CONTENTS

21.1. INTRODUCTION
 

Surface conditions must be appraised in considering the method of escape, inasmuch as the most successful of escapes may be rendered void by exposure to cold, prolonged salt water immersion, exhaustion with drowning from efforts to stay afloat, man-eating fish, enemy action, lack of water and food, and high seas, adverse tides or currents or unfavorable atmospheric conditions which impede rescue operations.

The availability of help from other vessels may be a decisive factor in the selection of the time and means of leaving the submarine. During daily peacetime operations, it is customary for a submarine upon diving to notify its base of the estimated time for surfacing; if the base has not received a surfacing message from the submarine

The extent of aid which the rescuing vessel is able to give may be only the picking up of survivors on the surface, and standing by until further help arrives. Each submarine base maintains submarine rescue vessels (ASR) which carry the rescue bell, a team of first-class deep-sea divers, and a submarine medical officer for the occasion.

Conditions inside the submarine may be so intolerable as to preclude any further delay in effecting an escape, regardless of the above considerations. The men may become so ill that they lose the will to live. It may be that all surviving personnel are crowded together in a single forward or after room, with relatively rapid depletion of oxygen and accumulation of carbon dioxide. The latter is efficiently removed by dry CO₂ absorbent in cans, stowed in each compartment, though the quantity is not unlimited. Oxygen is obtained from high pressure O₂ bottles inside each compartment; (the newest type boats have oxygen banks with manifolds for distribution throughout the ship), or by bleeding compressed air into the compartment from the high or low pressure air service lines. The air lines may have been ruptured in the initial casualty, so that there is no air supply to the compartment. The room air may be vitiated by fumes and smoke from fires incident to the casualty or by chlorine generated from lead storage batteries which have been

Emergency canned rations are stowed in small metal glass-fronted lockers in each compartment and may be supplemented anywhere by general stores, if the ship is loaded for a long cruise, because of the small volume of the dry storeroom and the necessity of utilizing all miscellaneous space in the ship for stores. Potable fresh water is stored in large tanks of 120-130 gallons each in the forward and after torpedo rooms, with small 10-20 gallon tanks in the control and maneuvering rooms; ordinarily these should suffice until help arrives. First aid kits are placed in each potential escape compartment, and should (but do not always) contain a small supply of narcotics. Light is furnished by battle lanterns, flashlights, and the emergency dc light circuits which take off the battery in series directly.

The depth of water at which the submarine rests may prohibit individual escape until help arrives. (See section 21.3.)

The fundamental plight of any submarine which is stranded on the bottom is that of negative buoyancy. In terms of Archimedes' principle, this means that the weight of the submarine, including the weight of the water which has been incorporated into its own weight by flooding, is greater than the weight of sea water which the submarine displaces.

21.3.2. Using submarine's own facilities.

The first step in such a situation is to take advantage of all the ship's reserve buoyancy by emptying all main ballast tanks; if the weight thus lost is greater than the weight flooded in, the submarine will possess positive buoyancy and rise to the surface. If any of the convertible fuel ballast tanks are rigged for carrying fuel, these also may be emptied to advantage. Emptying all variable ballast tanks, plus safety and negative

At the onset of flooding, the collision alarm is sounded, and the flooding compartment is isolated after being abandoned. Pressure is then built up in the flooded space, using the internal ship's salvage air fitting operated from the opposite side of the bulkhead either forward of or abaft that compartment. The air pressure above the water level, if relatively great enough, stops further influx of water through the defect in the pressure hull and reverses the flow of water until the water level has dropped to the level of the defect in the hull, remaining there as long as compartment air pressure is maintained. It is evident that

21.3.3. Using other than submarine's own facilities.

All submarines are fitted with external air salvage connections, enabling divers to connect air hoses from the rescue vessel to any compartment or ballast tank of the submarine. Each compartment has two such salvage air connections, so that air may be supplied through one connection and vented off through the other, thereby furnishing fresh air at near atmospheric pressure indefinitely to trapped personnel. One of the two compartment external salvage air lines goes via a pipe to the bilge level, so that water in a flooded compartment can be forced out through this "low salvage line" by applying air at a greater than sea pressure through the other line, or "high salvage line," thus decreasing the negative buoyancy of the vessel. Again, a flooded compartment may be emptied of water only as far down as the defect in the hull, unless that defect is plugged.

External salvage air connections are often called "soup lines," because of legendary suggestion that liquid nourishment might be afforded to the crew through these lines.

On rare occasions it might be possible to rig large submersible pontoons alongside the sunken hull, and by utilizing the pontoons as accessory ballast tanks, surface the submarine promptly, though that might require as long as three months. A few instances have been recorded in which cranes have been employed to lift one end of a small submarine lying in shallow water, liberating crew members. However, it must be emphasized that these methods are intended primarily to be salvage procedures, and it is reiterated that immediate recovery of living personnel is the paramount mission of the rescue team.

