Diving and hypothermia.

Hypothermia is not and should not be a prevalent feature of diving, yet many divers become extremely cold and uncomfortable during their work. It is not difficult to provide adequate insulation to protect the torso but if movement and dexterity are to be maintained, the extremities will inevitably suffer. Free swimming divers are limited by duration in cold (5 degrees C), shallow (10 m) water. Six hours is a typical maximum before both core cooling and extremity pain or dysfunction pose a threat. Habituation to cold may be observed in some divers. Surface supplied or bell supported divers, relying on supplementary hot water, need between 500 and 3500 Watts to preserve comfort over the range 10 to 300 m depth. Deep diving, using oxyhelium gas mixtures, can result in high respiratory convective losses in excess of 300 Watts. Heat exchangers are used to prevent damage to the tract. There have been a number of cases where hypothermia has been implicated in the cause of death in diving accidents, but generally the reason is not lack of physiological knowledge but equipment failure and inadequate contingency. Recent developments in diver protection have focused on electrically heated hand wear to preserve performance and prevent the risk of non freezing injury in a relatively inactive diver.