder gives a dull wooden sound. These procedures are useful when selecting rental or loan cylinders. They are not, however, to be considered as a substitute for visual internal inspections, If internal inspection reveals rust and corrosion, the cylinder should be cleaned by tumbling. The tumbling process involves filling the cylinder approximately one-half full of an abrasive material such as palet abrasive, carbide chips, or zinc oxide chips and allowing the cylinder to rotate, The abrasive materials remove rust and polish the inside surface of the cylinder, The cylinder is then rinsed to remove loose material and dehydrated internally to remove all traces of moisture. High pressure cylinders are subject to Department of Transportation.(formerly, Interstate Commerce Commission) regulations. These regulations require that high pressure cylinders transported from state to state be hydrostatically tested at least once every five years. Most states and cities have ordinances that cover transportation of high pressure cylinders requiring adherence to Department of Transportation regulations. Diving equipment suppliers and air station personnel will not recharge out-of-date cylinders. There are several methods of hydrostatic testing of cylinders including direct expansion, pressure recession, pressure and water jacket. The water

173 jacket method is commonly used. In this -method the valve is removed and a special test fitting inserted. The cylinder, filled with water, is placed in a water filled pressure chamber and all air is evacuated. A high pressure water line is attached to the test fitting and pressure is applied to the inside of the cylinder using a high pressure hydraulic pump. Before pressure is applied a burette reading is taken. The burette, attached to the test chamber by a water line, allows the tester to measure the amount of cylinder expansion in terms of water column displacement. The pressure is increased to 5/3 the rated pressure of the cylinder, or in the case of the standard SCUBA cylinder with a rated pressure of 2250 psi, the test pressure is 3750 psi. A second burette reading is taken under full pressure. The water column rises due to expansion of the cylinder. The hydraulic pressure is released and the water column starts to drop indicating that the cylinder is returning to its original diameter. After all pressure is released, a third burette reading is taken. Based on these burette readings the permanent expansion of the cylinder is determined. According to Department of Transportation regulations, permanent expansion of 10% or more of total expansion indicates that the cylinder is unsafe for use. Cylinders that fail hydrostatic testing and show signs of structural damage must be condemned. This can be accomplished by stamping out the Department of Transportation (or ICC) specification symbols and figures or boring a hole in the cylinder. A cylinder cannot be restamped for a lower pressure. The cylinder valve assembly and reserve mechanism should be periodically inspected. Immediate repair is necessary if it is determined that

174 assembly is malfunctioning or faulty. The entire valve assembly should be rinsed with fresh wate? after diving, and protected from unusual abuse. Frequently, the reserve lever is damaged when hit against the roof of caves, ship's hull or when the tank assembly is left unsecured on a boat deck in rough seas, Use a protective shield for cave diving and properly secure tanks at sea and during transport. Cylinders should be tied down, blocked or otherwise fastened to prevent shifting during transport in vehicles, When not in use the valve orifice should be covered with masking tape to prevent loss of rubber o-ring and accumulation of foreign material. Divers should carry extra cylinder valve orifice o-rings attached to the regulator or in the diving equipment bag. Cylinders containing high pressure compressed gas can be extremely dangerous if abused or misused, If the pressure of 2250 psi is multiplied by the number of square inches of surface inside a standard cylinder, the force is found to be approximately 433.3 tons. Property damage, physical injury and even death have resulted from the explosion of high pressure cylinders. A faulty cylinder is a potential bomb and if a valve is broken off of a cylinder, it is a potential deadly missile, High pressure cylinders should be stored in an upright position, Should moisture collect inside the cylinder, corrosion will be less detrimental on the thicker bottom than on the walls. Store cylinders with 100 to 300 psi pressure to prevent accidentally leaving the valve open and admitting moisture and corrosive agents from the atmosphere, A cylinder which is to be stored for a long period of time should not be

175 charged to full pressure, Tests have shown that less internal corrosion occurs at low cylinder pressures. Also, in the event of fire or physical damage, the low pressure constitutes a lesser hazard. Although compressed air normally does not show signs of contamination after storage for long periods, it is advisable to discharge the cylinder and recharge it after one year of storage. High pressure cylinders used with open-circuit SCUBA should be filled only with pure compressed air. The rated pressure should not be exceeded by more than 10% providing that over pressure is indicated by the plus (+) following the hydrostatic test date; otherwise never exceed the pressure stamped on the cylinder. Overfilling places extreme stress on the cylinder walls and may result in metal fatigue. Never allow the cylinder to overheat during charging. Excessive heat, especially involving temperatures above 500~F, can result in significant structural damage, AIR COMPRESSORS AND BREATHING MEDIA Air compressors for filling SCUBA cylinders are designed to deliver high pressure breathing air (Figure 4-8). Compressors for this purpose are available as portable units or for permanent installation. Portable units should have at least 2 CFM output at 3000 lbs/in2 and operate at a low RPM and with a low temperature rise. Larger units for permanent installation should have an output of 8 or more ft /min at a pressure of 3000 to 5000 psi. Air compressors may be powered by internal combustion engines or electric motors of sufficient capacity as specified by the compressor manufacturer. Internal combustion engines are a potential source of

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177 air contamination and proper precautions should be taken to ensure that the engine exhaust is prevented from entering the intake of the compressor, Electric motors are recommended for diver air compressors; however, the potential of air contamination is still present and safeguards and precautions are required, A thermal overload cut-off switch is recommended for electric motors. The compressor must be located in an area where the atmosphere is not contaminated and proper precautions must be taken to ensure that only uncontaminated air is admitted into the compressor intake. The air entering the compressor must not be exposed to contamination by exhaust from internal combustion sources (compressor engine, ship's engine, generators, etc,) or by contamination from any other source. The air intake must be provided with a suitable dust filter. If necessary, the air intake may be extended out of doors or to a specific source of clean air. If the air intake is extended out of doors, it must be properly protected to prevent entry of excessive amounts of moisture. The extended air intake length should not exceed that recommended by the compressor manufacturer. Lubricating oils (natural or synthetic) or other lubricants must have the quality and meet the specifications required for compressor service, particularly with regard to flash point, viscosity and resistance to decomposition and oxidation at elevated temperatures, as specified by the compressor manufacturer. The use of chlorinate lubricants, phosphate ester (pure or in a mixture) or tetrafluoroethylene piston rings must not be permitted. Water-lubricated and dry-lubricated type compressors have positive advantages in terms of precluding internal production of carbon monoxide,

178 Precautions should be taken to prevent overheating of the compressor which may result in fomoation of oil breakdown products. Methods of cooling high pressure copreasor heads which may be employed include air blowers, water spray systems or systems incorporated into the compressor. Operations y be cycled to insure against high temperature rises, A built-in temperatre indicator or fail-safe temperature controller may be used if desired, A filter system must be provided between the compressor and the supply, storage, or diving tanks as a standard part of the compressor equipmento The filter system ust be provided with activated carbon, molecular sieve or other appropriate filters in suitable combination to remove excess water, oil, particulate matter and odor in order to meet the specified air purity standard$s An oil and water (moisture) separator must be provided beteen the compressor and the filter system. Activated carbon and other filters in the filter system should be examined at least every 24 hours of total compressor operation and a schedule of periodic replacement of filters must m aintained in accordance with the manufacturer's instructions ad specifications, Mainetance and operation of internal combustion and electric motive power and air compressor should be in accordance with the,manufacturer's istructions and specifications unless such instructionstuti and specifications would result in infraction of the purity standards for breathable compressed air, Running periods and maintenance operations must be logged. Specific attention must be given to recording of elapsed operating time of the compressor and motive power source, details of maintenance, the type and number of filters used, elapsed operating time of each filter, oil

179 consumption and changes, filter replacements, air analysis and other pertinent details, A motor-hour meter is recommended to facilitate keeping accurate elapsed operating time records. Air compressors must be maintained in excellent operating condition and all diving personnel should be trained in the operation and maintenance of compressors. Periodic inspection and factory overhaul are mandatory in accordance with manufacturer's recommendations. Breathing air must be free from carbon monoxide, carbon dioxide, oil vapor, and other impurities. The air should be periodically analyzed to insure purity for breathing in accordance with the following specifications: Oxygen Atmospheric Maximum carbon monoxide 0.001% (10 ppm) Maximum carbon dioxide 0,030% (300 ppm) Maximum total volatile hydrocarbons 0.001% (10 ppm) Maximum total oxidants 0,000005% (.05 ppm) Dust and droplets of water and oil* Lack of any residue on membrane after passage of 5,000 cc of air through filter Odor Absent Maximum moisture content in compressed air for general use is saturated. Compressed air for SCUBA used at temperatures below 200 C is 0.02 mg/liter. Particulates including oil in environments up to 2 atmospheres gauge pressure must not exceed 5 mg/cubic meter and above 2 atmospheres must not exceed 1 mg/cubic meter,

