Instructor Manual
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Ocean Diver
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Adapting to the underwater world
Copyright © BSAC 2017
24
• Hypothermia
If nothing is done to remedy the situation and shivering stops, the body is
sinking into a state called hypothermia, which can become a very serious
condition as the body slowly shuts down.
Heat loss (2)
In water
• Heat loss is 25 times faster than in air
Water is an excellent conductor of heat; 25 times
better than air. A human body immersed in cold water
loses heat far more quickly than in air.
• Water temperature determines insulation required
Divers need to consider wearing thermal insulation to protect against heat loss.
The rate of heat loss in water for divers depends on the water temperature, the
amount of energy heat the body creates by swimming or finning and the time in
the water, but as a general guideline:
• Diving in water not less than 21°C the body is generally comfortable with
minimal insulation.
• Between 20°C and 10°C, a minimum of a wet or semi-dry suit is required.
• Below 10°C, a drysuit is strongly recommended.
• End the dive if getting cold
Common sense dictates that feeling cold on a dive is an indication to leave the
water to prevent further heat loss.
Insulation – wet & semi-dry suits
Many suits are made of neoprene that has been foamed
and expanded. The gas bubbles are sealed in the
neoprene fabric, so the suit does not act like a sponge.
This provides effective insulation combined with elasticity
to allow movement and for this reason neoprene suits
can be a close fit. This does not prevent water entering
the suit, but this has an advantage. A relatively stable amount of water directly in
contact with the body is warmed by the body’s heat but protected by the suit from
the surrounding cooler water. Therefore, the wetsuit and warmed layer of water act
as thermal insulation.
