Losses of disabled or distressed U.S. submarines to noncombat causes occurred all too frequently in the last century (19 boats). Given the Navy's renewed focus on operations in the world's littorals and growing commercial maritime traffic, the potential has increased for suffering submarine losses in waters where the boats can be salvaged. Thus, routine rehearsals and drills of escape procedures using submarine escape and immersion equipment (SEIE) are well advised.
If a sub is disabled, the decision to attempt escape or await rescue depends on the boat's internal circumstances. Reasons for escape can range from flooding to elevated radiation levels caused by reactor casualties. The factors that limit escapes are:
* Depth of the submarine. The maximum man-tested depth of the SEIE suit is 625 feet; theoretically, the suit could be used down to 750 feet.
* Angle of presentation. The angle of the escape hatch from the sea bottom cannot be greater than 45° for the hatch to operate.
* Time required for rescue assets to arrive on station. This normally is dependent on the particular geographic area of operation.
* Surface conditions. Rough seas often can prevent certain rescue platforms from operating.
The time between the casualty and escape or rescue of the crew is known as the survivability of the disabled sub. Internal conditions that the survivors would be exposed to would depend on the boat's depth and geographic position. The working environmental model is an internal temperature of 38°F with 98% humidity.
Exercise Sorbet Royal
In May 2002, the NATO submarine escape-and-rescue exercise, Sorbet Royal, was held off the coast of Denmark. Its purpose was to demonstrate the ability of NATO to cooperate in saving lives on distressed submarines of any participating nation, and to assess interoperability among NATO submarines, submarine rescue vehicles, and other assets of participating nations. Familiarization with the range of submarine escape-and-rescue equipment available to NATO's member and partner nations is essential to the conduct of combined operations.
During Sorbet Royal 2002, I had the opportunity to escape from the Swedish attack submarine Vastergotland using the SEIE suit that recently had been adopted by the U.S. Navy. The escapees were: four Vostergotland crewmembers (three men and one woman), two Danish sailors (one female physician and one diver), two British escape trainer instructors, and me.
Having trained and escaped in the SEIE suit at the British Submarine Escape Training Tank (SETT) and the Swedish SET (Submarine Escape Tank), I was prepared for an open-water event. After we transited to the Vastergotland and boarded her, she entered the area for the escape drills and settled on the bottom of the Baltic Sea at a depth of 115 feet. We were issued SEIE suits and underwent inspection and maintenance checks. We then inspected the escape trunk and found it to be a little smaller than the practice device at the SET. At the appointed time, the team suited up and filed to the escape trunk to prepare for a series of single-man escapes.
Escape Procedures
The procedure is simple. The escapee dons the SEIE suit, zips it shut, and climbs up into the escape tower; he then plugs the hood inflation system valve located at the left hand into the air supply. As the suit immediately begins to inflate, you feel cool air and hear the noise of the pressurizing gas. Valves on the suit allow excess pressure to escape.
The next step is to flood the tower with seawater. Pressure is kept at a constant level at the beginning of the pressurization phase by a vent valve. This chest-high valve is closed when the water reaches its level. At this point, water continues to enter the tower from the sea, thus increasing pressure in the tower at an exponential rate. The pressure doubles every four seconds. The escapee must remain plugged in, breath regularly to maintain lung volume, and equalize the pressure in his eustachean tubes by performing the valsalva maneuver (shutting mouth, blocking nostrils, and blowing hard.) A faster rates of compression and reduced time under pressure means less risk of decompression illness, because less nitrogen will be dissolved into the blood and body tissues.
When pressure in the tower is equalized (matches the outside sea pressure), the overhead hatch to the sea opens. With its 70 pounds of positive buoyancy, the SEIE suit floats the escapee out of the tower to begin the ascent. As the escapee rises to the surface, gases in the suit and in his body expand. To permit gases to escape from the lungs, the escapee breathes normally and makes sure not to hold his breath.
Climbing up into the escape tower in an SEIE suit with its life-saving raft attached was an interesting evolution. The best way to describe it is to imagine putting on all your winter clothing, zipping up your parka, and climbing into your gym locker. Any claustrophobic tendencies will be discovered immediately. Once you are cozy and plugged in, the noise starts at the same time the cold seawater enters the tower. Initially I felt no pressure on my ears; once it started, I was thankful I could equalize effectively. After a short period of time-it took 18 seconds to pressurize-the noise and pressure stopped. The hatch opened and the buoyancy of the SEIE suit carried me to the surface. I traveled 35 meters in 9 seconds and broached the surface to thigh level. A Zodiac boat picked me up and took me to the recovery vessel, with its recompression chamber and medical team. The surface recovery was accomplished in the three-minute safety period set by NATO for the exercise. all nine escapees left the sub successfully; no injuries were reported. The escapes were controlled as part of the exercise and averaged 15 minutes each. Actual recycling time of the escape tower on the Vastergotland is four to six minutes, which is the time required to drain the water in preparation for the next escape.
