survival at sea
survival at sea
Immersion in cold waterRepresents one of the greatest stresses to which the human body can be exposed and has been recognized as such since the beginning of recorded history. Around 450 bc, Herodotus described the ill-fated seaborne expedition by the Persian General Mardonius; he wrote: ‘those who could not swim perished from that cause, others from the cold.’ Thus, Herodotus clearly distinguished between the inability to swim and cold, a distinction which remained forgotten for over two centuries, despite evidence from countless shipwrecks that airway protection alone did not guarantee survival. The most notable of these was the tragic loss of the Titanic on 14 April 1912. The 712 people who boarded lifeboats survived, while all of the 1489 who entered the water died in less than two hours. The sea they entered was calm but icy cold, all were wearing life-jackets, yet evidence was provided at the subsequent enquiry that all cries for help from those in the water quickly waned, and disappeared completely in under an hour. The circumstantial evidence all pointed towards cold as the precursor to death, but despite this the official inquiry gave drowning as the cause of death in every case. Again the opportunity to identify the importance of protection against cold for survivors at sea was missed.
It was not until the height of World War II that the threat of cold and the inadequacies of the lifesaving equipment being provided were correctly identified. Post-war work by Molnar in the in the US, and groups such as the Royal Navy Personnel Research Committee in the UK, consolidated this thinking. Currently, predicted 50% immersion survival times for normally clothed individuals are in the order of 6 hours at 15°C, 2 hours at 10°C, and 1 hour at 5°C.
Up until recently, the primary threat associated with immersion in cold water was thought to be hypothermia. This belief is still perpetuated by the press, manufacturers, in standards and specification, and in the findings of fatal accident inquiries. However, later research has further refined thinking, and there is now a significant body of evidence to implicate other physiological responses as the precursors to death in many immersion incidents. In 1981 Golden and Hervey identified four stages of immersion associated with particular risk; these are:
(i) Initial immersion (first 2 minutes):a large percentage of those who die on immersion do so within three metres of a safe refuge, and many are regarded as ‘good swimmers’. Such statistics suggest much quicker incapacitation than can occur with the protracted period of cooling necessary to produce hypothermia. We now know that rapid cooling of the skin on immersion in cold water initiates a set of undesirable respiratory and cardiac responses given the generic title of ‘cold shock’. The responses include a ‘gasp’ response, uncontrollable rapid breathing, an increase both in blood pressure and with work required of the heart. The inability to control respiration can result in drowning, and the cardiac responses can result in a stroke or heart attack in susceptible individuals. The magnitude of the response can be reduced by entering the water slowly, or by keeping as much of the body surface as dry and warm as possible. It also shows a high degree of habituation, being reduced by as much as 45% following just six 3-minute, immersions in cold water. This habituation appears to occur in the central nervous system and lasts for at least 7 months.
(ii) Short-term immersion (2–30 minutes):cooling in water results in a rapid loss of neuro-muscular function, which can produce significant decrements in muscular strength, dexterity, proprioception, and co-ordination. These alterations can impair swimming performance and other actions essential to survival during the early minutes of an immersion. Survival may therefore depend on the immersion casualty understanding this and undertaking essential survival actions as soon as possible following immersion or on boarding a life-raft. Legislators and designers of survival equipment should recognize these limitations in their safety standards and design criteria.
(iii) Long-term immersion (30 minutes plus):for the first time, falling deep body temperature becomes the primary hazard. Progressive hypothermia can cause: confusion, disorientation, introversion (35°C), amnesia (34°C), cardiac arrhythmias (33°C), clouding of consciousness (33–30°C), loss of consciousness (30°C), ventricular fibrillation (28°C), and death (25°C). The figures in parenthesis represent deep body temperatures, and should be regarded as only a very rough guide, as great variation exists between individuals. Depending on conditions, consciousnes can be lost some time before death; this emphasizes the importance of wearing a good life-jacket, which will support the airway clear of the water and prevent death by drowning at an early stage. Protection against hypothermia is provided primarily by immersion suits and liferafts. People cool 4–5 times faster in water than in air at the same temperature and, therefore, should get out of the water whenever possible.