21.3.4. The rescue bell (McCann chamber).

This is the most efficient and practical means of escape yet devised, and when operating under favorable conditions it approaches the ideal in safety to the escapees. The chamber is an upright steel cylinder about 11q feet tall and 7 feet in diameter, weighing about 10iz tons and designed to withstand sea pressures equal at least to the test

The connections between the ASR and the bell are : (1) A backhaul cable for taking a strain on the bell if necessary; (2) a high pressure air supply hose; (3) an air hose for venting the bell to atmospheric pressure; (4) an electric lighting cable; (5) a cable for telephone communication.

Procedure: When the ASR, carrying the rescue bell on its fantail, has completed a multipoint moor at the spot where the submarine's messenger buoy has been plumbed, a large boom is used to hoist the rescue bell over the side, suspended by a pendant or padeye in the top of the bell. The submarine messenger buoy when released is connected at the bitter end of its cable to a bail in the center of one of the escape compartment hatches; if this cable is found not to be fouled, the messenger buoy is cut away and the free end of the cable is attached to the reel in the lower chamber of the bell, being fed first through a fairlead, an emergency cable cutter, and a spool guide. This is to be the downhaul cable. If the messenger buoy cable were found to be fouled, it would be necessary for a diver to detach the fouled cable, then attach a new cable from the surface to the submarine hatch bail, inspecting the deck area

From the bell's balanced position at the rescue ship's after rail, where the two operators have entered through the upper hatch, it is lowered away until it floats in the water. The lower chamber and the main ballast tank, each having a capacity of about 4,000 pounds of sea water, are both empty and in this condition the rescue bell has a positive buoyancy of about 5,000 pounds. All descents and ascents are made with the lower chamber filled with water and the ballast tank empty, in order for the bell to exert an upward pull of about 1,000 pounds, keeping the downhaul cable taut as it is reeled on and off the spool. As the bell descends, an operator may be able to see the submarine hatch through a thick sight glass in the lower bell hatch, aided by two pressure proof lights in the lower chamber. When the bell has reached the submarine, the ballast tank is filled first, after which the lower chamber is emptied by forcing the water level down to its bottom, using compressed air. A strain is taken with the air motor to seat the bottom of the bell securely on the flat surface around the submarine hatch, while the air within the lower chamber is vented until it has equalized with the upper chamber at near atmospheric pressure. This effects a very strong air seal, comparable to the relative vacuum existing inside an ordinary rubber suction cup, as well as permitting the lower hatch of the bell to be opened next. The seal may be made more secure by holding-down bolts which attach the bell to padeyes on the submarine deck adjacent to the hatch. A seal can be made by experienced men even though the submarine lists badly.

The submarine hatch is undogged slowly, using caution not to equalize too rapidly with whatever pressure might have built up in the submarine. The bell's air supply may be used to ventilate the submarine freely while taking aboard a load of six passengers. The additional weight is compensated for by removing an equivalent amount of ballast which has been carried in the upper chamber in the form of metal weights or containers of water, leaving it in the submarine. The ascent is accomplished in reverse order to the descent, followed by additional trips as required.

The air motor which propels the reel can be disconnected therefrom by releasing a clutch, so that the bell can return to the surface by virtue

Should the downhaul cable become snarled on the spool, there is an emergency hydraulic cable cutter which is operated by a hand pump in the upper chamber. The bell would then bob quickly to the surface, possibly colliding with the bottom of a surface vessel. To obviate this risk, it is possible to flood the ballast tank partially, making the bell negatively buoyant as the backhaul cable assumes this load, and then to lift the bell to the surface when the downhaul cable is cut. If the downhaul cable cutter fails, and a diver cannot be sent to cut this cable, it should be noted that the strength of the backhaul cable is greater than that of the downhaul cable, so that a strain on the former should break the latter, with the bell in a positively buoyant state; however, loss of the bell with its occupants would probably result in the event of a defective backhaul cable.

Evaluation.-The rescue bell possesses definite advantages over all other means of escape, in that the escapees are not exposed to increased pressure or forced to swim in cold water or suffer from the elements. Specialized training is not required of the escapees. The bell can deliver food and medical assistance, with intermittent ventilation during the procedure. If the original submarine messenger buoy with its downhaul cable is clear, a diver is not required, so that the rescue can be effected to great depths, not limited by human tolerance to sea pressure.

The principal disadvantage of the bell itself lies in its complicated mechanical nature and the possibility of operational failure, suggested in the above discussion. In addition, the delay entailed in searching for and locating the submarine, bringing a bell from distances which may be great, mooring the ASR, and rigging the bell perhaps in the face of adverse mooring and diving conditions, may be longer than the personnel within the submarine can survive.

