running out of air

[wetb4igetinthewater]

I'm going to try that on my next dive where I drain my tank sufficiently.

So, to answer the OP's original question:

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?

Dumpsterdiver touched on one indicator and that is a limp SPG hose. On your next dive note the stiffness of the high pressure hose and the amount of effort required to twist the SPG as the tank pressure changes. You should notice a marked difference between full and 500 psi.

It is not a reliable way to judge your tank pressure of course but it is the only other indicator of low pressure I can think of when the system includes a balanced first stage.

 

[Nemrod]

You are not going to notice limp hoses or anything like that or even the slight increase in breathing effort. The balanced first stages today and the high flow second stages will often breath right to the last few breaths with very little noticeable increase in effort. Yes, of course if all is well and normal and you simply run yourself out of air, you will likely notice the increase in effort. However, this is not the way it usually is presented. In most cases you run out of air because you are in an unusual situation, your are being stressed, distracted and often the first thing you notice is that there is nothing coming from the regulator, the last breath was fine, the next there is nothing there. Been there and done that.

BTW, the typical IP is around 125 to 150 psi, it will not be until the tank pressure drops below the IP that you notice any increase in effort unless you are dragging on the reg pretty hard.

Why ask, go do it and see for yourself, in a pool or a shallow and controlled situation.

N

 

[flots am]

Possibly all my regulators do not meet your criteria of "good and modern", but I think your statement is impossible to be factual. The reason being, as the pressure drops, the tank valve itself is going to limit flow. The regulator can not deliver air faster than the valve can supply and as the pressure drops to very low values, the diver WILL be able to detect an increase in breathing resistance.

You're probably better at detecting it than I am, but I demo it every few weeks in the pool and can't tell it's my last breath until it's my last breath, even when I know it's coming. There's no way I'd see it coming on a normal dive.

Everything is fine, then part of the last breath feels weird, then there is no "rest of the breath".

Your mileage may vary, however I'd never count on being able to detect OOA by judging work of breathing, especially in unexpected cases like a heavily contaminated tank.

flots

 

[Eric Sedletzky]

I have a question.
What certification levels should be included in basic scuba discussions?
If it's only OW material then that leaves a gap because I don't feel that AOW is really relevant to the "advanced" scuba forum based on what I've read. A lot of much more advanced material is being discussed like deco, special gas mixes, and other things way beyong typical recreational advanced classes.
Basic scuba education used to include everything up to rescue pretty much before they broke everything down to more basic segments.
So should OW, AOW, and rescue qualify for basic discussions?

BTW, I think gas planning and not running OOA are THE most basic scuba rules, right up there with "never hold your breath". And any discussions about it belong right here. I think new OW divers need to read this stuff and be aware of it. Maybe being a little scared is a good thing, all paranoid glancing at the SPG twice as much now, good...half as likely to do something silly like run out of air.

I just can't believe some of the willy nilly attitudes about running OOA, like "Oh yeah, it sometimes happens, you never know",.. Really??
So at what cert level has the scuba industry decided that it's important? At what level do regular divers decide it's important?
I see some here say they teach it from day one, but is it like that everywhere?

 

[diversteve]

With Atomics there's no warning since they do a pretty efficient job of providing air till there isn't anymore. Then it just clicks.

Had that happen once - filming turtles. I knew I was low but took a chance.

A couple minutes later when I heard the "death rattle".....

wait for it..




I stood up. - the turtles were in 5' off the beach...lol.

 

[halocline]

I've found that with unbalanced 1st/2nd stages, i.e. MK2/R190, I start to really notice an increase in breathing effort around 300 PSI, and that's with me paying attention for it. With a good balanced first/second stage, depending on depth, a diver might not notice anything until a breath or two from empty.

I agree that running out of air unexpectedly while diving is completely irresponsible on the diver's part. If your SPG totally fails (which is pretty rare) any diver should still have a reasonable internal 'alarm' about air consumption based on dive time and depth.

 

[Bob DBF]

I've found that with unbalanced 1st/2nd stages, i.e. MK2/R190, I start to really notice an increase in breathing effort around 300 PSI, and that's with me paying attention for it. With a good balanced first/second stage, depending on depth, a diver might not notice anything until a breath or two from empty.

