Tip of the Week

Reducing the Risk of Decompression Sickness

Without staying out of the water, divers can’t completely eliminate the risk of decompression sickness. Here are the basics, in what’s probably descending order of importance:

1Ascend Slowly.

The point is to reduce pressure on your absorbed nitrogen slowly so that you have a chance to exhale it before microbubbles become tiny bubbles and tiny ones become big ones. The recommended ascent rate has been slowing over the years, from “as slow as your slowest bubbles” to 18 meters per minute to 9 meter. Some now advocate 3 meters per minute. Though that may not be practical, the declining rate indicates growing recognition of how important a slow ascent is. Go slowest in the last 10 meters, when pressure changes fastest.

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2Safety Stop at 5 meters.

At 5 metes there’s still 50 percent more pressure than at the surface, and this is enough to keep a lot of your remaining nitrogen in solution. A three-minute stop allows your bloodstream to circulate through your lungs, where that nitrogen can be filtered out.

3Don’t push the limits.

Your dive computer makes predictions of safety based on averages, and can be wrong on any given day. To be safer, especially when you’ve made multiple dives on multiple days ,stay a few “clicks” back from the end of the green zone that defines no-decompression limits.

4End Shallow.

If you make the deepest part of the dive first and the shallow part last, the shallow part will act as decompression for the deep part. You’ll see that reflected in the decompression status on your computer, which will get “greener.” If, instead, you end deep, you will have to rely entirely on your ascent and safety stop for all your decompression.

5Avoid Sawtooth and Bounce Profiles.

The point is to minimize the number of ascents and descents in a dive because each ascent is a DCS risk, and when you crowd in more ascents, they tend to be faster. The only way to avoid DCS entirely is not to ascend at all. Since you have to come up eventually, do it as few times, and as slowly, as possible.

6Stay Hydrated.

Dehydration is common on tropical vacations, the result of heat, alcohol, dry air-conditioned air and dry scuba air. Dehydration makes your blood thicker, so it flows more slowly and doesn’t carry nitrogen to your lungs as quickly.

7Stay Warm.

When you get cold, your body shuts down circulation to your skin, your fingers and toes and then your arms and legs. If those tissues have already become saturated with nitrogen, there will be less blood flow to carry it away. Typically you’re warm at the beginning of the dive when you take on nitrogen, and colder later when you need to off gas. Wear a semi dry so you end the dive warm, and avoid getting chilled during the surface interval. 

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