180 The following air analysis procedures should be used to insure compliance with the above specifications: 1. Compressed atmospheric air at air pollution free locations will.be considered to met the oxygen and carbon dioxide requirements without testing, However, the content may be determined volumetrically with gas analysis apparatus. 2, Methods of-analysis for carbon monoxide (laboratory): -a Standard laboratory method of analysis -- iodine pentoxide method. b, Alternate laboratory method of analysis -- infrared spectrophotometry (subject to periodic calibration of test equipment by standard method), c, Method of field analysis for carbon monoxide -- NBS colorimetric tubes, 3, Oxygen content must be determined by gas chrometograph, standard volumetric gas analyzer, electrometric analyzer, thermal conductivity analyzer, paramagnetic type analyzer or color indicating tube, 4, Carbon dioxide content must be determined by gas chrometograph, tetreetric analysis, standard volumetric gas analyzer or color indicating tube, 5. Liquid water, oil and particulate matter content in a cylinder of air can be determined by supporting a cylinder, valve down position, for 5 minutes at room temperature. The valve is then slightly opened and air is allowed to flow lightly into a clean glass container, Condensed water (and oil) may be seen on the glass surface, Other methods to test for water include electrolytic monitor, piezo electric hygrometer, standard dew point apparatus or electrical conductivity, An alternate oil test is ultraviolet spectroscopy, Field tests for visible dust, oil, and water may be made by passing 5000 cc of air through a white-sieve membrane filter. If there is no visible material present on the filter, the air is considered to meet specifications, 6. Odors may be determined by sense of smell. 7. Total volatile hydrocarbons must be determined with a total hydrocarbon analyzer.

181 AIR REQUIREMENTS The diver must be provided with an adequate supply of pure air. Dive duration is determined by the volume of air contained in the SCUBA cylinders. Air consumption is a function of depth, exertion level, water temperature, and individual physiological variations. The theoretical duration of air supply in a standard SCUBA cylinder at various depths for five levels of exertion is given in Table 4-1. Air consumption may be calculated for various depths and levels of exertion by using the following formula: D ~- 33c. Cd \ r s " d where D is depth in feet, Cs is surface equivalent consumption, and Cd is consumption at depth. Cd will vary with water temperature, exertion level, physical condition, etc. The average Cs for moderate exertion levels is 1 ft3/min. This factor may vary from 0.5 (light exertion in warm water) to 3 ft3/min or more (heavy exertion in cold water). For example, the ft3/min air requirements for a SCUBA diver doing moderate work at 99 ft may be calculated, (99 + 33) 1 -4 ft3/min. 33 / On the other hand, a diver performing heavy work in cold water at a depth of 132 ft may require 15 ft3/min, (132 + 33)3 - 15 ft3/min. A simplified procedure for rapid calculation of air consumption at depth (Cd) is given by the formula: Pa-Cs Cd

182 TABLE 4-1. Theoretical durationl of air supply in a standard single opencircuit SCUBA cylinder2 at various depths for five levels of exertion. "No-decompression" limits are included for convenient comparison. (Modified after Dewey 1962. age 817.) _ Depth Pressure No-decompres- Total Duration of Air SuplX lat Each Depth by sion limits Exertion Level 95 Very Mild Mild Moderate Heavy Very Heavy Feet Atma, Min. Min. Min. Min, Min. Min. 0 1.00 - 113 90 65 51 34 10 1.30 - 87 69 50 39 26 20 1,61 70 56 40 32 21 30 191 - 60 47 34 27 18 33 2,00 -56 45 32 25 17 40 2,21 200 51 41 29 24 15 45 2,36 - 48 38 27 21 14 50 2,52 100 45 36 25 20 13 55 2.67 - 42 34 24 19 12 60 2,82 60 40 32 23 18 12 66 3,00 - 37 30 22 17 11 70 3,12 50 36 29 21 16 11 80 3.43 40 33 26 19 15 10 90 3.73 30 30 24 17 13 9 99 4.00 25 28 22 16 12 8 110 4,35 20 27 20 15 11 7 120 4,64 15 24 19 14 11 7 132 5.00 10 22 18 13 10 6 140 5.24 10 21 17 12 9 6 150 5,55 5 20 16 11 9 6 160 5.85 5 19 15 11 8 5 165 6,00 5 19 15 10 8 5 170 6.15 5 18 14 10 8 5 180 6,46 5 17 14 10 7 5 190 6,75 5 17 13 9 7 5 198 70 0 0 16 12 9 7 4 lComputed with use of a constant; average respiratory minute volume for each level of exertion: very mild, 0.64 ft /min; mild, 0.81 ft /min; moderate, 101 ft3/min; heavy 1.4 ft3/min; very heavy, 2.1 ft3/min. (Based on U.S. Navy 1963; Lanphier and Dwyer, 1954.) 2Values derived for standard cylinder of 72 ft3 capacity, charged to 2475 psi (includes +10%); for standard cylinder charged to 1800 psi and U.S. Navy aluminum cylinder charged to 3000 psi, multiply by 0.85 and 1.39 respectively; for twin cylinder SCUBA multiply by 2. 3No allowance for time taken in descent or ascent, nor for temperature changes, 4All figures are average values for persons in fairly good physical condition; there is considerable individual variation. 5To simplify dive planning these times may be used as "total dive time equivalents"; this allows a minimal air supply safety factor.

183 where Pa is ambient pressure at diving depth in atmospheres (rounded to the nearest 0.5 atm). For example, air consumption under heavy exertion at a depth of 75 ft is found as follows, 3.5 x 2 - 7 ft3/min. Total dive time on a given volume of air is found by the formula: V Cd Tt where V is the volume of gas available and Tt is total dive time. Although the diver will likely use less air during the time spent in descent and ascent, calculation of total dive time (Tt) which includes bottom, ascent and decompression times, provides for a slight safety factor. Moreover, this is the simplest procedure. Although SCUBA divers are encouraged to remain within "no-decompression" limits, occasionally a decompression dive will be required with SCUBA. Total dive air requirements (Ct) may be calculated using the formula: Cd(Tb + Ta) + T10 + 1.5T20 + 2T30 - Ct, where Cd is consumption at depth, Tb is bottom time, Ta is ascent time from bottom to first decompression stop, and Tlo, T20, and T30 are decompression times at 10, 20 and 30 feet, respectively. For example, the calculation to determine the total air requirement for a 25 minute bottom time moderate exertion dive to 130 ft is, 5(25 + 2) + 10 - 145 ft3 Assuming that the diver's cylinders contained only 132 ft3 of air, the diver would have to do one of the following: 1. Shorten bottom time by 3 minutes (preferable).

184 2, Provide auxiliary air for decompression, (always recommended for a decompression dive, whether one plans to use it or not). If the diver is working in a situation where it is not possible to provide an auxiliary air supply at decompression stops or he wishes to complete the dive on only the air in his cylinders, the following procedure may be used: 1. Calculate total air requirement for ascent and decompression. 2, Subtract this sum from the total volume of air available in the SCUBA to give the volume available for remainder of dive, 3. Divide the remaining volume by Cd to determine the maximum time allowable before the diver must begin ascent, For example, determine the maximum bottom time for a 130 ft dive assuming a volume of 132 ft3 air in the cylinders. Using the formula, CdaTa + T10 + 1.5T20 + 2T30 - Cat where Ca is total air consumption during ascent and decompression. Then 5(2) + 10 - 20 ft3 and, 132 - 20- 112 ft3 therefore 112 = 22 minutes allowable bottom time (approximately). 5 Another excellent method of determining when the diver must start ascent based on air requirements for ascent and decompression is by SCUBA pressure readout. For example, in the previous example a total of 20 ft3 of air was required for ascent and decompression. To calculate the minimum readout pressure that would still allow the diver sufficient air to ascend, use the formula: Cd'Ta + T10 + l.5T20 + 2T30 1k- i Pr

185 where k is the constant for a given SCUBA cylinder and Pr is the pressure gauge readout. Using the previous dive example, 5(2) + 10. 700 lbs/ln2 (approximately)..03 Therefore, the diver using a double cylinder SCUBA must terminate at a minimum readout pressure of 350 lbs/in2 since this is 350 lbs/in2 in each cylinder.

