Exceeding NDL on an al80?

Can your SAC rate allow you to exceed NDLs on an al80?


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I did some calculations in Excel to determine when the gas supply for an AL80 does not exceed the NDL for a given depth.
I calculate that the gas supply is the limiting factor until between 70-80 ft on air. The gas supply is the limiting factor until between 100-110 ft on EANx32. You gas supply is always the limiting factor on EANx36, but the partial pressure of oxygen exceeds 1.4 ata at around 95 ft.

The calculations use a RMV of 0.5 cuft/min. I don't know what most folk's RMVs are, but I don't get much lower than that. I used the PADI tables for the calculations, since everyone's computer can be a little different. Hopefully all of the calculations are correct, but I encourage everyone to confirm their veracity.

BTW: Does any one know why PADI limits dives to a maximum of 220 minutes no matter what the gas composition? I never noticed this before.

Here's the screenshot for air:
upload_2018-6-15_22-15-57.png



Here is a screenshot for EANx32
upload_2018-6-15_22-53-33.png


Here is a screenshot for EANx36
upload_2018-6-15_22-54-19.png
 
I think that's what I was saying. The OP question was "With your current SAC rate and staying within recreational depths can you have NDL become the limiting factor on your dive if you surface with 500psi in an al80 cylinder?" or didn't you read the OP?

Sorry. I was agreeing with your post but reading it again I can see why it might have read a bit weird. I definitely read the OP. You and I made the same point.
 
Reading all of these stories is really pointing out how much I suck air down.
 
I do remember my OW instructor in the 60s stating that you could not exceed NDL on a single tank. Of course this is highly dependent on a number of factors: SAC rate, dive computer conservatism, water temperature, etc. As I posted earlier, I have done it a number of times.
 
I do remember my OW instructor in the 60s stating that you could not exceed NDL on a single tank. Of course this is highly dependent on a number of factors: SAC rate, dive computer conservatism, water temperature, etc. As I posted earlier, I have done it a number of times.

I, too, remember my instructor from 1965 telling me that a 72 cu.ft. tank did not contain enough air to allow me to go into decompression on a single dive in one day. Of course, we did not have SPGs and had to figure our air requirements for every dive using a minimum SAC rate of 0.75 cu.ft. / minute.
 
Going into mandatory deco without the ability to do a lost gas calculation sounds like a bad idea. :)
 
I've heard it at least a dozen times that with 68cf of gas, there's no need to monitor NDL for the average diver if there are doing only one dive on a weekend.

If my memory serves me correctly Skin Diver Magazine did an article in the 60s or 70s called "Bent on One Tank?" and that was with a steel 72. Their conclusion was "yes."
 
I do remember my OW instructor in the 60s stating that you could not exceed NDL on a single tank. Of course this is highly dependent on a number of factors: SAC rate, dive computer conservatism, water temperature, etc. As I posted earlier, I have done it a number of times.

... even if he limited his comments to strictly an AL80 (aka "oversized beer can") ... it can still be done. On a larger single cylinder ... such as a 119 ... you can go into NDL even using EAN32, assuming reasonable air consumption rate ...

... Bob (Grateful Diver)
 
First time exceeding NDL for me was on Punta Sur. After aprox. 30 min. averaging 100 fsw, my suunto gekko was telling me I was 5 min. over the limit on ean 32.
Once I ascended to 50fsw the computer was happy again with many minutes to spare. This was first dive of the day after a 22hr SIT.
 

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