The theory of saturation diving had its inception in the dreams of a U. S. Navy diving medical officer, Captain George F. Bond, in 1958. Bond reasoned that if man could live for extended periods beneath the sea, he would eventually equilibrate the tension of the inert gases in his tissues with the ambient pressure and, therefore, be able to pay the decompression penalty in one lump sum, after performing as much work as his physical capabilities would allow him during his stay on the ocean floor.
Dr. Bond determined that in about 24 hours at any given depth, man’s blood and tissue contain as much inert gas as they are capable of holding. In a diver, this condition is known as saturation; hence, the name “saturation diving.” The length of time required to decompress a saturated diver from a given depth remains the same regardless of the length of stay beyond the 24-hour period. The implications are tremendous: the diver, given satisfactory living conditions and tools, may perform many hours and even days of useful work on the ocean floor at great depths, and then pay his decompression penalty all at one time at the end of his stay. Previous diving techniques greatly restricted the diver’s actual work period at greater depths. The length of decompression was computed as a function of both depth and time; thus, on a deep dive, long work periods were impractical because of the prohibitive decompression required.
In 1961, after several years of struggle to obtain the necessary funds, Doctors Bond and Commander Robert D. Workman, under the auspices of the U. S. Navy, commenced a series of studies and tests on animals at a depth of 200 feet to determine the effects of prolonged exposure to compressed air. Surprisingly the animals exposed to ordinary compressed air at seven atmospheres absolute (197 feet), all exhibited symptoms of pulmonary distress and expired within a 35-hour period after pressurization. Autopsies indicated death was due to pulmonary failure, akin to a pneumonia condition. The causative factors were determined to be pulmonic stress engendered by the increased density of the breathing media and the high oxygen partial pressures encountered. Further experiments were conducted using the lighter helium (atomic weight 4) to replace nitrogen (atomic weight 14) as the inert gas. The oxygen content was also decreased in the breathing mixtures. Animals exposed to a depth of 200 feet during a 12-day test period breathing a 97% helium-3% oxygen mixture showed no evidence of health damage.
During 1962 and 1963, physiological and psychological tests were conducted on U. S. Navy divers at the Medical Research Laboratory at New London, Connecticut. These tests were climaxed by a 12-day exposure to a simulated depth of 200 feet in a pressure chamber. The breathing mixture was composed of 92% helium and 3% oxygen, with the remainder being nitrogen. The small amount of nitrogen remaining in the mixture was due to the technical problems involved in removing nitrogen from any potential breathing space. Results of the tests (named Genesis I) indicated no harmful effects to humans, and the U. S. Navy scheduled tests to be conducted in the open sea in Sea Lab I.
Meanwhile, the now famous, former French naval officer, Jacques Cousteau, conducted the first underwater tests in saturation diving by placing two men at a depth of 33 feet, where they lived for one week in an underwater house with an opening in the bottom to allow them to exit to swim and work. Compressed air was used in this first test and no ill effects were noted, although the men experienced some discomfort owing to high humidity and increased breathing resistance. During the years 1963 through 1965, Cousteau’s Conshelf 2 and 3, and U. S. Navy’s SeaLab I and II experiments proved that man could indeed live and work at depths of up to 300 feet for prolonged periods of submersion provided that electrical power, communications, and a satisfactory breathing media were supplied to a house or habitat placed on the ocean bottom. In those tests, teams of three to ten men were used and diving work performed using various types of both open and semi-closed circuit SCUBA equipment with egress made through an open hatch in the bottom of the habitat. These tests resulted in the acquisition of valuable information in marine biological studies, deep water application of salvage techniques, underwater construction of oil well heads for drilling, and revealed potential for using saturation diving to mine valuable minerals for future use.
Problems were encountered in many areas during the test series, but one fact was clear: an entirely new concept of diving had entered the field of underwater exploration and allowed man to explore areas heretofore considered too deep for sustained diving work.
