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## Equations against hypothermia

01.09.2004

Sharks are, by tradition, the eternal threat facing divers. Yet, a diver is quite a lot more unlikely to meet such a creature under the water than, at some time or another, to come up against an even greater danger – hypothermia, or exposure. To enable divers to prevent this syndrome from creeping silently up on them, two researchers from the Area of Applied Physics at the University Jaume I (Spain) have formulated an equation that enables divers to calculate the time they can safely remain submerged in the water at a certain temperature before the onset of exposure.

Taking into account parameters such as the initial body temperature, the rate at which body heat is produced, the temperature of the water and the thickness of the diving suit, among others, the formula provides an estimated value for the amount of time it will take the diver to reach a level of heat loss that is critical for his or her survival. If the mean temperature of the human body is 37 ºC, exposure comes about when the temperature drops below 35 ºC, and collapse and death can occur when it reaches 30 ºC.

“The exchange of energy between the diver and the water is less relevant when we are dealing with the physics of scuba diving because the limited supply of air in the bottles means that dives usually last less than an hour. It is, however, important in breath-hold or apnea diving, where divers are often underwater for over three hours,” explains Marcelo Aguilella Arzo, one of the authors, in a paper published in the American Journal of Physics.

Water makes the body temperature drop up to 26 times faster than air at the same temperature. Thus, according to the equation developed by the researchers at the University Jaume I, without the protection afforded by a suit a diver submerged in water at 15 ºC will be able to remain underwater less than an hour before beginning to feel the effects of exposure. On the other hand, if the diver is wearing a 3-millimetre thick neoprene suit this figure rises to four hours.

Hugo Cerdà | alfa
Further information:
http://www.uji.es

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