186 CALCULATICN OF AIR VOLUME AT VARIOUS CYLINDER PRESSURES Occasionally self-contained divers are required to dive with partially filled SCUBA cylinders. For proper dive planning the exact volume of air available may be determined using the following formula: (Pr V V where, Pg is cylinder gauge pressure, Pr is the rated pressure, Vr is rated cylinder volurme and V is the volume of free air in the cylinder. For multiple cylinder units, multiply V by the number of cylinders. For example, the volume of free air contained in a standard 71.2 ft3 cylinder at a gauge pressure of 1600 lbs/in2 is, 1600 x 71,2 - 45,6 ft3 2475 To simplify the calculation of remaining volume, a "constant" may be used as follows: Pg (k) V, where the constant (k) is Vr/Pr. The following are constants for SCUBA cylinders currently used: Rated Volume (Vr) Stamped Pressure Rated Pressure (Pr) Constant (k) 71,2 2250 2475.0288 52.8 1800 1980.0267 50,0 2250 2475.0202 42 0 1880 2068.0203 38,0 1800 1980.0192 Approximate values, generally adequate for most SCUBA diving calculations, may be determined by using k rounded to the nearest.01, i.e.,.0288 w.03.

187 ACCESSORY EQUIPMENT Face Mask The face mask (Figure 4-9b) provides increased clarity and visibility underwater by placing an air space between the eyes and the water. There are two general classes of face masks: the separate face mask and full face mask. The separate face mask, covering only the eyes and nose, is normally used for diving with SCUBA equipped with a mouthpiece or for skin diving. Full face masks are used with specific SCUBA and surface or tether supplied apparatus, These systems will be discussed later. The face mask consists of a faceplate, a frame (face blank or body) and a headstrap. Faceplates of shatterproof, clear glass are recommended. Plastic faceplates are subject to discoloration, abrasive damage and considerable fogging during dives. The frame is a flexible rubber carrier designed to hold the faceplate and provide a watertight seal. The major portion of the frame should be of sufficient rigidity to hold the rubber plate away from the nose. The rubber edge should be soft and pliable enough to insure perfect fit to the contour of the face and comfort; however, it must be sufficiently rigid to retain its shape. This edge may be fashioned of tapered neoprene rubber or thick foamed neoprene rubber. A non-corrosive, adjustable metal retainer band is required to secure the faceplate in the frame, An adjustable rubber headstrap holds the mask to the diver's head. This strap should be approximately 1 inch wide and/or split at the rear of the head for better security and comfort. The headstrap should be secured to the metal reta eainer band or frame by metal strap anchors which facilitate adjustment and prevent slippage of the strap.,

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189 A mask may be equipped with a nose blocking device to facilitate equalization of pressure during descent. Three basic types of nose blocking devices include: (1) a foamed neoprene rubber pad positioned below the nostrils for sealing off the nostrils by pushing upward on the mask, (2) finger pockets in the mask frame on each side of the nose to facilitate pinching the nostrils shut with the fingers, and (3) a formed nose pocket to facilitate pinching the nostrils. The rubber pad is recommended for use when diving with neoprene mittens and the nose pocket is desirable for those who have difficulty equalizing or for skin divers, A mask may also be equipped with a purge valve, a device to facilitate clearing water from the mask. This purge device consists of a thin, circular rubber neoprene check valve, generally protected by a vented plastic cover and housing. Underwater this one-way check valve is held flush against its housing by increased water pressure. Exhalation through the nose forces water through the valve from inside the mask. Caution must be taken when selecting masks equipped with purge valves since many are subject to failure and leakage. Only high quality masks with large check valves are recommended. Face mask selection is a matter of individual preference, fit, comfort and diver requirements. Masks are available in a variety of sizes and shapes ranging from larger wrap-around models with side lenses for greater peripheral vision to small, lightweight, compact models with minimal internal volume. Avoid plastic construction, extremely large size mask, built-in snorkels, narrow headstraps and goggles. Purge valves and nose blocking devices are optional,

190 Those individuals who need to wear eyeglasses generally require some form of optical correction underwater. Large size prescription lenses can be permanently bonded to most faceplates with optically clear epoxy by an optician specializing in underwater vision problems. Williamson (1969) discusses vision problems and corrective measures in detail, The mask should fit comfortably and form an airtight seal on the face. To test for proper fit, the mask is placed in position without securing the headstrap, The mask is properly sealed if when the diver inhales through the nose, it will remain in place without being held. Ventilation across the faceplate is generally poor in any mask and the glass tends to fog easily. To minimize fogging, thoroughly smear the inside of the faceplate with saliva and rinse lightly prior to donning. Anti-fogging solutions such as mild liquid soap or a special commercial preparation may be applied to the inside of the faceplate. The faceplate should be frequently washed in detergent to remove oils and film that enhance fogging. If the mask fogs during use, admit a small amount of water into the mask and roll it across the fogged areas. Swim Fins Swim fins (Figure 4-10a) increase the propulsive force transmitted from the legs to the water. Used properly, the swim fins conserve the diverts energy and facilitate all underwater movements. Swim fins are available in a variety of sizes and designs. Variations in characteristics include size and shape of foot pocket; size, shape, angle and degree of stiffness of blade. Selection of fins is a matter of individual preference, mission requirements, fit and physical condition. Performance is dependent

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192 upon fin design, the style of diver's kick and the force in which this style is applied to the water. In general terms there are two styles of fins, the swimming and the power. Swimming style fins are smaller, lighter weight and slightly more flexible than the power style, and used with a wider, more rapid kick of less thrust. The blade may have a greater angle. Some utilize an open vent and overlapping blade principle which give the swimmer maximum thrust with minimum energy requirements. This style uses approximately as much force on the up-kick as on the downward kick. The swimming style fin is less fatiguing for extensive surface swimming, is less demanding on leg muscles, and more comfortable. This type of fin is recommended for trainees, Power style fins are longer, heavier and more rigid than swimming fins. They are used with a slower, shorter kicking stroke with emphasis on the down kick. This style fin is designed for maximum power thrust of short duration with a sacrifice in comparative comfort. They are desirable for working divers who are required to swim while encumbered with multiple cylinder SCUBA and heavy equipment. Many divers own both swimming and power style fins, Buoyant and non-buoyant models are available in both styles; this factor doesn't generally effect the quality or performance of the fin, Swim fins are available in open or enclosed heel models. Open heel models are recommended for use with coral shoes or rubber boots. They are much easier to don and fit more comfortably. The open heel models have either an adjustable strap or a one piece non-adjustable strap. Adjustable strap models are designed to accommodate a wide range of foot sizes; however, they are less comfortable when worn without foot protection.

193 The strap buckle must be sturdy and designed to hold the strap securely in place. Since open heel fins have a closed toe section, the fin must be properly size to prevent cramping of the toes. Open heel fins are generally larger and stiffer than closed heel models. Closed heel fins are often used for diving in warmer climates where exposure suits and boots are not required. Even in warmer waters some divers prefer some sort of foot protection (socks or boots) to prevent chafing and blisters, especially if they wear fins for long periods of time. Basically, the fin must fit comfortably. It must be properly sized to prevent cramping or chafing. Furthermore, the fin must match the individual's physical condition. Snorkel ne/rtulner The snorkel (Figure 4-lOb) is a J- or L- shaped.Hor high impact plastic tube which enables the diver to breathe without moving his head while swimming on the surface. For efficient and easy breathing the tube diameter should be 5/8 inch or larger and not exceed 15 inches in length. The mouthpiece should be pliable and non-restrictive with a cross section that is approximately equal to that of the tube. Snorkels with valve mechanisms are not recommended. Most self-contained divers carry a snorkel to facilitate surface swimming when the SCUBA air is depleted. Many divers carry the snorkel attached to the mask strap while SCUBA diving; however, the diver should be careful to prevent accidental dislodging of the mask. A "flexible" lower tube is advisable if the snorkel is attached to the SCUBA diverts mask. The snorkel may be more safely carried on a lanyard or under the

194 knife strap. Contoured, large tube snorkels are popular for skin divers. These offer minimal resistance to breathing and swimming. Lifcket A CO2 or air inflatable yoke type lifejacket (Figure 4-11) is mandatory for self-contained divers. It is one of the diverts best safeguards against drowning especially in rough seas or when highly fatigued. However, it is not and must not be used as a substitute for swimming ability and physical fitness. The lifejacket must be designed so it can be inflated by manual activation of the gas cylinder or an oral tube. The only acceptable lifejacket is the "yoke" type which holds the diver's head clear of the water when inflated even if the diver is unconscious. Lifejackets should be lightweight, relatively compact, rugged, comfortable, and provide maximum flotation, Neoprene impregnated nylon is a desirable fabric, The UDT type lifejacket is recommended for surface swimming and self-contained diving, This jacket is fitted with a 19 g CO2 cylinder and is capable of lifting approximately 19 lbs from 18 ft. The harness arrangement on this lifejacket has proven most satisfactory, Some vests are fitted with multiple C02 cylinders, pressure relief valves, and oral tubes located at the back of the neck, The compressed air type lifejacket (Figure 4-11) is similar in design and construction materials, however, it is considerably more bulky and has a greater capacity and buoyancy. A compressed air cylinder, refillable from a standard SCUBA cylinder, provides gas for manual inflation. This vest is fitted with pressure relief valves to facilitate purging excess

