Is it OK to turn off O2 in Rebreather Training?

[rjack321]

Oh, so you think that the instructor might have turned off his O2 before he splashed as a test? Yes, I agree, that would be a bad idea. But I don't think that anyone was suggesting simulating O2 feed loss at the surface in the part of the thread where we were discussing that specific drill at depth.

No I don't even know if this was a class dive? Didn't sound like it but the reports weren't specific - I guess anything is possible at this point. But I also don't think having done drills with it off at depth would have somehow "taught him a lesson" so that he'd be less likely to splash with it off either.

 

[doctormike]

But I also don't think having done drills with it off at depth would have somehow "taught him a lesson" so that he'd be less likely to splash with it off either.

Right, those are two different skill sets. One is doing a standard checklist before splashing, the other is being aware during the dive at depth. The drill we are discussing is for the latter.

 

[Colliam7]

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A ScubaBoard Staff Message...

This thread is a split from an A&I thread discussing an accident in Hawaii. Midway through that thread, the discussion evolved to consideration of a particular practice in training, reflected in the title of this thread. The relevant posts from the A&I thread have been moved here, to facilitate a discussion with a different focus from the A&I thread.

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[Germie]

I don't turn off oxygen in any course. And I never had instructors who did this with me.
For the BOOM I let them close the oxygen valve of course, but I check if it was opened again. Same with 'solenoid stuck open' drill.
Besides of the risk of not seeing a turned off valve by the student, why would you want to take the risk of moisture in the first stage or solenoid when the oxygen ist turned off and pressure is zero?

In blind mask drills, the student has to take the hud under the blind mask so he can monitor his own PO2. If you don't have a hud, then.....bailout.
In real: normally you can read your PO2 monitor. If not, then do what is teached: bailout. Always know your PO2.

 

[doctormike]

I don't turn off oxygen in any course. And I never had instructors who did this with me.
For the BOOM I let them close the oxygen valve of course, but I check if it was opened again. Same with 'solenoid stuck open' drill.
Besides of the risk of not seeing a turned off valve by the student,

So if it's OK from a safety point of view for you as the instructor to check their closed valve for the boom drill, why not for the O2 shutoff drill? In both cases, you are taking on that responsibility as an instructor.

why would you want to take the risk of moisture in the first stage or solenoid when the oxygen ist turned off and pressure is zero?

This is a good point, especially since the first response to a dropping PO2 is to hit the MAV, which will depressurize the LP line... It's not really a safety issue, though.

 

[Germie]

In the BOOM drill the student knows he closes the valve HIMSELF. Same with solenoid stuck open. But I never close a valve (nor in oc) without notice of the student.

If you do not know the oxygen is closed, the oxygen in the hoses will be used by the solenoid to hold the PO2 (or the leaky valve in case of mCCR). Then the hoses are empty. AS long as there is some pressure in the hoses, no water inlet. But if everything is depressurized? Normally no moisture entering, but I have had it with a valvedrill on oc, after depressurization of the hoses and reopen the valve the first stage O ring was not closing correctly anymore and I had a leak and had to depressurize the hoses again, wiggle on the first stage and reopen the valve again to solve the problem. If it is only 1 drop of water, salt water is worst, it can make you have to service your regulator, or in worst case the solenoid or leaky valve. So I try to avoid it. The risks are small, but I try to avoid.
If you don't know that an instructor did close the valve and you hit somewhere the first stage and it is coming loose a little bit. After opening the valve there is a risk of leaking and moisture getting in. It is not a risk for the student who directly see it that I have closed a valve, but if you wait till the spg shows 0, then there is a risk. Risk is small, but there is not written that I have to close valves on courses, so I don't do that. Not in open water, not in caves. If a valve is closed, you have done it yourself, or it was a roll off. I tell students this. I can do entanglements, show them 'wrong gasswitches', etc. But no, I don't close valves.

 

[cerich]

You know, I really respect all of the people objecting to this teaching method, but some these objections have a straw man quality to them. Even on the surface, it takes six minutes to become hypoxic. And Superlyte is not advocating just "turning off the O2" and leaving.

Let me ask you something. If the objection to the O2 shutoff is that (1) the student might be incapable of responding appropriately, and (2) the instructor might not intervene before the drill becomes lethal, why don't you have the same objection to a loop recovery drill? Wouldn't that situation become lethal much faster?

My objection is twofold 1/that in the event the drill goes pear shaped the instructor can't defend the action. 2/that you can achieve the same training outcome without the instructor being the one to shut off gas.

 

[PfcAJ]

Turning the thing off that keeps the student alive is not a good idea.

 

[LiteHedded]

Turning the thing off that keeps the student alive is not a good idea.

well yea

didnt this just kill a guy not too long ago in a class at blue grotto?

 

[rjack321]

well yea

didnt this just kill a guy not too long ago in a class at blue grotto?

While blindfolded yes