H.2.0.1 Introduction

Over the last decades scientific knowledge about immersion in cold water has increased significantly. This has led to modifications and significant technological progress in sea survival material and procedures (1). Abandoning a ship in distress is followed by a potentially prolonged period of using rescue equipment, primarily lifejackets, immersion suits, life rafts or small boats. Once people are on these platforms the hazardous situation is not really resolved, merely altered. Unprotected cold water immersion below 15°C is life threatening from the start. Floating devices and protective garments are crucial. However, all items of protective equipment must fit together and perform effectively as an “integrated survival system” (2). Getting wet inside an immersion suit reduces the chances for survival significantly. Sitting wet inside a life raft without a vaporisation barrier has the same effect.

Survival at sea is not only a matter of material and procedures; it is also a matter of leadership, discipline and determination.

H.2.0.2 Equipment

Lifejackets and Flotation devices

Professional seafarers usually use lifejackets, whereas flotation devices or buoyancy aids have their domain in recreational use.

The key issues of lifejacket designs are (3, 4):

 -       Requirement for self-righting.

-        Integrated spray-hood and light.

-        Compatibility with immersion suits.

-        Inclusion of a life-jacket retention system (e.g. crotch strap)

-        Easy donning for optimal user compliance.

Any lifejacket or flotation device must bring the wearer back to the surface immediately in order to prevent drowning. Back on the surface, it must ensure the airway is kept clear of the water and the body is supported at the surface, preferably at an angle of about 45 °. This should be achieved with as little effort required from the wearer and as much stability and self-righting capability as possible.  A retention system will prevent riding up with wear and drowning inside the lifejacket when unconscious in a rough sea (4).

Continuous education on the use of survival systems is mandatory for best performance in a real sea-survival scenario.

Immersion Suits

Over the last 25 years improvements in fabrics, insulating material, waterproof zippers and introduction of the spray-hood have led to much more reliable suit design. This was initiated by the International Maritime Organisation (IMO) immersion suit standards, the offshore oil industry demands for better quality and international military-commercial developments, such as submarine escape with the requirement for immersion suits with surface survival times of 24 hours under the worst environmental conditions. A common problem is the incompatibility between clothes or survival suits and lifejackets resulting in the inability of lifejackets to self-right immersed persons wearing high buoyancy suits. The best solution is an integrated immersion suit that includes the lifejacket as part of the system (2).

Importance of Dry Immersion Suits

As the name implies, “dry” immersion suits attempt to keep the area under the suit dry using watertight neck and wrist seals and zips. If normal clothing is worn under such suits to provide insulation, as is often the case, water leakage into the suit can significantly  reduce the overall level of insulation provided (as can sweat and urine), especially if such leakage is around the torso (5).

A fully functioning dry suit can significantly delay the long-term effects of hypothermia. The key issues of good dry suit design are:

-        Reliable neck and wrist seals by continuous rubber collar.

-        Easy entry, single-handled with perfect sealing zip closure.

-        Fitting neoprene gloves and correctly sized rubber wellington boots.


H.2.0.3 Physiology of Immersion

Sudden and prolonged cold water immersion situations correspond with distinct physiological stages. Death may occur from any one of the four stages of immersion (1):

Stage 1. The first 3 minutes - initial immersion responses (“cold shock”) (6).

Stage 2. The first half hour - short-term immersion (swimming failure).

Stage 3. 30 minutes plus - long-term immersion (hypothermia).

Stage 4. End of immersion (just before, during or immediately flowing rescue) (7).

Cold shock and swimming failure are the leading causes of death due to drowning during immersion, especially in accidental situations without appropriate sea-survival personal protective equipment (PPE). The cold shock response peaks in water below 15 °C and is greater the faster skin temperature falls and the larger the surface area of skin exposed to cooling.

Stage 1 – Cold Shock

The cold shock response on initial immersion in cold water includes a large uncontrollable inspiratory gasp followed by a period of severe hyperventilation. There is an increase in heart rate and blood pressure, and release of the stress hormones. These cardiovascular responses, especially if combined with face wetting and breath holding, can produce significant cardiac arrhythmias (8).

Death from cold shock by drowning or heart failure in the first three minutes of immersion is common. The inability to breath hold on initial immersion is probably the most dangerous response associated with immersion in cold water, acting as it does as the precursor to drowning, even when only periodically submerged by waves. With repeated cold water immersion most people will be able to reduce the cold shock response and increase their ability to breath hold.

