Is conventional wisdom just conventional?

[Pitchblack]

Yesterday, me and some fellow divers from the local club went to a recompressioning-chamber ''test ride'. In educational purpose to see how nitrogen narcosis effects can vary and how they show themselfs. Deepest dive so far I can say, 50 meters.

Anyhow after the ''test ride'' we got a 'lecture' in hyberbaric medicine and dcs in particular. Many of the topic questions were answered. Bounce profiles are considered high-risk profiles and should be avoided, sure go up once or twice to check orientation but not eight times. And I also asked the 'reverse profile' question, about doing the shallowest dive first and then on the deepest and got the answer that on recreational depths it has no connection to dcs what so ever. He didnt even understand why it's still in the books for scuba education, couse this study that proves that it has no connection was layed out for about 5-6 years ago.

 

[Crowley]

a 'bounce dive' is as originally described - rapid descent, no bottom time, rapid ascent. I've seen a video of a dive computer to 100 metres and back in just a few minutes. (The computer belongs to a guy I used to work with who wrote the decompression profiles for some of the world record attempts.) It is theoretically possible to accomplish because you can't absorb enough nitrogen during the descent for it to make any difference on ascent - however it's theoretical and I certainly wouldn't advise anybody try it!

Sawtooth is certainly not good - I know a guy who got bent doing exactly that - 40 to 20 metres and back (repeatedly) on a wreck dive - cerebral decompression sickness - the outcome could have been a LOT worse.

Reverse profiles - some mathematical models suggest that reverse profiles may be *better* at reducing your risk of DCS - but Suunto for one, disagree as their research indicating the prescence of microbubbles formed when you're off-gassing seems to suggest that reverse profiles are not recommended. As the OP so very well described though - one thing is for sure, you can't plan many convenient reverse profiles using a standard dive table, and they were the mainstay of diving for a long time. I have - for no real reason - always thought that there's something that seems sensible about deep first shallow second (or is that just me!?)

 

[Diver0001]

Yesterday, me and some fellow divers from the local club went to a recompressioning-chamber ''test ride'. In educational purpose to see how nitrogen narcosis effects can vary and how they show themselfs. Deepest dive so far I can say, 50 meters.

Anyhow after the ''test ride'' we got a 'lecture' in hyberbaric medicine and dcs in particular. Many of the topic questions were answered. Bounce profiles are considered high-risk profiles and should be avoided, sure go up once or twice to check orientation but not eight times. And I also asked the 'reverse profile' question, about doing the shallowest dive first and then on the deepest and got the answer that on recreational depths it has no connection to dcs what so ever. He didnt even understand why it's still in the books for scuba education, couse this study that proves that it has no connection was layed out for about 5-6 years ago.

The conclusion of that study was that reverse profiles with a depth differential less than 40ft carries no significant risk.

I read two things into that. Reverse profiles with large depth variations *are* possible within recreational diving and while they didn't find issues with minor depth changes the principle that it isn't good for you would appear to have been confirmed.

The general risk picture, however, would appear to be less severe than most of us were taught.

R..