23 Jan. 2007

Hypothermia safety

If your body’s core temperature falls below 96 degrees, it could signal hypothermia. A hypothermia victim may become bluish gray, shiver violently, develop muscle spasms and lose the use of arms and legs. Other signs are confusion and loss of coordination. Exposure to cold, wind or wetness can bring on the condition. Many boaters believe that it only happens in cold northern waters, but people have become hypothermic in 70-degree water if immersed for two hours or more. (See the hypothermia chart below.)


If the water temp (F) is…

Exhaustion or unconsciousness

Expected time of survival is…


Under 15 mins.

Under 15-45 mins.


15-30 mins.

30-90 mins.


30-60 mins.

1-3 hrs.


1-2 hrs.

1-6 hrs.


2-7 hrs.

2-40 hrs.


3-12 hrs.

3- Indefinitely

Over 80



When heading out on the water, avoid hypothermia by dressing warmly and staying dry. Put on rain gear before it rains, and wear wool, which traps body heat even when wet.

Also, know how wind affects cold weather. It may be 40 degrees and sunny, but a 10-mph wind could make it feel like 28 degrees.

Cold water survival also depends on other factors, including the victim’s body size, fat and activity level. Large or obese people cool more slowly than small or thin people, and children cool faster than adults.

Remember that water conducts heat much faster than air. Getting into or onto a boat or anything else that floats and moving as far out of the water as possible can save your life. Most boats will float even when capsized or swamped.

If you must remain in the water, keep your head—where about half your body heat escapes—above water. (Other areas of high heat loss are the neck, sides and groin.) Avoid the drownproofing technique, which requires putting your head in the water, as you’ll cool about 80 percent faster than if you kept your head dry.

Swimming or treading water cools you about 35 percent faster. So remain still, and if possible, assume the fetal or heat escape lessening posture (H.E.L.P.) to increase your survival time. Several people in the water can huddle close in a circle to help preserve body heat. Placing children in the middle of the circle will extend their survival time.

By keeping still, an average person wearing light clothing and a PFD may survive 2½ to 3 hours in 50-degree water. This survival time can be increased considerably by getting the body as far out of the water as possible and covering the head.

The following table shows predicted survival times for an average person in
50-degree water.


Predicted survival time (hours)

No flotation



Treading water


With flotation



Holding still






Wear a personal flotation device. It’ll keep you afloat even if you’re unconscious.

Whether you should swim for shore is a difficult decision. Some good swimmers can swim eight-tenths of a mile in 50-degree water before becoming hypothermic. Other people may not be able to swim 100 yards.

Furthermore, distances on the water are deceptive, so stay with the boat. Even a capsized boat is easier for rescuers to spot than a person in the water. Do not swim unless there’s absolutely no chance of rescue and you’re certain you can make it. If you do swim, use a PFD or other flotation aid.

Adapted from the 1997/1998 edition of “Washington Boater’s Guide.” Reprinted with permission. Copyright © 1997 Kalkomey Enterprises Inc.

Back to top

Privacy policy | Contact Compass staff | USPS website | Archived issues

© 2007 United States Power Squadrons. All rights reserved.