Back before I had an SPG, I was quite in tune with a difference in breathing when the pressure got low. It came in handy if the J-valve was in the fill position or when diving a K-valve. I tried it recently with my first reg and found I didn't notice the change like I used to.

I agree that running out of air unexpectedly while diving is completely irresponsible on the diver's part. If your SPG totally fails (which is pretty rare) any diver should still have a reasonable internal 'alarm' about air consumption based on dive time and depth.

Since I've had an SPG, I have never unintentionally ran OOA. I keep my SPG on my left D ring where I can glance at it at will, and on a number of occasions it has come in quite handy. I haven't had an SPG fail without noticeable symptoms, yet.



Bob

 

[bowlofpetunias]

Interesting read. I had to go check my original 1998 OW Training Record Log book. Air depletion is not listed. I remember having todo buddy breathing, changing regs, indicating low on air, Out of air and ESA's but not having a chance to breath a tank down.

I have never come close to OOA. I have on a number of occasions decided I would breath a tank down to empty just to see how my reg breathed but I have never been able to drive myself to actually do it. Maybe the message of "There is NO excuse good enough to justify running OOA" was drummed in too well? Perhaps my initial training instructor on O2 ranting about never letting a cylinder go to Zero did it.

I suspect but can't prove by personal experience that the average diver is likely to be distracted enough by other things to notice the subtle changes in breathing that a balanced reg is likely to give prior to that last breath. I have come to the conclusion that it is probably best that I chose to live without the experience of going OOA underwater!

 

[dumpsterDiver]

Interesting read. I had to go check my original 1998 OW Training Record Log book. Air depletion is not listed. I remember having todo buddy breathing, changing regs, indicating low on air, Out of air and ESA's but not having a chance to breath a tank down.

I have never come close to OOA. I have on a number of occasions decided I would breath a tank down to empty just to see how my reg breathed but I have never been able to drive myself to actually do it. Maybe the message of "There is NO excuse good enough to justify running OOA" was drummed in too well? Perhaps my initial training instructor on O2 ranting about never letting a cylinder go to Zero did it.

I suspect but can't prove by personal experience that the average diver is likely to be distracted enough by other things to notice the subtle changes in breathing that a balanced reg is likely to give prior to that last breath. I have come to the conclusion that it is probably best that I chose to live without the experience of going OOA underwater!

In my opinion, it is better for a student to have some knowledge of what it may feel like if they screw up and get very low on a tank. It is better to have an understanding of what this emergency may feel like, then to be so horrified by it that they spit the regulator and bolt.

We teach that you are to keep your regulator in your mouth in this sort of emergency and that you can expect to get a little more air as you ascend due to the decreasing ambient pressure and the concomitant increase in pressure differential between the tank and the external pressure... yes?

So does it make sense to teach that you can get useful air volume when the ambient pressure changes by say 15 psi? Does 15 psi REALLY give you air to use? The instructors will teach that coming up 30 feet (+/- 15 psi) will yield some air to use.

So next time you are gonna get your tank filled, hook the regulator up, press the pure until the gauge says 100-50 psi, and then see how long it takes to drain the tank by breathing from it. See for yourself if you can gently press the purge button and slowly sip the remaining few psi from the tank...

Either, some other people are correct and it will breath perfectly normal until one last breathe - where air will just completely stop, or am I correct and you will be able to sip the last dribbles of air from the tank as you press the purge.. almost like breathing through a straw..

I did mention, that the ability to detect the decreasing pressure is a function of the regulator AND how hard you are initially sucking on the tank. With a very hard and fast inhalation, you should be able to feel some restriction in flow rate - of course this is more pronounced at depth.

 

[Eric Sedletzky]

All I can say is, if you are the type of person that's naturally absent minded and get distracted easily and insist on solo diving without any redundant backup, then my advice to you is to use an unbalanced first and second stage, do an actual OOA test in a controlled setting so you know what it feels like to run the tank down, and don't dive deeper than 60'. It may also serve in your best interest to thoroughly study the fine art of emergency ascents, keep your NDL's way within safety margins so you can make a direct ascent with no stops (blow and go), and use a weight system that is easily dumped.

People will do what they do and nobody has any control over it except them. All we can do is pass on advice the best we can about strategies of not running OOA, and hopefully the ill informed will take the advice seriously.