Stage 2 – Swimming Failure

The period between three and thirty minutes after immersion is characterized by cooling of the peripheral nerves and muscle, whilst deep body temperature remains above hypothermic levels (35 °C).

Early swimming failure is related to ineffective swimming due to a mismatch between severe hyperventilation and swimming strokes and the inability to co-ordinate the two. This increases the risk of water aspiration and drowning (10). Delayed swimming failure is the result of neuromuscular incapacitation. Cooling reduces the transmission and contractility of the nerves muscles of the upper and lower limbs. Below 30°C tissue temperature in the extremities, peripheral blood flow reduces, oxygen delivery falls and nerves and muscles become dysfunctional. A muscle temperature of 28°C results in physical incapacitation (11).

An associated problem is the concurrent impact on manual dexterity and strength in the first 10 – 20 minutes of immersion in cold water. This results in an inability to carry out self-rescue procedures, such as activation or use of rescue gear or even climbing into a life raft (1).

Without a flotation device, or a correctly donned lifejacket, death by drowning will occur. Swimming failure is one reason why standards for correctly wearing lifejackets must not be neglected when operating in cold water seas.

Stage 3 - Hypothermia

The conductivity of water is 25 times that of air and humans cool about 4-5 times faster in water than air at the same temperature (1). Hypothermia is defined as a deep temperature below 35 °C and this is unlikely to occur in an adult in less than 30 minutes (1). As the skin and deep body tissues cool, light shivering is replaced by intermittent and then continuous heavy shivering. If the maximum heat production from shivering, about 1300 W, is less than the rate of heat loss, cooling will continue and unconsciousness will occur at a deep body temperature between 33-30 °C. Unless a properly functioning lifejacket is worn, drowning occurs at this time. Cardiac arrest occurs around a deep body temperature of 28 - 25°C, although this temperature varies significantly between individuals and conditions (1).

A number of environmental, individual and intra-individual factors affect the rate at which hypothermia develops:

  • Temperature gradient between the deep body tissue, skin and environment.
  • Waves, spray and wind-chill factor.
  • Insulation provided by clothing.
  • Use of a lifejacket with retention system, spray-hood and light.
  • The ability to produce heat by shivering.
  • Ratio of body mass to surface area.
  • Physical fitness and compromising health problems.
  • Subcutaneous fat layer.
  • Posture and activity in the water.
  • Mental state and coping strategies.

Because of the variations between individuals and conditions, it is difficult to predict survival time from hypothermia (1). Again, a crucial factor is whether the person is wearing a lifejacket that keeps the airways clear of the water and protects them from waves when severely impaired or unconscious.

The main cause of death after immersion is drowning, not hypothermia. Rescue-operations are often long lasting, and the survival time can be 24 hours or more under perfect conditions with a good lifejacket, spray-hood and survival suit, even in very cold water (1).

Stage 4 – Post rescue collapse

The rescue process has particular risks just before, during or immediately following removal from the water (7). At the time of rescue, the immersed person is likely to be suffering from one or more of the following threatening conditions:

  • Reduced blood volume.
  • Cardiovascular functional impairments.
  • Other trauma.

Physiological changes in head-out immersion are primarily the result of a reduction of the influence of gravity, together with the hydrostatic pressure. The most important of these changes are those that influence the cardiovascular system and blood volume, namely:

  • enhancement of diastolic filling, cardiac output and venous return,
  • immersion diuresis by central blood pooling
  • cold-induced diuresis.

General cooling of the body induces relative hypovolaemia through fluid shifts into the tissues and diuresis.

“Post-rescue collapse” is a physiological effect of removal from the water and is a consequence of postural hypotension. Following a prolonged period of immersion, rescue from the water removes the hydrostatic assistance to circulatory function at the same time as re-introducing full effect of gravity on the body (7). The circulatory system now becomes functionally hypovolemic. In a vertical posture gravity tends to induce a redistribution of blood, with venous pooling away from the heart and brain. The resulting reduction in blood returning to the heart will affect cardiac output and, if not corrected, the person will faint as the blood supply to the brain falls. Cooling impairs the usual baroreceptor reflex, and physiological adjustments to falling blood pressure fail to occur. Transition from water to air during rescue is likely to be less traumatic if casualties are lifted horizontally. Survivors whose airways are not under threat of aspiration, and who need to be lifted a significant distance, for example into a helicopter or high-sided ship, should be rescued with care, preferably horizontally, and handled as if they were critically ill. However survivors still in the water and whose airways are not protected should be rescued as quickly as possible by whatever means are available (1, 7).

