Deep Diving 108 feet w/ a single AL 80 (Air.) No redundancy.

[Russjstewart]

Back in the early 80’s the commonly used tank in Australia was an Australian manufactured AL88, and were the only tanks I used for many years.
Dive 33 after my O.W.course was 30 metres for 20 minutes
Dive 39 was to 34 metres for a total for 22 min
Dive 43 was to 37 metres for a total time of 23 minutes
Dive 54 was to 40 m for 18 min as part of a Cave Diving Association of Australia Cat 2 course.

All dives were done on a single 88, no redundant air supply. In fact I am not even sure if I had an octopus. Part of the CDAA test was to buddy breathe while the out of air diver was following a guide line, so they may not have required an octopus in those days.

None of this was exceptional in anyway for the time, it was quite simply what was done.

 

[Blackcrusader]

It all depends on your gas consumption, paying attention to your gas and NDL. I have 315 dives at >100 feet, only 32 below 130 feet, nearly all of these with a rental AL80. I have never come even close to running out of gas, occasionally, I do light deco. I'm fortunate, my RMV over the last 1500+ dives is O.36 cf/min

This would just be one of my normal 90 minute dives to this depth of 34m and staying above NDL and enjoying the dive and ending with 50 bar from an AL80 with 200 bar. I see no reason why many divers who are experienced and are good on air cannot do this dive. I have done the same dive site with other divers are they are at 50 bar after around 60 - 65 mins but that is still within safety margins.

This type of dive is an average dive for most people who stay within a few minutes of NDL. As a BSAC sports diver where Deco dives on air are normal even if I was doing this dive with planned deco time I would not need to worry about air even if I shortened my total dive time.

 

[Blackcrusader]

Hello. Staying within N.D.L.......I don't care how long you've been diving, or if, you' re the best breather on the planet your max bottom time is approximately 18 to 20 minutes, at 100fsw, not including the 3 min Safety stop..

Sorry that is just not true. Look at my dive graph above. I've stayed at 115 feet yet used less than 20 bar after 10 minutes. That's less than 10% of the air I started with. Even if I stayed for 20 minutes I would only be around 5 minutes past NDL and still have 80% of my air supply left. By the time I have gone back to 15m or around 50 feet NDL will be back to more than 1 hour and I would have cleared any deco time without needing a deco stop.

 

[halocline]

Conditions, location, experience. 108 fsw in clear, warm Caribbean water on a single 80 would not be a concern unless I was diving 32 nitrox.

And what would your concern be? You're already shallower, in ideal conditions, than a conservative MOD.

 

[jadairiii]

Ok, so now we are saying NDL divers need more contingency than cave divers? Anyone can be as cautious is they choose for themselves, but this is a bit over the top. Start the ascent at 1500, sure depending on your SAC that may be prudent. I would probably wait for about 1000, but would likely hit NDL first. All that said, I haven't dove to any significant depth with a single in years.

Not sure who you cave dive with, but me and my buddies surface will a lot more gas than that. Why we dive stage bottles. Most cave dives we never even touch our back gas.

Do the math, you wont get your OOA buddy and you off the bottom in 108' of water with safety stops. 13 cuft per diver will be cutting it close. The goal is to safely ascend.

 

[Storker]

Do the math, you wont get your OOA buddy and you off the bottom in 108' of water with safety stops. 13 cuft per diver will be cutting it close. The goal is to safely ascend.

I did the math some time ago. Now, that math is in metric units, but if I use those numbers as a basis for an estimate I'd need about 100 bar reserve in an 11L tank (Al80 = 11L 207 bar) at 30m. Even if I include a safety stop and want a 20 bar (300 psi) reserve at the surface. 100 bar is pretty close to 1500 psi, and a half-empty Al80 is around 20 cuft per diver, so I don't quite understand where you got the 13 from.

Interestingly enough, with an RMV of 15 SLM the first half of the tank would last me around 20 minutes at 30m/100'. Or IOW, pretty close to the NDL if I'm breathing air.

 

[skippy311]

A single dive with a buddy and some others on 190bars air over 35 meters is ok. Just be careful.

 

[J-Vo]

Not sure who you cave dive with, but me and my buddies surface will a lot more gas than that. Why we dive stage bottles. Most cave dives we never even touch our back gas.

Do the math, you wont get your OOA buddy and you off the bottom in 108' of water with safety stops. 13 cuft per diver will be cutting it close. The goal is to safely ascend.

Last I read the standard for a cave dive is 3rds, and I have no problem with that in a 3 person team. That means planning to exit with 1/3rd of your gas remaining. Granted, I am a new cave diver, but those are the rules as specified in all the manuals.

Now specific to this thread, it is extremely dependent on the divers SAC. Normal ascent with safety stop from 108' would be for me about 500psi. Factor in that the safety stop is completely optional and I have no problem starting my ascent with 1000psi and would expect it to be plenty for an emergency air share ascent assuming a similar buddy. I give more margin for deco dives. I run my PDC at a conservatism as to witch if it does not show deco, I don't need a safety stop, so I would be out of NDL way before I hit 1k psi in an 80.

 

[Storker]

Last I read the standard for a cave dive is 3rds

3rds is sometimes way too conservative, at other times not conservative enough.

Min gas. The only sensible standard. Do the math and compare the two.

 

[RyanT]

So you need a 133 to dive to recreational limits, geez

As per the topic of this thread, I don't think diving to 108' on a single AL80 is inherently dangerous for the experienced diver. I've also made 100s of solo dives to 130' on a single AL80. For me personally, I no longer think it's a good idea. My level of risk tolerance is lower now than when I was younger. For dives near the recreational limits, I'm diving doubles. That's just me, enjoy your dives.