To shop owners or owners of spare air tanks

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My problem with the spare air is that it is like trying to jump across a chasm in 2 or 3 jumps. If there is not enough air in it to get you to the surface, how does it help? If you need (say) 10 breaths and you only get (say) 3, are you really better off? The spare air give the illusion of redundancy, when it fact it is not sufficient. Yes, of course, if you are 15 feet from the surface and run out of gas, then it might help. But you don't need it if you are 15 feet from the surface. Yes, i believe in redundancy; but a spare air is not redundancy, it is a fantasy.


My method would be a little different than yours. With a full breathe, I can slowly exhale while ascending to prevent a lung OE injury and CESA 20 feet easily on that one breath. I know this because I've done it from 32 feet before. If I only get 3 breathes from a SA, I'm looking at at least 60 feet of ascent travel. Probably more like 75 in a "no other choice but to do it or drown" scenario.

My guess is you'll be breathing sea water at least 60 feet before I will. Here in the the SCUBA sport we call that drowning. Drowned divers don't have to calculate the added inconvenience of getting bent from a CESA or don't have to worry about the $70,000 bill for the decompression chamber ride that might follow. :)

And I can't say much for the "I'd rather have nothing than have three breaths" comment. That's pure bravado ego talking right there. I've been in a firefight in Iraq and used my 210 rounds basic load of ammo. **** was starting to get scary. I had grabbed a piece of a belt from the saw gunner before we left that had about 60 rounds on it and had crammed it in my butt pack for some reason, "just in case" but I had to go thru the hassle of breaking each round off the belt one by one and loading them into my empty mags before I could fire them. I'm here today because having a little is a proven winner over having none. Wishes and letters from mama don't kill insurgents. Bullets do. "You fight with what you have, not what you'd like to have." Fighting for your life to keep from drowning is the same as fighting for your life on the battlefield.
 
...//... Fighting for your life to keep from drowning is the same as fighting for your life on the battlefield.
I wouldn't know. Never been on a battlefield. However, I have watched my ADHD son do some really stupid life threatening stuff. So I *brilliantly* made sure that he always had a huge air/gas supply.

Maybe not so smart on my part. He gets creeped out on a dive, drops to the bottom and starts to take the long way out. I'm at 300 and start to breathe rapidly. One does that in nasty situations.

Forever more, I'll freaking guarantee that I will always have more air than he ever does. Always and forever.

I can't remember who it was who said it, but the quote was something like "real emergencies never go as planned". I agree. I'd probably need 3 cuft just to get a grip...
 
Hopefully as you gain experience in diving you'll have a better understanding of how to dive safely. The short answer is: Don't mistakenly find yourself OOA at 80 ft. Watch your gas consumption, your depth, and dive with a buddy who does the same. DIVE BEHAVIOR is what determines dive safety, not a particular choice of gear. If you have a good instructor, he or she will emphasize this very important bit of training.

Some OOA emergencies occur because of equipment failure. I've seen two first-person reports on SB. One involved a clogged dip tube, and the other delamination of the high pressure seat in the first stage.

Buddy separation can happen even when both divers are trying to be responsible, particularly in low visibility conditions.
 
I don't have a spare air and probably never will, but I think it's interesting to do some math.

I can do a CESA from 30'. From what depth could I get to 30' with 3 cf? To put the spare air in the best possible light, I would assume 60 ft/min and an emergency SAC of 1.2, which is what I've measured in high-stress situations. Under the most favorable assumptions I could make it from 100 feet and still have around 110 PSI left:

(100-30)/60 = 1.16666666 minutes

1.1666 minutes * 1.2 SAC * ( 1 + (100-30)/2 / 33 ) density compensation = 2.8846836 cf

Or if I'm trying to get to my buddy at 100', I'd have maybe 35 seconds of air.

The big problem with this is that it's not real world. In the real world, it takes time to recognize an OOA emergency, time to decide what to do, time to start an ascent, time to deploy a pony bottle. In the real world I probably couldn't do a CESA from 30' if I'm recovering from an OOA that took place 76 seconds ago. In a real OOA at depth I'm probably going to breath more than my nominal emergency SAC of 1.2 cfm.

