Sea Survival: Exposure: Hypothermia and Dehydration

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Hypothermia is one of the greatest immediate threats to the castaway in a survival situation. Hypothermia is a physiological condition caused by exposure that results in the lowering of the body’s core temperature. Acute or advanced hypothermia occurs when the body is losing more heat than it can generate. Extreme prolonged loss of body heat will result in acute hypothermia and eventually death.

Hypothermia and the Body

The body’s heating system is based upon what is known as the basal metabolic rate. This is a complex heat production system that maintains a balanced body temperature. The body’s heat production system responds to hypothermia by increasing the metabolic rate to compensate or counteract the large heat loss. The body’s initial defense, intense shivering, serves to generate and in crease the amount of heat in the body, but because it requires energy to shiver, it will eventually cause fatigue.

As exposure to cold continues, the body’s natural priority is to maintain a normal level of heat within the core of the body. The body’s defense systems automatically work to protect the temperature level of the inner core by sacrificing the extremities: hands, feet, legs, and arms. Numbness occurs in these areas as blood vessels close to the skin contract.

This contraction of blood vessels causes less blood to flow through those areas that are coldest. In this way, the amount of “cold” blood that will return to the inner core and threaten the vital organs is reduced. The head is a vital organ, and consequently there is no blood vessel constriction occurring to reduce the amount of blood going to the head. This is why the greatest amount of body heat loss during exposure is from the head.

Case studies have shown that persons who appear to be dead from hypothermia or drowning in cold water can sometimes be resuscitated successfully even after a considerable period without breathing and blood circulation sometimes for as long as 10 to 40 minutes. The primary reason for this is that body tissues require less oxygen when cold than when warm. Therefore, don’t give up! Maintain artificial ventilation and circulation on a hypothermic victim as long as possible.

Fig. 5-1 Survival time in cold water.


Figure 5-1 shows average predicted survival times of an adult in water of different temperatures.

The figures are based on data compiled at the University of Victoria. The scientists studied experimental cooling of average men and women who were holding still in ocean water and wearing a standard lifejacket and light clothing. The graph shows, for example, that predicted survival time is about 2½ to 3 hours in water of 50°F Fahrenheit (10°C).

Predicted survival time is increased by extra body fat and decreased by small body size. Although women usually possess slightly more fat than men, they often cool faster because of their generally smaller body size. Children cool much faster than adults because of smaller body mass and relatively little fat.

The warmest ocean waters near the equator reach temperatures of about 82 degrees Fahrenheit. Since a healthy body temperature stays around 98 degrees, pro longed immersion or exposure to water that is cooler than 98 degrees can result in hypothermia. This of course will depend upon the length of exposure, but it should be understood that the hypothermic process will begin lowering your body temperature immediately.

Table 5-1, compiled by NOAA (National Oceanic and Atmospheric Administration), indicates how the approximate survival time of human beings in the sea is directly related to sea surface temperatures.

Approximate survival time in the sea related to sea temperature


The most effective safeguard against hypothermia is to understand what it is and how to prevent it. Although the possibility of hypothermia is obviously greater in cold climates, hypothermia can be a danger in any climate, no matter how amiable the air and water temperatures seem to be. Hypothermia can be a significant threat to survival, even in the tropics.


Heat loss will occur any time the body is in contact or exposed to lower temperatures. Prolonged contact of your body to the floor of a life raft while adrift in cold water, for example, can chill you by transferring your body heat outward through the floor of the raft. This is why a double floor or insulating material in a life raft is particularly important in colder climates.

Exposure to the wind will also accelerate hypothermia, as will the wearing of wet clothing, especially in cold climates. During immersion in cold water, clothing can help by serving to “trap” and keep the water warmed by your body, next to the skin. But once you are out of the water, do not wear wet clothing. Obviously, wet clothing is preferable to no clothing, but you should at least make an attempt to remove the clothes wring them out, and then put them on again.

Wet clothes are no longer an efficient insulator, and instead of trapping warm air next to the skin, they conduct body heat outwardly and away from the skin. Strenuous activity in cold climates can also result in sweat saturated clothing, which must be considered a threat and dealt with accordingly.