Commercial companies began to apply themselves to the prospect of using variations of this new technique for offshore oil-well drilling, and have proved the basic principles of saturation diving to be economically feasible in commercial application. In general usage, it is not practical for a commercial company to place a habitat on the ocean floor for the divers to live in and work out of, but the same beneficial results can be achieved by transporting the divers in a pressurized transfer capsule or diving bell that allows them to exit on the bottom to perform work. After the desired work is accomplished, the men re-enter the personnel transfer capsule or PTC, close the lower hatch to maintain the same pressure inside as the pressure on the bottom, and are raised to the surface where the PTC is mated to a deck decompression chamber or DDC. The divers then exit the PTC and can live in reasonable comfort inside the DDC, still remaining at the pressure of planned work. The following day after a suitable period of rest, the divers re-enter the PTC and return to the work site. At the conclusion of a planned work period the divers can enter a decompression phase to return them to atmospheric pressure, and a relief team of divers can continue the work on the bottom.
Diving Physics and Physiology. In the realm of saturation diving, it becomes necessary to expand somewhat on the normal application of diving physics as applied to the physiological changes that occur in the body under prolonged exposures to gases, as against the body reaction to short exposures previously observed in normal diving techniques. For instance, a gas may not have any noticeable effect on a diver for a one-hour or two-hour exposure, yet become toxic or induce reduced efficiency when the diver has to breathe the gas for several days. This time-depth relationship pertaining to the effects of gases on the human body has caused wholesale revision of previously established theories accepted by most diving physiologists.
In normal closed and semi-closed circuit diving the limit on oxygen has been set at 2 atmospheres of pure oxygen. When breathing ordinary compressed air, we have approximately 20% or .2 atmospheres, of oxygen on the surface. Then, according to “Dalton’s Law of Gases,” at 297 feet (ten atmospheres absolute) we have ten times .2 atmospheres of surface oxygen. Thus, the safe limit of 2 atmospheres of oxygen has been reached, and to go deeper safely, the ratio of oxygen to inert gas must be changed.
Experimentation in the early animal tests conducted during Project Genesis proved that lowered partial pressure levels of oxygen were necessary if men were to survive during prolonged saturation periods. Tests resulted in the determination that during extended exposures, the oxygen partial pressure must be kept between .2 and .8 atmospheres in order to prevent the onset of oxygen toxicity or undesirable pulmonary complications.
At a depth of 300 feet (approximately ten atmospheres absolute), oxygen supplied at 2% of the total gas atmosphere supplies about the same effective percentage as atmospheric air at the surface. In the U. S. Navy SeaLab experiments, conducted at 193 and 205 feet, the oxygen levels were kept at about 4.25%; although slight variations were allowed during planned phases. No harmful effects were noted on individuals in exposures of up to 30 days.
At deeper depths, where the oxygen percentage becomes more critical, it is necessary to have an extremely accurate monitoring device for the gas, and it is desirable to have an automatic oxygen supply system. In tests conducted at the Experimental Diving Unit in Washington, D.C., excursion dives were made to a depth of 1,025 feet from a base level of 825 feet using an oxygen percentage of approximately 1%. This obviously required very careful monitoring and sensitive gas feed-in techniques in order to stay within the allowable oxygen partial pressure tolerances.
The narcotic properties of nitrogen when breathed under pressure, preclude its use as the major inert gas in depths beyond 200 feet in most instances in diving operations where helium-oxygen mixtures can be used. Experiments conducted, using both helium and hydrogen to replace nitrogen as the inert gas, led to the natural assumption that the density of the inert gas was the determining factor in its narcotic effect upon divers. Recent experiments have led to the wide acceptance of the Myer-Overton Theory which relates the degree of narcosis experienced by the diver to the gases’ solubility in fat. Tests using neon (atomic weight 20) as compared with nitrogen (14) seem to validate the Myer-Overton Theory, but the density of the gas appears to be a complementing factor in narcosis.
Psychological tests conducted to date have not indicated a significant decrement in performance owing to any narcotic effect on the diver when breathing helium-oxygen mixtures at depths less than 1,000 feet. Haldane postulated that a 1,500-foot depth would be the limit for helium-oxygen mixtures in diving but recent test dives made to a depth of 1,700 feet in a dry environment indicate man may proceed even deeper. Experiments have been conducted using multiple-inert gas mixtures with neon, hydrogen, and other rare gases combined in varying quantities to ascertain the desirable and undesirable effects of each when used in combination with others. As we continue to seek to extend the limits to which man can venture in seeking knowledge of the ocean bottom, it will become necessary for us to investigate the use of hitherto unexplored gas mixtures to minimize narcosis and breathing resistance.
