running out of air

[macado]

Read a recent thread regarding running out of air and it lead me to a question I thought I would ask outside that thread.

What are indications that a tank is getting low, other than the gauge, when you are underwater or do you take that last breath and that's it?

I ask about underwater, as I have run out of air after surfacing from a dive while waiting on a boat pickup (drift dive.)

Like others have stated, with modern balanced first stages you may not get a lot of indication that you're running low on air unless you look at your SPG. On an unbalanced first state it can be become noticeable harder to breath. You will have to work much harder to suck air out of the regulator, not a good position to be in. I have experienced this plenty of times intentionally in pool or on a shallow dive hanging out at 15-20ft in a controlled setting.

With that being said, SPGs can be notoriously inaccurate at the low end of the spectrum. There was a thread somewhere on here that stated there could be variants of 100-250psi +/- in gas calibration and accuracy. 250psi may not be 250psi, do you really want to risk that?

I'm a firm believer that gas planning and being that low on air shouldn't happen to the point where gauge accuracy becomes a factor.

I pretty bluntly tell all my students that running out of air barring any major issues or equipment malfunctions should NOT happen. You dive conservatively, constantly monitor your air supply and make sure you're aware of it.

The next thing I tell my students is that if you or your dive buddy are constantly running out of air, you need to find a new hobby and/or a new dive buddy.

 

[FinnMom]

I ran out doing a drill in the pool a couple years ago. It was half anticipated and not a problem but I definetely got one vaguely "stiff" breath and then a second breath that was distinctly harder to inhale and ended somewhat. It may be important though that I was at only about 3m depth, therefore I needed relatively very few liters of gas to fill my lungs. If I had been deeper those 2 breaths of gas may have only had the volume for 1 breath, or easily less.

 

[TMHeimer]

Yeah it stops really quickly. I recall doing the air off drill as a student and see it happen during the drills now- same for everyone. Once my analog SPG seemed to be on 1000 PSI a long time--stuck there. I knew this wasn't right for my dive time & depth so ended the dive. An indicator may be if you notice a really light tank due to very little air in it.

 

[jonhall]

When one employs correct gas management techniques (something almost totally lacking from most basic scuba training), running out of breathing gas is not an option... And, with the majority of modern balanced regs, there is no universal precursor to finding yourself sucking on an empty tank.

Agreed. Based my question on the situation of a diver in another thread who was rented a gauge that was cloudy and couldn't be read, so he didn't know his psi.

Second was unplanned and with a freeflow I could not stop. I was diving a 100 cf steel. Started my ascent. Again at about 20 feet depth I had about 8 breaths that I would say was noticeably different. Then switched to my pony. This was a balanced first and second.

Hope it wasn't that 13 cf pony used earlier!!!!!! Thanks for the info!

 

[seeker242]

Always thought that if I experienced that underwater, I would try and get buddy's/DM's attention and signal "out of air" and hope they were ready to surface!

I think the idea here is that if you run out of air, you don't actually run out of air! Because my buddy has MY backup air in his octo. I own that air so to speak. That's not his air, that's my air! I'm entitled to that air because he is my buddy and that is his responsibility as a buddy. To provide it to me if something were to happen. And it doesn't matter if they are ready to surface or not, they are going to surface whether they like it or not! They don't have a choice in the matter. It's not their decision.

But of course, all this should be understood by me and my buddy before even going under to begin with. And of course, unless I have some major equipment malfunction, I should not be running out of air to begin with. To run out of air, because I wasn't watching my SPG, well that would just be freaking plain old stupid!

 

[uncfnp]

Hope it wasn't that 13 cf pony used earlier!!!!!! Thanks for the info!

No. It was separate dives. The 13 was during my SDI solo class and the second was years later during a solo dive.

 

[The Laconic]

I'm surprised, and doubly surprised that no one else brought this up (unless I missed it): didn't you experience this in your OW training?

 

[wetb4igetinthewater]

One time while diving off Molokini towards the start of the dive, I found that I had run out of air at about 45 feet, but when I looked at my dive computer, I saw that I had 2900 psi. WTF? Oh, I'm an idiot and grabbed the reg for my 6 cu ft pony, so I just had to switch regs.

Basically in a few breaths, breathing becomes hard, really hard.

 

[dumpsterDiver]

The discussion here is really surprising. We have instructors claiming that it is a situation that we should never, ever have to face and ostensibly can therefore be considered so unlikely as to be unimportant.

The fact of the matter is that running out of air is probably a pretty big factor in scuba deaths. Somebody else can look up the stats, but if it commonly kills people, we should give it very careful consideration. It killed a moderator instructor on this board and a lady I worked with a few years ago, apparently.

So yeah, it is stupid and irresponsible to run out of air, but people also sometimes completely screw up and run right through a stop sign - simply because they were very distracted. They are not TRYING to be stupid or irresponsible, but people (myself included) screw up simple things all the time.

I have run my tank down to very low pressure, many dozens of times. Sometimes intentional, sometimes not. Running out of air at depth (assuming no mechanical problems) does not happen instantaneously. If you scew up and suck on a 6 cu-ft bottle.. yeah.. it will be MT with about zero warning. A full size tank... not so much.

I dive solo often. I carry a redundant system. I have no need or obligation to save air in my main tank for anyone else but me. Sometimes, if I really want to stay down, I will take my tank way down in pressure. When I feel my spg hose go limp, I know I am down too low and need to go up. Sometimes, I might not even look at my gauge.. We know the readings are notoriously inaccurate at low pressures, so if it reads 250 or 150 or less, it really doesn't mean a whole lot to me except that I need to go up.

So what do I do? When the hose is limp...Suck hard! Suck really hard and fast... This will give me a very good indication of how low I am on air. If i feel a slight restriction at the END of the inhalation, then I am not too worried if (say depth is 100 ft or less). I pretty much KNOW I can make a normal ascent and do a safety stop (if I am using a large steel tank). However, I can't breath fast and I can't kick and I can't delay and I must relax. If I screw up, I still have a whole nother tank to use.

If I test the pressure and suck as hard as possible and really get a major restriction in breathing... then I have a problem.. probably not enough for me to make a normal ascent.

A very important distinction should be made that being able to sense this restriction in breathing resistance is HIGHLY dependent on what you are doing. For example, if you are quietly sipping your air, ever so slowly, while you, sit still and try to take macro photographs and you want as little noise and bubbles to be made as possible... it is VERY easy to drain the tank down to very close to zero, without any warning. Conversely, if you are swimming hard and sucking air, you are more likely to feel the restriction/increase in breathing effort.

All this stuff should be obvious, but apparently it is not. Also having a really good regulator, will allow you to breath down further without noticing, but the really hard suck test does work pretty well for any regulator I have used.

My primary point is that, if you simply run low on air at depth... you have air and time to ascend.. It will not just stop.. If you are coming up alone and have no redundancy, it is best to use your precious air to auto inflate the BC, get a little buoyant, stop kicking and then press the purge to deliver air. Pressing the purge will provide air, will not require you to suck and feel restricted air flow and you will be more comfortable. And you MUST relax your legs and not kick, if at all possible. In such a situation, I would recommend ascending at 60 feet per minute for the first 30 feet or so, and then try to slow down to 30 feet per minute.

I think this is more useful then.. it will never happen to you - because you are too smart for this to happen.

Oh, BTW.. it is NOTHING like shutting off the tank valve and sucking the air from the regulator hoses.

 

[Steve_C]

For those new to diving following this thread I will remind them that air delivery depends on pressure difference between ambient and tank. As you go up the outside pressure drops and you might be able to get a couple more breaths once you are more shallow.