Shivering. Shivering is uncontrollable. Intense shivering follows in an attempt to increase the body’s heat production and counteract the large heat loss.

Loss of Awareness. Difficulty of speech, confusion of thought, and amnesia are all signs of loss of awareness.

Rigidity. Muscular rigidity replaces shivering. The person is semiconscious in appearance and the skin turns bluish and puffy.

Pulse Slows. The pulse in extremities is almost non existent. The pulse should be taken from the carotid (neck) artery.

Unconsciousness. Erratic heartbeat, lack of re flexes, and dilation of pupils are signs of unconsciousness. Unconsciousness can occur when the body’s “core” temperature falls from the normal 99°F (37 °C) to approximately 86°F (32°C). (Fig 5-2).

Relaxation. The victim experiences overall muscular relaxation and is similar in appearance to death.

Respiratory Control Failure.

Cardiac Failure. Heart failure is the usual cause of death when inner core temperature cools to intolerable levels.

Fig. 5-2 The graph indicates the relative length of survival for decreasing body temperatures.


In the advanced stage of hypothermia, the body has lost its ability to re-warm itself. The natural treatment is to introduce or replace warmth back into the body. Caution must be used, however, as many standard techniques of introducing warmth are dangerous and may only aggravate the condition.

In the case of an unconscious survivor, for example, massage, exercise, or any stimulation of blood circulation will only serve to worsen the condition. Such actions hasten the flow of cold blood from the numb extremities to the heart, causing a further drop in body temperature.

The most effective treatment is to introduce warmth into the core of the body by warm or hot liquids, or warmed oxygen. This heating of the body from the inside out is the only safe way to counteract advanced hypothermia.

Because hot liquids or oxygen are rarely available in the survival raft, the following is a list of tips and techniques that may be effective in controlling hypothermia:

Terminate Exposure. If possible, remove the victim from the water. Dry off or wring out wet clothes immediately. Stay out of the wind. Close the canopy openings to retain body generated warmth. Huddle together or, if alone, curl up into a fetal position.

Body Contact (warmth). Body-to-body contact may be the only source of warmth available. Extreme caution must be exercised to ensure that the other survivors don’t become chilled and hypothermic in the process.

Hot Liquids. Hot liquids is a most effective treatment, but never give liquids to an unconscious person. If possible, administer a hot bath.

Forced Exercise. If the survivor is still conscious try to get him to move around a bit.

Allow No Alcohol. Consuming alcohol will cause the blood vessels to dilate. This will allow more blood to flow into the cold extremities, causing a quicker return of cold blood to the inner core of the body.

Rations. Allow the victim to eat extra rations, if available, specifically carbohydrates.

Allow No Smoking. The nicotine in cigarettes will cause the blood vessels to constrict, which will impede and reduce the flow of warmed blood to the colder areas, such as the hands and feet.


The treatment and prevention of hypothermia are very similar. Each situation dictates the degree to which you can be successful in counteracting hypothermia. The object is to maintain your body heat.

The balance of body heat is maintained by either the regulation of heat loss, or by the body’s production of heat. Heat production can be increased by food digestion or exercise, but both are limited measures. The most effective preventive measure is to reduce and regulate the amount of heat loss. Here are some tips to keep in mind:

• Understand the conditions that encourage hypothermia.

• Protect yourself to the best of your ability against cold, wind, and wetness.

• Pay particular attention to protecting your extremities: head, nose, ears, feet, and hands. Great amounts of body heat can be lost through these areas.

• Try to retain body heat by huddling, curling up, closing the canopy, etc.

• Drink hot liquids, whenever possible, to heat the body from the inside out.

• Exercise muscles. Rub your hands, stretch your feet, move your body around, and keep your blood circulating.

• Clothing, if dry, will insulate the body by creating a dead air space between your skin and the inner garment. A tightly fitting garment will reduce the size of the air pocket or dead air zone, which will consequently reduce the amount of warmth retained. Loose fitting clothing is better, but not so loose that it exposes your body to wind drafts.

• In cold climates, control your sweating when engaged in vigorous activity. Sweat saturated garments conduct heat away from your body and can further the hypothermic process.


