Thirst

Can shipwrecked men survive if they drink sea water?

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survival equipment
Many airline companies provide desalting kits as part of survival equipment with rubber rafts carried by commercial planes.
survival equipment
The kit consists of cakes of silver aluminum silicate and a plastic processing bag.
survival equipment
The processing bag is filled with sea water and the cake dropped in.
survival equipment
It is then kneaded gently for an hour to grind up the cake.
survival equipment
Desalted water is drawn off from a filter in the bottom of the bag.
American Museum of Natural History

The accuracy of Adolph’s predictions has been borne out several times in actual survival incidents. An extensive study of shipwreck survivors during World War II showed that the maximum time without water recorded by any survivor was eleven days—just one day longer than the prediction.

Adolph also demonstrated that, as the body becomes increasingly deficient in water, certain symptoms follow in order. The degree of dehydration was rated by measuring the per cent loss of body weight. At the beginning of dehydration there is thirst and discomfort. Succeeding symptoms, in order, are lassitude, loss of appetite, sleepiness, rise in body temperature and, at about 5 per cent dehydration, nausea. At from 6 to 10 per cent dehydration, the victim will experience dizziness, headache, tingling in the limbs, dry mouth, difficulty in speaking, and inability to walk. At more than 10 per cent dehydration, delirium is common, and the senses fail. Dehydration of 25 per cent is probably fatal at any temperature. At air temperatures above 90 degrees F., 15 per cent dehydration is the theoretical fatal limit.

Yet records of shipwreck survivors show that very few die of dehydration alone. MacDonald Critchley, a British physician who made an extensive study of the factors affecting survival at sea, believes that as dehydration increases, the victim’s will to resist the desire to drink sea water weakens until finally he succumbs to the temptation and death is caused by the ingestion of sea water. Critchley says, “Sea water poisoning must be accounted, after cold, the commonest cause of death in shipwrecked sailors.”

Critchley tells what happens when a very dehydrated person drinks sea water. There is “immediate slaking, followed quite soon by an exacerbation of the thirst, which will require still more copious draughts. The victim then becomes silent and apathetic, with a peculiar fixed and glassy expression in the eyes. The condition of the lips, mouth, and tongue worsens, and a peculiarly offensive odour has been described in the breath. Within an hour or two, delirium sets in, quiet at first but later violent and unrestrained; consciousness is gradually lost; the color of the face changes and froth appears at the corners of the lips. Death may take place quietly: more often it is a noisy termination, and not infrequently the victim goes over the side in his delirium and is lost.”

Those who advocate the drinking of sea water argue that the effects so graphically described by Critehley do not follow when sea water is drunk by a man in water balance. They point out, moreover, that anyone who goes swimming in the sea swallows some sea water and that many castaways swallow substantial amounts of sea water before reaching the safety of a lifeboat or raft. The advocates of sea water maintain that by drinking small quantities of it immediately, a man can both slake his thirst and keep his body in water balance.

The question of whether or not a man can stop or avoid the sensation of thirst by drinking sea water is difficult to prove or disprove. In several experiments on drinking small quantities of sea water, the subjects have reported that they had no feeling of thirst. All these experiments took place in cool climates, and none of them ran for more than six days. In actual survival incidents under similar environmental conditions, survivors who had no water denied any feelings of thirst, and some who drank small amounts of sea water were thirsty.

Actually thirst is only a signal of the body’s need for water. Thirst is often satisfied while the body is still slightly dehydrated. This is especially true in cool climates. Tests made by the U.S. Army in cold climates show that if men drink only when they are thirsty, they stay in a continuously dehydrated state.

The sensation of thirst varies a great deal with individuals. A person’s description of how he feels changes with his psychological as well as his physiological condition, so the term “thirst” can be regarded as little more than an expression of personal opinion. However, the effect of drinking sea water on the body’s water balance can be computed and the computations verified by experiment. It is possible to determine by actual test how much sea water the body can tolerate, though for obvious reasons laboratory experiments cannot carry the study to a point where the subject’s life is actually endangered.

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