Minimum Gas chart for quick reference

[Ulfhedinn]

I recently had to work on some MIN Gas issues for a class. So I put together a quick reference for my wet notes. Thought I would share. Also... did my calcs come out correct? Math is not my strong suit. "The 80 is an AL80"

 

[Ulfhedinn]

Also welcome to add tanks or ? to fill out what I may have overlooked.


If this thread fits better elsewhere.. admins are welcome to move it.

 

[Ulfhedinn]

 

[rob.mwpropane]

Wouldn't it be different psi for different people though? And the type of dive, where, and the conditions?

If I had a set of doubles on and I'm ending a dive and dicking around on a 30' reef or something, doubtful I'm coming up with 500 psi. In a set of 130's that would be ~ 37cf, which is about 1/2 of an 80. You wouldn't turn @ the 1/2 way mark on an 80, right?

Just constructive criticism. Personally (just my opinion) I think it would be better to have people work out the math for themselves and see what works for them. I think that's why it's better to stick to % because it scales nicely and gets people to think about their gas usage more than just the blanket "one size fits all" end a dive @ "X" psi" approach. I think (another opinion) it would be better to talk about how many cf you want people to end a dive with and have for reserve, buddy, shtf, etc...

Thoughts?

 

[tursiops]

Wouldn't it be different psi for different people though? And the type of dive, where, and the conditions?

The chart says 1.5 at the bottom. Since the chart is in Imperial, I assume that means 1.5 cuft/min. That's about twice what I would put on any chart I would make. Or, perhaps the OP is speaking of what two divers might need?
In any case, I looked at the AL80 column and cannot reproduce those numbers.
Perhaps the OP could be more specific about what formula he used? Does it include 1 min at depth before ascending at 30 ft/min to half depth, then 10 ft/min? If depth is 60 ft or less, does he do the faster ascent in the lower half? Etc.

 

[inquis]

Wouldn't it be different psi for different people though? And the type of dive, where, and the conditions?

Sure, but typically a worst-case assumption is made for simplicity and reuse of notes, memory aids, etc.

 

[Lorenzoid]

The chart says 1.5 at the bottom. Since the chart is in Imperial, I assume that means 1.5 cuft/min. That's about twice what I would put on any chart I would make. Or, perhaps the OP is speaking of what two divers might need?

@Ulfhedinn can respond, but yes, the chart appears to be for what GUE refers to as the "Minimum Gas" calculation, which is the amount of gas needed for two divers to ascend to the surface while sharing gas, based on an assumption ("CAT" formula--Consumption x Avg depth in atm x Time) that Consumption of each diver is 0.75 cfm. If any calculation result is less than 500 psi, then GUE says to use 500 psi as the minimum.

Minimum Gas is GUE's term for what is sometimes referred to as "Rock Bottom."

I'm not sure why @Ulfhedinn posted this in the "New Divers" forum instead of GUE/DIR, Advanced or somewhere like that. Personally, I believe Minimum Gas or Rock Bottom IS something that new divers should know about, but others may believe it is a more advanced concept.

 

[tursiops]

@Ulfhedinn can respond, but yes, the chart appears to be for what GUE refers to as the "Minimum Gas" calculation, which is the amount of gas needed for two divers to ascend while sharing gas, based on an assumption ("CAT" formula--Consumption x Avg depth in atm x Time) that Consumption of each diver is 0.75 cfm. If any calculation result is less than 500 psi, then GUE says to use 500 psi as the minimum.

Minimum Gas is GUE's term for what is sometimes referred to as "Rock Bottom."

I'm not sure why @Ulfhedinn posted this in the "New Divers" forum instead of GUE/DIR, Advanced or somewhere like that. Personally, I believe Minimum Gas or Rock Bottom IS something that new divers should know about, but others may believe it is a more advanced concept.

Can you reproduce his numbers on that chart? That's my real issue, not the consumption rate.

 

[Lorenzoid]

Can you reproduce his numbers on that chart? That's my real issue, not the consumption rate.

I'm not interested in checking the OP's calculations. I know that's what the OP asked for.

There are charts like this out there--a search of old SB posts might turn one up.

 

[tursiops]

I'm not interested in checking the OP's calculations. I know that's what the OP asked for.

There are charts like this out there--a search of old SB posts might turn one up.

OK, I'm trying to help the OP with his calculations. He says he's not good at math. He's probably just fine at math.....but no way to tell without more info.