Stage 1 - Cold Shock

"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.

If you gasp underwater, you will immediately drown.

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 will experience a number of potentially lethal shock responses. These fall into three categories:

Threat No. 1
Loss of Breathing Control
2-3 Minutes or More

During the first several minutes of cold shock, and possibly 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. 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.

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 you’re breathing very rapidly (like 65 times per minute) 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 which can cause:

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.

Feeling of Suffocation
Paradoxically coinciding with hyperventilation is 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 much more difficult to eventually gain control of your breathing.

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, which is far more intense in water than in air. In vulnerable individuals, this greatly increases the danger of heart failure and stroke.

Threat No. 3
Mental Problems
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. Problems include:

Real World vs Lab Test
The Lab Test
The people who participate in scientific cold shock experiments are relaxed volunteers.

Nevertheless, despite all that reassurance, they experience cold shock for two – three minutes, and it can take up to five minutes for them to stabilize their breathing at around twice the pre-immersion level.

The Real World
Out in the real world, of course, the situation is far more intense. People are taken by surprise, and once they’re in the water, they very quickly realize that they’re fighting for their lives.

Person to Person
Individual people can also have different responses to cold water. For more information on this see:
Different Strokes

Case Studies:
Here are two excellent first-person accounts of near-death experiences from unprotected immersion in very cold water:
Randy Morgart - 32F (0C) water
KP - A Very Close Call & Miraculous Rescue

Stage 2: Physical Incapacitation >>