The senior person inside the submarine should decide without delay whether or not he intends to wait for the bell, since the condition of his group will undoubtedly deteriorate with the passing of time.

21.3.5. Chamber in submarine.

The remaining possibility of escape without

These chambers are usually proposed to be fitted detachably to the submarine, accessible by a water tight door or lock system, and by a cable and pulley arrangement to be able to make trips to the surface with one or more men inside at atmospheric pressure.

"Whilst new ideas must always be encouraged, it should be borne in mind that escape arrangements have to strike the right balance between the fighting efficiency of the submarine and reasonable measures for the safety of her crew."

21.4.1. Flooding down compartment.

The after torpedo room of the fleet type submarine hull features a cylindrical downward extension of its deck hatchway, called the "skirt." When rigged for escape, this extension telescopes the tube-like hatchway down to the shoulder level of men standing on the after room deck. The escapees, all assembled in the isolated escape compartment, strap on and check their escape appliances, and the room is flooded as quickly as possible through sea valves. The water level is allowed to rise until pressure is equalized, or until the water has reached the bottom of the skirt. At this point the flooding may be stopped and service air used to equalize pressure, at which time a man ducks under the skirt long enough to open the deck hatch. The men now charge their appliances from a nearby manifold and leave the ship one at a time, using one of the techniques described in section 21.6 below.

21.4.2. Escape trunk.

Above the forward torpedo room of any fleet type hull, permanently mounted in the super

The newer types of submarines are fitted with escape trunks of slightly different design, above both the forward and after rooms. In these models there is a short skirt from the upper hatch down into the trunk, so that when the trunk is flooded to the bottom of the skirt and the men stand with their heads in the air space which is concentric to and outside the skirt, and escape by ducking under the skirt and through the upper deck hatch.

In comparing the relative merits of the escape

Other methods which have been devised, but are not in common use, follow.

This method is feasible in the fleet type after room (see section 21.4.1) by extending the skirt down to form a trunk beginning about two feet above deck level and leading up to the hatch, and placing under the trunk a large tub (about 4 feet in diameter, round or oblong) whose sides rise above the bottom of the skirt. If compartment pressure is now equalized with sea pressure, using compressed air alone and without flooding, the tub and trunk may be filled with water and the deck hatch opened. This procedure is possible because by Torricelli's barometric principle, water will not flood into the compartment and the crew can escape without having been exposed to cold sea water in the compartment.

Belloni also suggested that another submarine could bottom herself alongside the sunken craft, and rig one of her own compartments in the tub-trunk fashion, permitting the men from the disabled submarine to transfer to the rescue submarine along a line strung between the two ships. The men involved would thereby not be likely to sustain air embolism, and a standard decompression table could be followed after the escape, at the leisure of the rescue vessel. This technique would be valuable in enemy controlled waters. Large quantities of compressed air would be

21.5.2. Torpedo tubes.

To the layman, it would seem to be a logical method of escape to shoot the men out through the tubes like torpedoes. Actually, the torpedo tube is of practically no use in escape, except when the submarine lies at a sharp up or down angle so that the torpedo tube leads downward at an angle from the room. Such a position would enable the crew to equalize the compartment air pressure with the outside sea pressure and extend the air space to the bottom of the tube or enable a skillful torpedoman to do the same with three men at a time in the inclined tube, equalizing the tube only. In such a situation it would not be possible to use the Momsen lung and the hazards would be prohibitive.

Escapes have been made from disaster submarines by crawling downward through the torpedo tube; also, instances are recorded of escapes made by climbing through the torpedo tube when one end of a small submarine has been lifted clear of the water by cranes.

The Momsen lung, figure 148, was developed in 1929 by Lt. Charles B. Momsen, USN, Chief Gunner C. L. Tibbals, USN, and Mr. Frank M. Hobson, a civilian employee of the Bureau of Ships. This apparatus in its latest stage of

Figure 147.-Techniques of individual submarine escape.
 

The metal fitting between the mouthpiece and the bag is made of two tubes, one inside the other, which are opened for use by a quarter turn of the control valve on the right side of the fitting. Two mica disk check valves in the fitting control the

A person wearing the gas-filled SEA usually has considerable positive buoyancy and should rise along the line rigged from the escape hatch to a buoy on the surface at a rate of 2-5 feet per second. He should maintain an erect standing position on the line, with toes crossed in front of the line, the trunk bowed slightly backward, head looking up toward the surface, eyes open, all extremities straight but relaxed, the hands at the crotch, the fingers interlaced in front of the line with thumbs together around the line forming a large opening for the line to pass through, figure 149. It is of great importance that he continue to breathe at a normal rate at all times, lest the air in

If the nose clip is lost during the ascent, or if there is a leak at the nose piece, one hand may be used to keep the nose closed. Any water coming in through the nose should be swallowed rather than discharged into the bag, to avoid wetting the soda lime and losing its effect. Breathing in of irritating soda lime dust is disagreeable but should not cause alarm. If the mouthpiece slips from the mouth, the SEA is of no further use, and

319

Figure 149.-Submarine escape trainee wearing SEA approaching the surface.

the escapee should exhale slowly and steadily as he continues upward by free ascent. (See sec. 21.6.3.) If he loses contact with the line he should continue in an upright position, backpaddling to slow his ascent.

