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May 2002 Vol. 17, No. 5   RSS Feed for Undercurrent Issues
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Those Chilly Second Dives: A Cause and Solution?

from the May, 2002 issue of Undercurrent   Subscribe Now

The air you breathe from your regulator, even in tropical water, may be so cold that it saps your warmth and increases your fatigue, says a yet unreleased report from the Dive Lab in Panama City Beach, FL,

Researchers there have discovered that the air passing through the flow orifice as it leaves the first stage drops in temperature by as much as 50 degrees F. The higher the tank pressure, the greater the temperature drop. Heavy breathing rates drop the temperature even further.

Even in 75°F water, the low-pressure air from a 3000 psi tank leaving the first stage can be below freezing. However, the temperature rises as the air travels through the intermediate pressure hose and into the second stage, thanks to the warmer surrounding water and the diver’s warm exhalations. While most divers don’t sense the chill, they are using body heat to warm their inhalations and subsequently shortening the time it takes to get cold.

In 40°F water, air leaving the first stage can drop to minus 10°F. Dive Lab found that one first stage equipped with a cold-water environmental cap mechanically failed after it became encased in ice. Even if the regulator doesn’t freeze, the extreme cold will rapidly cool the diver to the point of hypothermia. In addition, cold air or ice particles may travel into one’s throat and airways, presenting a real danger from reflex coughing and possible airway restriction. And cold air also contributes to dehydrat ion .

To counteract the problem, Dive Lab’s Mike Ward told Undercurrent that they are testing a relativly simple system to warm air passing through the first stage. Should it work, the practical effect may mean, even in tropical waters, that the second and third dives won’t be so chilling after all.

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