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196 gas during free ascent. A flexible tube Is fitted to the vest at the back of the neck, With proper training and practice the diver could use this tube (equipped with a mouthpiece and special valve mechanism) for breathing during emergency ascents A compressed air type lifejacket should not be used by an inexperienced diver. Its capacity for rapid inflation and ascent demands respect and careful handling. Lifejackets are frequently used as "buoyancy compensators" to compensate for improper weighting of the diver and wet suit compression at depth. Care must be taken to prevent overinflation and subsequent loss of control during ascent, Also, inflation and deflation procedures must be mastered under controlled conditions prior to use in deep water, Never use a lifejacket to compensate for extreme overweighting; remove weights from the belt, The lifejacket should only be used to compensate for a few pounds of excess weight, Some divers also use a small plastic container for buoyancy compensation. A gallon container (Figure 4-llb) will provide approximately 9 lbs buoyancy, The container is carried in the diver's hand or snapped to the cylinder harness in a convenient location. Since the lifejacket is essentially a piece of lifesaving equipment, it should be maintained accordingly. Rinse and inspect the lifejacket after each dive. Periodically inspect and lubricate activator mechanism. The cylinder should be checked prior to each dive and the cylinder threads lubricated, Periodic activation and inflation tests are recommended, The need for preventive maintenance is increased when vests are used as "buoyancy compensators." Water-must be drained from the lifejacket following each dive and activation tests performed more frequently.

197 Knife The diverts knife (Figure 4-12a) is his safeguard against entanglement and serves as a valuable tool. It should be made of high-quality non-corrosive metal. The blade is 5 to 7 inches long and approximately 1 inch wide, One side is a sharp edge and the other is serrated. The serrated edge is particularly useful for cutting water-soaked fiber lines and even lightweight cable. A large, contoured handle with a metal protector at the base is desirable. The knife is generally carried in a plastic scabbard attached to the diverts belt or leg. Placing the knife on the inside of the leg (Figure 4-12b) lessens the possibility of snagging it on line or plant growth. A "diver's tool" (Figure 4-12c), which is a combination knife and pry bar, is very useful in scientific work. Diverts knives and tools should be washed in fresh water after the dive and metal parts treated with a light coating of oil or silicone, Weight Belt A weight belt (Figure 4-13a) is frequently required to offset natural buoyancy or the buoyancy of a diving suit. Buoyancy factors will be discussed later. The belt is generally constructed of 2 inch nylon webbing with a quick release buckle, A "positive-release" type buckle (Figure 4-13b) is recommended since once it is released, it can not close again. The "positive-tension" type has special applications, i.e., cave diving. Molded lead weights are attached to the belt. Weights are available in 1 to 10 lb sizes, although 2, 3, and 5 lb sizes are used most frequently. Contoured hip weights (Figure 4-13a) are more comfortable;

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199:> 111 111.; *;: f:: ti:0:::::: l'^:';::^!!!!!!!!!!!!!!! - ~~~~A > a'sE~~~~~~~) FIGURE 4413. Weight belts for akin and SCUBA divers, (a) Weight belt with expandable section to compenaateo for wet sult compression, 3 lb weight, and 8 11b contoured hip weighto (b) Quick release buckle (below) and apring.loaded positive tension buckle (above), (Photos by author)

200 however, they limit weight adjustments. Always wear the weight belt over all other equipment so it can be readily released without obstruction, Watch A watch (Figure 4- 14 ) is essential to the SCUBA diver for determining bottom time, controlling rate of ascent, and navigation timing. It is mandatory for dives below 50 ft. The diver's watch must be pressureproof and waterproof; a screw type sealing crown is recommended. It should have a heavily constructed case, be highly shock-resistant, self-winding and nonmagnetic. A black or orange face with large, luminous hands and dial is necessary for utmost visibility in deep water. An external, self-locking bezel is required for registering elapsed time. A haevy-duty band of plastic, rubber or metal is desirable. Many inexpensive diver's watches are available; however, experience has shown that these watches have a tendency to leak and will not sustain repeated, rugged use. An example of a satisfactory diver's watch is the Rolex Submariner distributed by the American Rolex Company. These watches are expensive but they have proven themselves through years of satisfactory service. A heavy-duty, inexpensive metal case is available for use with inexpensive watches (Figure 4- 15d). This case has proven satisfactory to depths in excess of 200 ft. Since the case is not equipped with a bezel, the diver must set both hands on 12 or record descent time on a small slate. Do not rely on memory! All diver's watches should be washed in fresh water after use in salt water and serviced regularly in accordance with manufacturer's recommendations.

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203 Depth Indicator Self-contained divers must continuously monitor their depth for decompression and air consumption purposes. If the depth is constant and the diver is working in a limited area, a sounding line or fathometer will give indication of depth. Generally, self-contained divers move around the area, and the depths at which they work may vary considerably during a single submergence. This necessitates the use of a self-contained depth indicator (Figures 4- 15a,c ). Depth indicators available at present are generally of the open or sealed Bourdon tube, diaphragm or capillary type. The open Bourdon tube depth indicator consists of a spiral shaped metallic tube with one open end. This tube is contained in a metal case with the open end exposed to the external water. The closed end is connected, by linkage, to a pointer which rotates around a calibrated dial. The water enters the open end of the tube and pressurizes the bore. The differential between the bore and the sealed case causes the tube to deflect from the original shape; this movement is transmitted to the pointer. The sealed Bourdon tube depth indicator is completely enclosed in an oil-filled neoprene-metal and neoprene housing (Figure 4- 14 ), The water pressure acts upon the housing which is flexible and functions as a diaphragm. This allows the sealed Bourdon tube to be subjected to the ambient pressure. This type of gauge is subject to error because of temperature change, permanent set of the tube induced by impact or shock and corrosion of the tube. With proper care and adequate maintenance, these gauges will operate satisfactorily, The diaphragm controlled mechanism gauge (Figure 4-15c) is basically

204 composed of a pocket of dry air, separated from the surrounding medium by a metal membraneo The ressure differential between the air pocket and surrounding edium moves th metal membrane, which by linkage move the pointer, This type is reasonably shock resistant and is not affected by internal corrosion as the open Bourdon tube type, It is subject to temperature variation, The capillary type depth indicator (Figure 4-15a) consists of a tube closed at one end and secured to a calibrated dial. As the diver descends, ambient pressure forces water into the tube thus compressing the entrapped air. The water level indicates the depth. This type of depth indicator is inexpensive and relatively accurate in shallow water (to 60 ft). The diver is cautioned against jump type entries which may force air and twater into the tube with a subsequent broken water column and false readings. The depth indicator is generally secured to the wrist of the diver by a heavy plastic or n~oprene strap. The case should be of heavy metal or neoprene with a thick plexiglas port, A large dial is desirable with the numbers, calibrations and needle coated with radium paint to permit ease of reading in dark water. The gauge should be calibrated from 0 to 200 feet (or deeper depending on mission requirements). Depth gauges are generally calibrated for salt water. When using it t fresh water, multiply the reading by 1.025. After use, particularly in salt water, depth indicators should be rinsed in fresh water, The depth indicator should be protected from physical abuseS stow and transport in separate padded container. All depth indicators should be periodically calibrated by checking against a mealured line or pressurising in a chamber,