On reaching the surface, figure 150, the survivor can use the SEA to advantage as a buoy, first rolling up and clamping the flutter valve, blowing the bag up like a balloon through the mouthpiece, and then closing the control valve. He should stay with the other survivors as near as possible to the escape buoy until help arrives.

Evaluation.-The SEA is light and compact, easy to stow, will pass readily through the escape hatch, can be put on quickly without assistance, permits free breathing under water, keeps the carbon dioxide level relatively low, is effective against such noxious gases as chlorine, and can be used as a lifebuoy on the surface. The SEA must be overhauled frequently if these advantages are to be afforded. It is necessary for personnel to receive periodic training in its use.

Figure 150.-Submarine escape trainee closing mouthpiece and removing nose clip on completion of ascent using the SEA.

21.6.2. Miscellaneous appliances.

Other appliances for the individual have been designed for use by foreign navies; these also employ the principle of the breathing bag and the carbon dioxide absorbent canister. In addition, such devices as the Davis gear of Britain and the Draeger gear of Germany feature a small oxygen bottle for extending the underwater breathing time limit, The Davis gear provides an additional supply of oxygen in the form of two small steel capsules called "Oxylets," mounted inside the breathing bag. These capsules are provided with breakoff necks which are broken off by wrenching through the bag with the hands. A small additional bag on the front of the main breathing bag is for insuring buoyancy of the wearer on reaching the surface. A rubber extension from the bottom of the Davis appliance, similar to an apron, is unrolled and held out by the wearer in the horizontal position as a speed retarding vane during the ascent, in place of an ascending line.

21.6.3. Free escape.

This is that mode of ascent by which the individual, having equalized with sea pressure at the depth of the submarine, rises to the surface without the use of any breathing apparatus. In an extensive study of submarine disasters recorded in 1946, the British Submarine Escape Committee found that for every two successful escapes in which an escape apparatus was correctly used, there were three successful escapes without any apparatus at all, or with the apparatus so misused as to amount to making a free escape. Virtually all men whose lungs are filled to capacity at any given depth will have positive buoyancy at that depth if divested of all negatively buoyant equipment. In practice it has been observed that 3-4 percent of men have negative buoyancy, but it is likely that most of these exceptions have not taken a maximal inspiration and as a result did not have their maximal displacement.

In making the escape, the individual takes several slow, deep, deliberate breaths in the air of the escape room or trunk, then ducks out into the water with the lungs filled to capacity. If an ascending line attached to the buoy can be rigged, it is preferable for him to take position on this line; if not, he releases his hold on the submarine, in either case allowing himself to rise by virtue of his own positive buoyancy. A nose clamp is worn or the nose closed by hand to prevent the discomfort of water in the nose. It is of vital importance that the man exhale slowly and steadily throughout his ascent. If, for example, the escape is made from a depth of 99 feet, the initial pressure inside the lungs is four atmospheres absolute (58.8 p.s.i.) and the pulmonary air pressure upon reaching the surface must be one atm. abs. (14.7 p.s.i.). In applying Boyle's gas law of inverse pressure to volume relationship, it is appreciated that failure to exhale on the way up results in ballooning of the chest, and studies show that as little as 3-4 p.s.i. pulmonary differential

The speed of ascent can be regulated effectively by one who is properly trained in exhaling steadily as he rises, maintaining full chest expansion without overdistending the chest, and thereby controlling his own degree of positive buoyancy. A steady stream of fine bubbles is emitted when the individual blows out with the lips pursed as in blowing through a soda straw, the rate of exhaling increasing as he nears the surface. The danger symptom of chest over distension is sharp substernal pain, which may be relieved by increased exhalation ; this pain will rarely be experienced if the person rises no faster than his own bubbles, i.e., about 2 feet per second. If the person ceases to rise or begins to sink in the water because of exhaling too rapidly, he can regain his positive buoyancy with a few powerful upward strokes, his chest expanding at the shallower depth. He must avoid ineffectual threshing about in the water.

It might seem to the novice that an overpowering urge to breathe might jeopardize his free escape from great depths; in practice there is found to be a definite desire to breathe out. This is believed to be due to the stretching effect on peripheral Hering-Breuer receptors by the expanding pulmonary air and there is little or no desire to breathe in. Carbon dioxide tends to be blown off as rapidly as it is formed, so that CO₂ does not build up here as it would if the person were holding his breath for the same length of time at a constant pressure. Inasmuch as the person leaves the submarine under pressure, each of his lungs contains multiple lungfuls of air, equivalent in number to the number of absolute atmospheres from which he escaped. The danger of anoxia is not great if he has just ventilated well with good air and his lungs should be still full of air as he reaches the surface.