Escape Circumstances
In the U.S. Navy, diving and submarine medicine are taught together and are integral to the understanding of, and participation in, submarine escape and rescue. Crewmembers must be aware of the factors that influence the decision to stay or escape, the variety of hazards they may face on a disabled sub, and the problems that may occur once escape or rescue is attempted.
Remaining in place and awaiting rescue is perhaps the best situation in a disabled sub, provided the mechanical casualty has been stabilized. At the same time, there are several reasons why an immediate escape may become necessary. The decision to escape is made by the senior surviving crewmember, who assumes command in such dire situations.
Flooding will, of course, force survivors to escape or drown if it cannot be stopped. Flooding raises the atmospheric pressure in the compartment and makes the occupants involuntary "divers." Pressure, depth, and time pose the main risks for decompression illness under these circumstances. Also, if the compartment's atmosphere is compressed by flooding, the partial pressures of all individual gases in the atmosphere will be increased and may pose further hazards.
Several gases may become toxic in a disabled sub. Deadly chlorine gas can be generated if seawater contacts the sub's batteries. Oxygen, carbon dioxide, and carbon monoxide are monitored routinely-an unacceptable level of any of these can force crewmembers to escape.
If a nuclear-powered submarine suffers a major reactor accident, the survivors might be forced to escape and could be suffering from acute radiation exposure. Radiation can be absorbed by ingestion, inhalation, and contamination of clothing, skin, and wounds.
Medical Problems
The following problems are intended to familiarize submarine and rescue personnel with conditions and situations that might occur on board disabled or distressed boats:
* Barotrauma is caused by changes in pressure. This injury to the ears and sinuses is a major hazard in submarine escape because of rapid pressurization. Ruptures and serious damage to the physical structure of the inner ear may result.
* Pulmonary overinflation syndrome (POIS) is an overexpansion of gas in the lungs during ascent that leads to alveolar rupture, with injection of air into the capillaries so that air bubbles enter the pulmonary veins and left ventricle. These bubbles can enter the cerebral arterial circulation and give rise to cerebral arterial gas embolism. POIS also can result in air in the chest cavity that causes the lungs to collapse, and it can occur in shallow depths.
* Decompression illness is a complex series of events initiated by excessive formation of inert gas bubbles during or following decompression. Escapees are conducting, in effect, a rapid, deep dive with a short bottom time, followed by rapid ascent. Depth and time at depth increase the amount of nitrogen that is dissolved into body tissues. As the escapee ascends, pressure lessens and allows the gas to escape. If certain time or depth limits have been exceeded, some of those making an escape from a submarine may suffer from this illness. Although symptoms may begin soon after surfacing, it is possible for their onset to be delayed for hours. The incidence, rapidity of onset, and severity of the illness will increase as the depth of the escape increases.
* Hypothermia can occur from prolonged exposure to the cold. In an escape situation, hypothermia can be an issue prior to escape and on the surface. Heat is lost faster in water than in the air: the thermal conductance of water is 25 times that of air, which greatly increases heat loss in the human body. Additional factors limiting heat production are fatigue, malnutrition, dehydration, and poor physical conditioning.
* Thermal stress as a result of heat can occur while on board a disabled sub or on the surface. Loss of ventilation, air circulation, and air conditioning in tropical waters may predispose survivors to various forms of heat stress.
* Drowning or near drowning on the surface is a danger in higher sea states, when escapees cannot pull themselves into rafts or they become exhausted.
* Traumatic injury may occur during the initial accident or during the escape. If it is serious enough, it could impair the survivor's ability to enter and operate the escape trunk.
Conclusions
Escape with the SEIE suit greatly improves the ability of crewmembers to survive a disabling accident to their submarine. This practical tool is the current standard of submarine escape in 21 navies around the world. Data from the United Kingdom, Sweden, and Australia show that the suit is a thoroughly tested and proven method of egress.
The U.S. Navy now outfits its submarines with the SEIE suit and conducts escape-and-rescue training in the United States and overseas. The procedures are being introduced throughout the submarine community. In addition, extensive research continues on the safest and best ways to medically treat crewmembers who are forced to escape. A Navy escape tower facility is in the planning stages.
Captain Cohen, formerly the senior medical officer for Commander, Submarine Force, U.S. Atlantic Fleet, is director of medical accessions at the Naval Medical Education and Training Command.