On board the rescue craft, the rescued person should be placed in the optimum position to offset any potential problem in maintaining blood pressure. In a fast rescue craft, it is desirable to lay the casualty in a feet-forward, head-aft attitude (7).

The major aim of immediate management at the rescue site is to ensure that the airway is clear and assisted ventilation is provided if required. The most important cause of post-immersion death is hypoxia (drowning) secondary to the aspiration of water and vomit and drowning victims should receive oxygen as soon as a clear airway is established. All drowning and/or accidental hypothermic survivors should receive medical attention as soon as possible.

Survival Time: drowning while floating

It should be clear form the above that drowning rather than hypothermia is the primary concern associated with immersion in cold water. The physiological pathways to drowning (12) include cold shock, physical incapacitation and hypothermia-induced incapacitation or unconsciousness when no lifejacket or an ineffective lifejacket is worn. It should be emphasised that a lifejacket should not be consider suitable for long-term survival in a seaway unless it includes: sufficient buoyancy; a retention system; a spray-hood to protect the airway when incapacitated and turned to face the oncoming waves by the legs acting as sea-anchors; and a light (1, 3, 4). A fully functioning lifejacket significantly extends survival time in cold water by preventing the occurrence of drowning with cooling-induced incapacitation/unconsciousness.


Management of Drowning

Detailed treatment protocols for drowning and hypothermia are beyond the scope of this chapter, additional information can be found in other publications (13, 14, 15) and the International Medical Guide for Ships or national equivalent.

As the majority of fatalities from immersion in cold water occur in stages 1 and 2 above, before severe hypothermia has had time to develop, sea-survival equipment and strategies must focus on the short term incapacitating effects and on protection from drowning.

The primary aim of the initial treatment of drowning is to interrupt the drowning process by the provision of oxygen. The treatment delivered at the prehospital stage gives the majority of the survival benefit. Ventricular fibrillation in drowning is relatively rare (<10%), so incorporation of an automated external defibrillator in initial minutes of treatment should not interfere with oxygenation and ventilation

Significant gastro-intestinal ingestion of seawater and subsequent repetitive vomiting is frequent on rescue. Aspiration of vomit enhances drowning-related lung lesions, making the clinical situation worse.

H.2.0.4 Management of Hypothermia

Cold survivors must be protected from further heat loss, in particular evaporative heat loss and heat loss through forced convection. Wrapping in blankets with an outer covering of heavy duty plastic will achieve this. Re-warming regimes must start as soon as possible.

The “After drop” Phenomenon

This refers to a further drop of deep body temperature following rescue. There is no good evidence about its importance but it is seen with the regular measurement of deep body temperature via the rectum (7). In the case of a sudden and dramatic deterioration following rescue, other causes should be considered first, including the effects of drowning, post-rescue collapse, cardiac problems, internal haemorrhage or re-warming collapse due to excessively rapid re-warming (7).

Rewarming on board

Unless immediate electrolyte and blood gas measurements are available, great caution should be shown in trying to re-warm patients rapidly. Major changes are likely to have occurred during immersion. Re-warming should only ever be attempted with persons lying down at rest. Allowing hypothermic patients to stand, sit, or exert themselves makes them liable to post-rescue collapse. Excessive heating of the skin can cause re-warming collapse.

Fully Conscious and Stable Survivors

Survivors who are cold, shivering, but otherwise well and conscious can be re-warmed by immersing the torso and limbs in a bath at 38-40°C. Continuous supervision is mandatory. Water temperature must be measured using an accurate thermometer, and maintained carefully during re-warming. Once the deep body temperature is rising and has reached about 36.5°C, and before they start to feel hot or start to sweat, they should carefully get out of the bath. Care is needed as an erect posture may again cause circulatory collapse with syncope, due to peripheral vasodilation. Drinking of hot, sweet fluids may be helpful. Alcohol must be avoided.

