500 psi for two divers?

[tbone1004]

depends on the dive profile, what tanks you're using, and what tanks your buddy was using, this is why gas matching is important.

Situations
You are a small female with a SAC around 0.4 cubic feet/minute.
Your buddy is a large out of shape male with a SAC ~1.0cfm

*easy math here so go with me
You dive an AL60 with a service pressure of 3000psi
He is diving a 120cf tank with a service pressure of 3000psi

He runs out of air, you have 750psi left, i.e. 15cf.
He uses 1.0cfm at surface, you use .4cfm at surface, for total of 1.4cfm at surface. You're at 66 feet, come up to your safety stop and he runs you out of air because at 66 feet your cfm is now 4.2 and at your safety stop it's 2.1. it takes 2 minutes to get to the safety stop depth, so call it 7cf used there, and 3 minute safety stop is another 6. You're cutting it real damn close. Depending on your body time, which is why you have to consult tables, a 3 minute safety stop with the risk of you running out of air and not having anything left in the tank is far less "Safe" than making a 1 minute safety stop and finishing your ascent. If you were pushing your NDL's, then it would make sense to get as much of that safety stop in as possible and then try to finish what what you can and hop on O2 if possible.


The 500psi return to boat should really be the CF required for you and your buddy to make a safe ascent from depth to the surface with safety stop, and that has to be recalculated every dive.

 

[TN-Steve]

NWGratefulDiver has a great article on it, also I found this piece at "Spherical Chicken": Rock Bottom and Gas Management for Recreational Divers to be really good for the calculations, some quick rules of thumb, highly recommended reading.

Steve

 

[yardpro]

depends... 500 psi on my lp120 is still quite a bit of air...

 

[Kharon]

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's not supposed to be the situation. You should be planning (and diving to the plan) on reaching the surface with 500 psi not starting your ascent at 500 psi with one diver out of air. That's not at all bright and it's begging for a double Darwin Award.

And to answer you question - IMO no it's not enough air for even one diver to ascend and do a 3-5 minute safety stop - safely.

 

[tursiops]

As everyone has said, the answer is NO if you try and do a safety stop, and are using an AL80 tank.
But with a bigger tank, maybe.
With no safety stop, YES is the answer.

And as some have said, why do a safety stop in this situation? It is not mandatory, and DCS is treatable while drowning is not.

More importantly, you DO need to know WHY the answers are NO or YES, and not just have somebody tell you the answer.
And most importantly, you DO need to know HOW to not get into this situation.

 

[doctormike]

More importantly, you DO need to know WHY the answers are NO or YES, and not just have somebody tell you the answer.
And most importantly, you DO need to know HOW to not get into this situation.

Best point so far.

 

[TSandM]

As has already been stated, the answer is, "It depends."

It depends on tank size. 500 psi in an Al80 is very different from 500 psi in an HP130.

It depends on the divers. Very experienced divers who are far less stressed by an out of gas situation will do better than novice divers, whose gas consumption at baseline is already very high.

But the bottom line is that there is only one true emergency underwater, and that's being out of breathing gas. Since the essence of recreational diving is that the surface is always an option, and a safety stop is optional in almost all dives, in the face of an out of gas emergency, you omit the safety stop and proceed to the surface at the fastest ascent rate compatible with your decompression model. If you do not want to do this, you need to do more gas planning and keep more generous reserves.

 

[fire_diver]

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?

did you bother to read the link rivers posted?

 

[PhatD1ver]

uh, in that situation, assuming that you haven't busted your no-deco limits, there is no stop, you get to the surface whenever you are sharing air, especially if one of your is out and the you are now in the red (at 500psi)

 

[TatianaSilva]

guys, im not expecting this to happen and i kind of know how to avoid it, i say kind of because i only have 4 dives in my log book so dont expect much from me as a diver . thats why im here its hard to just jump to the water without having all the situations solved in my mind .

my dive instructor told me once 500 psi would last like 15 min ( average) so , in case it happens to me, i dont want to panic