Cold Water Immersion

In boating and paddling terminology, cold water immersion refers to the unexpected entrance to cold water, such as when a boat capsizes. This is not to be confused with the practice of using cold water therapy for athletes (where they are submerged on purpose!).

Victoria’s waterways have a wide range of temperatures, from near-freezing in winter to pleasantly warm in summer. Recent research has suggested that if a person is suddenly submerged in water less than 15 degrees Celsius, it can cause a cold shock response that can lead to death even before the victim experiences symptoms of hypothermia. Proper protective paddling attire can reduce the effects of cold water immersion, so it is a good idea to check the weather and water temperature before you head out.

There are 4 phases of cold water immersion:

  1. Cold Shock Response
  2. Cold Incapacitation
  3. Hypothermia
  4. Circum – rescue Collapse
  1. Cold Shock Response
    The first reflex of the body is to gasp for breath which progresses to hyperventilation. In this period of breathing difficulty you are at risk of accidental water inhalation and drowning, especially if you struggle to keep your head above water. This is a situation where wearing a lifejacket greatly increases your chance of survival.
    Once the initial surprise has worn off, you can try to do a self-rescue or use your safety equipment such as flares or EPIRBs to raise the alarm. It is important to remain calm and try not to panic as this may cause prolonged hyperventilation and loss of consciousness.
  2. Cold incapacitation
    This stage usually occurs between 5-20 minutes after entering cold water. At this point, any useful strength or coordination to assist your self-rescue or recovery is lost, such as the ability to use feet, hands and legs to swim or climb back onto your craft. Those who are not wearing a lifejacket are at significant risk of drowning during this period.
  3. Hypothermia
    Hypothermia can can start to occur after approximately 30 minutes of cold water immersion. It usually begins in a mild form (such as feeling cold and shivering) and gets progressively more severe (such as becoming unconscious or death) the longer the individual is exposed to the cold water. Unconsciousness due to hypothermia from submersion in cold water usually occurs between 1 and 3 hours. It is important to note that even after a person is no longer in the cold water (e.g. if they have been rescued or climbed back onto their craft) hypothermia symptoms can continue to develop.
  4. Circum-rescue Collapse
    Circum-rescue Collapse is a term used to describe the body’s reaction to a situation of high stress followed by a period of sudden relaxation, causing a loss of consciousness and cardiac arrest. As part of the “fight or flight” response to stress (such as sudden immersion in cold water), hormones are released to increase blood pressure. When a rescue opportunity presents itself (such as performing a self-rescue or climbing ashore) the associated mental and physical relaxation can reduce this release of hormones, leading to decreased body function and reduction in blood pressure. This is what can cause a loss of consciousness and cardiac arrest, and can occur before, during or after a rescue. 

See Maritime Safety Victoria Boating Safety Hand Book for information on cold water immersion and hypothermia.

For more detailed information regarding cold water immersion you can check out the Beyond Cold Water Boot Camp website.

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