Beyond Cold Water Bootcamp


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The most common misunderstanding about Cold Water Immersion is that it leads to immediate Hypothermia. The real truth is, other serious events occur long before hypothermia sets in, each with its own physiological challenges.

The four phases are:

1 Cold Shock Response
2 Cold Incapacitation
3 Hypothermia
4 Circum-rescue Collapse

Cold Shock Response lasts for only about a minute after entering the water and refers to the affect that cold water has on your breathing.  Initially, there is an automatic gasp reflex in response to rapid skin cooling.  If the head goes underwater, water may be breathed into the lungs during the gasp.  The result is simple: drowning.  That’s one of the many benefits of a life jacket or PFD: it helps to keep your head above water during this critical first response.

A second component of the Cold Shock Response involves hyperventilation. Like the gasp reflex, this is a natural reaction to the cold.  Although this physiological response will subside, panic can cause a psychological continuance of hyperventilation.  Prolonged hyperventilation can lead to a faint, so the key thing is to concentrate on controlling your breathing.

The other significant Cold Shock Response is cardiac related. As the arteries narrow (vasoconstriction), the heart has to work harder to pump the same volume of blood throughout the body.  Especially for people with underlying heart disease, this additional workload can cause the heart to go into cardiac arrest.


  • If you have the choice, immerse yourself slowly to minimize the shock.
  • If you’re going out in the shoulder seasons of Spring or Fall, consider wearing clothing that will provide you with thermal protection and minimize the Cold Shock Response.

Cold Incapacitation occurs within 5 – 15 minutes in cold water.  Vasoconstriction decreases blood flow to the extremities in an effort to preserve heat in the core, thereby protecting the vital organs but allowing the periphery to cool.  Unfortunately, muscle and nerve fibres don’t work well when cold. Within this critical time frame you will lose meaningful movement in your hands and feet, and then your arms and legs, so if you’re not wearing a floatation device, you will be unable to stay afloat and will drown.  Other important life-saving/survival activities will also become more difficult and then impossible. 


est_time_to_hypothermiaHypothermia - There are a number of misconceptions when it comes to hypothermia. The first deals with how long it will take to become hypothermic. While it varies with water temperature and body mass, it can take 30 minutes or more for most adults to become even mildly hypothermic in ice water.  Knowing this is vitally important in a survival situation, since people would be far less likely to panic if they knew that hypothermia would not occur quickly and that they have some time to make good decisions and actions to save themselves.  See the graph.

Figure 1. Responses of 681 individuals to the following question, “If you fall in ice (0°C) water while wearing regular winter clothing, how long do you think it will take to become hypothermic?”

In order to fully understand the advancement of hypothermia from entry into the water until death, consider it in three stages. (Mild, Moderate and Severe)

Stage of Hypothermia

Body Temperature

In Water Duration (minutes)




>30 mins




30-120 mins

Unconscious, will drown without floatation



90-180 mins

Cooling to Cardiac Arrest

Note: In Canada, our water can be quite cold even in summer. Don’t let your guard down just because it’s July or August. Hypothermia can still occur, although its onset will take longer. 

Circum-rescue Collapse can happen just before, during or after rescue. The symptoms can range anywhere from fainting to death. But, why does this collapse occur so near rescue?

Several factors are working here: while you are fighting to stay alive, your senses are heightened and stress hormones are surging through your body, helping you survive. Once rescue is imminent, is in progress, or has just taken place, a mental relaxation occurs, creating a decreased output of those stress hormones. Blood pressure can drop and muscles can fail, causing collapse and in some extreme cases, even cardiac arrest and death. The key thing to remember is that heart function is dramatically impacted by the way that a victim is handled and removed from the water. Knowing what NOT to do can make a life-saving difference.

For First Responders, it is this critical time (from first encountering the victims until they are transferred to appropriate medical resources), that special extraction and treatment-related actions can have the greatest impact on their survival. Some of these actions might even seem counter-intuitive to your emergency training for other types of rescue, so it’s vital that you understand the key elements of Circum-rescue Collapse.

To watch Dr. Gordon Giesbrecht’s video on the 4 Phases
of Cold Water Immersion, click the icons below.

Part 1 

Part 2

Part 3