How does someone run out of air???

[TBURKE]

I've been OOA a couple of times myself.
The first time was A blown disk at 90ft. It started as a hiss and developed into a scream then the air was gone. I switched to my pony and did a safe controlled ascent. No problem.
One time it was my fault. I was inattentive. But I had my pony so it was no problem. I did some serious soul searching and gave myself a mental tongue lashing.
Another time a helpful rescue student turned off one of my doubles just before I entered the water. Surprise.

I witnessed a few OOA situations.
As a DM I saw a buddy team, one with a stream of bubbles coming from her valve. I brought it to their attention. He had 2600psi and she had 600psi. I took them back to the anchor line where she switched to her pony and I accompanied them to the surface.
I had a "pick up" buddy on one dive. He found a lobster and couldn't get it out of the hole. After a lot of shaking and pointing at his SPG I left. He had 200psi left. When he got back to the boat he had an empty pony and no bug. He was banned from the boat and the shop.
On a vacation dive I stopped a guy with a stream of bubbles coming from his safe second. He was letting it drag in the sand.
On a dive in the Bahamas, a member of a buddy team ran out of air. (short fill?) He spit out his reg and raced to his buddy. His buddy saw him coming, panicked and started swimming backwards as fast as he could. They had to keep them separated back on the boat.

As long as divers have a finite supply of air, someones going to run out.

 

[gypsyinabigtown]

The only time I've seen an OOA diver was in a liveaboard in Thailand. One of the novice, fresh open-water divers in my group had some sort of allergy that made him itchy/scratchy at his arms and prevented a good night's sleep. Next morning he was quite tired I assume, but did the early morning dive anyway. There was a fair bit of current and he was falling behind slightly but managed to keep up by finning furiously. The group was about 5-6 divers so the DM wasn't able to check up on everybody all the time. All the furious kicking against the current and tiredness must have made him guzzle his air fairly rapidly, as in less than 40 mins he was getting the occy from the DM ascending towards a safety stop.

In other cases I've also seen some of my buddies run down to 20-30 bars left only at safety stop (critically low - in fact as far as I know, Queensland regulations mandate a minimum of 50 bar at return to boat in boat dives) after being tired from last night and/or fighting currents. I've seen it happen to Rescue+ divers from the local area with more than 150 dives logged as well, so it was more of an issue of physical conditions, rather than inexperience or unfamiliarity.

 

[Nudi-K]

I was in a situation where my buddy ran out of air once. He was not particularly fit and we were swimming in to very heavy currents. The DM had swam off ahead trying to get out of the current not realising my buddy was struggling, we had to stop a couple of times by holding on to rocks so he could get his breath back and were we out of reach to alert him.

The last stop my buddy signalled OOA and grabbed my octo, at that point we both lost our position in the current and was swept away. The current took us up quite quick to the surface but we managed to hang on to a rock and do a 5m safety stop (that hurt my hand!), luckily my buddy had a SMB and deployed it whilst doing the safety stop. When we surfaced our boat was nowhere to been seen but thankfully there was another dive boat in the vancinity who saw the SMB and came over. They radio'd our dive boat and they came to pick us up.

It was quite scary and i was very shaken afterwards. If it was me by myself i would have been fine in the current and would have made it round the corner however, it goes to show you can not just trust and rely on you're own abilities. Oh and i have purchased an SMB as i really dont know what would have happend if we hadnt of had one.

 

[beester]

Almost happened to me too...

North sea wreck dive. Bottom depth 35 m (115 feet). At end of dive (turn around pressure about 70 bar on 15 L tank = about 13 min of air left at that depth) got caught together with buddy in monofillament net. Took as 5 min to get out together, surfaced with 25 bar.

Bad points:

- **** happens at the worst moment. If this trapping would have happened at the beginning or middle of dive it would have been an non issue.
- Might have been better to do a planning based on rules of thirds... however with a square north sea wreck dive this makes not much sense. Since you don't have much deco obligation (max 5 min), we don't penatrate the wreck. With using rules of thirds on a normal dive we would surface with half pressure left which seems like a waste.

Anyway still think about it from time to time... and might start using double 10s or 12s for serious wreckdiving.

 

[rstory]

Depth of course affects how much air you have, so people can run out of air by staying at their bottom depth for too long

 

[boulderjohn]

The OP wondered

All this talk in many threads about OOA situations get's me wondering what the hell people are doing that there are that many people running out of air.

and lots of people posted some interesting anecdotes about OOA situations.

