How long after falling into really cold water does hypothermia set in? How does hypothermia affect reactions?

How long after falling into really cold water does hypothermia set in? How does hypothermia affect reactions?

— Marilyn K., Medford

Given the chilly weather of late, coupled with Memorial Day weekend when a lot of folks want to take a dip, that's an excellent question, Marilyn. Even when it hit 100 degrees in the Rogue Valley a week ago, the local waters fresh from melted snow were deadly frigid.

Experts say hypothermia begins when too much heat escapes from your body. Your core temperature normally hovers around 98.6 degrees Fahrenheit. A drop of just a couple of degrees sparks hypothermia.

When someone becomes hypothermic, one of the first reactions is shivering as your body attempts to generate heat through muscle activity. Slurred speech, abnormally slow rate of breathing, fatigue and lethargy along with cold, pale skin are also common.

As a result, the hypothermic victim will have problems with muscle coordination as well as staying conscious.

A good rule of thumb is that the colder the water and the longer you are in it, the greater the risk, according to the United States Search and Rescue Task Force.

When water is less than 32 degrees and not yet frozen, the task force estimates a person will have less than 15 minutes before becoming exhausted or unconscious. Survival in that water would be less than 45 minutes.

In water 32.5 to 40 degrees, you will have no more than 30 minutes before becoming unresponsive and less than 90 minutes to survive.

If the water is 40 to 50 degrees, the time until exhausted or unconscious is no more than 60 minutes with up to three hours to survive.

At 50 to 60 degrees, you can remain conscious for up to two hours and survive up to six hours.

But other factors also weigh in, including a person's age and overall health. The ingestion of alcohol or drugs will also lower your ability to survive. For instance, both alcohol and marijuana can keep your blood vessels dilated (thus restricting your shivering response), impair your judgment and alter your awareness of weather conditions.

And if you become unconscious or unable to swim in swift water and then drown as a result, the end comes quicker still.

Send questions to "Since You Asked," Mail Tribune Newsroom, P.O. Box 1108, Medford, OR 97501; by fax to 541-776-4376; or by e-mail to youasked@mailtribune.com. We get so many questions we can't answer them all, but we'll try.