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“ ‘People were going to die’: submarine crew trapped in searing heat after catastrophic systems failure.”

Those headlines on 4 June 2014 from the UK newspaper THE TELEGRAPH reported an incident on board HMS TURBULENT, a Royal Navy fast attack submarine, as she left Fujairah in the United Arab Emirates on 26 May, 2011. CDR Ryan Ramsey, RN, Commanding Officer of TURBULENT at the time, who related the incident from his home after retiring from the Royal Navy, said “I genuinely thought there was going to be a loss of life on board.”

That could never happen on a US submarine, right? Our boats are too redundant and have too many backups to let things get that bad. The fact is it has happened in the past on earlier classes of US submarines, and the progression of events was strikingly similar to TURBULENT’s experience. TURBULENT’s casualty was caused by marine organism buildup in air conditioning condensers while operating in warm waters. While it is tempting to respond “That could never happen on my ship”, what if it did?

A catastrophic loss of air conditioning (AC), while a rare and unlikely scenario, is a possibility every Commanding Officer should thoughtfully consider and plan for, because its potential downside is a major medical casualty and potential loss of life. By the time the first heat casualty comes to medical attention, catastrophic loss is imminent: planning and preparations must have occurred long before the first heat casualty presents itself. The means to recognize this situation early, take preventative measures and respond rests squarely with the command team. In truth, from a medical point of view the cause of AC loss is immaterial. Would you know how to handle what could quickly become a mass casualty? It’s not just the Corpsman’s problem. He will be heavily involved in limiting the danger to the crew, and stands a fair chance of becoming a casualty himself. What will you do if his advice is no longer available? How can you best prepare to overcome the threat to your crew regardless of who remains standing? How long do you have? When do you call for help?

The Timeline

Within the first hour following a total loss of air conditioning, temperatures in the engineering spaces will rise to approximately 140° F, while temperatures in forward spaces will rise to approximately 120° F; possibly higher depending on outside water temperature and the insulating effectiveness of anechoic coatings. Humidity will similarly rapidly approach 100%. Navy Physiolog- ical Heat Exposure Limits (PHEL) recommend stay times in temperatures exceeding 120° F be limited to 15 minutes or less. Where will you evacuate crew who show signs of serious heat stress? Pierside, perhaps, if you are in port. But, what if you are in the Middle East and outside air temperature is 110° F? What if you are at sea in the Persian Gulf or Indian Ocean where sea water temperatures at the surface can approach 95° F? Can you return to port quickly? Are you in a location where local authorities are able to comprehend and accommodate a nuclear submarine with a reported casualty?

A combination of high air temperature, high humidity, thermal radiation (from the sun and boat surfaces) and low air movement contribute to heat stress. The loss of AC on a boat in tropical environments could very quickly result in these conditions. If there is no decrease in crew physical activity then heat illness casualties would quickly present to the medical team. As the whole ship’s company will soon be experiencing similar conditions, waiting for the first casualty to occur is likely to lead to multiple simultaneous heat injuries. Heat injuries are more likely to occur first in occupations with a higher thermal load such as engineers or cooks, but are often masked in fit, healthy individuals who are highly motivated and focused on their task. This makes predicting exactly who will be affected and when they will reach their limit very difficult.

Well prepared Army units that have time for acclimatization still run into problems with heat stress. In 2011 during training in the United States an 18-year-old cadet at the U.S. Military Academy died during an exercise and, days later, a paratrooper died after physical training at Fort Bragg, N.C. 1 An Army unit normally has time to acclimatize and the opportunity to limit or prevent heat illness. In the event of an AC failure in a submarine the crew will not be acclimated to high heat and humidity and there will be no time to plan countermeasures.

What Happens to Your Body?

Physiology, fitness and, to a lesser extent, genetics determine how well and how quickly each of us responds to heat stress. In high temperatures the main means of heat regulation is evaporation of sweat from the skin, however when air temperature and humidity are high, the capacity for evaporative cooling is significantly impaired. The cardiovascular system directs heat to the skin to help increase heat transfer, but this places a considerable burden on the heart. Physical activity further contributes to heat injury by generating heat from metabolism, which strains the cardiovascular system further.

As body temperatures increase above about 104° F the risk of heat injury rises significantly and organ function begins to deteriorate. Organs most susceptible to this deterioration include the central nervous system, the kidneys, the heart, and the body’s regulatory system. Regulatory failure can occur early in the course of heat illness, accelerating the severity of the heat illness. As core body temperature increases there is a progression of heat injury from mild to severe. Although many casualties develop mild symptoms first, there can also be a rapid progression to severe illness and sometimes severe cases present without reporting mild symptoms at all. However, there is no doubt that when mild cases occur, if there is no change to the environmental conditions and no means to mitigate this heat burden, they will progress to severe heat casualties.

Consider what happens to your crew when operating on the surface in heavy seas, often resulting in significant numbers of personnel sidelined by seasickness. Then think seasickness on steroids; and it gets worse. Heat illness would similarly result in crew becoming severely dehydrated and the provision of plentiful fluid replacement becomes critical. More than one severe heat injury requiring intravenous fluids would essentially overload the system, as the medical department has very limited stocks of intravenous fluid for rehydration. When the demand outstrips the resources it becomes only a matter of time before the situation deteriorates.

