Exceeding NDL on an al80?

[northernone]

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? Not a repetitive dive.

I can normally, including plenty of profiles run on the U.S. Navy tables.

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.

 

[Kharon]

First dive on the double reef on Bonaire. Looked down and was within 6 minutes of NDL with a lot of gas. Did a slow small ascent and headed for the 1st reef. Another first dive at near 130' on Bonaire I got within 2 minutes of NDL and still had a lot of gas. So, at least for me it's something to watch.

 

[uncfnp]

Interesting question that I really could not definitively answer from recall so pulled up my dive log and looked at a recent Cozumel trip since it would be most representative of my typical al 80 dives.

First dive first day, Columbia Deep hit 3 minute before I ascended shallower to extend dive. Max depth 110. 32% gas

Next day first dive, Cathedral and hit 2 minutes before going up. 36% gas

Both cases I had to ascend secondary to NDL and not gas.

Caveat: I dive a very conservative algorithm and these were both deepish dives although my algorithm conservativism doesn’t really kick in until repetitive dives.

Edit: Bob brought up another factor, nitrox. Added to post.

 

[hammet]

With an rmv of .5, a little calculation shows that any dive deeper than about 70 will show air consumption times less than padi NDLs.

(assuming rmv of .5 and consuming 64.5 cf of air)

 

[MXGratefulDiver]

On air ... easy to exceed NDL on an AL80.

But I dive neither air nor AL80's ...

... Bob (Grateful Diver)

 

[swimlikethefish]

To answer this question honestly I would need to know if I'm diving tables or a computer.

On a computer my NDL would be the limiting factor due to the conservative profiles, unless I adjust the G/F's to a less conservative number. But even then I think the NDL would be the limit hit first.

Diving U.S. Navy dive tables, air would be the limiting factor instead of NDL. This is using 60ft for 60min as an example. However, there might be a few circumstances where it could be a toss up. Nitrox would not be one of those cases. If on nitrox, you would most definitely run out of air long before ndl on a 60ft dive. Your ead would be a shallower depth with a longer ndl, one which I do not think is easily reached on an 80.

 

[drbill]

On air ... easy to exceed NDL on an AL80.

But I dive neither air nor AL80's ...

... Bob (Grateful Diver)

I do both and have exceeded NDL many times... with full knowledge of it and sufficient reserve to complete required stops

 

[Fastmarc]

Very easy for me. On my last dive, the 1st of two was to a wreck which was 100 - 120+ft. I maxed at 107 and stayed 100ish. Eventually had to start adjusting my depth so as not to ride the limit too much. Dive time ended up being 32 mins. I started with 2900 psi and was in the boat with 1400 psi.

 

[Brian G]

I'e only heard this in combination with the PADI limit of 60ft depth for newly minted OW divers.

 

[northernone]

I'e only heard this in combination with the PADI limit of 60ft depth for newly minted OW divers.

Interesting! I just ran the numbers. Looks like 55minutes @ 60ft plus 5 minute safety stop would take more than an al80 worth of air if the diver's SAC is over .5cfpm.