Slowing the offgassing

[ Follow Ups ] [ Post Followup ] [ California Scuba Diving BBS ] [ FAQ ]

Posted by Wayne on February 18, 2001 at 21:35:59:

In Reply to: Re: d. reduce safety stops posted by RabidYak on February 18, 2001 at 19:35:24:

Faster offgassing is accomplished with a fast reduction in pressure. At the safety stop, you are actually offgassing more slowly than at the surface. Stopping at a shallow depth gives the body a chance to offgas safely with less chance of bubble formation. Ideally we want to avoid getting to such a low pressure that we are super-saturated and gas comes out of solution in bubble form. Saturation is a function of pressure, among a few other things. A pause at 1.5 atm keeps the saturation down while still allowing ofgassing of nitrogen which was dissolved into the blood and tissues at greater pressures during the dive. Then, when you surface, there is less risk of DCS.

It might seem that you would still be taking on dissolved nitrogen at 15-20 fsw, but in truth your body is working toward saturation at every depth. If you stay long enough at 15 fsw, your body would become saturated at that presure (just like it is now saturated at 1 atm) but a pressure reduction of that amount (15 fsw to the surface) would not cause excess saturation of such a level as to cause bubbles to form.

Slowing your ascent does the same thing. If you stay away from extreme super-saturation, you reduce the formation of bubbles. Doing deep stops is similar. You will be offgassing on the way up, albeit at a slower rate than a fast ascent, but your saturation level stays lower.

For me, I still like to move up fast at first. For example, on dives on the Yukon, I scooted up to the 30 fsw mark at 60 fpm. Then stopped for a minute, and proceeded at 30 fpm to the safety stop. Stayed at about 15-20 for five, then came up. This on dives which never hit the NDL. Not saying mine is the best, but it works for me. It is fun to watch the computer during this and see the credit I am getting durign the ascent. Makes me feel better emotionally!


Follow Ups:

Post a Followup




[ Follow Ups ] [ Post Followup ] [ California Scuba Diving BBS ] [ FAQ ]