Rock Bottom Gas Management - A Hypothetical Accident Study

[Uncle Pug]

rakjar once bubbled...
Although I read all the information on these posts, I can not remember or better yet, I don't think I was ever taught SAC.

SAC or surface air consumption is defined in psi/min used at the surface by some folks and others as cf/min... which still others call RMV.

Don't get side tracked by that debate... but know this, SAC figured in psi/minute works for a single size of tank while SAC figured in cf/minute works for all sizes of tanks but must be converted back to psi/minute for the specific size tank you are using.

To find out what your psi/minute SAC was during a dive you can take the average depth reading from your cobra (if it gives average depth) and use this formula:

PSI used/((Average depth/33) + 1) X dive time in minutes

For example:

2000 PSI used on a 30 minute dive that averaged 45'

2000/ ((45/33)+1) X 30 = 2000/~71 = ~ 28 psi minute
Which for planning purposes I would round up to 30 psi/minute.


If the tank you were using happened to be an AL80 then you could figure ~ 2.6 cubic feet per 100 psi so you would have used roughly 52 cubic feet on this sample dive (20X2.6=52).

The number 71 in the above example is ATA minutes... that is atmosphere absolute minutes... the equivalent amount of time at the surface.

I you wanted to figure your SAC in cubic feet per minute you could divide 52 by 71 to get your approximate SAC of .73 cf/minute.

 

[Otter]

First, where did Dick and Jane find a dive shop/boat that rents AL63s AND HP100s? Second, Dick has a fine ATX-200, why didn't he use it instead of renting some POS regulator? Dick and Jane were right next to the upline, why did they struggle with maintaining their buoyancy -- were there hands otherwise busy? Which leads me to the last point, Dick and Jane are both known for their sexual promiscuity and as such, it is likey that during the stops, they were involved in activities which added to their gas consumption AND the confusion of hand signals....Jane was sure that Dick REALLY didn't mean for her to descend.

The real moral of this story is to not learn diving techniques exclusively from the internet AND while Jane is cute, it is best not to be a Dick.

Edited: I must apologize for my lack of seriousness on this thread....when it started off with the agency bashing, my mood went into @#$@#$ mode

 

[nradov]

MikeFerrara once bubbled...
So each would turn after using a MAX of 21 cu ft.

None of you guys are getting this, not even close. Where do we turn the dive? The answer is: AT THE DOCK. We do not do 100ft dives with ridiculous little tanks and completely mismatched buddies. And someone with a 1.2ft^3/min SAC rate needs to be at the gym, not out wreck diving. That is a horrible breathing rate even for a new diver. Let's put away the calculators and rock bottom geekery and try a little common sense.

-Nick

 

[Uncle Pug]

this was a dead thread that I directed rakjar to so that we could start a discussion about the concept of gas management.

Relax, check the dates, go back to lurk mode or contribute to the new theme but please don't rehash the thread itself.

Thanks.