Communication Problems. The difficulty in understanding speech under pressure, even while breathing compressed air, is well known in the diving field. When helium is used in the breathing media, its reduced density causes the human voice to take on characteristics that make it extremely difficult to understand, even at relatively shallow depths. This “duck-like” voice quality is apparently caused by the inability of the resonating voice chambers to adjust to the lighter carrying-medium of helium.
In an attempt to eliminate the speech distortion experienced in the artificial atmosphere, the U. S. Navy used a helium speech unscrambler in its SeaLab series of tests. This unit consisted of an electronic device that removed some of the higher frequency modulations during communication. This was generally viewed as being an improvement over the diving telephone, but still left much to be desired concerning speech intelligibility.
These problems in voice communications in saturation diving necessitate the use of other methods to communicate. Among these are closed circuit TV, the use of electro-writers to reproduce handwriting, and even Morse code usage.
Cousteau and others have experimentally breathed neon-oxygen and other gas mixtures during communication periods to facilitate good recognition. Further experiments should reveal better breathing mixtures for this purpose.
Thermal Protection Problems. The saturation diver is faced with the continuing problem of maintaining body heat at an acceptable level. Heat loss is generally so severe that even during periods of short exposure the diver will experience reduced efficiency. During periods of prolonged submersions, the retention of body heat becomes vital to his very existence.
Helium conducts heat at a ratio of approximately 6 to 1 when compared with nitrogen. This increased thermal conductivity results in a rapid heat transfer from both the lungs and skin. For long submersions, it is essential that supplemental heating be furnished the diver, as insulation alone will not suffice. The efficiency of neoprene wet suits is markedly reduced by compression of the air cells in the material, and experiments conducted during the SeaLab II tests showed that a diver commenced losing efficiency after the first few minutes of exposure, using 3/8-inch wet suits at a depth of 205 feet, with water temperatures of 48 to 53 degrees Fahrenheit. Most divers were able to withstand exposure periods of only 30 to 40 minutes.
Tests have been conducted using both electrically heated and hot water heated type suits and seem to indicate that a suitable hot water supply to a working diver while breathing helium-oxygen mixtures is the simplest answer in most cases. Divers working on the Smith Mountain Dam project reported that body comfort was maintained during work periods involving several hour-exposures to 40-degree water while using hot water-heated wet suits.
Temperatures inside of habitats emplaced on the ocean floor must be maintained at a minimum of 85 degrees Fahrenheit in order to have a “shirtsleeve” environment when helium-oxygen is used as the breathing media. Even then a man will become uncomfortably cold when air movement causes a draft.
Battery-powered, electrically-heated suits proved satisfactory on tests in which they were used by the U. S. Navy, but the bulkiness and weight of the battery pack, along with additional suit equipment were undesirable features. Hot water heating is somewhat superior in most situations.
A prototype model of a suit using radioactive isotopes to heat a closed-circuit water supply has been tested by the U. S. Navy and appears to hold great promise in diver thermal protection. Shielding problems and miniaturization of component units are the major problems remaining to be solved.
Decompression Problems. As should be expected, returning the saturated diver to atmospheric pressure unharmed after prolonged exposure to increased pressure is the major problem of saturation diving. At present, firm decompression tables have not been published as accepted standard procedures to be used in saturation diving. Most major programs have diving medical supervisors who program decompression in regard to type of ascent used, oxygen partial pressures, and inert gases used in the breathing media.
Decompression schedules established by the U. S. Navy SeaLab tests and test dives conducted at the Experimental Diving Unit in Washington, D.C., indicate that a steady constant ascent rate of four-to-six feet per hour is acceptable. Variations in ascent rate can be considered when higher oxygen partial pressures are used during decompression periods. Obviously, the desaturation rate of inert gases is more rapid when higher O2 partial pressures are acceptable, but the previously mentioned pulmonary problems must be considered when decompression authorities are computing their schedules.
In constant ascent techniques used during decompression phases, pressure is slowly released at a uniform rate. The tissue tension of inert gas is thus maintained at a level that permits the highest possible efficiency of gas elimination from the tissues. When the diver is decompressed, using stage decompression, a high rate of desaturation is achieved when he first reaches a pre-determined stop, but this desaturation rate is gradually lessened during the stop as the tension of the inert gases in the tissues more closely approaches the ambient pressure. By the time the diver is programmed to leave for the next scheduled stop, he is at a relatively low efficiency level for expelling gas from the tissues. This situation repeats itself at each stage level.