205 Safety Line and Reel A safety or life line (Figure 4-16 ) is the cave diver's only dependable link with the surface. In addition a line and reel are useful in search and recovery work and as a distance line on decompression dives. The line reel should be of simple design, lightweight, foul-proof, rugged, easy to handle and dependable. The line should reel-off smoothly and effortlessly without backlash. Thus when the diver stops pulling off line, the reel stops. The diver should be able to rewind the line with a minimum of effort and no fouling. Until recently nearly all diving reels or "line retainers" (Figure 4-18b) were of individual design and construction. Some were simple, some elaborate and many unsatisfactory. Now a satisfactory safety line reel (Safline Reel) is manufactured by the Ideal Reel Company of Paducah, Kentucky. A detailed description and evaluation of the reel has been published by Tzimoulis (1968). The Safline reel accommodates 100 ft of 1100 lb test, 200 ft of 525 lb test, or 400 ft of 315 lb test braided nylon line. Nylon is the first choice for diving safety lines due to its high strength versus size ratio and resistance to rotting. A line of 525 lb test is considered as minimum and 1100 lb test is used for adverse conditions. The increased diameter is easier to handle as well as stronger. To traverse long distances, each diver can take a reel and simply use several reels in series. The junction between these lines must be secure. Some cave divers do prefer to use a lighter line contained on one reel. One cave diving group requested 1200 feet of 160 lb test line on a single reel (Ideal Reel Company, personal communication); the use of extremely light line is not

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208 recommended, Reels and lines should be inspected prior to each dive. After a dive, unreel the safety line to dry and inspect for damage. If the line shows signs of damage or weakness, it should be replaced, Underwater Lights An underwater light (Figure 4- 17) is necessary for cave diving, night diving, and working around submerged objects where sunlight is cut off, Do not expect a light to aid in murky or dirty water. In fact, under these conditions a light will given an undesirable effect due to reflection on suspended particles, much the same as auto headlights in a fog. Early model hand lights were frequently inadequate in candle power, sealing method, resistance to pressure and dependability. Now there are several underwater lights available that are brilliant, strong and reliable. Most major diving equipment manufacturers or distributors offer one or more models, Basically, most underwater lights are constructed of a durable plastic case with a pistol grip handle, plastic headpiece, removeable o-ring between the case and a seal beam lamp. switch and internal wiring system. A 6-volt spring or screw terminal lantern battery powers the seal beam lamp producing about 40,000 candle power. A few brass or aluminum case models are available, and some are powered by standard "D" or nickel cadmium batteries, Lentz (1967) summarizes standard diving lights and their construction. A highly satisfactory underwater light is the Dive Bright 500 B (Figure 4-17a) by the Allan Engineering Company of Belmont, California,

209 This light features an extremely durable aluminum case, anodized and painted with epoxy paint, and a 1/2 inch o-ring sealed optical grade plexiglas lens. The light utilizes 10 standard size "D" or nickel cadmium batteries to deliver in excess of 80,000 candle power. A hermetically sealed internal reed switch is operated with a permanent magnet affixed to the exterior of the case; there are no case penetrations. The light weighs one pound in water. All components are easily replaced if repairs are necessary. Excellent, moderately priced, rechargeable, nickel cadmium lights are also available. Many experienced Florida cave divers design and construct their own lights from nickel cadmium batteries and seal beam lamps (Figure 4-17b). This unit is powered by six nylon 1.25 volt nickel cadmium wet cell batteries. The bulb used is a standard 6-volt automobile spotlight seal beam. The battery is built by connecting the 6 cells in series, positive to negative, with wire or metal connectors. The cells are held together by wrapping with plastic tape. The seal beam is contained in a housing which will protect the bulb and connections and provide a means of handling the light. Automobile "plug-in" trouble lamps have been used for this purpose. The 6-volt seal beam in this unit is also satisfactory for underwater use. A two-way weather-proof switch is placed at a convenient location in the line. A length of two conductor insulated wire completes the unit. The most convenient wire is a self-coiling two conductor cord. One end of the cord is attached to the positive and negative poles of the battery and the other to the seal beam. A DC battery charger is required for charging the batteries. Charging currents should not exceed amperes required to charge the cell in a period of one hour. These lights are

210 extremely powerful, but often lack the durability and dependability of better comreial units. Som cave divers prefer to use a battery pack attached to a belt or the SCUBA with a seal beam unit on an extension cord. The author, after using many underwater lights of commercial and homemade varieties, favors an underwater light of the Dive Bright or equivalent design. A metal housing is desirable for durability. Bulbs are cheaper to replace than seal be lap units, and bulb units appear to have the edge in brightness, For the average diver, the "D" batteries are readily available throughout the world, cheaper and operational maintenance is considerably simplified. The light should be equipped with a lanyard so it can be looped over the diverts arm if necessary, leaving both hands free for line work. After use, all underwater lights should be washed in clean water and dried Never leave the lamp head attached to the battery. This prevents possible "shorting out"' of the battery which can happen even if the light switch is an off position, If the battery is contained in a metal or plastic housing, remove and stow separately. Inspect before use and keep spare switch, bulb and batteries in diving locker. Observation Boards Slate: A sheet of 1/8 to 1/4 inch thick plastic with both surfaces roughened with fine sandpaper serves as a writing slate for recording data underwater (Figure 4-18a), A convenient size is 3 inches wide and 10 inches long. An ordinary pencil (#2) is secured to the slate with a length of nylon or rubber cord. The slate may be secured to the diver

211 FIGURE 4l 18, Acce.ssor'y equ tipmoet for skin and SCUBA divers (a) Left to riglht, re$ctu light:, undoerateo slatLe with opancil and scale, and MK... 13~, Mod 0 day and night: f lae'o (b) lin o talinar, (Photos by aut.lhor)

212 or his equipment by a lanyard. When a considerable amount of data must be recorded, several sheets of thin white roughened plastic may be used with a plastic or metal clipboard. Instrumented Observation Board: The combination of several basic instruments used in research diving into one functionable unit has resulted in increased efficiency of observation and data recording. Instrumented observations boards are generally built to individual specifications, the components and dimensions being dictated by mission requirements. The Dowling (1963) board measures 6 by 8 inches and consists of the following: a. Writing board b. Depth indicator c. Compass d. Inclinometer a. Pull-out protractor (with bubble level on one edge) f. Ruled edges for measurement g. Bubble levels on two edges h. Holder for two pencils i. Rubber straps on back for attaching folding aluminum (or brass) rule, thermometer, etc. j. Belt clip The body of the unit is constructed of a 6 x 8 x 1 inch sheet of plexiglas. The thickness is required in order to provide recesses for the protractor, inclinometer and pencils, to allow flush mounting of the depth indicator and compass, and to provide sturdiness. The writing area is covered with 1/16 inch roughened opaque white plastic. Two adjacent perpendicular edges are ruled in inches or centimeters and a bubble level is recessed in one edge. A recessed pull-out protractor, constructed of 1/2 inch plexiglas, marked in 1 degree increments and fitted with a bubble level, is hinged to the corner of the board. The inclinometer, a weighted pointer suspended in a hollow 90 degree sector of the body, is marked in 1 degree increments. Pencils are secured in a recessed hollow under spring

213 tension. The compass and depth indicator are secured in recesses in the top of the body. All metal components must be nonmagnetic so they do not affect the compass. Rubber straps are attached to the back of the board for securing additional instruments. The board may be secured to the divert by a special belt clip or a lanyard. Details of construction and use of the instrumented observation board are given by Dowling (1963), Whistle A whistle is a valuable item of safety equipment for signaling other swimmers on the surface. When carried, it should be attached to the oral inflation tube of the lifejacket by a short length of rubber strap, Flare: MK-13 The flare (MK-13, Mod 0, Signal Distres, Day and Night) (Figure 4.18a) is carried taped to the belt or knife scabbard. One end of the flare contains the day signal, a heavy red smoke. The opposite end, which has raised beading around the edge, contains the night signal, a red light. The raised beading enables the diver to locate the night signal when unable to see. Both ends are activated by means of a pull ring. This signal flare is used as a distress signal or as an indicator of the commencement or end of the phases of an operation. After either end of the signal has been pulled, it should be held at arms length and the activated end pointed away from the diver, at an angle of about 450, The diver's body should also be upwind of the signal. At night, the diver should not look directly at the light because it destroys night vision for several seconds, The flare will work well after submergence to any standard diving

214 depth, The user should, however, change flares at least every six months or 10 dives, whichever come firste In the event the flare does not ignite immediately, waving it will cause ignition after a few seconds. The flare will not ignite if pulled underwater, Rescue Lighti ACR-4F The rescue light (ACR-4F, Fire Fly, Military SDU - 5/E) (Figure 4-18a) is carried attached to the diver's belt, harness or arm. The rescue light is a compact (4~" x 2" x 1"l 8 oz) high intensity flashing strobe light with an output of 200,000 peak lumens per flash, visible for 10 to 15 miles f om 1500 ft altitude. It is completely waterproof and will operate submerged to a depth of 200 feet, With continual use, the light has an operational life of approximately 9 hours. The operational life can be greatly extended by using the light intermittently. The special mercury battery has a 5 year shelf life, If necessary, it can be easily replaced underwater. The unit is designed to withstand heavy impact and shock. Batteries for ACR-4F rescue lights are available from ACR Electronics Corporation, 551 West 22nd Street, New York, New York 10011, The rescue light is designed for emergency use or diver tracking at night. The diver should not look directly at the light because it destroys night vision for several seconds. Wireless Communications S stems Voice communication from diver to diver and diver to surface is required on many research diving operations. Continuous underwater voice comaunications greatly enhances the safety of the operation, and

