Despite the fact that two boaters were wearing Type III life jackets, they did not survive their plunge and prolonged exposure in the chilly waters of Chamberlain Lake Monday afternoon. A third boater who was not wearing a life jacket managed to survive by clinging to a floating gear bag, wardens said.

The fate of the trio is hard to explain given that the advice from the Coast Guard and other water safety experts is to wear personal flotation devices.

But the variables are many, and personal fitness, dress and cold water survival knowledge all can play a part in surviving exposure to cold water. And wearing a PFD, the experts say, is often key to survival.

Here’s what the Coast Guard’s safe boating division has to say about PFDs.

There are several common types of PFDs. Type I is used offshore on open coastal waters or rough seas where a quick rescue may not be likely. They offer a high degree of flotation and are designed to keep an unconscious wearer face up in the water.

A Type II flotation device is for use in water that is not rough and where rescue is likely to be imminent. Such a device will float an unconscious wearer in a vertical or slightly face-up position. It is not suitable for extended survival in rough or cold water.

Type III is the kind most often worn by recreational boaters. These personal flotation devices are intended for use where rough water is unlikely and quick rescue is available. They are designed to float a conscious person face-up in calm water with the head tilted back. They are not intended to turn or maintain an unconscious wearer face-up.

Here’s what happens when someone falls into cold water, according to “Off Season Boating, Cold Shock and Hypothermia,” a brochure produced with the help of the Maine Association of Sea Kayak Guides and Instructors and the Maine Department of Marine Resources-Marine Patrol, the Coast Guard and others.

Cold water takes heat from the body 25 times faster than cold air. Turbulent water or attempted swimming may double that rate of heat loss. Victims can stay warmer longer by huddling or floating in the water with arms and legs crossed, head out of the water.

Immersion in cold water causes a powerful gasping reflex. If momentum drives the person underwater, water inhaled because of this gasping may cause unconsciousness and-or drowning in minutes.

Exposure of the head and chest to cold water causes sudden increases in heart rate and blood pressure, which may cause cardiac arrest.

Uncontrolled rapid breathing follows initial gasping and immersion and may lead to unconsciousness. The person in the water must attempt to recover normal breathing rhythm as rapidly as possible.

Within minutes of cold water immersion, hands, arms and legs become numb and the person is unable to swim or climb out of the water or hold onto a capsized boat.

Hypothermia develops more slowly than the immediate effects of cold water immersion. Survival tables show that a clothed adult may remain conscious for 30 minutes in 40 degree water, for maybe an hour at 50 degrees. Without thermal protection, the victim is soon helpless because of swimming failure, and without a PFD drowning is most often unavoidable.