I wonder, though, how often this really happens.

I, too, have read many threads about OOA situations, but it seems to me that the predominant theme of the ones I have read has been the concept of OOA, not discussions of actual incidents.

If I count all my dives and the people I have dived with whem doing them, we are talking thousands of dives, and I have only been anywhere near one true OOA emergency. Yes, I have been with a couple intentional OOA's (including my own) of the nature of Bob's manta ray experience, but I don't count it if you know you are doing it in a perfectly safe situation. The one true OOA in my experience came when a task loaded diver forgot to switch tanks for the second dive and was OOA just after reaching depth.

So perhaps I wold like to repeat the OP's question with a twist. Are a whole lot of people in your experience encountering true OOA emergencies? Just how common is this in reality?

 

[boulderjohn]

When I started diving we used to OOA on almost every dive. We would dive until the tank started to get hard to breath and then go up a few meters and stay there for a few minutes and then go up. Most OOA situations turn into panics because the diver has never experienced OOA. I am not suggesting this for PADI and certainly not for new divers but it might be a good excercise once you have 50+ dives up to dive at 15m until OOA. Once this has happened it is not so scary (unless it happens at 30m). I have had a couple of newbies go OOA on me and they are convinced they are going to die and they won't touch their reg again as that is OOA!!!! They just suck up all my air.

Does some smart bugger here now how much more extra air you would get in a tank going from 15m to 5m? my memory of it was that we used to get a fair amount.

If I understand you correctly, you are talking about much the same thing PADI is talking about when it says a normal ascent is your first choice in a LOA/OOA situation. It is not that you have extra air in the tank. When you think you are OOA, you really are not. Your regulator is just not able to give you air at your ambient pressure. As you ascend to a lower pressure, your regulator is once again able to give you more of the air that is in your tank.

That is why I emphasize over and over again to students that an OOA diver should never discard the regulator. Even when going for a buddy's alternate, the OOA diver should maintain control of his or her regulator until it is certain that there is a working regulator to replace it. If the buddy's alternate fails, going to the surface with the regulator in the mouth should deliver air at some point in the ascent.

The ability to do that is in large part dependent upon the quality of your regulator. There should be a difference between a balanced and an unbalanced regulator in this regard.

Or did I misunderstand?

 

[Slonda828]

There should be a difference between a balanced and an unbalanced regulator in this regard.

Or did I misunderstand?

Obviously we are talking first stages and not second stages. We must also be talking about downstream and not upstream unbalanced first stages as upstream first stages become easier to breath under reduced supply pressures. A downstream unbalanced design like a flow-by piston would get harder to breath as supply pressure would go down since less HP air is acting to force the seat open. I am not sure an unbalanced regulator would provide less air during an OOA ascent though. Have you found evidence to support this, and if so, could you provide a link so that I could research it and add it to my material about regulator design?

 

[boulderjohn]

Obviously we are talking first stages and not second stages. We must also be talking about downstream and not upstream unbalanced first stages as upstream first stages become easier to breath under reduced supply pressures. A downstream unbalanced design like a flow-by piston would get harder to breath as supply pressure would go down since less HP air is acting to force the seat open. I am not sure an unbalanced regulator would provide less air during an OOA ascent though. Have you found evidence to support this, and if so, could you provide a link so that I could research it and add it to my material about regulator design?

My thinking is much simpler than all of that, and it's more a guess. A balanced regulator should do a better job of delivering air at depth, so it should function better with less air in the tank than an unbalanced reg. Thus, once a balanced reg is unable to deliver air at depth, the tank should have less air.

 

[Slonda828]

My thinking is much simpler than all of that, and it's more a guess. A balanced regulator should do a better job of delivering air at depth, so it should function better with less air in the tank than an unbalanced reg. Thus, once a balanced reg is unable to deliver air at depth, the tank should have less air.

A balanced regulator just delivers the same IP regardless of supply pressure. The reason you have to wait for the tank volume to increase is because once tank pressure goes below 145 (or whatever IP is set to), then it would be hard to exert enough suction via your lungs to overcome the cracking pressure of your regulator. I think this problem may be exacerbated by an unbalanced downstream reg, but it would actually be easier with an upstream unbalanced reg. Furthermore you could overcome this all by simply using your BC inflator as a tertiary second stage by holding both buttons down at once (note that this doesn't mean you are breathing from the bladder).