Severe Hypothermia

Without any dedicated equipment for active re-warming, most hypothermic patients should be insulated and rewarmed slowly and passively in a warm, but not hot, room. Frequent monitoring of their vital signs is essential. Rapid evacuation to a specialist centre is critical. Full care, including life support and symptomatic management, should be continued until they can be carefully evacuated.


H.2.1 Abandoning Ship


H.2.1.1 Hazards

Immersion after abandoning ship is associated with many other hazards besides cold and drowning. Acute dangers to the individuals in the water include entanglement or traumatic contact with structures from the sinking ship, suction, inhalation and contamination with fuel oil, trauma from surfacing buoyant objects from the sinking ship and underwater explosions.

Protection from the hazards of the environment should have highest priority and, as survival is likely even after some days without water and some weeks without food, water supply should have a far higher priority than nutrition. In water temperatures below 15°C crew must abandon ship wearing cold water immersion suits in addition to modern inflatable lifejackets, even if they are kept initially safe in boats or life rafts. Every effort should be made to board the life raft dry if possible (1).

Avoid contact with surface fuel oil as far as possible. Direct contact is not inherently dangerous due to its negligible systemic toxicity. However, if swallowed it may cause vomiting, if inhaled it may produce pneumonia and if brought into the eyes it will produce conjunctivitis.

Burning oil at the sea’s surface is also a hazard. If a person has to jump from the ship into burning oil they may be able to avoid being burned if they remove their lifejacket and cumbersome clothing and        jump feet first through the flames.

H.2.1.2 Survival in Life Rafts

Long term survival in life rafts is a specific problem characterized primarily by a cold, wet environment or extreme heat and insufficient potable water and, to a lesser degree, food. Maintaining the discipline and morale of the survivors inside a life raft is of utmost importance.

Disturbances of fluid and energy balance are closely related. They may affect performance, health, discipline, morale and survival. Modern communications and location devices make it rather unlikely that survivors will spend the time needed to develop nutritional deficiencies in a life raft. Thus, supply and conservation of water is crucial (1).

Cold – Thermal Insulation

Thermal insulation in a life raft is the highest priority. Free water inside a life raft reduces the insulation significantly and seafarers must take all measures, from the very beginning, to control any ingression of water. A common source of water is partially inflated buoyancy tubes that lead to waves breaking inboard at the open windward entrance.

Sitting positions on the life raft floor contribute to conductive heat transfer. Any free fluids sloshing around the floor will aggravate this, for example, leaking water, condensation, vomit, urine. Fluids will accumulate in the depressions of the inflated floor created by the sitting occupants. Additional blankets are beneficial. If the risk of capsize is small it is recommended that lifejackets are removed inside the life raft and used as insulating cushioned seats instead (1).

Occupants in wet clothing should remove the outer layers, squeeze them dry, and put them back on. The manoeuvre will cost little body heat and will not affect heat balance over the long period.

Heat given off by the occupants will warm up the environment within the life raft reasonably quickly if good sealing of the openings is maintained. Any dry clothing, preferably wind stoppers, capes and head coverings will reduce heat loss. This will lead to prolonged periods without shivering. During shivering, energy (food) demands and discomfort will increase significantly. Unfortunately, good sealing of the life raft is difficult to maintain over time (1).      Water

Dehydration in excess of about 5% body weight may be associated with headache, irritability, and feelings of light-headedness. With losses of 10%, performance declines significantly. Further losses lead to hallucinations and delirium. Death usually occurs with acute losses of 15 to 20% of body weight. In a marine environment this occurs in 6 to 7 days (1).

For the average resting adult, recommended minimum daily requirement for fluid is 1 litre. In a survival situation this may be reduced to a daily in take of 150 to 450 mL of water for a limited 5-6 days period. Survival packs in life rafts contain a water supply of half a litre for a 5 day period per person. Water balance can be maintained best on a diet that is rich in fat and carbohydrate but low in protein (1).

Survivors can reduce water requirements by minimizing energy expenditure and water losses. Methods to achieve this include (1):

  • No drinking at all in the first 24 hours, except the injured.
  • Never drinking seawater.
  • Never mixing seawater with fresh water.
  • Minimizing activity.
  • Resting during the heat of the day.
  • Optimizing the use of shade and breeze.

The life raft survivor should take anti-seasickness medication to reduce fluid loss by vomiting. This should commence as soon as possible, either before or immediately on entering the life raft.

