Hypothetical Pony Bottle Ooa Situation

[Yoyoguy]

All I was just thinking of a situation that was never explained to me before. I am deep diver and nitrox certified. Let's say for example Im going to do a nitrox dive to 130ft on 28%. On my dive computer this gives me a NDL of 11 minutes. Now whenever I dive deep past 75ft I typically bring a pony with me. The pony I have is always filled with air. So let's say for example we are at 130ft and approaching our NDL when something goes wrong such as complete regulator failure or free flow or whatever causes you to switch to pony. Now let's pretend you calmly switch over to your pony which is a 40cuft so you have plenty of gas to make a safe ascent. Should you then switch your dive computer to the second gas setting which let's say was set to air and then safely make your ascent. This way your computer keeps calculating things appropriately? I honestly never really gave it a thought that my pony is never filled with the same mix as my back gas is on nitrox dives. Please don't flame me...just looking at honest answers here.

 

[rongoodman]

It's not going to make any difference to your ascent. It might affect how much tissue loading your computer thinks has happened when it calculates NDLs for subsequent dives, although it's hard to say how much, given how little time the ascent and safety stop will take.

 

[CuzzA]

I would think it really doesn't matter much if you switch your computer in the grand scheme of things. You're going to the surface and may be done diving for the day, unless you can fix whatever went wrong. In that case I would extend your safety stop and likely be fine. Why add another task to a situation that probably has your heart pumping.

 

[Yoyoguy]

I would think it really doesn't matter much if you switch your computer in the grand scheme of things. You're going to the surface and may be done diving for the day, unless you can fix whatever went wrong. In that case I would extend your safety stop and likely be fine. Why add another task to a situation that probably has your heart pumping.

That was what I was thinking, however, if in the off chance you are fine and calm...why not? But yeah...if it really doesn't make any real world significant difference in the gas in your body...figuring 4 minutes to get to safety stop...assuming 30ft per minute ascent...and then a 3-5min safety stop at 15ft...I doubt it would likely put you into a a NDL violation. You could also extend your surface interval by quite a bit if you had the time and spare items to get you back diving

 

[PfcAJ]

Just ascend. Fiddling with your computer gives zero real benefit.

 

[CuzzA]

That was what I was thinking, however, if in the off chance you are fine and calm...why not? But yeah...if it really doesn't make any real world significant difference in the gas in your body...figuring 4 minutes to get to safety stop...assuming 30ft per minute ascent...and then a 3-5min safety stop at 15ft...I doubt it would likely put you into a a NDL violation. You could also extend your surface interval by quite a bit if you had the time and spare items to get you back diving

Yeah, extend your surface interval or set your computer to air and dive Nitrox on your repetitive dive if you were really concerned. In all honesty though, every rare account I've read of someone having to go to their pony to finish a dive they were done diving for the day. Think about it... You just had a serious failure of your primary life support system and depleted your backup, assuming you think you fixed whatever problem you had are you really going to go back down again without that backup? Not likely. Lol

 

[Yoyoguy]

Yeah, extend your surface interval or set your computer to air and dive Nitrox on your repetitive dive if you were really concerned. In all honesty though, every rare account I've read of someone having to go to their pony to finish a dive they were done diving for the day. Think about it... You just had a serious failure of your primary life support system and depleted your backup, assuming you think you fixed whatever problem you had are you really going to go back down again without that backup? Not likely. Lol

This is an excellent point

 

[The Chairman]

Just switch the gas on your PDC. It should be easy to do. If not, practice it until it is. At 130 FSW, you're narced and simply cannot rely on your senses. IOW, you have no idea if you're coming up at the rate of speed you think you are and if you already have a deco obligation, your body won't clear it as quickly on air. Don't muddy the waters any more than they already are. Set your PDC to the gas you are breathing and stop worrying about it.

 

[uncfnp]

Yeah, extend your surface interval or set your computer to air and dive Nitrox on your repetitive dive if you were really concerned. In all honesty though, every rare account I've read of someone having to go to their pony to finish a dive they were done diving for the day. Think about it... You just had a serious failure of your primary life support system and depleted your backup, assuming you think you fixed whatever problem you had are you really going to go back down again without that backup? Not likely. Lol

Hmmm. I guess it depends on the actual circumstances. NDL dive, freeflow regulator, switched to pony, did SS. Back on board, switched regs, checked gear, dropped for second dive with about half the gas in the pony. Then again these were dives less then 100. Might have felt differently if deeper.

To the OP, if the computer is set up and capable of making the switch. Sure, once all is under control. But I would guess that the majority of recreational divers, even "advance" do not have a multigas dive computer. And as already pointed out, not critical to the dive.

 

[Bob DBF]

Well, first I don't have a computer that can switch gas, and second, switching gasses on a computer would not be on the top of the list in an emergency. In the stated case, since I can't switch gasses on the computer, I would just burn my pony at the safety stop.

I guess the good news for me is that I rarely use Nitrox.


Bob