215 the quality and quantity of data aquisition is significantly increased. Currently, direct acoustic transmission and modulated carrier systems are used for most wireless units, Direct acoustic transmission of sound underwater is the simplest wireless communication method since it involves nothing more than amplification of the voice and projecting it underwater through a loudspeaker. The transmisssion is received directly by the diver's ears without special receiving devices. Problems arise with this system because of its very low frequency. Water noises are high and underwater obstructions interfere with transmission. A loud speaker unit of sufficient capacity to handle the low frequency and high power necessary for long range transmission is relatively large in size. This factor makes the system impractical for divers to wear underwater. However powerful units may be used under favorable environmental conditions to transmit information from the surface to divers in the immediate vicinity of the loud speaker. This is useful for diver training. One of the best methods of underwater transmission is the use of a modulated carrier frequency. Three schemes currently used are amplitudemodulation (AM), frequency-modulation (FM), and single-sideband amplitudemodulation with supressed carrier (SSB), AM and FM techniques are the same as for ordinary radio except for the frequency of transmission and the antenna used. In AM and FM units the voice is picked up from the microphone, amplified, and used to modulate the amplitude of a higher carrier frequency (AM) or vary the frequency of a higher carrier frequency (FM). The signal is projected and later received by a transducer (surface station or another diver) for transformation back into audio or voice frequencies. Carrier frequencies must be selected

216 to handle the voice frequency band width and transmission characteristics of the water, AM is more widely used because the higher FM carrier frequencies necessary for voice transmission have higher absorption characteristics in water and are limited in range, and FM electronics are more complicated than AM. An optimum AM carrier frequency, compromising between water noise and absorption, is about 40 kHz, Compact units operating on this frequency are satisfactory for a communications range of several hundred yards, A single-sideband suppressed-carrier (SSB) uses a lower frequency to provide greater transmission efficiency and range. SSB is similar to AM except that after the voice has modulated the carrier, the carrier is removed, and the resultant signal is amplified, filtered, and transmitted, In the receiver the carrier must be reinserted to obtain the original voice frequencies, Using a frequency near 8 to 10 kHz, ranges in excess of several thousand yards have been reported using a selfcontained diver unit. Higher frequencies (28 to 33 kHz) provide excellent short range communication. Several self-contained diver units and surface units are shown in Figure 4- 19. Special lip enclosure mouthpieces or full-face masks equipped with waterproof microphones are necessary for proper articulation when speaking, Waterproof, bar conduction earphones are commonly used. For more information the reader is referred to a publication by Hydro Products, a Division of Dillingham Corporation (1969), which served as principle reference for the above discussion. Other references are Kenny (1966) and Hollien (1967,1968).

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218 Many divers are frequently disappointed with the quality and intelligibility of underwater wireless voice communications. Tests have indicated an upper level of 52.3 percent intelligibility for selected wireless units (IHollien, 1968). With practice and proper procedures, satisfactory results have been obtained by University of Michigan research divers. Success is largely dependent on diver technique. When transmitting, the diver must speak slowly and distinctly using simple words and short sentences. He should avoid lengthy and unnecessary transmissions. The lip enclosure mask must be completely free of water or the listener will receive an extremely garbled transmission. The diver must also be certain that his bone-conduction earphone is placed directly behind or in front of the ear. If an audio earphone is placed over the ear, unnecessary layers of neoprene should be avoided. Proper pressure equalization in the diver's ears is necessary to avoid interference with sound wave action on the eardrum. Diver to surface communication will be greatly enhanced if the same surface communications man is used throughout the operation. A transmission will be 20 to 50 percent more intelligible to a tender who is accustomed to listening to a particular diver than a person listening to that diver for the first time, In addition to diver-surface communications units, small self-contained cassette tape recorders in waterproof housings are used by many research divers (Figure 4-19b), Utilizing the same lip enclosure mouthpiece with a microphone arrangement as used in the wireless units, the diver can record underwater observations. A control switch activates the recorder only when the diver desires to record in order to conserve recording tape,

219 Equipment Bags and Boxes All divers should have some sort of bag for transporting and stowing equipment. Equipment bags are generally constructed of heavy cotton or nylon canvas, or vinyl with snap, drawstring or zipper opening. Various sizes and shapes are available to fit individual needs; however, the bag should be large enough to accommodate all of an individual's gear for normal diving with the exception of SCUBA cylinders. Some divers use large, rigid plastic containers (such as waste baskets or garbage containers) with tops to transport and stow gear. Regardless of the type of bag or container, the weight belt should be placed at the bottom of the container or transported separately. Regulators, decompression meters, depth indicators, compasses, cameras, etc. are frequently stowed in a separate, padded, rigid container for protection from abuse during transport, When equipment must be transported or shipped long distances, it is desirable to use shipping boxes. These boxes may be constructed of wood, metal or plastic to individual specifications. They are extremely useful for stowing gear aboard ship. Surface Floats Many divers tow surf mats, surf boards, inner tubes or similar floats when swimming offshore. The float is used for carrying equipment, samples, catch or as an object on which to rest. It is a very useful item of rescue equipment. The float is towed on a piece of nylon line which should be coiled on some sort of reel or line retainer. Line length will depend on the diver's depth and personal preference. The float should be fitted with a short pole and diver's flag. A small hook type anchor is useful

220 for anchoring in kelp or rock. Small surface floats, 6 inch diameter net floats or equivalent, are useful for training purposes or when working near a support vessel. These floats enable surface personnel to keep track of the divers. One float per two man team is sufficient. These floats may also be fitted with a diverts flag when required or a small light for night operations. Net Sam le Bas Various sized nylon net bags with top spreaders and handles are available for carrying sampleso Large size bags may also be used for transporting and stowing equipment.

221 SCUBA DIVING PROCEDURES Basic diving procedures have been discussed previously; however, certain procedures unique to self-contained diving are included in this chapter. First, all aspects of the mission must be evaluated to determine whether to use self-contained diving or surface-supplied diving techniques. Environmental conditions unfavorable for self-contained diving include extremely poor underwater visibility, strong currents, cold water, and contaminated water. Under these conditions, use surface-supplied diving techniques if possible. Self-contained divers should avoid entry in heavy surf. If dive depth and duration require decompression, surfacesupplied diving techniques are preferable, Personnel The responsibilities of the diving supervisor, surface personnel, tenders, and divers have been discussed previously. Frequently, SCUBA diving operations will involve only two divers and one surface crewman. It is unwise to conduct any diving operation without at least one person remaining on the surface to aid divers before and after the dive and to tend the surface vessel. Minimum Equipment The minimum equipment for a SCUBA diver is: Swim trunks Lifejacket Knife Swim fins Face mask SCUBA

222 Many SCUBA divers prefer to carry a snorkel to facilitate surface swimming when returning to the boat or shore with exhausted air supply. When diving to depths in excess of 50 ft, a waterproof watch and depth indicator (gauge) are required. A weight belt is required when wearing an exposure suit. Details on accessory equipment have been discussed. The use of the buddy system is the greatest single safety factor in self-contained diving. No self-contained diving operation should be undertaken without the use of the buddy system. This safety procedure requires that the divers work as a single unit. Each member of the buddy team is responsible for his partner's safety throughout the dive, Both have joint responsibility for completion of the mission assigned. The divers must maintain continuous contact with each other. When visibility is good, sight contact at short range is adequate. However, when visibility is poor, a short length of'line (buddy line) is necessary for maintaining contact, "Buddies" must learn to work together and should know and understand a standard set of signals. It is best to stay within touching distance when possible without interferring with diver movement, Hand (Visual) Signals Hand signals (Figure 4-20 ) are used by self-contained divers to convey critical information rapidly. The signals recommended by the Underwater Society of America are recommended as "standard" signals. However, a survey of literature and interviews with divers from various parts of the United States reveals discrepancies in the hand signal system,

-6 ~223 lgo down wait<low rIolooo /,.l ^HOau~ser~a *"eptbti-e e or tdirctles okti l'ook come sty shark-or cold any dangerous fishb Tt~~~~ l" subo novt worndtng FIGURE 4-20, Hand signals for SCUBA divers as recommended by the Underwater Society of America. Society of America,

