Chapter 2: What’s Different
About Being Under Water?

Study Question

As you read this page, look for the information that answers these question:

Water conducts heat away from your body how many times faster than air does?

Staying Warm: Video


Staying Warm: Key Points

One of the must significant challenges the underwater environment presents is staying warm.

Heat Loss

Water conducts heat away from the body about 25 times faster than air does. This is why air that is 22 °C/72 °F feels comfortable — but water that is the same temperature feels downright cold.

As a general rule, while it is very difficult to be too warm under water, it is very easy to be too cold. Any time the water is colder than 30 °C/86 °F, you need some form of thermal protection. And, let's face it: The odds of you ever being in water that is naturally that warm are fairly slim.

Knowledgeable divers seldom wear anything less than a full-length, 3mm wetsuit — regardless of how warm the water may seem.


Even with proper insulation, lengthy exposure to water can cause you to become chilled. When you feel yourself begin to shiver, get out of the water, dry off and seek warmth.

The consequences of being cold under water go beyond simple discomfort. Cold can affect judgment, coordination — and your body's ability to resist decompression sickness. So why risk any of these problems when it's so easy to dress right, stay warm and have fun?

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