Hypothermia – it’s not just for winter in the Great Lakes!

Can someone become hypothermic in August in less than one hour? Read on!

In August, Michigan State University Extension staff working as instructors aboard a Summer Discovery Cruise were participants in a water rescue on the Great Lakes where the Detroit River enters Lake Erie.  As described in the article MSU Extension to the rescue – literally!, one of the victims was exhibiting symptoms of hypothermia after having been in 71 degrees Fahrenheit water for only 45 minutes. Hypothermia in August?

Hypothermia occurs when your body gets cold enough so that its core temperature drops below 95 F, less than 4 F below normal body temperature. It’s a very real possibility for anyone fishing or boating on the Great Lakes, where water temperatures are frequently below 80 F.

Cold water can conduct heat away from your body 25 times faster than air of the same temperature. Within minutes, your body’s core temperature—the brain, heart, lungs and other vital organs—begins to cool, and your body responds by trying to keep as much heat as possible in the core. The flow of blood to the arms and legs is reduced, and your body tries to generate heat by shivering.

Shivering is unlikely to produce enough heat to balance the heat lost to the cold water. Your body has limited energy reserves, and survival depends on making those reserves last as long as possible. If its core continues to cool, your body gives up its attempt to produce heat. Shivering stops. As the brain cools, its functions become impaired. You will probably become confused and your muscles will become increasingly rigid until you become unable to help yourself. If your body continues to cool, you will lapse into unconsciousness. You may appear already dead—there may be no signs of a heartbeat or breathing, because these functions slow dramatically. Death typically occurs after your heart cools to about 77 F and stops beating.

How fast does all of this occur? The answer depends on many factors, such as water temperature, your age and physical condition, how you behave while in the water, the amount of insulation provided by your clothing and your mental attitude. Under the worst circumstances, you may lapse into unconsciousness in 30 minutes or fewer; you could be dead in less than an hour.

Hypothermia chart graphic

You can, however, take steps to extend your survival time and increase your chances of being rescued. Many of these steps will help your body to conserve energy and retain heat in the core area.

  • Use some means of flotation so you don’t have to use energy to keep yourself afloat. The best means of staying afloat is a personal flotation device (PFD).
  • Even the very best PFD is ineffective if it doesn’t accompany you into the water—wear it while on or near the water.
  • Keep as much of your body out of the water as possible, especially your head and neck. As much as 50 percent of your body’s heat loss occurs in these areas.

Michigan is the Great Lakes State, and we need to remember that our Great Lakes are usually cold enough, year around, to cause hypothermia if immersion is prolonged. Michigan Sea Grant was among the early national leaders in hypothermia and cold water near-drowning research, with Michigan Sea Grant Extension educators extensively involved in educating first responders and the public. Let’s not forget earlier lessons learned. For more information on hypothermia, see Minnesota Sea Grant’s Hypothermia Prevention - Survival in Cold Water website.

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