A disadvantage to this means of escape exists if the visibility in the water is poor, with a loss of directional sense. If the escapee cannot see his own bubbles or become oriented otherwise, he may feel that he is rising when actually he is sinking, or vice versa. A good countermeasure for poor visibility is to hold in the hand some relatively buoyant object, such as a blown up pillowcase,

Devices which have been proposed for giving positive buoyancy to any wearer include: inflatable bags which do not rupture during ascent because the expanding gas is vented off through spring-loaded valves, and plastic, rubberized canvas, or metal hoods which fit over the head of the wearer. Any such device which endows the escapee with a

21.7.1. Air embolism.

If an individual refrains from exhaling 'while rising toward the surface, by free ascent or by whatever type of escape appliance he might be using, he is providing no avenue of escape to the expanding air within his lungs. It is believed that air retention may also occur because of laryngospasm in the case of some persons who became panic stricken during ascent. The resultant rupture of lung tissue permits egress of air from the alveolar spaces directly into pulmonary blood vessels in the form of bubbles of varying size. A bubble mass proceeding through the pulmonary vein to the left heart might accumulate in the left ventricle, nullifying its action; this is analogous to the "loss of prime" or the "air-binding" of any other type of pump. Cardiac output drops sharply as the ventricle contracts ineffectually against the compressible bubbles, churning them with every stroke into a fine froth. This frothing is heard stethoscopically as the characteristic "millwheel" murmur. A person with air in the left heart should be rolled onto his right side, the feet slightly higher than the head.

More often the air bubbles pass through the left heart and course in the systemic arterial distribution, proceeding through vessels of ever decreasing size as the arteries dichotomize, until reaching a point where a small vessel is occluded by the bubble. Such an occurrence produces an ischemia to that area of tissue which is supplied

21.7.2. Symptoms.

Symptoms and signs of air embolism include: (1) Unconsciousness, (2) convulsions, (3) weakness or inability to use the arms or legs, (4) any visual disturbance, (5) dizziness, (6) loss of speech or hearing, (7) severe shortness of breath, or (8) shock. All of these symptoms are classed as serious, and must be treated immediately by recompression, using table 3 or 4. (See ch. 5.) Any delay in reducing the size of the bubble, allowing it to pass into smaller arterial branches, and to be reabsorbed more readily, will result in necrosis of the ischemic area. Relief under pressure is usually very prompt and dramatic when successful, but edema at the affected site, caused by the embolus, may delay return to normalcy by days or weeks.

Air bubbles may also migrate by routes other than the blood stream, dissecting to the pleural cavity, mediastinum, along the fascial planes of the neck, and into the subdermal space (subcutaneous emphysema). On occasion it has been found necessary to relieve pneumothorax by

21.7.3. Decompression sickness.

This syndrome, synonymous with bends or caisson disease, is likely to occur when the escapee's time of exposure to increased pressure has been prolonged beyond the maximum allowable exposure time specified for that depth without gradual or stage decompression. This is expected to occur most often at great depths or when the last men in a large escape party to leave a flooded down compartment have been overexposed to pressure.

The bizarre deep, boring joint pain in the extremities which is characteristic of decompression sickness is due to spontaneous bubble formation within the bone marrow, supporting tissues, blood vessels and nerve endings of the joints. Dizziness, paralysis, shortness of breath "chokes", extreme fatigue, collapse, unconsciousness, and possible death, sometimes occur because of bubble formation within nerve tissues or large blood vessels. If the individual has been exposed to bottom pressures long enough to force an appreciable amount of respired air into solution from the lung alveoli to the blood stream and other body tissues, then with a critical fall in pressure this air comes out of the supersaturated solution in the form of bubbles. These may then cause symptoms by pressure on nerve cells or blood vessel walls, or may coalesce to form large air emboli.

Immediate recompression is required in the effective treatment of this disorder. Proper treatment tables are selected on the basis of type of symptoms and their response to recompression and therapeutic decompression.

21.7.4. Oxygen toxicity.

Exposure to increased partial pressure of oxygen can develop very shortly such symptoms as dizziness, nausea, muscular twitching, and blurring of vision; convulsions may ensue, or may be the initial manifestation. (See ch. 14.) This syndrome is greatly potentiated if the effective carbon dioxide tension is also elevated, as in the case of a large group of men sharing the air of a small compartment. Oxygen is also toxic at lesser effective pressures, following exposures proportionately longer. Pure oxygen is used in escape appliances at depths which are beyond the range of safety,

Treatment of oxygen toxicity is the immediate reduction of the effective oxygen tension, with supportive treatment of any convulsions.

