ianr33
Contributor
If you are in deco and relying on a Spare Air then you deserve anything bad that may happen to you. 
Switching gasses at depth?
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ianr33
Contributor
That's assuming you believe spare air can be used safely on any dive
Spare Air can be used 100% safely on any dive. The problem comes when you are not using it after a couple of minutes.
Kind of like when I was into rockclimbing. Never hurt myself climbing. Falling was fine as well,but man,the stopping part can hurt
Well....they're awfully cute !
rstofer
Contributor
Or you can buy a computer that can handle gas switches. The Dive Rite Nitek Duo is such a computer and I believe all of the clones are also capable.
If you really want to put Nitrox in the Spare Air, consider a wimpy mix like 28% as the MOD (Maximum Operating Depth) is 132 feet - the recreational limit. You probably don't want to use 40% because the MOD is just 83 feet.
If you assume a SAC (Surface Air Consumption) rate of 1 cfm and you're hanging around at 100 feet, you will consume 4 cfm. Trying to ascend from that depth, you will probably consume 2.5 cfm average over the 3 minutes you should take to make the ascent and thus require at least 7.5 cf, far more than a Spare Air contains. Of course, your first breaths are likely to be huge gulps, far exceeding 1 scfm (4 cfm at depth) so the SA will be nearly empty before you even begin the ascent.
I suggest you experiment with the Spare Air while you still have a functioning regulator. Try making an ascent from whatever depth you believe is practical.
Don't be surprised when you figure out that a 19 cf pony bottle is just about right for 100' dives. Oh, and your buddy is NEVER your backup plan!
Richard
If you really want to put Nitrox in the Spare Air, consider a wimpy mix like 28% as the MOD (Maximum Operating Depth) is 132 feet - the recreational limit. You probably don't want to use 40% because the MOD is just 83 feet.
If you assume a SAC (Surface Air Consumption) rate of 1 cfm and you're hanging around at 100 feet, you will consume 4 cfm. Trying to ascend from that depth, you will probably consume 2.5 cfm average over the 3 minutes you should take to make the ascent and thus require at least 7.5 cf, far more than a Spare Air contains. Of course, your first breaths are likely to be huge gulps, far exceeding 1 scfm (4 cfm at depth) so the SA will be nearly empty before you even begin the ascent.
I suggest you experiment with the Spare Air while you still have a functioning regulator. Try making an ascent from whatever depth you believe is practical.
Don't be surprised when you figure out that a 19 cf pony bottle is just about right for 100' dives. Oh, and your buddy is NEVER your backup plan!
Richard
Reg Braithwaite
Contributor
ligersandtions
Contributor
So are kittens but i wouldn't take one of those diving either
Okay, that was really funny!Not much to add here, but as you've read, having air in your spare air and Nitrox in your tank will not be an issue in the case that you need to use your spare air. However, I would strongly suggest you do some reading about the debate on spare air versus a pony tank versus the buddy system. Make your decision on what you'd like to use after you've done a fair amount of research....people will fight over what's best (I'll bet this thread blows up!), but ultimately it comes down to what you feel will work best for you. I can offer my opinion, but in the end, it's just MY opinion....and you need to make YOUR opinion.
NorthWoodsDiver
Contributor
go out and buy an aluminum 40 and get some stickers to write "Spare Air" on the side, then you can actually say you are carrying enough gas to get you up safely from 150' or so even with some deco.
you will learn all about nitrox in your class and your concern about gas switching is actually legit but not for nitrox to air. if a diver was diving heliox or a rich trimix and switched to air from very deep depths you would run into issues but for semi recreational nitrox diving within the recreational limits there is no worries.
no worries other than the fact you have a spare is in any place besides a pool. dump that thing, ebay will gladly help you sell it. then put that cash towards something useful.
you will learn all about nitrox in your class and your concern about gas switching is actually legit but not for nitrox to air. if a diver was diving heliox or a rich trimix and switched to air from very deep depths you would run into issues but for semi recreational nitrox diving within the recreational limits there is no worries.
no worries other than the fact you have a spare is in any place besides a pool. dump that thing, ebay will gladly help you sell it. then put that cash towards something useful.
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