If you are wearing a flotation device, less body heat will be lost by remaining still in the water rather than swimming or treading water. Curling up into a fetal position will increase your survival time.

Because about 50 percent of your body heat is lost from the head area, try to keep your head as far out of the water as possible and turn your back to the waves and wind. Covering your head with a hood will help conserve body heat.

If there are several people in the water, huddling close together can help preserve body heat (Fig. 5-3).

Fig. 5-3 Survivors should huddle close together to maintain body heat.


Guard against paradoxical cooling. This refers to the dangerous condition resulting when a survivor has been warmed by external methods. His skin’s surface may feel warm to the touch and he will tell you that he feels better, but in fact, his inner core temperature is still dropping dangerously.

It can often take hours to restore all of the lost body heat. Fatalities of this kind are particularly tragic, and result from neglect and a general misunderstanding of the hypothermic process. Hot liquids or warmed oxygen are the most effective treatment against paradoxical cooling.

Because dehydration is such a grave threat to the castaway, the mariner must have an ample supply of water and water collecting devices in his survival provisions. This is especially crucial in geographical areas where rain fall is scarce or seasonal.


• Lassitude and apathy

• Loss of appetite

• Drowsiness and sluggishness, headache

• Acute thirst, very dry mouth, cracked lips

• Slowness of speech

• Weakness of legs


The treatment for dehydration is simply to increase the intake of water until the process is reversed. Anyone suffering from dehydration should increase his water ration, if supplies permit.

Because water is often the most precious commodity in the survival situation, your rations may not be enough to reverse the acute stages of dehydration. It is vital to understand the dehydration process and learn what preventive actions can be taken to help slow down the process.


• When in conditions where dehydration may occur and water is available, drink as much water as possible.

• Unless there is an ample supply of water, avoid the intake of salt. Your body will regulate your level of salt by excreting the proper amount in your sweat. Excess salt will cause the loss of precious body fluids in the form of sweat.

• Do not smoke because it will increase your need for water.

• No alcohol. Alcohol will not fulfill your body’s need for water, and may result in vomiting, thus losing precious fluids.

• Minimize food intake, relative to the amount of water available. In situations where food is available, but water isn’t, you should avoid the intake of food. The digestion of food, and particularly carbohydrates, requires water. In fact, you would probably succumb to a lack of water long before you would die from starvation.

• In arctic areas, never eat snow directly. The body must expend energy and moisture to melt snow that you have eaten. You must melt the snow before consuming it.

• Ration your sweat. In situations where water is not avail able in any significant quantity, the only way to conserve what body fluids you do have is to control and minimize the amount that you perspire.

• In hot climates minimize your activities during the hot periods of the day. Rowing, working, and any strenuous activities should be saved for the cooler periods of the day or for night. The less sweat your body uses to cool itself, the more moisture your body will retain. Work at a slow pace if work is necessary during the day.

• Create some shade and remain under it as much as possible. Use a canopy, tarp, a hat, or even your clothes to construct a sun barrier.

• Wear protective clothing such as a long sleeve shirt, trousers, or a hat. This traps the perspiration and slows down its evaporation, which gives you the fullest cooling effect. This principle is illustrated in desert areas, for example, where desert tribesmen cover themselves completely.

• In warm areas where hypothermia is not an immediate threat, saturate your clothing with sea water. This will increase the cooling effect to some degree.

• Be prepared to recognize the imaginings and hallucinations that come with acute stages of dehydration. Castaways have been known to become irrational and delirious and drink anything in their desperate attempt to slake their thirst.

• Never under any circumstances drink urine or straight sea water! Both urine and seawater have an extremely heavy salt content. Body fluids must be used to flush the salt out of the kidneys, and this process speeds up the dehydration process considerably.

Note: Some castaways have successfully reported mixing seawater with their water stores in closely con trolled proportions (such as 1 part seawater to 2 parts fresh water). A noted marine researcher, Dr. Alain Bombard, purports to have survived for 65 days in a raft by mixing seawater with fresh water, as well as obtaining liquids from fish. However, this is a controversial issue, and most experts still advise castaways against the ingestion of seawater in any form whatsoever.

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