224 Consequently, until there is nation wide and/or world wide agreement on "standard" hand signals, the diving team members must agree on a set of signals prior to the dive, This is best accomplished by the diving supervisor during briefing sessions. Prmelimina Pre aration In addition to general planning, the following procedures should be carried out prior to the dive: 1. Gauge cylinders immediately before entering the water to ensure that there is sufficient air for the dive. 2- Attach regulator and open cylinder valve to determine if there are any leaks in the SCUBA. 3, Inhale and exhale through the mouthpiece (or mask) to ascertain that the SCUBA is functioning properly, 4, Inspect breathing tubes, harness, etc. to insure that the unit is properly assembled, 5. Close the air reserve mechanism. 6. Inspect lifejacket and its gas cartridge to insure readiness for operation. 7. Don accessory equipment, 8, Don SCUBA and secure harness properly to insure quick release in an emergency. Diving partner and/or surface personnel will aid with donning SCUBA. 9. Check diving partner's equipment and finalize (or review) dive plan. 10o Prepare to enter the water after clearance from the diving supervisor. The Dive Both divers will enter the water at the same time. Entry techniques will depend upon staging area or type of vessel. Upon entering the water, the divers will stop at the surface and make a final equipment check:

225 o1 Adjust buoyancy if necessary. 2. Check SCUBA operation and inspect partner's SCUBA for leaks. 3. Check to insure that your partner's reserve mechanism is closed (lever in up position). 4. Report any inadequacies or malfunctions of equipment to your partner and the diving supervisor. Correct any deficiencies before making the descent. If deficiencies can not be corrected simply and immediately, abort the dive. Upon completion of the final equipment check, the divers will signal each other and the diving supervisor that they are ready to descend. When the divers are ready, the dive supervisor will signal them to commence the dive. The divers will observe the following procedures during descent and while swimming underwater: 1. Descend together. If one diver-experiences difficulties equalizing pressure, the other diver should stay with him. Although the divers will set their own rate of descent, exceeding 75 ft/min is not recommended. 2. A descent line or anchor line should be used when possible even in clear water. This aids the diver in maintaining depth and controlling descent for pressure equalization purposes. 3. When descending without something to facilitate orientation, some divers experience vertigo, nausea, and severe disorientation. If these conditions develop, it may be necessary to abort the dive. 4. Upon reaching the bottom, the divers must confirm that everything is satisfactory and immediately establish orientation. One diver will have been previously designated as leader. 5. Swim against the current so return to the boat or starting point may be facilitated by drifting with the current at the end of the dive. 6. If visibility is limited, the divers may wish to use a "buddy line" and/or a distance line (on a reel) to facilitate return to the descent line. This is especially necessary for proper decompression procedures.

226 7, Proceed with the mission and avoid excessive exertion. At the first sign of increased breathing rate, fatigue, etc., 6eSTOP, RES T and V'ENTILATE." 8, Observe proper buddy procedures and follow the dive plan. 99 The diver should monitor his air supply pressure gauge readout throughout the dive. Terminate when the low air warning is evident if not before, 10. When the mission is complete, air supply depleted, or the dive ti is up, the divers should acknowledge to each other that it is time to terminate and will proceed to the line or ascend directly at a rate of 60 ft/min, Both divers must ascend together. Never leave one on the bottom to complete the mission even though he may have sufficient air. Make decompression stops as previously determined in dive plan, Post Dive The divers should be helped from the water and with removal of equipment by surface personnel, Observe the divers for signs of sickness or injury resulting from the dive and commence warming procedures as soon as possible, Undertake preventive maintenance as soon as possible after the dive, The divers should report any defects noted during or after the dive and the defective equipment should be tagged for corrective maintenance, Underwater Navigation Establishing arid maintaining orientation underwater is essential for the safety and efficiency of any SCUBA diving operation. Sense of direction is easily lost underwater, especially when visibility is limited and the diver is unfamiliar with the area. Orientation begins at the surface and continues throughout the dive. Proper underwater navigation entails, (1) establishing surface orientation relative to the underwater are to be explored and arriving at the bottom with a fixed reference point in mind,

227 (2) establishing orientation on the bottom in reference to this fixed surface point and bottom features, (3) steering a reasonably accurate course on the bottom, and (4) returning to a predetermined point. The fixed reference point on the surface may be a boat, shoreline feature, or man-made structure. Underwater the reference point may be a prominent natural feature such as a -reef area, a man-made structure such as pipeline or cables, an anchor, the general ripple mark trend, the current or a combination of these factors. For example, if the ripple marks are orientated parallel to shore, the diver may determine his orientation with respect to shore by observing the ripple marks and relative depth, It should be emphasized, however, that ripple marks are not always orientated parallel to shore and that their orientation should be checked with a compass. Self-contained divers commonly use a liquid-filled magnetic compass (Figure 4-15b) for underwater direction finding and navigation. Generally, the compass is secured to the diver's wrist; however, it may be carried fastened to a compass board or observation board. A diver's compass should have the following features: (1) correct dampening action, (2) liquid filled, (3) the compass rose marked in degrees, (4) lubber's line showing direction over the face, (5) a course setting line, and (6) a movfable bezel. A good compass will respond rapidly to even slight course changes and have a high degree of luminescence for use in dark water. The wrist compass is generally placed on the wrist (right for righthanded and left for left-handed persons) so no other metallic object can

228 cause deviation, Watches, depth gauges, and decompression meters should be worn on the opposite wrist, When using a proper diverts compass, the diver will first obtain a bearing in degrees to his target relative to magnetic north. While sighting on the target, rotate moveable bezel until the parallel lines on the compass face (moveable) are aligned with the North needle, The bearings, in degrees, will be indicated at the end of theNorthneedle, To maintain proper direction while swimming, the diver must keep the North needle aligned with the parallel lines on the compass face, When swimming underwater, the "compass-lock"position is recommended. In this position the arm without the compass is extended straight in front of the diver. The diver bends his compass arm 900 at the elbow and then grasps the extended arm near the elbow. This places the compass directly in front of the diver's eyes and aids in keeping the diverts body on a straight line. The two most serious mistakes when using a compass are failure to keep the lubber line parallel to the longitudinal axis of the body and the diver looking down at the compass instead of sighting over the compass, The diver must maintain his body straight and swim in a straight line if he hopes to navigate accurately. Assuming that the diver has swam a straight course, he can return to his original point of entry by following a course 1800 opposite his original course bearing with an accuracy of t 5 degrees, Basic pilotage and dead reckoning navigation can be used by divers. The simplest method of navigation is pilotage. This involves establishing a posi n relation to known features and plotting a course toward a destination from a known positions. The diver simply determines the

229 bearing and swims on course to a specific point or area. Dead reckoning, on the other hand, requires following a compass bearing in a specific direction taking into account speed and time. An estimated time of arrival (ETA) may be computed. Approximated distance or time required to swim between two points may be determined by the simple formula, Speed x time m distance. Consequently, an ETA can be determined. Distance traveled underwater can be determined by time or counting the number of kicks. On the average, at normal swimming level, a diver wearing a wet suit will travel 2.5 ft/sec or 3.25 ft per kick cycle. The same diver without a wet suit will travel 3.6 ft/sec or 4 ft per kick cycle. The individual can measure his own underwater swimming rate by swimming a given course and recording the time and number of kicks. An average of several swims should be used.

