Spare Air Question

Ok, here's a question...

I was teaching an open water class last year and two of my students proudly pulled out their newly purchased spare airs. Immediately I started doubting myself, wondering what I had done wrong such that my students had bought these bouncing disasters (they do bounce, try it sometime. If they dont bounce try harder.)

What do you tell someone under these circumstances? I did my best to provide them with realistic advice about just how useful the spare airs would be. I felt like I was crapping in their frosted mini-wheats...

Atticus:

What do you tell someone under these circumstances? I did my best to provide them with realistic advice about just how useful the spare airs would be. I felt like I was crapping in their frosted mini-wheats...

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As you said, you educate them.

They are small, they are self contained/100% redundant to the primary air system, that's good.

They may let you cover a little distance to reach a buddy on a deeper dive, they will offer some breaths on a deeper ascent.

They won't allow for a propper ascent on a dive to any real depth. From there just reinforce the gas planning work you may have done or walk the through a quick rock bottom for 1 calculation. Anything can be mis-used these things just have a slim margin in a life safety situation.

Personally when I decide to have a redundant air source I'll go pony.

Pete

I showed them what I use as a redundant air source - an alu40 setup as a sling/stage bottle. The difficulty of course is that they had already purchased their goodies and I was giving them advice after the fact. I attempted to emphasize the positive aspects of their choice for the appropriate environment - namely for diving within the open water certification depth range. Truthfully a spare air could actually be useful to someone who unexpectantly (shudder) hit the bottom of their tank and is too far from their buddy. It's enough gas to make what would be a CESA for you and I go more smoothly for a novice diver.

I'll stick to teaching good gas management and awareness, but I just thought I'd point out that the things could be useful in some limited circumstances.

Atticus I think you are spot on. The best you can hope for is to have students leaving you informed. There are too may sides to almost any scuba issue to ever expect 100% alignment.

I have not stopped considering myself a novice diver yet FWIW.

Pete

Pete

Take them to 18m ( or whatever depth they are certed to) turn off their air, wait till they start to panic and then hand them thier spare air. If they survive then they made a wise purchase. If they dont make sure no one can find the bodies.

Atticus:

Truthfully a spare air could actually be useful to someone who unexpectantly (shudder) hit the bottom of their tank and is too far from their buddy. It's enough gas to make what would be a CESA for you and I go more smoothly for a novice diver.

I'll stick to teaching good gas management and awareness, but I just thought I'd point out that the things could be useful in some limited circumstances.

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that's what i was gonna say..... "could actually be useful". i know i don't hit the water unless i have my handy-dandy spareAir tucked in and ready to go. i don't have numbers, but i'd 'guess' that most dives ARE within recreational limits so therefore the spareAir would be a fine addition to a SCUBA 'kit'.

there is NO argument that a PONY setUp is superior, but realistically who's gonna wanna deal with the 'hassle' of a full PONY setUp for a 60' dive? the spareAir isn't big, but it IS convenient. wouldn't it be better to be like a boyScout and "BE PREPARED"?

i tried it once.... 10 minutes of air sitting on my sofa. that's 3 minutes at 60' - but guess what? if the poop has hit the fan, you can bet i'm NOT hanging out at 60'. at the recommended ascent rate of 30'/minute - even if you factor in that you'll probably be breathing twice as fast due to the 'incident' that caused you to use the spareAir.... you might even have enough for a relaxed safety stop at 15'

meekal:

i tried it once.... 10 minutes of air sitting on my sofa. that's 3 minutes at 60' - but guess what? if the poop has hit the fan, you can bet i'm NOT hanging out at 60'. at the recommended ascent rate of 30'/minute - even if you factor in that you'll probably be breathing twice as fast due to the 'incident' that caused you to use the spareAir.... you might even have enough for a relaxed safety stop at 15'

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I am no expert here but don't spare airs hold 1.5 cuft? That means your RMV is .15 cuft/min. Wow that is amazing:06:

Sometimes teaching involves saying things that people don't necessarily want to hear ... but it sounds like you did what a good teacher should do - show both sides of an issue, what you prefer and why, then let them learn and make their own decision. Far better than letting them become dependent upon something that may not be adequate in an environment they end up using it in, because they didn't know it was not designed for that environment.


Aloha, Tim

meekal:

i tried it once.... 10 minutes of air sitting on my sofa. that's 3 minutes at 60' - but guess what? if the poop has hit the fan, you can bet i'm NOT hanging out at 60'. at the recommended ascent rate of 30'/minute - even if you factor in that you'll probably be breathing twice as fast due to the 'incident' that caused you to use the spareAir.... you might even have enough for a relaxed safety stop at 15'

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Hi Meekal, thanks for the response. I'm responding with the pitfall of the spare air not to rehash an old tired subject, but because I think it might make a difference to someones safety. Please make your own decision and understand that I in no way am attacking you for making that decision.

I breath about 0.6cfm when I'm calm and scuba diving. On the couch I do quite a bit better. Most newer divers that I've seen breath around twice this fast. If choose a nice number like 1 cfm for a novice under normal conditions, and assume a 50% increase during an out of air situation then we have 1.5cfm at the surface. At 66' that would be 4.5 cfm.

Let's sanity check that number. That means that a novice diver during a normal dive would go run an alu80 down to 500psi at 66' in around 20 minutes (77cf in an alu80, we're using 2500/3000's of it, RMV=1.0 (non-panic), 3cfm consumed at depth). This is inline with what I typically see people do in their first 30 dives or so. Remember that this is spending the entire time at 66', not a dive where they touch 66' and then spend some time shallower including a 3minute safety stop.

Ok, so at 4.5cfm they have about 20 seconds on the spare air. If they are swimming towards the surface at a reasonable rate then they'll get a couple (like 2 to 3) breaths during the ascent.

If they kept their regulator in their mouth they'd have less going on (no reg switch), might be more likely to do the aaaaah bubbles / keep their airway open, and they'd like get a breath or two of air as they ascended (due to the drop in ambient pressure - an empty tank at 60' is good for a breath at 30').

Just something to consider.

Kindest Regards,
Merlin

Atticus:

Ok, here's a question...

What do you tell someone under these circumstances?

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You could tell them ebay is their friend. It's amazing how many people bid on those things when they come up for auction. Selling them wouldn't be difficult.