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Submarine Safety SUBSAFE

Few US Navy submarines have sunk since World War II, and none since the loss of USS Scorpion (SSN-589) in 1968. Since then, Navy submarines have achieved an unparalleled record of safe operation. Although going to sea on submarines will always pose a certain amount of danger, the best way to reduce the risk to Sailors is to prevent accidents from happening wherever possible, and to train the crew to respond properly when the unexpected does happen. Following the loss of the USS Thresher (SSN-593) in 1963, the US Navy instituted the SUBSAFE program. By establishing certain operating and casualty control procedures, implementing maintenance and material requirements for greater reliability, and installing emergency recovery systems, the US Navy dramatically improved the integrity and recoverability of submarines in the event of a casualty. Thorough crew training and qualification programs further reinforce that foundation of safety. The impressive safety record of the Submarine Force since the implementation of these programs is a testimony to their effectiveness.

It is frequently argued that since US submarines spend 95 percent of their time operating in waters [in which the ocean bottom is] deeper than the hull crush depth, discussions of escape or rescue are for the comfort of wives and mothers back home. Nevertheless, the chance of a mishap is much greater while the submarine is over the continental shelf because of the increased risks associated with sea trials, diving and surfacing, and transiting with open hatches and other hull penetrations in areas with greater sea traffic density, such as near major seaports.

Submarine survivability and rescue is an area that requires ongoing attention to ensure maximum readiness of current assets, proper equipping and training of crews, and introduction of newer capabilities into the program. The goal is to ensure each submariner is given every chance for survival should the unthinkable happen.

In the unlikely event an accident should occur which puts a submarine in distress, the US Navy has a very capable, three-pronged rescue program consisting of Survival, Escape, and Rescue. In addition to current capabilities in each one of these pillars, there are also significant modernization programs in progress. Most of these programs were initiated as a result of a thorough review and subsequent recommendations provided by the Submarine Escape and Rescue Steering Group established in 1999.


The first pillar of the US Navy program gives crews the tools to survive should a potentially catastrophic accident occur. Damage control training and specially trained Independent Duty Corpsmen (IDCs) are important elements. However, the limiting component in extended survival is atmosphere control. Re-distribution of the Lithium Hydroxide canisters, as recommended by the Steering Group, better supports survival of the largest part of the crew in the forward compartment. Passive carbon dioxide scrubbing and Emergency Air Breathing systems can support the crew for up to four days. To extend that, by the year 2000 the US Navy was proceeding with procurement of the Micropore Improved carbon dioxide scrubbing system, which will increase survivability to at least seven days.

Longstanding guidance for emergency control of high CO2 levels called for opening lithium hydroxide canisters and spreading the granules on horizontal surfaces. However, testing in 2003 showed that this method absorbs CO2 too slowly and creates high levels of caustic dust that can cause eye and skin burns, as well as coughing and respiratory irritation. To solve this problem, workers evaluated several methods and found that a mesh curtain container used by the French Navy scrubbed CO2 fairly well. This design was modified by the Battelle Corporation into a 6-foot long, polypropylene-fabric, curtain-shaped device that crewmembers can load with a canister of lithium hydroxide granules without spreading large amounts of dust. Each curtain, when hung from the overhead, passively absorbs the CO2 production of one man at rest over two days. The new passive CO2 scrubbing curtains performed well in the simulated DISSUB conditions. At the start of a simulated casualty in 2003, the crew quickly filled and hung 98 curtains, which maintained CO2 levels below the upper limit goal of three percent over three days. By 2003 these curtains were being implemented in the fleet.

Planners assume that a sunken submarine will be without electrical power and unable to run carbon dioxide (CO2) scrubbers and other equipment necessary to maintain normal atmosphere control. As a result, in nearly every potential scenario, the greatest threat to survival is the buildup of respiratory CO2 as crewmembers wait for rescue. Other likely survival risks include depletion of oxygen, hypothermia, heat stress, toxic gases, or pressure buildup in the boat.

