Hypothermia: What is it?



People always want to know
how long they can survive

in the water.

– John McMillan,

Offshore Survival Training


Every year more American fishermen die at work than in any other occupation. The cause of death has been described differently over the last 100 years. For most of history the cause of death was believed to be drowning. The sinking of the Titanic in 1912 was the first example of exposure to cold for so many people. Following the attention this loss of life from exposure to cold received the cause of death from this kind of exposure was believed to be caused by hypothermia. But as hypothermia has become better understood the cause of death from going overboard is now known to be hypothermia-induced drowning.

Hypothermia caused by going overboard at sea is not one specific condition but a progression of worsening conditions that can lead to one thing—death. In water, not necessarily very cold water, the human body begins to cool from the outside at the skin toward the organs at the center or the body core. At 70 degrees a room is warm, but 70-degree water is cooling the body’s normal temperature of 98.6 degrees. At 60 degrees it is cooling it faster and more significantly.

Symptoms begin to develop in the skin. The longer the body is in the water at this temperature the closer the cooler temperature gets to the vital organs, the blood and most of all the brain. As the blood cools it thickens, stressing the heart. Less blood gets to the hands, muscles and brain. A body is defined as being hypothermic when the body’s core drops 2 degrees. It is the loss of the brain’s ability to think about these circumstances that cause the body to give up, slip under the surface and ultimately drown.

“When the body’s core drops 2 degrees with no protective measures having been taken, the value of survival techniques are made apparent,” said John McMillan of McMillan Offshore Survival Training in Belfast, Maine. McMillan has been involved in survival training for 32 years, having trained in Africa, Chile, Mexico, Argentina, Canada and throughout coastal United States including Alaska.

A life jacket can keep the body afloat but it cannot prevent hypothermia. The survival times at various water temperatures are in an instruction booklet provided with each PFD, which provides the survival charts. These survival times are based on individuals minimally prepared and not trained in survival techniques, said McMillan. A thick layer of body fat can slow the onset of hypothermia. Floating on debris from a shipwreck or an overturned hull will reduce the rate of the onset of hypothermia. Immersion in water cooler than the body draws down the body temperature until the core body temperature approaches the temperature of the water. At 1.4 degrees above the normal body temperature a school child in the U.S. is considered to have a fever high enough to be kept home from school. Immersion in 60-degree water can take the body much further, much faster in the other direction with fatal consequences.

Cold water shock is another factor affecting survival. When someone goes overboard in cold water the body feels a shock from the temperature difference. That shock causes an automatic gasping reaction, which can draw water into the mouth creating panic.

“People always want to know how long they can survive in the water,” said McMillan. He said he refers them to the “One–Ten–One Rule.” In 50-degree water you have one minute to catch your breath. Then you have ten minutes of functional use of manual abilities for tying knots, lighting a flare, etc., before the hands begin to stiffen. Finally, at 50 degrees there is one hour before the body’s core temperature begins to be affected.

But, said McMillan, with survival training all of these time references change and the chances of surviving increase. One obvious thing today is the value of a survival suit. But the clothes someone has on when they hit the water also matters. Even whether their collar is turned up and the neck buttoned make a difference. A layer of body fat buys time before the body’s core begins to cool. The ability to shiver, an auto response that generates body heat, is another of many survival tools that can make the difference between surviving and not.

McMillan said, “The bottom line for determining if the water is cold is if a person continues to shiver after initial immersion (2 minutes) and does not adjust to the water. In a survival training session that person will be required to perform a cold water survival skill.” (The water could be 80 degrees, as cold water shock is relative to the individual person.) “The skill performed will be dictated by the following : Are they wearing a personal floatation device? If so, they can perform the Heat Escape Lessening Position [HELP]. Are they with other people wearing PFDs? If so, they should perform the HUDDLE position. If the person is not wearing a PFD and alone, they will be treading water, which is usually the case in a man overboard scenario—this being the worst case situation,” said McMillan.

In addition to the initial immersion cold shock and subsequent gasping, being fully clothed in the water is very different from diving in wearing just a bathing suit. The surprise is that the wet clothing is heavy and drags the body down into colder sub-surface water. This is where the “doggy paddle” is a useful survival skill. It generates heat, keeps the body afloat and provides a sense of being more in control. “Good swimmers have drowned because they think the doggy paddle is not effective,” said McMillan.

“The” book on sea survival: Essentials of Sea Survival, F. Golden & M. Tipton, Human Kinetics Books, 2002. www.HumanKinetics.com