How much gas should one surface with

[Scuba]

not in terms of pressure but of volume cf. or bars. I read in another post that in countries outside the U.S. the standard is 700 psi or 50 bars as opposed to 500 psi. here.

Which amount, please refer to volume, as pressure varies dependant on cylinder size and pressure, is optimum, in terms of safety without unduly cutting dive time.

Peter

 

[MSilvia]

700 is definately safer than 500, but it definately gives you a shorter dive too. I guess it's a matter of how safe you want to be, and how much time you're willing to sacrifice for that safety margin. I usually go for 500 for shallow dives, but like to have a bigger safety margin as I get deeper. On a dive to 88 feet, I returned to the boat with 750.

 

[divrnr]

I guess I've been diving so long that I can usually judge my gas consumption and I regularly have less than 500. It all depends on the dive, if I'm on a killer reef and fairly shallow, I'll go to 250, but never less than 200... Of course it usually pisses off the rookies on the boat who have just sucked up an AL80 and have been sitting on the boat for 30 minutes waiting for me and my bud to surface=-)

 

[Dea]

I guess it mostly depends on a situation. If you are flipping around in calm sea at 50 ft, you only need a couple of breaths to surface very comfortably, so even 200 is allright. If you are doing overheads or the sea is choppy, better leave some reserve.

Also, it depends on how stressed out you get when low on air.
The very last dive I did I surfaced with 0. (though that one was not my fault)
But at that point I was only about 40 ft down so I wasn't worried.

 

[Rick Murchison]

For open water, no stop dives, 10-15 CF is plenty to reserve for the end of the dive.
Another point - many folks miss the point of this reserve - it's there to use if you need it. You should never modify your safety stop or your ascent rate to preserve the reserve.
Rick

 

[sheck33]

How much you surface with is really not the burning issue.
Unfortuneately in the PADI OW, AOW, rescue classes and up no attention is paid to real gas management.
The volume or pressure that IS important here is your turn around pressure/volume. You plan your gas in such a way that you have enough gas to get you AND your buddy to the surface at the normal ascent rate and including a safety stop at any point in the dive. This in case one of the two has a catastrophic gasloss. In order to calculate this you need to know your SAC rate and that of your buddy.
This turnaround pressure depends on the maximum depth of the dive, SAC rate and tank size you dive with. If i have enough gas at any time during my dive and ascent to get me and my buddy safely to the surface i dont really care how much air i have left when i surface. If you do some calculations it will also show you how a lot of divers falsely rely on pony bottles as small as 13 cuft to get them out of trouble. There are plenty of very common dive scenarios where 13cuft is just barely or sometimes NOT enough to get to the surface.

 

[art.chick]

Yes, you can;'t generalize about amount needed to surface. I had a buddy 2 weeks ago who said he only needed "500psi" on his AL80 to surface. I took his word for it. But we were going to 90', & he was basing this figure on his usual 35'dives. He ran out of air at about 65'! You should also allow more if the current is strong because if u have drifted, you may need to descend a bit again to get out of the heavy surge & swim back to your entry point.

 

[MikeS]

From a safety point of view, the amount of air you have when you start your safety stop is much more relevant than the amount of air you surface with.

Assuming that you reach 15 fsw with a set amount of air, which of the following is safer?

a. Not making a safety stop, this would give you the most air at the surface.

b. Making the minimal safety stop and going to the surface at an ascent rate of 60 fsw/min.

c. Making a five minute safety stop and going to the surface at an ascent rate of 10 fsw/min which would result in the least amount of air at the surface.

Obviously option c is the safest despite the fact that it results in the least amount of air at the surface. So from the standpoint of safety, the amount of air you surface with is immaterial.

Mike

 

[JimC]

You should plan your safty stop(s) as part of your dive. You should plan your gas to have enough to be able to abort from any position on your dive for you and your buddy.

The gas your buddy would have used for that and your safty margin for error is what you should have when you surface.

Now, what you do with that gas after you have met all of the above obligations.. be that extending your stop or farting around on the surface. Its all good, so long as you don't ever put your self into a situation where you don't have gas for you and your buddy.


Your reserve is not YOUR gas, its your buddies.


For most of my dives I have a few turn points. On a typical boat/wreck dive I will have a 'find the line psi' which is when I should start heading back to the line, and a 'start accent psi' which is when I need to be accending.

My find the line gas gives me time to swim down the wreck find the line. My start accent gas tells me when I have to start accending NOW. If I'm not on the line and I hit my accent gas, its time to shoot a bag and surface.

If I hit the line with plenty of time untill my accent gas, I can fart around a bit near the line.

 

[MikeS]

Jim,

Would you agree, that since a controlled ascent from 15 fsw is not only possible but also highly practical, once you safely reach that point your obligation for maintaining a reserve for your buddy has been met? If not when is it?

Originally posted by JimC On a typical boat/wreck dive I will have a 'find the line psi' which is when I should start heading back to the line, and a 'start accent psi' which is when I need to be accending.[/B]

Great description. Can you provided some insight and perhaps and example of how you decide what the “find the line” and “start the ascent” psi values should be?

Mike