I bring a pony on deep dives whenever I can reasonably do so. With experience I have found that I prefer a 40cf cylinder for deeper dives. I have smaller cylinders available but use them less and less. My 11 cf is great for inflating tires and dusting stuff.
 
I find that my trim and bouyancy control is spot on when I sling my pony - not to say that I couldn't tweak the rig without it but the real benefits of the pony is in its added safety.
 
One of the things I think is missing from the various "larger pony" vs. "spare air" discussions is that it is important to be able to practice safely with whatever you dive. I would be reluctant to practice with a "spare air" in some of the scenarios where people advocate for its use, because the rapid ascents, skipped safety stop, and possible CESA partway through the ascent are, at best, difficult to conduct safely as a training exercise.

I complete my dive on my pony cylinder occasionally (leaving a large reserve in my primary cylinder) to maintain skills.
 
One of the things I think is missing from the various "larger pony" vs. "spare air" discussions is that it is important to be able to practice safely with whatever you dive. I would be reluctant to practice with a "spare air" in some of the scenarios where people advocate for its use, because the rapid ascents, skipped safety stop, and possible CESA partway through the ascent are, at best, difficult to conduct safely as a training exercise.

I complete my dive on my pony cylinder occasionally (leaving a large reserve in my primary cylinder) to maintain skills.

Want to practice with a Spare Air? Pull it out and breath off it! You don't have to do a fast ascent to practice with it. Remember that however long it lasts at depth, it will last longer when you are heading up. You may find like I have that when practicing I finally stow it because I have better things to do than wait for it to run dry.
 
Want to practice with a Spare Air? Pull it out and breath off it! You don't have to do a fast ascent to practice with it. Remember that however long it lasts at depth, it will last longer when you are heading up. You may find like I have that when practicing I finally stow it because I have better things to do than wait for it to run dry.

Well, sure, I could practice breathing off it.

To my way of thinking, the entire emergency ascent is something I would like to be able to practice. That is what I do when I practice with a pony cylinder. I switch regs, I ascend, I make a safety stop, I inflate my BC orally at the surface (and if I need to inflate it to adjust buoyancy at my safety stop). I observe the SPG on my pony cylinder and confirm that I still have sufficient reserves.

Some questions for you and other spare air users to consider. Which hand do you hold it in? Can you still see your computer (or depth gauge)? How are you going to release air from your BC?
 
Well, sure, I could practice breathing off it.

To my way of thinking, the entire emergency ascent is something I would like to be able to practice. That is what I do when I practice with a pony cylinder. I switch regs, I ascend, I make a safety stop, I inflate my BC orally at the surface (and if I need to inflate it to adjust buoyancy at my safety stop). I observe the SPG on my pony cylinder and confirm that I still have sufficient reserves.

Some questions for you and other spare air users to consider. Which hand do you hold it in? Can you still see your computer (or depth gauge)? How are you going to release air from your BC?
You can hold it in your mouth if you want to. This isn't a pony. It's a device to get you out of a situation that you plan to never be in. If you think you will need it, you probably should carry a 40 at least. Maybe sling another 80. The Spare Air is the smallest, lightest emergency backup that might, just might, save you in a really bad situation where most people have no backup.
 
You can hold it in your mouth if you want to. This isn't a pony. It's a device to get you out of a situation that you plan to never be in. If you think you will need it, you probably should carry a 40 at least. Maybe sling another 80. The Spare Air is the smallest, lightest emergency backup that might, just might, save you in a really bad situation where most people have no backup.
BRT, I think you missed the point. How do you hold it while ascending in an emergency? If in left hand, how do you run your inflator? If in your right hand, and computer is on right wrist, how do you read it?

You really need to think about this BEFORE you need it, and not blow off questions about it. You might even help someone else who has not thought about it either..
 
https://www.shearwater.com/products/perdix-ai/

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