Recent study has shown that multiple random samples of high pressure service air from submarine banks have been found to be pure enough for use in the escape appliance at depths up to ten atmospheres absolute, as a substitute for oxygen. This would permit escapes at much greater depths than would be feasible using pure oxygen, but nitrogen narcosis while deep and anoxia when shallow then become the limiting factors.

21.7.5. Anoxia (hypoxia).

Depletion of oxygen in the escape compartment or trunk can materially reduce the absolute amount of oxygen in the lungs of a man who is beginning a free ascent by ventilating this hypoxic air. Even with this reduction, he should be able to make good an escape at shallow depths, but at greater depths his oxygen supply problem may be critical, since oxygen is not only metabolized during the ascent, but is also spilled from the lungs during steady exhalation on the way up. A good preventive measure in such an instance is to stand near a source of compressed air or oxygen during ventilation preliminary to escape ; or to ventilate the escape compartment or trunk briefly before escape, and to equalize the space with fresh compressed air with the flooding down process. Any escape appliance should be filled with fresh air or oxygen if possible. In emergencies an appliance can be inflated like a balloon by the escapee's own breathing, but this should be done only when there is no other source of air or oxygen.

21.7.6. Carbon dioxide toxicity.

At low concentration, carbon dioxide is a respiratory stimulant, but when its effective partial pressure is increased this gas incites the General Adaptation Syndrome, and at great enough concentrations it will cause the collapse of the individual. When the inspired air at atmospheric pressure contains 3 percent carbon dioxide, the respiration becomes rapid and shallow, with headache; at 6 percent there is impairment of the efficiency and judgment, with respiratory distress;

It must be emphasized that the effective carbon dioxide increases as its absolute tension in the inspired air is increased. For example, if the escape compartment air contains 1 percent CO₂ at atmospheric pressure, then an increase in compartment pressure to 5 atmospheres absolute by flooding down alone (that is, without diluting compartment air with fresh compressed air), would increase the effective CO₂ by five times; this would be equivalent, then, to a concentration of 5 percent at atmospheric pressure. This demonstrates the importance of keeping the CO₂ concentration as low as possible at the time of escape.

Increased CO₂ tension also potentiates the toxic effect of oxygen as well as the narcotic effect of nitrogen under great pressure. The mechanism involved is unknown, but various hypotheses have been advanced.

21.7.7. Nitrogen narcosis.

Deep sea divers breathing fresh compressed air experience a decrease of mental acuity and judgment below 100 feet, which increases with greater depth until there is appreciable impairment of mental clarity at 200 feet, and at 300 feet few people can be depended upon for accurate observations, logical deductions, or reliable responses. (See chapter 11.) This is believed to be due to the narcotic effect of nitrogen, which has been described as having about the same effect as a strong alcoholic cocktail for each one hundred feet of depth. This is one basis for setting a limit of 250-300 feet as the maximal depth from which submarine escape is practicable, breathing compressed air. The Meyer-Overton Theory regarding the narcotic effect of certain gases is borne out here, since nitrogen has a 5/1 fat/water absorption coefficient. Investigation has been made into the possibility of substituting other gases such as helium in the place of nitrogen in the breathing medium for escape purposes, but in the case of helium other problems have arisen, such as a greater potentiality for the occurrence of decompression sickness.

21.7.8. Noxious gas effects.

Occupants of an escape compartment are subject to the actions of whatever objectionable or poisonous gases may have accumulated therein. Examples

Again, the collective harmful influences of these gases are functions of their partial absolute pressures, so that any increase in pressure which is not accompanied by dilution from a fresh air source will serve to multiply the effects of these gases.

The submarine escape appliance may be an asset in such a situation, inasmuch as its canister of soda lime absorbs many of the noxious gases mentioned, particularly chlorine. Cans of CO₂ absorbent stowed inside the room should also be opened and distributed for this purpose.

21.7.9. Pressure equalization.

This should be a minor problem in relation to the above, but in at least one disaster virtually the entire crew has been lost because one of its members complained of pain in the ear during the flooding down of the escape compartment. If the natural opening to a bony sinus or middle ear space is blocked by mucus collection during a head cold, or by presence of excessive lymphoid tissue at the eustachian tube ostium, severe pain to the individual may occur during the flooding down process. Pain caused by stretching of the eardrum ceases abruptly after the drum is ruptured.

Submarine escape is a lifesaving means to the group as a whole; it may seem inhuman, but in such an emergency the person who is unable to equalize pressure must endure the pain for the interval required to save his life. The prognosis of a ruptured eardrum is relatively not serious if medical attention is received, and there is no turning back once the escape has been initiated.