(iv) Post-immersion:approximately 17% of immersion deaths occur during, or immediately following, rescue. Originally it was thought that the continued fall in deep body (rectal) temperature seen following immersion, the after drop, was responsible for these deaths. More recent work has suggested that they are more probably caused by the collapse of blood pressure when hypothermic casualties are removed from the water and re-exposed to the full effects of gravity. One practical way of reducing this effect is to remove casualties from the water in a horizontal rather than vertical posture; this helps to maintain venous return and cardiac output. These considerations apply equally to the rescue of survivors who have been adrift in life-saving craft for some time.
Survival in a life-saving craftAccounts of epic survival voyages are newsworthy and tend to be recounted in folklore or make media headlines, with descriptions ranging from heroic selfless behaviour to cannibalism. However, such accounts, involving dehydration and starvation, tend to obscure the more serious immediate thermal threat, which is frequently the major problem confronting survivors in such craft even in temperate waters. In thermoregulatory terms man is a tropical animal and, in order to survive outside a tropical environment, he must use clothing and shelter to prevent body cooling. In a survival at sea situation these are usually unavailable; the survivor is then at the mercy of the elements. As a result, in temperate and subarctic environments, death from a fall in body temperature (hypothermia) usually occurs long before dehydration or starvation come into consideration.
Longer-term non-thermal problems manifest themselves with time adrift. These include: motion sickness; dehydration; starvation; sunburn; salt-water ulcers. Of these, dehydration and starvation are worthy of special mention here, along with the importance of refraining from drinking sea water or eating protein (fish/seabirds) when drinking water is not freely available. The concentration of salt in body fluids is normally maintained at 0.9%. Any excess salt ingested is excreted by the kidneys in urine, and the maximum urinary salt concentration achievable is in the region of 2%. Sea water contains about 3.5% salt and, in the absence of copious amounts of fresh drinking water, the extra salt ingested can be excreted only at the expense of body fluids, thereby accelerating the onset of the deleterious effects of dehydration.
When starvation is present in a survival at sea situation, the body will catabolize its own muscle protein. The end product of this process is urea; a toxic substance which is excreted in urine by the kidneys. In the absence of drinking water, the excretion of urea can only be achieved at the expense of body water, thereby increasing dehydration. It follows that when water is scarce, protein consumption (fish/sea birds) will hasten death by dehydration. Survival rations of carbohydrates (sweets), or a mixture of carbohydrate and fat in fudge-like compounds, not only reduce this catabolism, but also provide additional water to the body as an end-product of their metabolism.
It is concluded that the four essential biological ingredients for survival in any environment are, in order of priority: (i) an adequate supply of breathable air; (ii) a tolerable ambient temperature; (iii) the provision of potable water; (iv) sufficient edible food.
In terms of survival at sea, these can be translated into: (i) protection against drowning; (ii) protection from temperature extremes, both in and out of water; (iii) protection from dehydration; (iv) amelioration of the longer effects of starvation.
When planning for surviving at sea one must identify, in order of priority, the physiological threats which are likely to be encountered, and the appropriate protective measures. The thermal threat must be given a high priority.
Michael J. Tipton, and Frank St. C. Golden
Adam, J. M. (1981). Hypothermia ashore and afloat. Proceedings of the Third International Action for Disaster Conference. Aberdeen University Press, Aberdeen.
Keatinge, W. R. (1978). Survival in cold water, (reprinted). Blackwell Scientific Publications.
Tipton, M. J. and and Golden, M. J. (1994). Immersion in cold water: effects on performance and safety. Chapter in Oxford Textbook of Sports Medicine (ed. M. Harries, C. Williams, W. D. Stanish, and L. J. Micheli). Oxford Medical Publications, Oxford.
See also cold exposure; drowning; hypothermia; near-drowning; protective clothing; starvation; water balance.