hypothetical deco regulator failure

[PfcAJ]

My gas choice for a 100ft cave dive is the exact same as it would be for a 100ft ocean dive: 100%. Howevern for a deeper cave dive (which, for me, implies a longish bottom time) ill be bringing two gasses each and every time. But for a short duration tech 1 type dive, a single bottle of 50% remains the answer. I'm curious to who these tech 1 instructors are who take a stage with them for class dives. That certainly didn't happen on my class with Dean Marshall.

Stating that you know of divers who take extra tanks with them doesn't mean a lot to me. I know plenty of divers that take pony bottles with them (heck, I know one that takes a pony on cave dives). It doesn't make it the best idea. From what I've seen, less is almost always more when it comes to equipment, and getting onto a deco gas a little deeper is a pretty good idea. Id love to read this dan study and see how it is similar or different to the way I was taught to utilize 50%.

Btw, I personally know a diver who got bent after an o2 deco, another after a ccr deco, and another after a deep trimix deco with multiple gasses. I've had some serious "deco stress" after o2 dives, but that (for me) has been less common when I used 50% only or in conjunction with o2. I think the real money maker in any deco dive is the intermediate and deep stops.

 

[rjack321]

I've used bottom stages on ~150ft, 20-30min BT dives before. But it was for reasons other than needing a TON of gas to get from 150ft up to 20ft with an OOA diver to go onto 100% as our lone deco gas. Saying "some GUE instructors bring a bottom stage" without elaborating or even knowing why is not useful.

Reasons I've used a bottom stage in this range before:
No access to fills for the doubles & 2nd or 3rd dives planned
Wreck penetration it takes a ton of gas to even do a short penetration diving 1/3rds after taking away rock bottom.
Changing mixes with this being a slightly shallower dive and saving the richer helium backgas for a different dive.

I would not bring just 100% for an otherwise short duration ocean dive. These exposures are characterized by mostly fast (neurological) tissue loading and very modest slow tissue loadings (fat, tendon etc). Getting onto a deco gas lower in the water column without having as much pressure reduction as ascending all the way to 20ft is a wise decompression strategy. Off-gas the fast tissues sooner, before any bubbles present in those tissues have had a chance to grow. Since there's less slow tissue loading, 100% or other very high O2 content gases are not really required to finish decompression (unless this is the 2nd or 3rd deco dive of the day for instance).

Taking 100% alone is optimizing for an off-gassing problem which doesn't exist at the detriment of a problem which does.

 

[Amphiprion]

Lots of good replies. Thanks.

I suppose I should qualify my original post by saying that while there is enough gas for everyone to decompress, everybody has a single deco bottle. If your deco reg is out of order at the point where you typically switch to deco gas, I see three choices. Put another regulator on your deco bottle, deco on back gas which is longer, or buddy breathe deco gas (since I have yet to see anyone octo a deco regulator).

I suppose I am thinking of a typical 170' dive with each diver having some helium to avoid narcosis and a single bottle with enough EAN50 for their own deco plus extra. One choice is to deal with water in your regulator, another is a longer deco due to helium and the third is something we can all do, but is admittedly a bit of a pain for half an hour of deco. I guess stem breathing is also an option, but again a pain for half an hour of deco.

By the way, I didn't run actual numbers on this hypothetical dive so whether I am using EAN32, EAN50, EAN80 or O2 wasn't really my point.