Experiments conducted using multiple-inert mixtures of gases during decompression have shown promise in accelerating decompression schedules. For instance, desaturation of nitrogen from tissues can be hastened by using a helium-oxygen breathing media during decompression. It can be assumed that in the future, decompression schedules for saturation diving will include variations in ascent rate predicated on oxygen partial pressures and the type of inert gas used for breathing mixtures.
The incidence of bends in saturation diving indicates that much remains to be learned in the physiological problem area encountered. The length of time required to saturate or desaturate a given tissue in the body has never been firmly established. It has been postulated that certain tissues in the body saturate more rapidly than others, owing to variations in the respective circulatory values. However, the path of a single drop of blood on its gas exchange voyage through the tissues of the body has never been traced. Bone marrow must be considered to be one of the slowest tissues to saturate and desaturate, and it is conceivable that the deep-seated pains of joint bends could often be traced to bubbles originating in the bone marrow.
Life Support Systems. In the realm of equipment for saturation diving, most of the problems confronting us are in the life support system area. These may be generally separated into the internal, or habitat area, and the external diving area. In addition to the habitat problems discussed previously, carbon dioxide removal, dehumidification problems, logistic support, atmosphere contamination, gas monitoring systems, and helium-initiated electronic failures are areas of major consideration.
Electrically-powered dehumidifiers were used with varying success in the SeaLab tests. The large temperature differential between the habitat and the surrounding water requires that dehumidification systems operate at peak efficiency. In the past it has been noted that helium has the insidious quality of seeping into sealed electronic units and causing electrical failures that cannot be anticipated or prevented by normal test procedures. Men working in SeaLab II were subjected to a 60-92% humidity with debilitating results. Ear channel infections were encountered along with skin rash, and other health problems to be expected under these conditions. Cryogenic removal of excess moisture from the habitat seems to offer the best solution in the future.
Removal of CO2 has been accomplished by use of a carbon dioxide absorbent in the gas recirculating system in most cases. Lithium hydroxide has been the most effective agent in removal, but presents a storage problem for long submersions. Cryogenic CO2 removal was tried briefly by Cousteau in Conshelf 3, and offers promise for the future, where the CO2 level will become more critical owing to increased partial pressures at deeper depths.
In supplying gas to the working diver, the most expeditious method is to use a positive-negative compressor to pump the gas from the habitat to the diver and return it to be purified in the atmosphere control system inside. This method prevents the unacceptable loss of gas that would occur with an open-circuit supply method, but requires that the diver work on a tethered supply hose—thus limiting his effective working radius. A semi-closed circuit diving apparatus can be used alternately with only a small amount of the valuable gas being lost into the water, and allowing the diver greater freedom of movement.
Excursion Dives. One of the most dramatic accomplishments of saturation diving has been the demonstration of the ability of a saturated diver to make excursion dives to depths several hundred feet beyond his equilibration depth, and to return safely to his base level with no decompression required. This phenomenon is readily explained by the ratio of ambient pressure change. The ratio (2:1) from atmospheric pressure to a depth of 33 feet is about the same as an excursion dive descent to 600 feet from a saturated depth of 300 feet. This fact becomes more significant as we progress to greater depths, and will become a factor in the ultimate depth limitations imposed by physiological changes in man due to pressure.
Diver Selection and the Future. Psychological and physiological tests indicate that the environmental stress on the saturation diver will require that special attention be given to personnel. To combat the increased hazards encountered, it is necessary that the man selected to enter the field of saturation diving be highly trained in the problem areas involved, and screened to ensure that their psychological makeup is such that will allow them to adapt rapidly to environmental changes and enable them to live compatibly with fellow divers in crowded, uncomfortable quarters. It is highly desirable that the diver be motivated by a natural love for the sea and a desire to further man’s knowledge of this alien environment, rather than by a regard for diving as an occupational area in a purely commercial sense. This may appear to be an idealistic approach to the problem but in almost all cases observed by the author, divers who exhibited a vital interest in the ocean itself were the more valuable to a given program. Psycho-physiological problems in man’s exploration of outer space are approximated in extended underwater sojourns. Breathing medias, weightlessness, waste-disposal problems, communication difficulties, and environmental stresses engendered by hostile environments but a few of the problem areas that project this similarity. Therefore, as much attention should be given to the selection and training of aquanauts as is presently given to men venturing into space.