Alternative safe means of acquiring water should be considered early and include the collection    of rain or condensation water. Rain is often the only source of water replenishment available to the survivor at sea. It is a safe source but the initial wetting must not be collected as it will contain salt crystals from the collecting awning or canopy. Other safe alternatives are reverse-osmosis pumps and solar stills, if available, squeezed extracellular fish fluid (lymph) and spinal fluid or turtle blood.

Seawater is never a safe alternative. Deaths in life rafts following the drinking of seawater seem to be the result of rapid onset of respiratory failure, mostly preceded by mental derangement. Delirium leads to apparent insanity, aggressiveness, risk of suicidal actions and death. Usually there are no typical signs of dehydration. There is no beneficial effect in mixing fresh water with seawater. On the contrary, it will lead to the same catastrophic events (1).


Death from starvation takes 40 to 60 days and a lack of food is usually not the main problem in survival at sea. If sufficiently hydrated, physical and mental capabilities will be stable until more than 10% of bodyweight is lost. Furthermore, the absence of vitamins, minerals, or trace elements is unlikely to pose a problem to life raft survivors at sea for less than two months.

For the average resting adult, daily energy expenditure and therefore energy requirement is 1400 kilocalories. In a survival situation this daily requirement may be reduced to an intake of 600 kilocalories for a limited period. For the prevention of catabolism and dehydration, the food taken should be in the form of carbohydrate. This means avoiding eating protein unless fresh water is freely available. Fat reserves are plentiful, but glucose is required to enable the metabolism of fat. Protein reserves are also reasonably plentiful and can be used to provide the glucose to enable fat metabolism, but muscle wasting and protein deficiency disorders will quickly follow. A minimal daily intake of carbohydrate will help offset this. Food packs in life rafts are assembled accordingly (1).

Morale and Discipline

The prospects of survival in this sort of incident increase significantly if survivors manage to react calmly, appropriately and effectively. An assortment of physical and psychological ailments in combination with other stressors can erode morale and decrease survival at sea (1).

A leading person who is acting as the senior survivor in the life raft should set a good example, guide others, and contribute to a positive mental attitude until final rescue. A Ship’s doctor is one of the trusted persons to do this job.  Important rules for raising morale and discipline are:

  • Never abandon hope for rescue.
  • Keep comradeship at a high level.
  • Provide every survivor with special tasks.
  • Avoid brooding.
  • Monitor each other for suicidal actions.
  • Set a good example for others.


  1. Golden FStC & Tipton MJ (2002) The Essentials of Sea Survival. Human Kinetics, Illinois.
  2. Tipton MJ (1993) The concept of an "Integrated Survival System" for protection against the responses associated with immersion in cold water. Journal of the Royal Naval Medical Service 79: 11-14.
  3. Pointer K, Milligan GS, Garratt KL, Clark SP & Tipton MJ (2018) A 10-year retrospective analysis to determine whether wearing a lifejacket would have prevented death by drowning in the United Kingdom: An analysis of Maritime and Coastguard data. Safety Science. 109: 195-200. https://doi.org/10.1016/j.ssci.2018.06.003.
  4. Lunt H, White D, Long G & Tipton M (2014) Wearing a crotch strap on a correctly fitted lifejacket improves lifejacket performance. Ergonomics. 2014 May 1:1-9. [Epub ahead of print.
  5. Tipton MJ & Balmi PJ (1996) The effect of water leakage on the protection provided by immersion protective clothing worn by man. European Journal of Applied Physiology 72: 394-400.
  6. Tipton MJ (1989) The initial responses to cold-water immersion in man. Editorial Review, Clinical Science 77: 581-588.
  7. Golden FStC, Hervey GR. & Tipton MJ (1991) Circum-Rescue Collapse: collapse, sometimes fatal, associated with rescue of immersion victims. Journal of the Royal Navy Medical Service 77, 139-149.
  8. Tipton, M. J., Franks, C. M., Gennser, M. & Golden, F. St. C. (1999) Immersion death and deterioration in swimming performance in cold water. The Lancet Vol 354 (Fast track) 21 Aug: 626-9.
  9. Schmidt AC, Sempsrott,JR, Hawkins SC, Arastu AS, Cushing TA, Auerbach PS (2016) Wilderness Medical Society practice guidelines wilderness medical society practice guidelines for the prevention and treatment of drowning. Wilderness & Environmental medicine, 27, 236–251.