How much air does an LP85 hold at 2400 PSI?

[kelemvor]

I've never know a dive shop anywhere in the world that uses a gas flow meter like your link. It might be what is needed. It surely is expensive or they'd tell you the price!

That's a super fancy one, but cheaper models such as analog ones are only a few hundred bucks. You can even find them on Amazon. Drop in the bucket for a shop fill station from the numbers I've seen floating around.

FYI, the one I linked sells for $2,000.00 USD new and about $600-$800USD used. They seem to be quite available on the second hand market (ebay, new life scientific, other refurb scientific suppliers)

 

[CaveSloth]

When you have used 1200psi of 108s and your buddy who's got the better consumption has used 1200psi of 95s... You are both turning <now>. If you run OOA at maximum penetration your buddy now has 1200psi to get you out and 1200psi for him.

1200psi is 42cf in his 95s.
Except you used 1200 of 108s or 48cf to reach that point.

You both drown.

Out of curiosity, how would someone run OOA right after turning having 2/3 left in their tanks?

 

[runsongas]

In this case it is because the diver with the smaller tanks would not have enough gas to cover the diver with larger tanks losing all their gas. It is worst case scenario planning.

 

[Bowers]

Out of curiosity, how would someone run OOA right after turning having 2/3 left in their tanks?

failure of an oring that either was not resolved fast enough to preserve much air or that required manifold isolation (such as a tank oring failure) that eliminates the use of that half the air supply.

 

[CaveSloth]

failure of an oring that either was not resolved fast enough to preserve much air or that required manifold isolation (such as a tank oring failure) that eliminates the use of that half the air supply.

So a second stage free-flow which is allowed to go on for as long as it takes to drain the air in both tanks... is that the only way that the diver loses all their air? I guess if their second stage starts free flowing while they are attacked by electric eels or something? A first stage free flow would take a long time to drain all the air which is why I think it's unlikely to be allowed to happen.

In the case of a first stage free flow in which the isolator is closed, the diver will still have 1/3 of original air supply available to him, so enough to get part way out of the cave and then switch to buddy's long hose.

Both first stages or second stages free flowing would also be a scenario in which all the air would be made unavailable, but that is incredibly unlikely isn't it?

So... silt out requiring a long search for the line, multiple regulator failure and eel attack seem to be the scenarios in which divers with mismatched tanks and breathing rates don't have enough air to get back out of a cave after turning at 1/3. I am sure there are other scenarios I am not thinking of. I personally am wary of going more than a couple hundred feet from open water and have never done so yet because I don't feel confident I have all the bases covered.

 

[Bowers]

So a second stage free-flow which is allowed to go on for as long as it takes to drain the air in both tanks... is that the only way that the diver loses all their air? I guess if their second stage starts free flowing while they are attacked by electric eels or something? A first stage free flow would take a long time to drain all the air which is why I think it's unlikely to be allowed to happen.

In the case of a first stage free flow in which the isolator is closed, the diver will still have 1/3 of original air supply available to him, so enough to get part way out of the cave and then switch to buddy's long hose.

Both first stages or second stages free flowing would also be a scenario in which all the air would be made unavailable, but that is incredibly unlikely isn't it?

So... silt out requiring a long search for the line, multiple regulator failure and eel attack seem to be the scenarios in which divers with mismatched tanks and breathing rates don't have enough air to get back out of a cave after turning at 1/3. I am sure there are other scenarios I am not thinking of. I personally am wary of going more than a couple hundred feet from open water and have never done so yet because I don't feel confident I have all the bases covered.

you are right that a second stage freeflow should be easy to detect, but what about a LP port blowing an oring? or a hose failure close to the first stage? or the isolator valve itself failing after a hit on some rock? those could easily go unoticed until its too late. also a tank neck oring would be catastrophic and air loss would be rapid. not to mention that even a HP hose, though slower, could go unoticed if your the guy in the back and therefore air could have time to completely deplete.
these may not be common but when in IDLH atmospheres we try to prepare for the worst within reason.

 

[Lorenzoid]

. . .

In the case of a first stage free flow in which the isolator is closed, the diver will still have 1/3 of original air supply available to him, so enough to get part way out of the cave and then switch to buddy's long hose. . . .

It has been said that a total loss of gas in both cylinders could occur if the isolator is physically damaged, say, from impacting a cave ceiling. I do not recall ever reading of such a thing happening.

 

[CaveSloth]

Well, I don't question the wisdom of designing the procedures around the idea of total failure of one individual in a pair's gas supply at deepest penetration. That necessitates either...

1. Both buddys have same gas volume at beginning of the dive, turn when first one hits 2/3 remaining. (Sheck Exley's rule)
2. If one individual has smaller tanks, individual with larger tanks must consider his turn point to be when he has breathed 1/3 of the smaller tanks volume of air.

As an example of #2:

A has 30 units of air at 3000 PSI. B has 21units of air at 3600 PSI. B's turn pressure is 2400 PSI. A's turn pressure would be ((30-21/3)/30)*3000 = (23/30)*3000 = 2300 PSI.

 

[reefrat]

So... silt out requiring a long search for the line, multiple regulator failure and eel attack seem to be the scenarios in which divers with mismatched tanks and breathing rates don't have enough air to get back out of a cave after turning at 1/3. I am sure there are other scenarios I am not thinking of. I personally am wary of going more than a couple hundred feet from open water and have never done so yet because I don't feel confident I have all the bases covered.[/QUOTE]

“Eel attack”?
I thought the OPs questions on basic tank nomenclature were the topic of this thread!
Diving in overhead environments is a pastime that is historically unkind to people who play down the risks, bolster their own bravado with unearned confidence or step one inch beyond their training and abilities. Get some personally challenging dives in and some trek training, then come back to the forum with some insight on such diving- we honestly look forward to it!

 

[CaveSloth]

Seems impacting the ceiling is enough to cause total gas loss. Sobering thought.