Quote:
| Originally Posted by [b Quote[/b] (Mark Chase @ Aug. 29 2003,21:10)]OK there are several threads I could start offering the DIR chaps a chance to educate me but folowing on from recent posts I would like to start with this.
When I plan a dive, I plan a 1.4 ish max PP02 at dive max depth. That being the sea bed i doubt if I will be there longer than it takes my ego to log it and the rest of the dive will be somthing like 1.3. 
My travel gas has to provide a bail from the bottom option. This means that i will be within 10m of gas switch depth to travel from the top of the wreck
This invairably means that the piss gets taken out of me for taking two stages on a relitavly shallow 45m trimix dive but ridicule I can cope with death is harder for the kids to bear. On more serious stuff I will take a pony of somthing to get me to first stop depth.
One of the big problems I had with going DIR is they wont allow me to do this.
I was limited on back gas and limited on deco gas to the standard gas list provided by GUE. This lead to longer deco due to low pp02 on deeper dives and reduced bail out options.
Quote from JJ:
A diver will quickley see that a dive to 45m using 100% 02 and 50% Nitrox is more than suficient for efficient decompression, while adding 35% Nitrox to these has negligable impact on decompression but adds drag, weight and risk.
End quote
I would counter argue that a diver using 50% travel / deco has nothing to bail too at 45m
So my questions are:
1: Do DIR insist on the standard gas issue and if so what is the justification. I can see that standardising the mix across the teem is good but across ALL dives seems a little restrictive.
2: Why if standard mix is a must do, does JJ include a chapter in his training manual Beyound The Daylight Zone about air topping fills??
ATB
Mark Chase |
Quote:
| Originally Posted by [b Quote[/b] ]I would counter argue that a diver using 50% travel / deco has nothing to bail too at 45m |
As with most things DIR, we allow for two failures (with the exception of lights). We have two first stages, two second stages, two methods of deploying an SMB etc. The third "backup" is our buddy. So, if you are unfortunate enough to have two regulators fail, you have a buddy close by with a third. If you have a deco gas failure you have a buddy with sufficient deco gas for you to use, or you can finish the deco on your backgas etc. To answer your question, your backup gas at 45m is with your buddy.
Quote:
| Originally Posted by [b Quote[/b] ]1: Do DIR insist on the standard gas issue and if so what is the justification. I can see that standardising the mix across the teem is good but across ALL dives seems a little restrictive. |
Standard mixes mean everybody in the team have a uniform approach so we all do our gas switches at the same depth, we all plan the same bottom time, same ppO2 etc. more important we can all share the gas we are breathing at *all* depths and at any time during the dive.
Quote:
| Originally Posted by [b Quote[/b] ]2: Why if standard mix is a must do, does JJ include a chapter in his training manual Beyound The Daylight Zone about air topping fills?? |
You can successfully air top a fill and still get a useful mix. The important thing about being in a team situation is that your buddy's gas must be breathable by you, so it figures that the gas must be the same (within reason)
I don't really understand why you are needing a travel gas and a bail out gas? Although I suspect this might have something to do with solo diving? But of course, we don't do that ;-)
Bob