Increasing atmospheric pressure in a DISSUB is highly probable and can result from flooding, rupture of compressed gas banks, air leaks, or prolonged use of emergency breathing apparatus (EABs). This increased pressure in the boat causes gas to dissolve in human tissues just as if the survivors were scuba diving. Like divers, survivors breathing a pressurized atmosphere corresponding to 23 feet of seawater or more for longer than a day will be at risk for decompression sickness, or the "bends," after reaching the surface. For this reason, today's guidance calls for survivors at risk of the bends to await rescue - after which decompression chambers will be available - instead of performing escape to the surface before rescue forces and chambers have arrived. Also, as internal pressure rises, the increased partial pressure of oxygen in the boat can cause respiratory and nervous system effects, such as respiratory failure and seizures. The risk of these conditions increases rapidly when atmospheric pressure in the boat exceeds five atmospheres.

COMNAVSUBFOR's goal is for the crew of a disabled and submerged submarine to have a survivable environment for up to seven days while awaiting rescue. With this in mind, in March 2003 and December 2004, the lab conducted survival exercises (SURVIVEX) with crew members on USS Dallas (SSN 700) and USS Salt Lake City (SSN 716), respectively. In these pierside exercises, ship's power was shut off and external hatches were closed to evaluate DISSUB equipment and procedures. The exercises confirmed the ability of the carbon dioxide-scrubbing curtains and oxygen release system to maintain a breathable atmosphere during DISSUB conditions. It appears that COMNAVSUBFOR's goal of seven-day survivability is definitely realistic in 2006. A surprising finding in these exercises has produced a new challenge for DISSUB research. Although it had been expected that a DISSUB would experience lower internal temperatures and create a risk for hypothermia, the opposite occurred. Survivex 04 was terminated early due to the increase in ambient temperatures and the resultant heat injury risk.


The US Navy equipes submarine crews to escape should it become necessary. While submarine escape procedures carry with them certain limits and risks based on the water depth, the Navy was pushing back those barriers. By 2000 the Navy was in the process of installing new Submarine Escape and Immersion Equipment to replace Steinke Hoods onboard all of US submarines. These full body suits include thermal protection and a built-in life raft to allow crew members to escape at depths down to 600 feet and survive on the surface. The Navy was also reviewing our training programs to ensure crews are properly trained, as well as equipped, to perform submarine escapes.


There has been no need for submarine rescue in the US Navy since the sinking of the USS Squalus in 1939. The USS Thresher, which sank in 2,520 msw (8,400 fsw) in 1963, and the USS Scorpion, which sank in 3,000 msw (10,000 fsw) in 1968, were too deep for rescue.

The US Navy maintains various state-of-the-art submarine rescue equipment. As of 2000 there were two Submarine Rescue Chambers (SRC) that can be rapidly transport to a support vessel to be used at the location of a disabled submarine. If a US Navy auxiliary vessel cannot respond to the scene fast enough, any one of the world's estimated 4,000 commercial supply/handling vessels can be used if made available. The SRCs, capable of rescue down to 850 feet, can be mated to a disabled submarine by using a down-haul cable attached to a special pad-eye on all US submarine hatches.

The US Navy maintained one Deep Submergence Rescue Vehicle (DSRV) as of 2000, capable of rescues down to 2000 feet in a ready status at all times. It too can be deployed rapidly by aircraft to a nearby port where it would be mated to a mother submarine (MOSUB) and then transported to the scene of the stricken submarine. Depending on the distance from the Deep Submergence Unit to the nearest airfield and the distance from the nearest port to the position of the disabled submarine, the nominal timeline places the DSRV at the scene anywhere from 36 to 48 hours after first notification. However, this capability is also dependent on the proximity of a MOSUB to the port closest to the casualty.

Following its extensive maintenance availability, the DSRV Mystic remained in a constant rescue-ready status until her inactivation in 2005, with the exception of one 3-week upkeep in 2003. Based on requirements to keep only one DSRV rescue-ready at all times, plan were to lay-up or inactivate the DSRV Avalon in November 2000. Its final status will depend on a review now under way to determine the best course of action.

