Staying Warm: Protection From Cold Water Immersion and Cold Shock

Turquoise Lake, Lake Clark National Park

Turquoise Lake, Lake Clark National Park, Alaska - notice how the incoming streams meander as they deposit sediments. The net effect is that the lake fills with sediment along a nearly straight line.

When participating in water sports, hypothermia from immersion in cold water is a frequent issue. When should one wear a wet or dry suit when paddling in cold water? On warm days paddling over cold waters dressing for the water is uncomfortable. What are the tradeoffs of wearing a wetsuit or drysuit rather than ordinary clothing in cold water? If one doesn't have a wetsuit, will clothing provide some protection? or is it better to enhance mobility to facilitate self rescue? Is hypothermia the greatest danger or cold shock?

Experiments on subjects immersed in cold water indicates that wet clothing does act to extend survival and functional time. By functional time I mean the time period where one has a chance to self rescue. Survival time is generally longer when you don't move in the water, so if waiting for a rescue try to reduce the surface area of the body (draw up the knees), keep the head out of the water, and don't move. If you like to travel to remote areas, often solo, as I do then self rescue is usually the only alternative to death & keeping still accomplishes nothing.

Figure 1. Benefits of wetsuit and wet clothing on immersion in freezing water relative to unclothed body.

Figure 1 simulates the rate of heat loss in freezing water in relation to heat loss from a naked body as a function of layer thickness for normal clothing and for a wet or dry suit. The calculation agrees with experimental research. Putting on warm clothing prior to a long crossing when kayaking or canoeing is far superior to no clothing, but inferior to a wet or dry suit. Even a thin wetsuit or a drysuit with little clothing underneath is more effective than wet clothing. In order to be as effective as shown in the figure, the clothing must be tightly fitting and dense to reduce water flow inside the clothing. Outer garments should be cinched tight to reduce water movement. Note that this is the type of clothing that does not optimize warmth for weight when outside the water.

Typically high loft materials with a wind proof shell outside are the most warmth for the weight in air. When worn under a drysuit they may compress during immersion and lose most of their loft. Loose fitting layers will also not trap stagnant water effectively during immersion.  Tightly fitting, densely woven fabrics make sense during immersion (and for protection from abrasion and contusions is accidents) but do not provide the warmth for the weight of lightweight down clothing during ideal conditions.

As in dry conditions, it is important that the entire body be covered.

Keatinge and Evans (Q J Exp Physiol Cogn Med Sci 1961;46;83-94 also measured the effects of sudden exposure to cold water. This is of interest because it is thought that many cold water deaths in kayaks come as the subjects take water into the lungs upon first becoming immersed - cold shock. Keatinge and Evans found a rapid increase in heart rate and breathing when the skin temperature was rapidly lowered by sudden immersion in cold water. The response was too rapid for the core temperature to cool, so this is triggered by cooling of the skin, not by hypothermia. Two of their observations are of interest:  a) clothed subjects were less susceptible to cold shock and b) eight immersions over a period of two weeks lowered the cold shock response of test subjects. The common sense interpretation is that subjects are less susceptible to a panic attack in cold water when they are used to being exposed to the cold water. Clothing probably helps by blunting the initial shock of the cold water. Being fully clothed when boating thus helps with both cold shock and temperature loss and is clearly better than no protection. Preparing for potential cold shock situations with exercises of quickly dousing the face in cold water under safe conditions seems to also make sense given the ability of the body to acclimate.

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