Minimum Gas chart for quick reference

[Ulfhedinn]

You don't/shouldn't need to use tank factors -- for your calculation in your head -- when you are making a chart. And you don't need to round off more than once....at the end. For example, where you use 41.25/2.5x100=1650, you'd be better off using 41.25/77.4x3000=1599, and that row would become 1600 rather than 1700.

I realize that 77.4x3000 is using the cylinder volume by rated pressure. So I was using 80Cf.. yes.. More numbers.. more math.. at least from were I sit.


Would love to have a GUE instructors jump in and clear up any... confusion going forward.
@mer @johnkendall @kierentec

 

[rjack321]

A stressed 0.75 cf SAC per diver? So two divers, one of them OOA are sharing at 1.5cf/min?

That is a fairly low volume. I've seen new divers using well over 0.75cf/min all by themselves.

 

[Lorenzoid]

@Ulfhedinn , some GUE instructors chimed in on the thread below regarding the CAT calculation, which I believe was introduced around that time as a simplified way to calculate Min Gas. Check it out:

CAT calculation for GUE Fundies

Going throught the worksheets I noticed that the calcutaltion is adding (1) ATA to 4ATA and then taking the average of this for the average ATA. 100' depth (4 ATA +1)/2 =2.5 So I do realize that 100' is actually just over 4 ATA, is this to be conservitive? I also noticed that its no longer...

scubaboard.com

 

[Ulfhedinn]

@Ulfhedinn , some GUE instructors chimed in on the thread below regarding the CAT calculation, which I believe was introduced around that time as a simplified way to calculate Min Gas. Check it out:

CAT calculation for GUE Fundies

Going throught the worksheets I noticed that the calcutaltion is adding (1) ATA to 4ATA and then taking the average of this for the average ATA. 100' depth (4 ATA +1)/2 =2.5 So I do realize that 100' is actually just over 4 ATA, is this to be conservitive? I also noticed that its no longer...

scubaboard.com

Ah yes.. Perfect. I have some notes from that feed. Thanks.

 

[Ulfhedinn]

A stressed 0.75 cf SAC per diver? So two divers, one of them OOA are sharing at 1.5cf/min?

That is a fairly low volume. I've seen new divers using well over 0.75cf/min all by themselves.

Agreed and my calcs at the start are for quick reference. Example If I was doing some strenuous underwater work such as net removal in high surge water I might revisit the number. Last week while doing a night dive I feel I was at 1.0Cf as my mask was squeezing the life out of my face and I could not get it to equalize.

 

[Ulfhedinn]

Update as 1-100 is at I'm suppose to use min gas for...

Will fix the AL80 and repost.

 

[inquis]

I suggest you put your assumptions as input cells (SAC rate, problem solving time at depth, etc.) I only glanced at the AL80 column, but it looks high to me (for the values I would assume).

 

[tursiops]

Update as 1-100 is at I'm suppose to use min gas for...View attachment 693241

I give up.
You are still using 80 cuft for your AL80, which it is not.
You are still using your highly rounded off tank factors, which is wrong.
You insist you are using simple numbers so you can do stuff in your head...but you are not doing stuff in your head, you are making a chart of the correct numbers.
You've had good suggestions from several posters, which you've ignored.
What are you trying to achieve here?

 

[Ulfhedinn]

I give up.
You are still using 80 cuft for your AL80, which it is not.
You are still using your highly rounded off tank factors, which is wrong.
You insist you are using simple numbers so you can do stuff in your head...but you are not doing stuff in your head, you are making a chart of the correct numbers.
You've had good suggestions from several posters, which you've ignored.
What are you trying to achieve here?

Sorry @tursiops but I'm just following the GUE Min gas CAT formula. Would I be correct in that at least?

And I'm just showing for reference that's all.

I tell you what... I will change the AL80 to the actual CF and see what turns up.

@tursiops What is the Tank Factor of an AL80.

 

[tursiops]

Sorry @tursiops but I'm just following the GUE Min gas CAT formula. Would I be correct in that at least?

And I'm just showing for reference that's all.

I tell you what... I will change the AL80 to the actual CF and see what turns up.

So your CAT is Consumption * Average ATA * Time. OK.
You say your consumption is 2+0.75=1.5 cuft/min. OK.
You say your average ATA is (use 100 ft) 50/33 + 1 = 2.515. OK.
You say your time is 1 + 100/10 = 11 mins. OK
So CAT gives 41.58 cuft. OK. (you said 41.25, but that is because you used 2.5 for the Average ATA.
Now, what do you do with the 41.58?

You should then calculate 41.58/77.4 * 3000 = 1612 psi, the gas you need to surface.
Then you round up to 1700, per GUE dictums.

I have made exactly that calculation here, except not the roundoffs until the end. All the steps are shown so you can see where everything is coming from.

depth	avg depth	avg ATA	time	2*SAC	CAT	AL80	Tank PSI	MINGAS	Roundup
30​	15​	1.45​	4.0​	1.5​	8.727​	77.4​	3000​	338.3​	500​
40​	20​	1.61​	5.0​		12.045​			466.9​	500​
50​	25​	1.76​	6.0​		15.818​			613.1​	700​
60​	30​	1.91​	7.0​		20.045​			777.0​	800​
70​	35​	2.06​	8.0​		24.727​			958.4​	1000​
80​	40​	2.21​	9.0​		29.864​			1157.5​	1200​
90​	45​	2.36​	10.0​		35.455​			1374.2​	1400​
100​	50​	2.515​	11.0​		41.500​			1608.5​	1700​

The Excel formula for MINGAS is: =F2/$G$2*$H$2.
For you Excel buffs, the roundoff formula is:
=IF(ROUNDUP(I2/1000,1)*1000<500,500,ROUNDUP(I2/1000,1)*1000)