In order to facilitate realistic escape training for all submarine personnel, large training tanks were constructed at the New London and Pearl Harbor submarine bases in 1930-32. These are tall steel cylindrical towers, 138 feet in height overall, providing a vertical column of water 100 feet high and 18 feet in diameter. (See figs. 151 and 152.) Their capacity is about 315,000 gallons of water. A large room overhangs the main cylindrical portion of the structure, its deck a few inches above the surface of the water, with space enough to accommodate control equipment, instructors, large groups of trainees, a urinal stall, and miscellaneous small equipment lockers. Integral with the tank on one side are two pressure locks inside small houses to provide means of entering the water column at respective levels of 18 feet and 50 feet below the surface. An elevator shaft alongside the tower is connected to the top room and to the 18 and 50 foot locks by enclosed runways, with its fourth stop at ground level. These four levels are also accessible by a spiral steel stairway, nonenclosed, around the outside of the tank.

At the 100 foot level (ground level) is a large boiler-shaped pressure lock. Besides its access door at one end are two openings in the overhead: (1) A conventional submarine type hatch with a skirt beneath to the chest level of men standing inside the lock, comparable to the rig in any fleet type after torpedo room, and (2) a hatch which is the lower opening to an escape trunk situated just above, comparable to any fleet type forward torpedo room escape trunk. The 100-, 50-, and 18- foot locks are equipped with facilities for flooding or draining from inside or outside, and with supply lines for fresh compressed air or oxygen, vent lines for release of pressure, and talkback speakers for two-way communication with the surface, other locks, fixed and roving bells, and other speaker stations at ground level. Further description applies in particular to the New London tank.

Two fixed underwater bells are situated inside the water column itself at the 25- and 85-foot levels; a third bell is the movable or "roving" bell, which can be raised or lowered like an elevator anywhere between the surface and the 90-

Figure 151.-The submarine escape training tank.

Figure 153.-The submarine escape training tank's "Roving" bell.

at the bottom only, with fixed platforms suspended beneath in such a position that as many as three or four men may stand with their heads in the air space inside the bell. Each bell is provided with side windows, a compressed air supply, a vent line to the surface, and a talkback speaker; the roving bell also has an oxygen charging connection.

Located at the foot of the tower is a building for administrative office, sleeping quarters for a duty section, air compressors, facilities for treating casualties, and a large fresh water purification system. The latter consists of a large overflow tank from the tower, electric centrifugal pumps, a water chlorinator, and a bank of sand filters. This arrangement, with continuous recirculation

The training tank is staffed by a complement of : (1) Two officers who are qualified in submarines or in diving, (2) submarine medical officers, and (3) 17 enlisted men, all of whom are chief petty officers or first class P. 0.'s of any rating group, and all previously qualified as submariners or as first class divers. They are picked from the fleet for these billets because of outstanding qualities of dependability, stability, leadership, and teaching ability. They undergo rigorous training in submarine escape, becoming well versed in all escape methods, and after about 6 months of gradually increasing responsibility each man is considered qualified to rotate among all of the stations.

21.8.2. Training procedures.

All personnel reporting for training at the submarine School are required to complete a half-day basic training course in the use of the SEA, after a thorough physical evaluation at the Medical Research Laboratory (MRL). The trainees are divided into groups of 12-15 men, each group going through the following steps:

1. Brief exposure in the pressure chamber to compressed air at 50 p.s.i.;

2. A 20-30 minute lecture by an instructor in the use of the SEA, including the strapping on of the SEA under supervision, demonstration of proper procedure in leaving the lock, assuming position on the line, etc. (See section 21.6.)

3. Ladder training in the topside room, during which each man learns to breathe from his charged SEA with his head 2-3 feet below the surface, under close observation of instructors at the water's edge.

4. Two trips by elevator with an instructor to the 18-foot lock, with escapes as a group along a line from the lock to a fixed buoy at the surface, each man accompanied by an instructor who has skindived from the surface, and has met him at

5. Two escapes from the 50-foot lock in similar fashion; during this phase two instructors are stationed in the roving bell at a depth of 40 feet taking turns in meeting escapees at the 50-foot lock door, passing them up to one of the two instructors stationed in the 25-foot bell, and in turn to other instructors from the surface.

6. One escape from the 100-foot level. This is not done on the same day as basic training since the exposure to 100-foot pressure in itself consumes most of the compression time which is considered safe for 1 day.

The trainees receive a few words of correction and criticism following each group escape. When several groups are being trained, it is customary for escapes to be conducted simultaneously from the 18- and 50-foot levels as required.

All submarine crews are required to requalify in escape training once during each training cycle of the submarine, which at present is about every 18 months. Requalification training consists of: (a) two 18-foot escapes, (b) one 50-foot escape, and (c) one 100-foot escape, optional.

