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lamont · January 20th, 2007, 04:57 AM

The DIR divers that I know who do big dives all carry bags and reels so that if they get separated they can extract themselves. Typically everyone has a bag, a reel, safety spool, a backup mask, backup cutting tools and a deco plan which can handle loss of a single deco gas. That makes any separated diver pretty self-sufficient. This has been tested through real-life sepearation and the separated diver has operated fine independently.

So, what does the argument center around here, is it just the backup depth gauge / timer?

The peril of going down this road too far is that you start to take failures which are not likely to be part of a cascade due to stress (like complete failure of an isolator resulting in total gas loss) and combine that with the separation scenario and wind up switching to independent twins because of the possibility of a massively remote failure case occuring at the same time as team separation. The correct answer there is to make team separation as infrequent as possible (if team separation is 1 in 100 and complete isolator failures are 1 in 100,000 then the combined risk on any dive is 1 in 10,000,000 which is getting into the struck-by-lightning its-just-your-time-to-go category).

So, there's a limitation to the incident pit analysis where different failures are more or less likely to be affected by stress. Messing up shooting a bag is more likely to occur while stressed. Having an isolator valve blow or even a depth gauge crap out is not going to be more likely while stressed (although the impact while already stressed of having a depth gauge go will be magnified). And I don't think that you can take a separated team member and do 'failure mode analysis' on their situation in the same way that you would a solo diver -- already you've hopefully got only a 1 in 100 chance of being separated or less, and if the failure is not stress-related then it should be at least two orders of magnitude less likely to occur on the same dive as separation as it would on a normal dive with a solo diver. I'm not generally going to be worried about those happening unless they're already fairly common (1 in 100 dives or so).

January 20th, 2007, 04:57 AM	#3 (permalink)
lamont(Offline) APLP Join Date: Nov 2005 Location: Seattle, WA Posts: 181	The DIR divers that I know who do big dives all carry bags and reels so that if they get separated they can extract themselves. Typically everyone has a bag, a reel, safety spool, a backup mask, backup cutting tools and a deco plan which can handle loss of a single deco gas. That makes any separated diver pretty self-sufficient. This has been tested through real-life sepearation and the separated diver has operated fine independently. So, what does the argument center around here, is it just the backup depth gauge / timer? The peril of going down this road too far is that you start to take failures which are not likely to be part of a cascade due to stress (like complete failure of an isolator resulting in total gas loss) and combine that with the separation scenario and wind up switching to independent twins because of the possibility of a massively remote failure case occuring at the same time as team separation. The correct answer there is to make team separation as infrequent as possible (if team separation is 1 in 100 and complete isolator failures are 1 in 100,000 then the combined risk on any dive is 1 in 10,000,000 which is getting into the struck-by-lightning its-just-your-time-to-go category). So, there's a limitation to the incident pit analysis where different failures are more or less likely to be affected by stress. Messing up shooting a bag is more likely to occur while stressed. Having an isolator valve blow or even a depth gauge crap out is not going to be more likely while stressed (although the impact while already stressed of having a depth gauge go will be magnified). And I don't think that you can take a separated team member and do 'failure mode analysis' on their situation in the same way that you would a solo diver -- already you've hopefully got only a 1 in 100 chance of being separated or less, and if the failure is not stress-related then it should be at least two orders of magnitude less likely to occur on the same dive as separation as it would on a normal dive with a solo diver. I'm not generally going to be worried about those happening unless they're already fairly common (1 in 100 dives or so).