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Stage 1: Cold Shock

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If you gasp underwater, you will immediately drown

"The sudden lowering of skin temperature on immersion in cold water represents one of the most profound stimuli that the body can encounter."
- Golden and Tipton in Essentials of Sea Survival

Translation:  Short of being hit by a bus or struck by lightning, cold shock is one of the biggest jolts that your body can experience.

More Than Just A Gasp

Cold shock is a lot more complicated and dangerous than just gasping for air. The instant that cold water makes contact with your skin, you experience a number of potentially lethal shock responses.


These responses are intense and completely involuntary, which means they're totally out of your control.  You can't wish them away any more than you can mentally control your heartbeat. 


A Desperate Struggle

Desperately struggling in the water, people often find this loss of control terrifying. They're completely taken by surprise, but they know within seconds of hitting the water that they're fighting for their lives. That's why safety messages telling them not to panic are a big waste of time. 

This kind of experience is one thing if you're a member of an elite military unit and you're participating in a survival exercise - but it's another thing entirely if you're just out for what you thought was going to be a fun time on the water.

A Very Traumatic Experience:

For many victims, cold shock is a horrific, terrifying experience.  It can obviously kill you, but it's also the kind of thing that really rattles your cage. Many survivors can't get near their boats or boards for a long time afterwards without feeling really stressed out and creepy. That's the way your brain processes a traumatic, near-death situation over which you have no control.


It's also common for survivors to have nightmares for months afterwards. In other words, suddenly winding up in the water desperately fighting for you life is something that you really don't want to experience.

Life-Threatening Responses

Cold shock responses fall into three threat categories, each of which is discussed below to give you a clear and realistic view of what you're up against in an unprotected cold water immersion:

  • Loss of Breathing Control

  • Heart and Blood Pressure Problems

  • Impaired Mental Ability

Threat No. 1
Loss of Breathing Control
3-5 Minutes or More
Threat 1

During the first several minutes of cold shock, and often for much longer, most people find it impossible to get their breathing under control. Breathing problems include gasping, hyperventilation, difficulty holding your breath, and a scary feeling of breathlessness or suffocation.


This isn’t just a little gasp, like the kind you’d experience if somebody jumped out of a closet and scared you. It’s a huge gasp that totally fills your lungs. You may experience several of these gasps in a row.


Sudden Drowning

If your head is underwater when you gasp, you will immediately drown, and without the support of a PFD, you will head straight for the bottom. Before cold shock was identified as the cause, this phenomenon was known as Sudden Disappearance Syndrome.

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Gasping is immediately followed by hyperventilation - very rapid, out-of-control breathing.  Swimming as short a distance as 6- 10 feet while hyperventilating is often impossible, even for good swimmers. When your breathing is out of control, swimming strokes cannot be synchronized with respiration.  The result is swimming failure.  If you're not wearing a PFD, you will drown.


Hyperventilation also results in hypocapnia, a reduction of the level of carbon dioxide in your blood.  Read About Randy Morgart's Experience

Hypocapnia Can Cause

  • Dizziness.

  • Faintness.

  • Ringing or buzzing in your ears.

  • Numbness of your fingers and toes.

  • Cramping of your hands and feet.

  • Reduced ability to complete simple and familiar tasks.

  • Eventual Loss of consciousness.

Flush Drowning

Difficulty Holding Your Breath
Cold water immersion greatly reduces the length of time that you can hold your breath. An average person’s ability to hold their breath in water below 60F (15C) is one-third of what they can do in warmer water. The lower the water temperature, the greater the problem. One study of volunteers in 41F (5C) water found average breath-hold time reduced from 45 to 9.5 seconds, with one subject reduced to 0.2 seconds.

Overwashing and Flush Drowning

This loss of breathing control has ominous implications in rough water where the swimmer is submerged by steep or breaking waves, and is likely a primary cause of flush drownings - a whitewater paddling term that refers to drownings that occur when the paddler capsizes and gets washed downstream through rapids.  When that happens and your breathing is out of control and your ability to hold your breath is compromised by cold shock, drowning is very likely.

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Feeling of Suffocation

At the same time that they're hyperventilating, many people experience a strong claustrophobic feeling of not being able to get enough air. This frightening sensation, which continues for up to three minutes before gradually declining, increases the potential for panic and disorganized behavior in the water and makes it even more difficult for them to eventually gain control of their breathing.

Threat 2
Threat No. 2
Heart and Blood Pressure Problems

Cold water immersion causes an instantaneous and massive increase in heart rate and blood pressure because all the blood vessels in your skin constrict in response to sudden cooling. In vulnerable individuals, this greatly increases the danger of heart failure and stroke. 

Beyond the cardiovascular stress placed on the heart by cold shock lies another concern: the development of abnormal heart rhythms that could themselves lead to sudden cardiac arrest. Research has demonstrated that these arrhythmias can be caused by a conflict between cold shock and the mammalian dive reflex. As Tipton and Shattock write in Autonomic conflict’: a different way to die during cold water immersion?, a 2012 article published in The Journal of Physiology:

“The co-activation of the sympathetic and parasympathetic divisions of the autonomic nervous system can reproducibly produce cardiac arrhythmias. During cold water immersion, this powerful pro-arrhythmic stimulus occurs at a time when the QT interval does not match the underlying heart rate, further increasing the likelihood of problematic cardiac arrhythmias.”

Figure 5 in that article is an excellent graphic that charts the autonomic conflict:

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Special thanks to Michael Tipton, Professor of Human & Applied Physiology, Extreme Environments Laboratory, Department of Sport & Exercise Science, University of Portsmouth, UK, for permission to reproduce this graphic.

Threat 3
Threat No. 3
Impaired Mental Ability

The moment you hit the water, cold shock causes a huge reduction in your ability to think and function. This can continue for a long time – even after you get out of the water.  See A Closer Look, the 3rd article in a series about a near-death incident on the freezing Mississippi River.

Mental Difficulties Include

  • Disorientation

  • Fear

  • Panic

  • Inability to think clearly

  • Inability to evaluate options

  • Inability to carry out a plan of action

  • Freezing in place

  • Failure to act

  • Helplessness

  • Lethargy

If the water temperature is below 40F (5C) add Severe Pain to the list

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Click To Start Video

Cold shock is a far more traumatic experience in real-life than in scientific research experiments.  This is a very important safety point to understand.  Learn More About It

Real Life vs Physiology Lab Test

If cold water is so dangerous, how can all those people do polar bear plunges without drowning?  It's a good question, and this 2-minute video answers it.

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