Cold Water Shock

What is Cold Water Shock and why is it important?

Cold Water Shock is the leading cause of death in the marine environment and is often mistaken with hypothermia. Cold Water Shock is a short term, involuntary response to being immersed in cold water, with cold water defined as between 10°C and 15°C. Around our coasts, these temperatures are dominant for 9 out of 12 months of the year and in the middle winter months, fall well below this.

The first stage of Cold Water Shock, which usually lasts up to three minutes, is immediately after immersion in cold water. Rapid cooling of the skin causes a number of instinctive reactions, including gasping, hyperventilation, restriction of blood flow and panic. Breathing rates can reach 10 times that of normal conditions and Cold Water Shock induces an automatic gasp reflex. If your head goes under the water during this time, water may enter the lungs leading to drowning.

Cold water immersion also leads to a significant increase in heart rate and blood pressure as all the vessels in the skin contract in response to sudden cooling. This results in an increased risk of heart failure and stroke.

After the first stage, blood flow decreases at the extremities in an effort to preserve heat at the core. Therefore you will lose movement in arms and legs, which makes it more difficult to stay afloat, unless you are wearing a suitable flotation device.

It usually takes at least 30 minutes for hypothermia to set in after entering cold water. If you have lasted that long in cold water, particularly without a flotation device, you are doing well.

Facts about cold water shock

What can you do?

Wear a lifejacket or PFD (Personal Flotation Device) at all times of the year.

If you are intending on entering cold water, enter slowly to reduce the initial reactions of the body. Wear clothing that will help protect you from the cold water, such as a full body wetsuit or dry suit.

If you find yourself in the cold water unexpectedly, do not try and swim until the first stage of cold water shock, which can last up to three minutes, has passed. Once your heart rate and breathing has started to normalise then, if sensible, try and swim to shore.

For more information and an informative video on Cold Water Shock, click on this link to the RNLI website, rnli.org/safety/know-the-risks/cold-water-shock