Calculating Search gas

[MXGratefulDiver]

The instant the decision is to go into search mode, my gas requirement calculations change, based on "what does it normally take me to get out from here?"
I then set my abort gas at somewhere between four and eight times that amount, depending on conditions.
For example, if I need 200 psi to make my normal exit, then I'm going to double that so that if I find my buddy as he's running out of gas I have enough for both of us - then I'm doubling that again for the excitement factor - that's four times. If the visibility is blown then I'm doubling it again, eight times.
Note that this is not an exit gas supply point, but rather an abort point for a position - that is, the point at which I begin my retreat towards the exit... I can retreat at one fourth to one eighth my normal speed and still retain my abort gas for my position as that position gets closer to the exit.
Rick

I like it.

The way I understand the rule of thirds, it's more like a turn pressure ... i.e. the point at which you begin making your way back toward the point where you have another source of gas to breathe (deco bottle or surface air). And it's dependent upon the conditions in which you're diving (in other words, doesn't apply in certain types of caves).

I see calculating exit pressure during an emergency more as being like calculating rock bottom, where as you get closer to the surface (or entrance, in this case) in that that the usable number depends on having sufficient gas for two divers (whereas you've only been breathing it for one up to that point). So you can recalculate as you get closer to the entrance.

I also agree that conditions is something you need to take into consideration.

Your rules of thumb is as good as any I've seen so far.

... Bob (Grateful Diver)

 

[Rick Murchison]

If you are in a low to no flow cave you could easily be 800psi or more from the exit...

Then if you find yourself in a lost buddy situation and you'd like to have enough gas to get him out too in an OOA situation, you'd best be getting closer to the exit... until your gas supply is 4X what you need to get out yourself. If you want to take the chance that your buddy will still have gas, no problem.
Rick

 

[ucfdiver]

Then if you find yourself in a lost buddy situation and you'd like to have enough gas to get him out too in an OOA situation, you'd best be getting closer to the exit... until your gas supply is 4X what you need to get out yourself. If you want to take the chance that your buddy will still have gas, no problem.
Rick

That would be 3 critical failures on one dive. (left/right post and team failure). I would assume that my buddy has slightly lower gas than I do because of an increased SAC, but the chances of me finding him OOA *and* still alive, meaning I got there within 30 seconds of him going ooa, seem a bit like over planning.

PFCAJ and I were talking about deep cave diving. and he made a comment how you can plan yourself out of a dive. I think if we're not careful, we could plan ourselves out of a rescue effort, in any cave.

 

[Rick Murchison]

That would be 3 critical failures on one dive. (left/right post and team failure). I would assume that my buddy has slightly lower gas than I do because of an increased SAC, but the chances of me finding him OOA *and* still alive, meaning I got there within 30 seconds of him going ooa, seem a bit like over planning.

PFCAJ and I were talking about deep cave diving. and he made a comment how you can plan yourself out of a dive. I think if we're not careful, we could plan ourselves out of a rescue effort, in any cave.

Well, let me just say that I use the rule of thirds in JB (what do you use?), where I can typically make it out on a fifth - or less - what it takes to get in; I use the rule or sixths in no flow or wreck penetrations (what do you use?). So I really am unlikely to be 800 psi from an exit on a no-stage dive. I ain't lookin' to set any records, just have fun.

Rick

 

[TSandM]

I don't think it's post failures we're looking at here. I think we're looking at someone who is lost, maybe got caught in a siltout, maybe got stuck, and has been looking his own mortality straight in the eye. I can easily imagine my gas consumption quadrupling if I were stuck, silted out, and got myself out of it only to find my buddy gone and me maybe confused about where the exit it -- and as my gas gets lower, getting even MORE anxious. That's Rick's dragon, and it's breathing my gas.

 

[UCFKnightDiver]

Is it even physically possible to quadruple your breathing rate? That would be like me usually at around a .55 or a .6 going to a 2.4.

 

[LiteHedded]

ur no .55!
who are you kidding ryan!?

 

[Cave Diver]

Is it even physically possible to quadruple your breathing rate? That would be like me usually at around a .55 or a .6 going to a 2.4.

Maybe not your breathing rate, but your gas consumption rate could easily do that or more.

Think of the difference of taking slow deliberate breaths in and out. Then imagine a rapid, shallow breathing where you are just sucking in gas then blowing it back out. You can easily blow through a large volume of gas, especially since you're not really retaining it and it C0 buildup tends to make you breath even harder/faster.

At times when I find my own breathing level escalating, one trick I use is to partially block the mouthpiece with my tongue, causing me to have to breath slower and deeper. I've found that quite effective for getting control of breathing during heavy exertion or "oh ****" moments.

 

[MXGratefulDiver]

Is it even physically possible to quadruple your breathing rate? That would be like me usually at around a .55 or a .6 going to a 2.4.

It's definitely possible. I've seen ranges that go well over 4X when I stress my students during gas consumption measurements.

... Bob (Grateful Diver)

 

[Lab Rat]

Some observations if I may:

Any system should be simple enough to teach NEW cave divers.

Any SYSTEM should work under all dive conditions.

Any system should be EASY to remember under stress.

Any system should be relatively FOOL-PROOF to deploy by said new diver, under stress...

All of that being taken into account, I would also add that I have personally seen folks with consumption rates of about 0.5 go to well over 1.0 when things went sideways...even very experienced folks.

Now...with all that in mind...the average new cave diver should think long and hard about going when they hit thirds, especially in a low flow cave. If they have doubled their SAC rate, thirds may not be enough to get out...

If they want to stay and look and are calm enough, take 1/3 of the emergency third (1/6 of the remaining gas) and do so (we are all used to that math)...I think 1/3 of ‘their third’ is adequate to find anyone you are likely to find.

For those of us that KNOW we can get from the 2000'p arrow out on 400psi and deco to our O2 bottle...we can re-calc however we like...most newer cave divers aren't that familiar with the cave. For the record…I wouldn’t wait that long as it unreasonably endangers me (and it would have to be 400+200 for my IP+ gas for deco, anyway…so lots more gas).

As a reminder to all:
Your regs don't work below 200 psi...take that out of your equation
You will have more DECO than expected...save gas for that
You will be distraught if you think your buddy is dead...consumption will go up
You could get turned around and make a mistake in low vis...keep some reserve
Your buddy may have already left and be endangering himself/herself looking for you
You will do whatever you trained to do. Think on it, train with it (2 teams of 2 divers can simulate this if you are looking for something different to play around with)

Have a plan that works...and have the discipline to stick to it!

Best,

Richard