With rare historical exceptions, man’s attempts to project himself into the future and foresee events have resulted in gross underestimation of final achievements. Nevertheless, the author makes these predictions for the future:
► By 1973, man will have made simulated dives to 2,000 feet from a saturated depth of 1,500 feet using helium-hydrogen-oxygen gas mixtures. Physiological effects of gases on the body through to breathing resistance will be the limiting factor to extending the diving depths much beyond this predicted limit while using a breathing media to furnish oxygen to the tissues.
► In the near future, habitats emplaced upon the ocean floor will be completely autonomous. Electrical power will be supplied by nuclear energy fuel cell sources, and gases for the breathing media will be stored cryogenically. Both carbon dioxide and excess moisture in the atmosphere will be removed by cryogenic method and the same cryogenic generator will keep food supplies frozen for the aquanauts.
► Most diving work will be accomplished using gas supplied through a hose from habitat to diver, but excursion dives and other dives of limited duration will be conducted in semi-closed circuit diving equipment using liquid oxygen and closed circuit SCUBA with sensor-controlled oxygen supply. Gas bottles will be developed to withstand internal pressures of five to ten thousand pounds per square inch, thus extending the exposure time allowed the divers.
► By 1974, experimental dives will have been made to over 2,000 feet by flooding the lungs of a diver with a hyper-oxygenated liquid solution. Pioneer work has been accomplished in this field, but no method has been devised to remove the CO2 given off by body tissues during the period of lung flooding. This method can conceivably be used to extremely deep depths as no decompression is required to eliminate inert gases.
► In the next few years, major nations will be competing with each other to establish possession rights to seamounts that are close enough to the ocean surface to allow structures to be erected. These seamounts will have great military value in national defense, and particularly in submarine detection.
► By 1975, floating laboratories will be constructed for marine biological studies in receptive areas of the continental shelves.
These predictions close with one philosophical observation. As man attempts to reverse the evolutionary process by returning to the watery environment of the seas, we must expect trials, tribulations, and even deaths. As the mysteries of the oceans slowly unfold and increase the knowledge of man, it is to be hoped that he will use this newfound knowledge for the benefit of all mankind, and not to further his selfish interests. The resources of the sea are not inexhaustable [sic], and man must establish guidelines for conservation early in this investigative phase of our exploration of the continental shelves. As Jacques Cousteau so aptly phrased it, “Let us be cautious.”
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Enlisting in the U. S. Navy in 1935, Chief Sheats’s diving career commenced in 1937 on board the submarine tender USS Beaver when he qualified as diver second class. He graduated from first class diving school in Washington, D.C., in 1939, and continued diving in the South Pacific until the outbreak of World War II. His ship (the USS Canopus) was bombed and scuttled in Mariveles harbor on the Bataan Peninsula in the Philippine Islands. He was in charge of an outpost machine gun nest on Bataan. When Bataan fell, he escaped to Corregidor where he fought with the Fourth Marines until the surrender of Corregidor in May 1942.
His postwar diving career included submarine rescue, salvage, submarine escape training, and diving supervision, and instructor duty in all major areas of Navy diving. He was master diver in charge of support diving operations on SeaLab I conducted in 1964 off Bermuda, and spent 15 days at 205 feet as Team #3 leader on SeaLab II in 1965. Since retirement from the Navy in 1966, he has worked part-time as a diving consultant for Supervisor of Salvage and other activities.
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In Full Command
The USS William R. Rush (DD-714), a Sixth Fleet destroyer, was backing into her mooring in Dockyard Creek, Valletta, Malta. Her berth necessitated passing close aboard HMS Eastbourne of the Royal Dartmouth Training Squadron. Three first-year cadets interrupted their painting of the Eastbourne’s sides and, from their vantage point on a floating stage, they cast a professionally critical eye on the U. S. destroyer’s maneuver.
A sudden gust of wind caught the Rush and her stern swung toward the cadets. She cracked on ahead bells, while two of the cadets scrambled for the deck of the Eastbourne. The remaining cadet, stalwart and undismayed, remained with his craft as the Rush’s propeller wash carried the float away. Drifting past the destroyer, he stood at attention and saluted crisply.
Queried later, he explained, “I had to do something; after all, it was my first command.”
—Contributed by Cdr. F. M. Sullivan, USN
(The Naval Institute will pay $10.00 for each anecdote published in the Proceedings.)