OP
Deco tank SPG ** POLL **
- Thread starter Mike Edmonston
- Start date
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Before:
pressurize
deploy
burp (with L hand on knob)
turn on (L hand still on knob)
switch
breath - no gas = screwup
I do the interruption test after I get on the gas as a backup to the double check from a buddy. Having a buddy go OOA at this point could be an issue, but probably only if they were OOA to begin with.
Do you do the interruption test after you unstow the deco reg or before?
Interesting - although I'm a bit confused about your procedure. How do you do an interruption test when you're breathing off the gas? This is assuming the valve is open and breathing or purging the reg should not result in the SPG moving unless there was an issue with the regulator or the valve isn't all the way open. Or you do the interruption test another way altogether?
What I do is as we're approaching the gas switch depth, unstow the reg, trace it back to the cylinder and visually verify that I have the correct cylinder. Do a quick purge on the reg to watch the SPG needle move - this verifies the reg I have in my hand is connected to the cylinder I am looking at. Once that is done, I turn the gas all the way on. Then have my buddy visually verify that I have the correct cylinder, then final check on the depth gauge and switch.
To do the interupption test while breathing the reg, I close the valve and either watch the needle bounce or I'll feel the reg bottom out- no gas. Then I turn the valve back on and continue breathing. On paper, it's not that different than pushing the purge button, but I'm just happen to be breathing the gas. Also, on paper, I think our procedures are similar, but the order is reversed- buddy check first, then interruption test versus interruption test first, then buddy check. Of course, in the water, those slight differences appear larger.
rjack- I think you meant to say that you do the interruption test after you unstow the reg but before you actually breath it
ohh and the point of this slight hijack as to show that you don't need the SPG to do the interruption test if you are breathing it. I have a dedicated O2 reg and it has an SPG on it.
To do the interupption test while breathing the reg, I close the valve and either watch the needle bounce or I'll feel the reg bottom out- no gas. Then I turn the valve back on and continue breathing. On paper, it's not that different than pushing the purge button, but I'm just happen to be breathing the gas. Also, on paper, I think our procedures are similar, but the order is reversed- buddy check first, then interruption test versus interruption test first, then buddy check. Of course, in the water, those slight differences appear larger.
rjack- I think you meant to say that you do the interruption test after you unstow the reg but before you actually breath it
ohh and the point of this slight hijack as to show that you don't need the SPG to do the interruption test if you are breathing it. I have a dedicated O2 reg and it has an SPG on it.
That's an interesting way to approach it. I would have a couple of questions, though.
If you're already breathing the gas and it happens to be the wrong bottle you're on, I do realize that a couple of breaths are not likely to result any problem, but is that not much of a concern? If you breathe the reg down to nothing, does the risk of the 1st stage coming unseated due to lack of pressure become an issue?
As far as breathing the wrong bottle, the bottle was already verified by my buddy (with deco reg unstowed and in front of me so the hose can be visually traced to the bottle) before I switched.
Yes, there is a possiblity that the 1st stage could leak, although I think the same would exist IF you purge the reg completely as well. Admittedly, it's probably easier to purge the reg just enough to see the needle bounce but not enough to drain the hose.
For me, the confirmation is much stronger when I can feel the reg bottom out and then work again, versus watching the movement of the needle. What if you bump the SPG at the wrong time and the needle bounces? Depending on how many deco bottles you have, it's possible that pushing them around could depress the purge on a different deco reg at the wrong time. Yes, these are a little thin, but certainly possible.
EDIT: oh and yes, your procedure would catch these errors since you would get no gas when you made the switch.
I think there are pitfalls and advantages to both approaches, and it really depends on which poison you and your team consider scarier or more frequent. Although that shouldn't stop us from hashing them out to see if there is a better way.
What I´m saying is that the dive isn´t over until you break the surface, your O2 is part of your delimiting factor at that depth and the basis of my actions during a dive.
I do the same thing (pressurize then shut off valve) but there are still a fair number of scenarios where O2 becomes a scarcity, in such scenarios knowing how much O2 remains in a team or among divers on an upline becomes valuable. I believe that the utility of the spg is greater than that of the alternative (=no spg).
It does boil down to what you and your team are comforable with.
But the way I'm looking at it is this. Before getting on the gas, Doing a buddy verification and the interruption test are two ways. Getting on the gas only after a buddy verification is going to be less certain in my mind. It would then depend on what you're comfortable with. What do you gain by switching before you do an interruption test? Well, you get on your deco gas sooner. What is the risk? I suppose you have less certainty with only the the buddy check than with both the buddy check and interruption test. Is the benefit vs. risk worth it? Not sure, only you can answer that.
If we do both the buddy verification and interruption test first before switching, what is the benefit? Well, for me, greater certainty I have the right bottle. What is the risk? Perhaps not getting on your deco gas as quick. So again, is the benefit vs. risk worth is? This latter method was how I was trained. Getting on deco gas a few extra seconds later won't make much of a difference, but the extra verification to me would be worth it.
As far as the purging is concerned and the unseating of the reg, sure, if you purge and hold it down until it completely bleeds off, then yes, you run the same risk. However, I generally give it a light tap so that the needle moves, but doesn't depressurize the reg- and the chances that the needle moves due to a bump at the exact instant I tap the purge probably isn't much to worry about.
In the end, you're right. It's what you're comfortable with.
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