Perhaps the most vivid example of the use of hyperbaric chambers is in the treatment of divers who are suffering from "bends" or nitrogen narcosis. It is well known that isolation of such injured diver in a high pressure atmosphere is one of the few known treatments for this often fatal or crippling malady. Even as well known as hyperbaric treatment is in situations where a diver has surfaced too quickly and begins to suffer from bends, too few hyperbaric treatment centers are available for such divers. Oftentimes, diving vessels have no hyperbaric treatment center or chambers at all. And, even if a vessel or offshore platform has some type of hyperbaric chamber on it, it is generally insufficient for any type of long term treatment. The only available chambers for long term treatment are located at hospitals and medical centers often far away from the scene of a diving accident. And, a diver may be already permanently injured if not dead by the time he is transported to such a suitable hyperbaric chamber facility. For even if a diver receives some temporary treatment on a vessel or offshore platform, the benefits of that temporary treatment may be lost in a period of transfer of the diver to a more permanent treatment area.

Recompression chambers are essentially cylindrical with a hemispherical portion at each end thereof. Being so configured, in order to accommodate both a patient and an attending medical technician they must be of considerable internal dimensions. So dimensioned the wall thickness of the chamber must be considerable to contain the requisite elevated internal pressure and therefore they are inconveniently massive.

International Cooperation

Other nations have deemed escape and rescue as a small insurance policy in the event of an unforeseen tragedy. The British, for example, use the term duty-of-care. They have a somewhat more comprehensive submarine rescue program. Other countries are beyond the United States in end-to-end capability, from first responders to mobile compression chambers, and even using parachute assistance. They also have responders parachute into the DISSUB site and toss life rafts out of planes. In an emergency, the US Navy would likely deploy SEAL teams and request Coast Guard assistance, but these measures had not yet been exercised as of 2002.

In addition to providing equipment, the US Navy has gone to great lengths to ensure the readiness and interoperability of the submarine rescue program. The US has partnerships worldwide with other nations with similar rescue capabilities, and US submarines and rescue assets are completely interoperable and compatible with those nations. For example, by the year 2000, in addition to the eight compatible US MOSUBs, there were four United Kingdom and one French MOSUBs that could be used with one of the US DSRVs. Equally important, the US conducts regular exercises to train crews and practice these procedures with participating nations. For instance, in 1999 the US launched a DSRV from a US submarine, mated it with a Japanese submarine on the bottom, and transferred personnel. The US conducted a similar exercise earlier in 1999 with the French. In 2000 the US conducted one NATO submarine rescue exercise involving the DSRV and another exercise, PACIFIC REACH, using an American SRC with the Koreans, Japanese, and Singaporese.

The Kursk tragedy in August 2000 added a powerful impetus towards an internationalization of submarine escape and rescue that had already begun among the submarine operating nations of NATO. With over 40 different nations now operating submarines worldwide, interest in the exercise is expected to extend to the entire global submarine community including China, Japan, India, Pakistan, Brazil, Chile and many others.

Submarine rescue requires specialized and expensive rescue vehicles and systems. Only a small number of nations operate such systems and the capability, capacity and limitation of the systems can be quite varied. Optimizing these assets and ensuring compatabilty and interoperability between rescue systems have become global issues. Given that the crew of a distressed submarine may have little more than 72 hours of survivability, some rescue systems have been designed to be air portable so that they can be deployed at short notice anywhere in the world.

The International Submarine Escape and Rescue Liaison Office [ISMERLO], located in Norfolk Virginia in the USA, has an international staff. The aim of ISMERLO is to be the international co-ordinating authority for submarine rescue system and support ships. Thus ensuring that one of the world's several rescue systems is available to be deployed at immediate notice. ISMERLO maintains immediate access to a miriad of databases essential to mount a complex rescue operation, such as information of suitable mother ships for portable rescue systems.

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Page last modified: 07-07-2011 12:58:00 ZULU