Within roughly a few hours of working in greater than 120° F heat a significant portion of the crew will show clinical signs of heat exhaustion (moist skin, heavy sweating, fast heartbeat, weakness, light headedness, dizziness, nausea/vomiting, headache, thirst and irritability) (see Fig 1). Physical and mental performance deteriorates, tasks are performed slowly, reaction times are reduced, decision times increase, errors of omission are more common; attention to detail, concentration and short term memory are degraded. Physical exertion in this environment exacerbates the problem by generating heat from muscle metabolism and can result in exertive heat illness with similar symptoms to heat exhaustion. Studies in Israeli helicopter pilots 2 have shown there is an increase in errors associated with increased thermal load. Laboratory experiments have confirmed the effect of heat on physical and mental performance. In large part this is probably due to the high degree of discomfort and hence distraction in a hot environment.

With additional heat exposure the symptoms can progress to heat stroke (confusion, fainting, and seizures). The end result is multiple organ failure followed by death without heroic reduction in core body temperature. Passive measures for heat reduction (drinking fluids, cooling mists, rest) are not effective once heat stroke has set in. Aggressive intensive measures must be taken at this point which include cooled IV fluids, intra-abdominal cooling baths, ventilator support, and dialysis…all measures not available on an underway submarine. Normal rehydration and cooling are typically not sufficient to manage heat stroke; these patients require emergent hospitalization and treatment in an intensive care unit, capabilities not available on a submarine. It is this type of heat injury which ultimately defines the actions by the Command- ing Officer. Actions must be taken well in advance of the symptomatic heat casualty in order to avoid heat stroke, as the only practical management strategy for heat stroke underway is prevention and avoidance. A case of heat stroke on an underway submarine will be uniformly lethal.

What Can You Do?

With any loss of AC, a contingency plan should be immediate- ly activated, just as we would with our DoD active shooter action plans. The loss of AC should trigger a shipboard wide announce- ment that AC is lost, activities such as exercise should stop, and efforts to rest encouraged. Command leadership should begin to estimate the time AC will be lost. If no estimate can be made, or the time to restoration of AC is on the order of hours, then an immediate SITREP needs to be sent. As soon as it becomes clear that AC cannot be restored within hours then a request for assistance needs to be sent. In a serious loss of AC accident the responses available to you are limited: minimize heat exposure (place your crew in the coolest areas available), remove excess clothing, limit activity, provide rehydration and, if possible, provide further cooling such as cooled vests (e.g., if refrigeration plants are still available, filling plastic bags with ice or frozen stores and stuffing them inside clothing would provide some necessary cooling for crew who must continue to work to resolve the casualty). Some ships have provided saltwater cool-down showers using seawater vents. However, once the AC has failed there will inevitably be heat casualties. Rapid recognition and response will be essential. References exist for the management of heat illness, but the majority of these focus on prevention and safe exposure limits. Exposure limits essentially become irrelevant in the event of a loss of AC.

Minor and major heat illnesses overlap; hence symptoms of relatively minor heat illness such as heat cramps, exertional heat illness and heat exhaustion can be common to or the harbinger of more serious illnesses such as heat stroke. Heat injuries tend to occur in clusters. One case of heat exhaustion is often quickly followed by others, and if left untreated often progress to more serious heat stroke. In a sustained loss of AC accident heat illness is likely to cascade, so waiting for the first casualty to occur will most likely lead to multiple heat injuries, as HMS TURBULENT found. Heat injuries are likely to occur first in those rates with a higher thermal load such as engineers or culinary specialists. Your Corpsman and his Emergency Medical Assistance Team (EMAT) will be heavily involved in stabilizing the casualties and will themselves be subject to significant heat stress. Medical supplies will be rapidly depleted in a sustained loss of AC and the Corpsman may also succumb to a heat casualty. Action plans should account for these issues.

Preparing for a Loss of AC

Practically speaking, this is not a casualty for which you can drill. It is, however, a casualty that lends itself to a serious tabletop exercise where key players sit around the wardroom table and discuss the casualty progression, learn the warning signs of heat illness, and fix in their minds the key decision points and the actions they might take or recommend. Your Corpsman and his EMAT are key players here, and their inputs would be enlighten- ing. The principles learned from this type of exercise apply equally well to any mass medical casualty, and are well worth the training investment.

A Command Perspective Should Type Commanders prepare a contingency plan for this situation and exercise the plan regularly? Should they identify the resources that would be required to assist a stricken submarine and how these supplies are delivered to a submarine at sea in sufficient quantity within time? What might those supplies be and where will they come from? Who will provide medical support? Would specially trained teams such as the USAF Parachute Jumpers or UK Submarine Parachute Assistance Group (SPAG) be mobilized to provide support? Where is the nearest appropriate medical facility? Will the crew be capable of sailing the boat to port or will they require additional personnel to help stabilize the situation and recover normal operation?


Loss of AC sounds serious, and it is. If you suffer a loss of air conditioning casualty and are not certain you can restore air conditioning within 1-2 hours, you should seriously consider advising your operational commander and requesting assistance. Provide as much time as possible for command staff to locate nearby assistance and start the cavalry enroute. Heat stroke as part of a mass casualty is a serious medical emergency requiring immediate hospital-level assistance. Heed CDR Ramsey’s warning. Don’t delay until you are past the tipping point to request help.

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