Out of Air

[Skeeter1097]

I see he said it was rented equipment so he could not of had it serviced. If he was using nitrox 32 he had 21 min not 12. If thay where diving a asending reef that could be more. He stated after the dive he and the DM found the gage to be off. But he did good with all that happened. I am sure that he is going to be more careful and travel with hes own regs in the fewcher. Good job. But I do see red flags too!!! At 115' whought did the gage read whin you ran out of air?

 

[mislav]

...and travel with hes own regs in the fewcher.

Nice word. Very nice word.

 

[mislav]

I have never run a tank completely empty.
I assumed possible wrongly, that breathing would get progressively more difficult not suddenly just stop.
Also if I ascend and the pressure decreases then I should be able to breathe again, obviously not for long.
Next time I am doing a checkout dive I must arrange with my buddy to run a tank right down to empty at about 15ft to find out what happens.

I have, but in a controlled situation - at 3m below the surface, just practicing what it would feel like.

Obviously, I couldn't ascend to get more air out of my tank at that depth, but I did get to feel what it's like to run out of air. Breathing does get progressively more difficult, but you also feel you're not getting enough of air in your lungs. Your body tries to compensate by making you breathe faster and you suddenly find yourself in an OOA situation.

At least that's what it felt like for me the only time I emptied my tank.

35 meters is 114.83 ft. Not a deco dive. I certainly hope a 30 dive newbie was not approaching deco.

Yeah, take your own reg & mask with you on trips - always.

Hm, is there a way to study this more accurately, since according to PADI dive tables, any 35m dive is a deco dive. I need to know more about this!

 

[Skeeter1097]

I liked it, glad you did too.

 

[Damselfish]

I have never run a tank completely empty.
I assumed possible wrongly, that breathing would get progressively more difficult not suddenly just stop.
Also if I ascend and the pressure decreases then I should be able to breathe again, obviously not for long.
Next time I am doing a checkout dive I must arrange with my buddy to run a tank right down to empty at about 15ft to find out what happens.

the behavior is going to depend on your reg. An unbalanced reg will start to get harder to breathe around 500PSI, a balanced reg you will get much closer to empty before it happens.

Be careful about running a tank down, you don't want to get water in it.

 

[alo100]

I think the only reliable leak check is in the water. You could have a slow leak that's going to get worse that you wont notice on your gauge.
If you look at a pressurized system u/w any leaks ought to show up.

Example: I have a slow leak on an SPG on a deco bottle. on the surface there's no way I will notice it but it's plain to see underwater.

Of course you still ought to to a check for any obvious (big) leaks on surface as they are easier to fix there.

Do you mean observing small bubbles for the leakage u/w or look at the SPG?
I am thinking about this, once I entered water I started to use air, and I expect that the SPG should be moving, how can I observe by reading the SPG? May I ask?

 

[KMD]

Do you mean observing small bubbles for the leakage u/w or look at the SPG?
I am thinking about this, once I entered water I started to use air, and I expect that the SPG should be moving, how can I observe by reading the SPG? May I ask?

Check your spg and note the pressure. 5 minutes later, check your spg again. Did the pressure change? If so by how much. Was the change the expected amount for the depths you were diving at.

 

[lamont]

Do you mean observing small bubbles for the leakage u/w or look at the SPG?
I am thinking about this, once I entered water I started to use air, and I expect that the SPG should be moving, how can I observe by reading the SPG? May I ask?

do both.

you should do a bubble check with your buddy after entering the water (or if you're doing a hot drop the next day, put your gear together and bubble check it the night before). make sure to check the first stage o-rings, second stages, SPG and inflator mechanism (and drysuit inflator if you have one).

during the dive you should know roughly what your air consumption is. for a 0.75 SAC rate and an Al80 you should use roughly 300 psi / 10 min / ata. that means that at 60 feet you will be going through 900 psi / 10 min. if you start with 3000 psi and 10 mins into a 60 ft square profile dive you are at 2100 psi then you are roughly on target if that's your SAC rate. if your SAC rate differs substantially from 0.75 then adjust the number you use -- for a person with a .35 SAC rate they may use 400-500 psi / 10 min @ 60 feet. if you are using gas up at a substantially faster rate you will know that something is wrong -- either you're stressed, or you've sprung a leak.

 

[jgmaroe]

With all of the rental equiptment I've used (tending to be inexpensive (unbalanced?), and used usually on non-deep dives), it seems to always get harder to breath around 300-400 psi. This usually tends to warn me it's time to start to ascend.

 

[miketsp]

I think the only reliable leak check is in the water. You could have a slow leak that's going to get worse that you wont notice on your gauge.
If you look at a pressurized system u/w any leaks ought to show up.

Example: I have a slow leak on an SPG on a deco bottle. on the surface there's no way I will notice it but it's plain to see underwater.
..snip..

On the few occasions I've had serious leaks UW there has been no ignoring them due to the noise they make. At least so far if I couldn't hear them then it wasn't serious. I've had some that looked quite bad but when checking the air loss in bar/minute they've hardly interfered with the dive. Just kept a careful watch on the SPG and a buddy close.