500 psi for two divers?

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TatianaSilva

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Hi ,

the situation is ... two divers, max of 18 m, one diver has a problem with regulator or no air left, etc . They share one tank to surface. if the other has diver s tank is 500 psi, with slow , controlled breathing , is that enough to do safety stop and ascend for both of them?

i just cant figure out how long 500 psi would last and i think is useful to know in case i get to that situation.

thanks !
 
That is a predicament that shouldn't have happened..... thirds, half WITH 500 reserve, Rock Bottom, etc, coupled with paying attention to your gas.

Also, FWIW - a safety stop is optional (a good idea, but optional)....
 
It depends on number of factors.
Tank volume (is it an 80, 63, 72, 100, 120?), Both diver's SAC rate, rate of ascent, and time spent at varying depth stops.
You can do that math and see how long it lasts, if you have those answers.

I'm just going to keep it realistic, no it won't last them through a safety stop or safe-slow ascent rate.
This is why you plan your air and time turn-arounds in your dive plan.
 
I agree with the others that this should never happen, but lets look at some math.

Assuming you are using aluminum 80's and a SAC of .8cft/min as well as rounding numbers for easy math.
They hold 77.4cf of air at 3000psi
To determine how much air you have divide volume by pressure and multiply by your 500 remaining (77.4/3000)*500=12.9cft
SAC of .8cft/min for both and 30ft/min ascent rate with safety stop at 15ft for 3 min.
SAC*ATA*time- .8*1.5*3= 3.6cft per diver for the safety stop
for the ascent SAC* average ATA*time- .8*2*2= 3.2cf per diver
3.6+3.2=6.8 times 2 divers =13.6 cft

So to answer your question NO way to complete the ascent and safety stop with 2 divers starting at 500psi.
 
also factor in the fact that regulators really don't like tank pressures below 150psi and it will start becoming increasingly harder to breathe as the balancing mechanism fails.

You should have been taught this math in your basic open water class, especially how psi means nothing in the grand scheme of things, it's all about cf
 
this should simply never happen. With 35 years of diving, I have NEVER run out of air. NEVER.
Plan your dive, dive your plan. Be on the surface with no less than 500psi (750 is generally my plan).
 
also factor in the fact that regulators really don't like tank pressures below 150psi and it will start becoming increasingly harder to breathe as the balancing mechanism fails.

+1 to all above, and also SPG inaccuracy becomes more of an issue the closer you get to empty.


TatianaSilva:
i just cant figure out how long 500 psi would last and i think is useful to know in case i get to that situation.

Far less useful than knowing how not to get in that situation.
 
right so no with other diver but my first dives were around 40/45 min and usually is 750 , 1000 psi left . in case of being 500 ( my dive buddy situation in that moment) i would still have time to ascend with a safety stop? or should i just skip it and ascend?
 
right so no with other diver but my first dives were around 40/45 min and usually is 750 , 1000 psi left . in case of being 500 ( my dive buddy situation in that moment) i would still have time to ascend with a safety stop? or should i just skip it and ascend?

It looks like underH20man did that math for you, and the answer was no, because you wouldn't have enough gas, and that is assuming that you actually have 500 psi (12.9 CUF). In actuality, between the SPG accuracy issue and the fact that the reg doesn't work at very low pressures, the answer is probably double no.

I will assume that you are not actually asking if you should do a safety stop when you have no gas.. :)
 

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