Riding deco ceiling on ascent

[boulderjohn]

I first read about it in Buhlmann's Decompression Sickness so it's been around, in reputable circles, since at least 1984.

The debate between continuous ascent and staged ascent has been going on since Haldane.

 

[EFX]

Similarly, this discussion assumes two possibilities--1) stay at scheduled decompression stop depth or 2) ride the ceiling. If you know you have a ceiling that is, say, 8 feet above your current scheduled deco stop, is there any reason you can't ascend to, say, 4 feet shallower?

I don't think it matters much in regards to safe off gassing, but you may end up getting locked out of your computer for those using recreational dive computers, when you disregard a scheduled deco stop.

 

[BlueTrin]

Similarly, this discussion assumes two possibilities--1) stay at scheduled decompression stop depth or 2) ride the ceiling. If you know you have a ceiling that is, say, 8 feet above your current scheduled deco stop, is there any reason you can't ascend to, say, 4 feet shallower?

It’s not exactly the same but I get closer to my rounded stop when the ceiling is getting closer to the next stop for the shallow stops.

 

[boulderjohn]

I don't think it matters much in regards to safe off gassing, but you may end up getting locked out of your computer for those using recreational dive computers, when you disregard a scheduled deco stop.

Yep.

It would be nice if the computers would not get angry when you see that you can safely move up a few feet and still be below the ceiling. That is especially nice when you are the 20 foot stop using oxygen. The computer gets mad if you go up a foot or down a foot.

It would also be nice when your deco stop is a few feet below a thermocline.

 

[EFX]

Yep.

It would be nice if the computers would not get angry when you see that you can safely move up a few feet and still be below the ceiling. That is especially nice when you are the 20 foot stop using oxygen. The computer gets mad if you go up a foot or down a foot.

It would also be nice when your deco stop is a few feet below a thermocline.

You would need to display the raw ceiling on the main display in order to appease the computer. This change could be incorporated to allow divers to decompress following the ceiling where flashing red alarms for bypassing staged stops would be unnecessary and annoying. However, there might be legal issues. Shearwater gives a warning for this kind of decompression they call a "man on a rope", asserting that there is not enough established evidence that this method of decompression is safe.

 

[inquis]

You would need to display the raw ceiling on the main display in order to appease the computer

FWIW, a Shearwater Perdix can be set to automatically switch the NDL slot to display the Ceiling once in deco. Doesn't stop the red warnings, though.

 

[boulderjohn]

FWIW, a Shearwater Perdix can be set to automatically switch the NDL slot to display the Ceiling once in deco. Doesn't stop the red warnings, though.

It would be nice to be able to hit a "yeah, I know" response to that warning if you are still below the ceiling and have it shut off.

 

[Wibble]

Just checked MultiDeco and the minimum stop size is 3m/10ft.

Wanted to set it to 1m/3ft to compare with 3m runtime.

Anyone got another planner which allows for 1m stops?

Try a 60m/200ft dive for 40mins bottom time using 50:80 GFs as this has roughly 80mins of decompression.

 

[wnissen]

Would it be theoretically possible to test this theory analagously to the way that fatal doses are calculated? Take a group of goats, divide them in half. Calculate a staged dive profile that will lead to bends in half of the control group. Then run the same profile but with riding the ceiling. See if it's measurably better or worse. Do mice experience DCS the same way as humans?

 

[BlueTrin]

Would it be theoretically possible to test this theory analagously to the way that fatal doses are calculated? Take a group of goats, divide them in half. Calculate a staged dive profile that will lead to bends in half of the control group. Then run the same profile but with riding the ceiling. See if it's measurably better or worse. Do mice experience DCS the same way as humans?

A New Measure of Decompression Sickness in the Rat

In this study we assessed the reliability of a tilting-board grip score as a measure of decompression sickness in rats. In experiments using a hyperbaric compression/decompression protocol, rats were observed for signs of decompression sickness and their ...

www.ncbi.nlm.nih.gov