Re: Deep stops

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Posted by Kendall Raine on November 07, 2001 at 21:39:35:

In Reply to: her deep deco stop (60fsw) on air may have done more harm posted by Karl S. on November 07, 2001 at 15:07:14:

Just for fun, I thought I'd lay out three deco schedules side by side. These are all air dives. The schedules show required deco for a 15 minute air dive to 130 fsw according to the Navy, Buhlmann ZHL-16 and VPM tables. The Navy and Buhlmann schedules are based on neo-Haldanean dissolved gas models. The VPM is a so-called bubble model that assumes inert gas resides in tissue in both dissolved and free phase form (micro bubble nuclei).

Navy Buhlmann VPM
Stop fsw
10 1 4 5
20 3
30 2
40 1
50 1

Those who recall Bennett's article will recognize the VPM schedule as pretty similar to Bennett's suggestion to stop half way from the bottom to the 15 foot stop for five minutes. This was found to substantially reduce post dive venous gas bubbles.

The point is that by doing deeper stops, bubble seed (free gas phase) excitation is minimized. With less and smaller bubbles to clean up at the shallow stops, the deeper stop schedule allows a diver to get out of the water with much less bubbling.

It's not just a pretty theory, but has demonstrated results based on Doppler testing in long range deep dives. In California, we have found we can get out of the water with 20-30% less deco time and still maintain low bubble grades versus the schedules we used to use from Buhlmann. In Florida, the use of deep stops have enabled dramatically reduced deco schedules with acceptable bubbling.

Say what you will about the efficacy of deep stops. Say what you will about the efficacy of deep stops with different inert gasses. The fact is the people doing the high decompression stress dives are using these deep stops, and have for years. We are seeing dramatic reductions in hang time as well as feeling better after the dives. The results support the theory and the model works. Period.

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