Ascent rate below off gassing ceiling?

[Duke Dive Medicine]

In the context of the post from Dive Duke Medicine - As fast as possible to your first stop, as your only on gassing otherwise,

Cathal, can you clarify "as fast as possible"? Also, off-gassing does not start at the first decompression stop. It begins on ascent at some point before the first stop; exactly where depends on tissue inert gas load.

Best regards,
DDM

 

[DevonDiver]

This study:

What Ascent Profile for the prevention of Decompression Sickness? DAN Europe DSL Special Project 01-2002

From which, this table:

Some further discussion in this article:

Best Ascent Speed for Scuba Diving

 

[TrimixToo]

?? 9mps is about 30fps. 9 meters per second is *very* rapid ascent. I think 9mpm is what the op meant.

Yup. I spaced it entirely. I read "s," I *wrote* "s" and I thought *m*. Sigh....

 

[shurite7]

For depths below four atmospheres a rate of 60fpm up to three atmospheres is fine. From three to two atmospheres the rate should be slowed to 30fpm. From two atmospheres to the surface the rate should be slowing down significantly. The slower the better. A fast ascent in the shallower depths does pose a higher risk which is why the slow ascent is recommended.

 

[cathal]

Cathal, can you clarify "as fast as possible"? Also, off-gassing does not start at the first decompression stop. It begins on ascent at some point before the first stop; exactly where depends on tissue inert gas load.

Best regards,
DDM

As you can appreciate I can only give empirical observations on my part. When I leave the shot I don't attempt to slow down until the first stop appears. This is done in combination with a 1.5 SP on ascent and a high Low gf of 70. At 90M your on-gassing inerts a lot more than your off gassing them. Hence the rapid ascent rate.

 

[Germie]

I know 'off gassing point' from bounce dives, touch and go (I don't discuss if there is any fun or any reason to do bounce dives). If you go down as fast as possible, let's say to 130-150m depth, then you will be there in 10-13 minutes. If you go up directly again, you can go up to a 100 (or around 120m if you come from 150m) with 20-25 m/minute (as long as it is controlled). The theoretically reason is that you are still ongassing and if you go up 'asap', you can avoid some ongassing and offgassing is not a point at these depths. From the 'off gassing point' you go up with 9-10m/minute.
This is done by people who do bounce dives to 130+ meters. Going up so fast is difficult as it feels not natural. And it must be in control. But if you don't do that, the divetime will be much longer and more gas needed.

 

[Duke Dive Medicine]

As you can appreciate I can only give empirical observations on my part. When I leave the shot I don't attempt to slow down until the first stop appears. This is done in combination with a 1.5 SP on ascent and a high Low gf of 70. At 90M your on-gassing inerts a lot more than your off gassing them. Hence the rapid ascent rate.

Cathal, am I understanding correctly that you're ascending as rapidly as possible from a depth of 90 meters to a shallow first decompression stop?

Best regards,
DDM

 

[Duke Dive Medicine]

I know 'off gassing point' from bounce dives, touch and go (I don't discuss if there is any fun or any reason to do bounce dives). If you go down as fast as possible, let's say to 130-150m depth, then you will be there in 10-13 minutes. If you go up directly again, you can go up to a 100 (or around 120m if you come from 150m) with 20-25 m/minute (as long as it is controlled). The theoretically reason is that you are still ongassing and if you go up 'asap', you can avoid some ongassing and offgassing is not a point at these depths. From the 'off gassing point' you go up with 9-10m/minute.
This is done by people who do bounce dives to 130+ meters. Going up so fast is difficult as it feels not natural. And it must be in control. But if you don't do that, the divetime will be much longer and more gas needed.

Germie, I'm not condoning dives that deep or ascent rates like you describe, but I understand your point w/r to extremely deep bounce dives. The practice doesn't always correspond with the theory though, and it's worth mentioning that dives like this carry a high probability of severe decompression sickness. Commercial diving companies got away from doing them years ago for that very reason.

Best regards,
DDM

 

[leadduck]

In Uwatec computers, the off-gassing ceiling is called PDIS (profile dependent intermediate stop). The ascent rate depends on the absolute depth only, not on PDIS. The diver should stop a little above the PDIS (not below like for a deco stop).
See https://www.scubapro.com/sites/scubapro_site/files/galileo_luna_eng.pdf

 

[Germie]

Germie, I'm not condoning dives that deep or ascent rates like you describe, but I understand your point w/r to extremely deep bounce dives. The practice doesn't always correspond with the theory though, and it's worth mentioning that dives like this carry a high probability of severe decompression sickness. Commercial diving companies got away from doing them years ago for that very reason.

Best regards,
DDM

True, but I know it is done by some 'record dives'. (world record I don't know). I don't have problems with deep diving. But it must have a reason like a nice wreck, a nice wall, a nice cave.
From my own personal experience, the problems start around 130m depth. 1 time I had some hpns, on another dive I felt relaxed but was breathing 14-16 times a minute (normally 6-8 times), so it was time to leave that depth, and around 110m I was breathing normally again. But the best dives are cave dives in shallow caves with warm water. Deco is boring too