The 100-foot escape may be made with larger groups, of 25 or more, using the hatch with skirt,. With the hatch open and the water level at chest height inside the 100-foot lock, each man in turn ducks briefly under the water to check for leaks following the charging of his SEA with oxygen by the instructor who stands at the hatch. He then stands up for his SEA to be topped off with oxygen, and ducks under the skirt, rising slowly through the hatch. He is met here by an instructor from the 85-foot bell or from the roving bell which has been set at 90 feet, and begins his ascent under the successive supervision of instructors stationed in all locks, all bells, and on the surface. Escapes are not simultaneously made from any other level during 100-foot training ascents.

Touch signals are used by the instructors to

Training in free escape was afforded to all submarine personnel successfully and routinely from 1946 until terminated in 1952 because of two fatalities. At present, free ascent is taught only to special groups.

21.8.3. Management of casualties.

A medical officer must be in attendance at all training evolutions other than the 50-pound air pressure test. MRL doctors are assigned additional duty at the tank for this purpose, serving a rotational duty period of one-half day each as designated by the MRL senior watch officer. Although the doctor must be able to handle himself in an experienced fashion in the water, and may take part in the training program in rotation with the regular instructors, his capacity must be regarded as advisory rather than authoritative. During normal tank operation his attention is devoted to prevention of casualties; any violation of safety measures or other undue hazards should be brought tactfully to the attention of the tank officer who is present in order for the situation to be remedied. In medical emergencies the doctor takes charge of his patient.

Any symptomatic complaint of trainees or instructors is referred to the duty medical officer, whose responsibility it is to evaluate and begin treatment promptly as necessary. The most frequent type of complaint is ear pain caused by inability to equalize pressure, particularly during the cold and rainy seasons, when cold and upper respiratory infections are prevalent. An eardrum which has been stretched will exhibit one of several degrees of reddening and injection, up to a

Sinus pains caused by occlusion of the sinus ostium during pressure changes, are lancinating and localized to the involved area, with acute tenderness in the frontal or maxillary areas if these are involved. Treatment here is also with analgesics and heat or cold over the area.

One of the enlisted instructors billets at the tank is filled by a hospital corpsman, trained in S/M medicine, who assists the medical officer.

As would be expected in stressful conditions, psychosomatic manifestations of every kind are encountered. When faced with the new and unnatural circumstance of the compression chamber and the escape tank, the borderline claustrophobe or neurasthenic may recall or even reexperience the symptoms, real or imagined, of some past illness or injury. Not many of this type are malingerers, inasmuch as these trainees are in a voluntary status. Regardless of how bizarre a symptom may be, if the possibility exists that it might have an organic basis, the trainee should be excused temporarily for further evaluation. Otherwise the medical officer should use tact and reassurance, refraining from the embarrassment of the trainee before other members of his group. Permitting him to drop out for the day might make it more difficult for the trainee to succeed later. Any obvious misfits who disclose themselves at the tank should be noted for the final assessment interviewer. (See ch. 19.)

The prevention, early detection, and immediate treatment of air embolism is the primary concern of the medical officer at the tank. He must be quick to take action in the event of unconsciousness, convulsion, paralysis or weakness of one or more extremities, any visual disturbance, dizziness, loss of speech or hearing, or severe shortness of

Treatment of air embolism inside the recompression chamber is in conformity with treatment tables 3 and 4, recompressing to 165 ft. (6 atm. absolute) without exception. (See ch. 5.) When treatment is successful, the recovery of the individual is one of the most dramatic phenomena to be observed in clinical medicine. The patient is under the supportive treatment of the medical officer, and a continuous thorough neurological evaluation is made, noting time and depth of each observation or examination during treatment. A written report of the casualty is submitted by the cognizant medical officer on NavMed 816 (Report of Decompression Sickness and all Diving Accidents).

Symptoms of decompression sickness (bends) are seen rarely at the escape training tank, its incidence being chiefly among instructors. The underwater training stations are rotated among the instructors so as to minimize the amount of time under pressure for each. Because of the repeated short dives to varying depths, it would be very difficult to devise a working formula for determining the depth versus time at which an individual would require decompression. A running estimate of times and depths is kept by each instructor, and at his own discretion, or that of the officer in charge, he may be given a brief decompression stop in a

REFERENCES

21a. Submarine Escape History: Chap. XIII of Notes for Submarine Officers, as revised by United States Naval Experimental Diving Unit, United States Naval Gun Factory, Washington 25, D. C., 1952.

21c. Manual of Free Escape from Submarines: Alvis, H. J., MRL No. 184, XI, No. 1, 1952.

21d. Theoretical Considerations of the Use of the Air-Filled Submarine Escape Appliance at Great Depths: Alvis, H. J. MRL No. 185, XI, No. 2, 1952.

21e. The Suitability of Submarine Compressed Air For Use in the Submarine Escape Appliance: YAGLOU, C. P. and BORUM, V. F., MRL No. 221, 1953.

21f. Diving Accident Reports and Records: Procedure For Preparation and Maintenance of. MRL INST 6420.1 of 1 June 1953, New London.