Posted by Ken Kurtis on October 29, 2000 at 23:40:27:
In Reply to: Half as bad posted by Eins on October 28, 2000 at 22:46:28:
(Eins stated) My concern was that you appeared to deny the added safety margin of a dive to only 75 fsw (25% safety margin) or 81fsw (19% safety margin) vs. a dive to 100fsw.
Arno, I think you're getting in over your head here. A 75' dive is not 25% safer than a 100' dive just because it's 25% shallower. (Although I'll concede that a 0' dive is 100% safer than a 100' dive, or any other for that matter.)
To compute the actual theoretical safety margin, you'll have to figure it based on controlling tissue, tissue half-time, M-values, etc., etc. etc. And you'll also have to cover the debate on whether or not a diver at an NDL at 100' is at the same DCS risk as a diver at an NDL limit at 75'. Is saturated saturated and the risk the same? Or is there evidence to suggest that since the controlling tissues change, the risk factor of an unexpected hit changes? And what would be the data to support the findings?
(Eins continues) All under the assumption that the deeper the dive, the greater the risk of an unexpected hit . . .
I'd be curious to know where this assumption comes from. There are a number of hyperbaric folks (who know much more about this than any of us "experts" here do - myself included) who feel that "unexpected" hits more likely come from slow tissues (aka shallow dive) rather than fast tissues (aka deep dive).
As far as unknowingly "agreeing" with you, please re-read what I said. It had nothing to do with doing the dive on nitrox. I said you can do the dive safely on air (even to 100'). And if you want the "safety" factors you can either dive shorter or dive shallower (since the wreck starts around 60', you don't have to go to 100'.)
Enough said. (And the diving today was wonderful. 60' vis on Catalina's West End with most of the day non-drizzling. Water temp 61º with a 59º thermo at 50'.)
Ken Kurtis
NAUI Instr. #5936
Co-owner, Reef Seekers Dive Co.
Beverly Hills, Ca.