Emergency Preparedness

Cold Water Immersion and Hypothermia Prevention

Cold Water Immersion and Hypothermia Prevention

Cold water immersion and hypothermia are serious risks that exist even in the most unexpected conditions. Boaters can easily be exposed to the risk of hypothermia, even on warm, sunny days. Sportsmen who hunt or fish from boats in cold temperatures and climates are at a greater risk of death from falling overboard or a capsizing. Operators should be fully prepared for cold water immersion and hypothermia risks and should ensure that their passengers are prepared as well.

In the event of a capsizing or a fall overboard, boaters’ and passengers’ risk of death increase greatly when the temperature of the water is colder. Water temperatures can vary based on the location and the time of year, but water does not have to be exceptionally cold for the effects of hypothermia to take hold. In fact, an initial reaction to cold water immersion can occur in water that reaches temperatures even up to 77° Fahrenheit. For this reason, boat operators need to be fully knowledgeable about the effects of cold water immersion on the body and should be prepared to respond appropriately. 

Physiological Reaction to Cold Water Immersion

Sudden immersion in cold water can cause a person to begin breathing uncontrollably and rapidly and can cause cardiac arrest or other physical reactions that can result in death.


Because immersion in cold water speeds the loss of body heat, it can often lead to hypothermia. Hypothermia is the abnormal lowering of internal body temperature that occurs when your body loses heat more quickly than it produces it, and it is extremely dangerous and deadly because it cools the internal organs.

The key to avoiding hypothermia in a capsizing or fall overboard is to try to get as much of the body out of the water as possible. Boats that were built after 1978 are designed to support passengers even if they are capsized by floating just under the water. Submerged passengers should try to get in or on the boat. If that is not possible, a life jacket can enable the person to keep their head out of the water. Because nearly half of the body’s heat is lost through the head, this is extremely important for preventing hypothermia.

Four Stages of Cold Water Immersion

Researchers have (Golden and Harvey 1981) identified four distinct physiological stages in which a person responds to being immersed in cold water and may become unconscious and die. Boaters who understand the physiology of cold water immersion are better able to respond to an immersion emergency. The four stages in the body’s reaction to cold water immersion include:

Initial reaction (involuntary gasp reflex)– This stage, also known as “cold shock,” usually lasts just about a minute and involves an initial deep and uncontrollable gasp followed by hyperventilation.

Short-term immersion/swimming failure– The following 10 minutes will involve the loss of the effective use of extremities, including fingers, arms and legs. This prevents meaningful movement. In this phase, it is essential that the victim remain concentrated on self-rescue efforts and techniques, despite their limitations.

Long-term immersion/immersion hypothermia– Depending on the water temperature, clothing, body type and behavior of the victim, long-term immersion hypothermia usually sets in around 30 minutes after immersion. A person who succumbs to hypothermia eventually loses consciousness and often dies, with or without drowning. Loss of consciousness may occur in as little as one hour.

Post-rescue collapse– Even after being rescued from cold water, a person is still in danger of cardiac arrest or lung damage from inhaled water. Heart problems may also develop as the cooled blood from extremities is released into the body’s core.

Additional information about hypothermia and the four stages of cold water immersion can be found in the Cold Water Boot Camp at www.watersafetycongress.org.

Cold Water Survival

When a boater or passenger unexpectedly plunges into cold water or in instances where it is necessary for them to enter cold water, the following guidelines can improve their chances of survival:

·        Cover up the head and keep it out of the water, if possible. Nearly 50% of a person’s body heat is lost through the head.

·        Button up all clothing.

·        If entering the water voluntarily, do so as slowly as possible.

The Heat Escape Lessening Posture (HELP) is an effective survival method for people who cannot immediately get out of cold water or who may not be rescued quickly. A submerged person in the HELP posture draws his knees to his chest and wraps his arms across the chest, hugging his life jacket. This strategy is effective because it helps to protect major areas of the body from heat loss.

In the event that a boat capsizes and several passengers are in the water together, they should huddle together with their arms around each other. This works because it keeps everyone together, raises overall morale and makes the group much easier to spot in the water.

Person in the water in HELP position and another group of persons huddling together

Because sometimes victims can be resuscitated even after showing no signs of life for a considerable amount of time, unconscious immersion victims should administered CPR immediately after rescue. They should be taken to the closest hospital as soon as possible. There have been numerous documented cases where victims have been revived after lengthy cold water immersions.

Boaters should fully understand the behaviors and conditions that cause immersions; including reaching overboard and standing while in movement. These behaviors should be avoided to prevent a fall overboard. However, accidents sometimes happen despite efforts, so operators should be adequately prepared for a cold water immersion event. To do so, boaters should understand proper response, wear life jackets and carry communication devices. By understanding the decisions that should be made during such an event, boat operators have a greater chance of surviving if cold water immersion does occur or avoiding it altogether.