230 EMERGENCY PROCEDURES Emergency situations occasionally arise on even the best planned and supervised undeerater operations. Many of these emergencies are the result of failure to observe some safety precaution; others are unforeseen and unavoidable, Very few underwater emergencies are so desperate as to require instantaneous action, Take a few seconds to thinkl Instinctive actions are seldom the right one. They may prove to be blind impulses brought on by panic. Adequate training will prepare the underwater swimmer for almost all emergencies provided that he keeps his head. Do not panic and above all, never abandon your breathing apparatus underwater unless ascent is impossible without doing so. Exhaustion of Air Supl1 This should be no problem to the properly trained and equipped diver. When breathing resistance becomes noticeable, simply open the air reserve mechanism and start ascent, Even if the reserve fails, increased breathing resistance prior to exhaustion of air supply give some warning. Do not panic and ditch the SCUBAS The reduction in pressure and subsequent gas expansion during ascent provides additional air for breathing. The emergency ascent or "free ascents is a last resort, All divers should experience exhaustion of air supply during traainngl Loss or Floodin of Face Mask The self-contained diver must learn to swim underwater without a face mask and how to purge water from the mask in the event of flooding, If the mask becomes dislodged and partially or completely fills with water, it should be repositioned on the face and purged of water by tilting the

231 head backwards to place the lower edge of the mask at the lowest position. The diver then presses the upper portion of the mask firmly against the forehead and exhales through his nose. The exhaled air will displace the water and force it out under the lower edge of the mask. If the mask is equipped with a purge valve, simply position the head so the purge valve is in the lowest position relative to the rest of the mask and exhale through the nose. Some divers prefer to press the top portion of the mask against the face while purging to limit the loss of air. Purging Water from the Breathing System There are various methods of purging water from flooded mouthpieces and hoses. Each method should be mastered and the trainee should learn the procedure for both double and single hose units. The simple method is to place the mouthpiece in your mouth and exhale. This will generally purge the water from the assembly and free breathing is restored. Inhale cautiously following the purging procedure to be sure that all water is out. When purging the single hose regulator, position the exhaust valve so that all water will drain through it. This may require the diver to look straight ahead or tilt his head slightly backward. Turning the left side down so that the water will run into the exhalation hose will facilitate clearing two-hose regulators. If the diver does not have enough air in his lungs to expell the water, he will have to use the "free-flow" method. In two-hose units the air will flow freely through the mouthpiece when it is raised above the level of the regulator housing. Therefore, raise the mouthpiece above the housing until it free flows, turn the mouthpiece down to trap air in it, tilt the head back,

232 insert the mouthpiece into the mouth while free flowing, and resume breathing, The same method may be used with a single hose regulator; however, a purge button must be depressed to initiate the free flow of air. An alternate method of purging a single hose regulator is to place the tongue into the air inlet opening and depress the purge button, The water is forced out through the exhaust valve, The diver should be alert for the cause of flooding of the system, Some problems such as damaged breathing tube, diaphragm or exhaust valve may hamper successful clearing of the system. Recovery of Lo st Mouthpiece When the mouthpiece of a two hose unit is lost, it will float to the highest point. When in the swimming position, bring the feet forward and lay on your back, The mouthpiece will be directly above your face. Single hose regulators generally lead over the right shoulder. If the mouthpiece is dropped, reach back, feel the first stage of the regulator and follow the hose to the second stage mouthpiece. The use of a neck strap to retain the regulator in front is discouraged; harness clips are permissible as long as they release readily in emergencies for sharing air. Entn ement The diver's knife is his safeguard against entanglement. The entanglement situation generally requires more thought than action. Do not struggle; this may only increase the degree of entanglement. This is where the "buddy system" is useful, The buddy can carefully cut the entangled diver loose. Only as a last resort should the diver remove his breathing apparatus and make a "free-ascent,"

233 The Role of the "Buddy"' in Underwater Emergencies "Buddies" must learn to work together and should know and understand a standard set of signals. They should be in visible range at all times and keep an eye on each other. In poor visibility a short buddy line may be required. The diver should signal his "buddy" at the first sign of trouble. If your "buddy" shows signs of distress, get to him at once whether he signal or not. The hardest job for a "buddy" will be in the presence of panic. You may be able to do no more than take him to the surface at once. In handling a panicked or unconscious person underwater every effort must be made to keep the mouthpiece in place. In ascent, the possibility of air embolism exists. It may be necessary to tilt the victim's head far back to facilitate exhalation, especially in panic situations. Never strike the victim in the stomach or chest; this procedure could cause an air embolism. It may be necessary for SCUBA divers to share air (buddy breathe) in the event of air supply exhaustion or equipment malfunctions. There are several methods of sharing air and the diver must use the one best adapted to the situation. Generally air sharing is necessary only for direct ascents, The divers simply face each other and exchange the mouthpiece of the operative SCUBA while making a slow, controlled ascent. When sharing air with the single hose regulator, the diver providing the air should be slightly to the left (when facing the stricken diver). Do not fill your lungs and then hold your breath while your "buddy" is taking a breathi Remember you are ascending and that you must continue to exhale as you rise to prevent air embolism. The diver supplying the air should always retain control of

234 the mouthpiece and grasp the harness of the victim. He is generally in a better position to regulate breathing cycles and to control the ascent than the diver who has experienced air supply failure. When working in caves or under ice, divers may find it necessary to move in a lateral direction before ascending to the surface. In this case the diver wearing SCUBA containing air swims with his left side down, The distressed diver swims on his right side, holding his "buddy's" harness with his left hand and exchanging the regulator with his right. An alternate method of lateral swimming is for the "buddy" with the air supply to swim face down, The other diver swims directly above him holding onto the neck of the air cylinder. The diver on the bottom passes the regulator up and the top diver places it back in view of the bottom divere These methods may be used for both double and single hose regulators, Another method of lateral swimming while sharing air with a single hose regulator is to have the divers swim side by side in a prone position. Sharing air under emergency conditions is difficult even for the best trained and most experienced divers. Divers should practice the skill frequently. Furthermore, the use of auxiliary breathing systems is encouraged, Emergenc Ascent Learning the technique of "free ascent" is an important part of training; however, the "free ascent" should only be used as a last resort to resolve an emergency situation. It is hazardous and difficult to accomplish safely in situations of stress, Unless the breathing apparatus is entangled, the diver should not

235 abandon it even though it may be useless. The diver should drop his weights, exhale prior to the start of the ascent and continue to exhale throughout the ascent. The head should be extended back. This allows maximum opening of the throat area and a good overhead view. The diver should swim to the surface, constantly being aware of becoming entangled or of striking obstructions, and the consequences of holding his breath. The mouthpiece may be left in place. Training for free ascent is a serious and hazardous exercise. In the pool students should make proper supervised ascents. At first the mouthpiece should be left in place. For later ascents the mouthpiece can be removed and held by the diver. Long free ascents may be simulated by having the trainee swim the length of the pool while exhaling in a free ascent fashion. The same procedure should be followed if emergency ascent training is conducted in open water. The instructor and trainee should surface facing each other with the instructor close enough to control all phases of the ascent and give aid if necessary. Practice first in shallow water and progress to deeper at the discretion of the instructor. In desperate emergency situations where the diver feels that he may pass out, etc. it may become necessary to make a positive buoyancy ascent and risk entanglement, injury, and air embolism. This is accomplished by inflating the lifejacket (lnly high capacity lifejackets are dependable). The ascent will be slow at first and will become more rapid as the lifejacket expands, especially near the surface. A few kicks may be necessary to initiate the ascent. Positive buoyancy ascents are to be used only in a life - or - death situation, and no other. Remember, in all emergency

236 ascents, exhale continuousl thro hout the ossibility of air embolism is always resent, At the Surface Upon reaching the surface after emergency ascent or if you are in trouble at the surface following normal ascent (rough water, exhausted, etc.) inflate your lifejacket and signal for pick up. If you are a long distance from assistance, it may be necessary to use your signal flare to attract attention, The surface crew should be alert for divers in trouble at all times. If you are not in difficulty, swim for the craft or shore base, If the breathing apparatus interfe rs with swimming, remove the equipment and tow it to safety while swimming on your back (jacket inflated or deflated) or on your front with a snorkel. The diver may have to ditch his equipment if he faces a long swim to safety. The above procedures and skills must be mastered during training, Various exercises are used to test the trainee's ability to cope with underwater situations, Empleton (1968) covers basic SCUBA training, The U.S. Navy considers drowning as the most frequent cause of death in self-contained diving. Drowning may result from simple mechanical malfunction of equipment, but is most frequently the result of underwater accidents and environmental factors. The most common cause is physical exhaustion resulting from swimming on the surface after the air supply has been depleted, Surface swimming in rough seas presents even a greater hazard. Another primary cause of drowning is the inability of

237 the diver to cope with emergency situations. Any of these conditions may result in panic and consequent drowning. Any underwater accident that causes unconsciousness generally results in drowning. Self-contained divers must take every precaution to prevent drowning. The following preventive measures must be considered by all self-contained divers: 1. Adequate training with drill in emergency procedures. 2. Good physical condition. 3. Use a lifejacket at all times - with or without SCUBA. 4. Proper maintenance and use of approved equipment only. 5. Good diving practices with adequate preparation. 6. Observe personal limitations. 7. Provisions should be made for aiding divers in distress (keep someone in the boat at all times). 8. Training in lifesaving and water safety. 9. Each person must be trained in the use of artificial respiration. LIFESAVING PROCEDURES Since self-contained divers spend more time in the water under more hazardous conditions than do most swimmers, it is essential that they know the fundamentals of lifesaving and water safety. One of the first principles of water safety is fulfilled by the "buddy system" - never swim or dive alone. Divers have another important factor in their favor, the lifejacket. Through the "buddy system" and the