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| Originally Posted by Foggy Whilst this is true, it was also true at step 1. For the same logic you applied in chosing to shut down the RHS first rather than isolate, I think you should shut the LHS post next. Indeed, I think you already know this.....
So why waste time shutting it? If it wasn't the RH post, the left is the only thing you can do anything about so surely this should be shut next? |
You can shut either post and still lose all the gas from that cylinder. Shutting the isolator will stop the gas migrating from one side to the other
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Whoa, back up there. You shut the RH post = lets say its not the problem. You've already said that leaves the manifold which you can do nothing about or the LH post - You have already diagnosed this just by shutting the RH post..... or did I miss something??
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yup, I said we can do nothing about the isolator. We can certainly do something about the manifold. By closing the isolator we can isolate leaks at the point where the isolator joins the right and left posts. A leak at one of these points will result in the los of all gas from one cylinder, but isolating limits it to one cylinder.
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I know it is a drill, but drills do more than just build muscle memory - they aid in calming a dangerous situation because you just F'n do it - you know its the right thing to do and you do not have to engage the brain. I personally go all weak kneed at the sight of blood, but I have treated some gory first aid incidents by reverting to drill.
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"just F'n do it" is actually what we are trying to avoid. the DIR approach is to think about what might be wrong and diagnose the problem, rather than leaping in. Other approaches might then take a "OK, now calm down and diagnose the problem", I guess DIR just tries to do that from the first step.
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Now I am confused. If I follow this last piece of logic, why do you use twins with all those extra failure points? If the team has enough gas anyway??
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Becuase hopefully none of these failures will occur and we get to take advantage of having all that extra gas. It's the same logic as using thirds. Using thirds means a team of 3 divers comes up with a spare twinset of gas between them. How is that any different from us planning to keep enough to get two divers up to the next gas source? Using DIR's principle of minimum has means we always reserve enough gas to get outselves and another diver up to the next gas source, whether that be a gas switch or the surface. That's a calculation that tells us how much gas we need should one diver lose ALL their gas. It's just a gas rule like thirds is, with a little more refinement as it is calculated based on depth.
However, you've just got me thinking, and expect another thread on this subject imminently
