Aluminum 80s versus larger steel tanks

[Ron Lee]

In that case, he must also wonder, as I do, about the opposing arguments that seem to be simultaneously stating that the larger tanks do not provide greater bottom times and that they also increase the risk of DCS because of increased bottom times.

1) 50% more air. That you can get a longer dive with more air should be obvious.

The three folks who made an extremely deep dive resulting in one death and one paralysis might have fared better had they used 120 cu ft tanks. It still would have been a hazardous dive that I would not attempt.

2) Who stated with medical certainty that a longer dive means increased risk of DCS? Perhaps the dive profile typically used reduces the risk of DCS. Then there is the statistical element. If the risk is known exactly to be 1 in 10,000 dives with an AL80 at a given dive site and it becomes 1 in 9800 dives using a steel 120, is that a real increased risk? Maybe the dive profile makes it 1 in 10,100 dives so it is really safer.

Those are made up numbers just for discussion.

 

[boulderjohn]

You have apparently missed the fact that I did not make those arguments. I was observing that others seemed to be making those arguments.

1) 50% more air. That you can get a longer dive with more air should be obvious.

The three folks who made an extremely deep dive resulting in one death and one paralysis might have fared better had they used 120 cu ft tanks. It still would have been a hazardous dive that I would not attempt.

2) Who stated with medical certainty that a longer dive means increased risk of DCS? Perhaps the dive profile typically used reduces the risk of DCS. Then there is the statistical element. If the risk is known exactly to be 1 in 10,000 dives with an AL80 at a given dive site and it becomes 1 in 9800 dives using a steel 120, is that a real increased risk? Maybe the dive profile makes it 1 in 10,100 dives so it is really safer.

Those are made up numbers just for discussion.

There is no need to make up numbers. I have given real numbers in a number of posts not far back.

 

[Skittl1321]

The three folks who made an extremely deep dive resulting in one death and one paralysis might have fared better had they used 120 cu ft tanks. It still would have been a hazardous dive that I would not attempt.

This is incredibly presumptuous to make a statement that using a 120 would have made what they did safer. For all we know, using a 120 may have made them reason they had plenty of air and go even deeper.

If you're just making stuff up, it would be just as easy to say that in the general population a 120 is going to encourage riskier behavior because divers think they have enough air to handle a problem scenario. Maybe some people who wouldn't go to Devil's Throat get more confident due to more air, but then, due to their inexperience they freak out at depth and in a swim through. More air isn't going to help someone who is spitting out a regulator in panic. And I absolutely think that people get over confident and these things happen.

But just like you have no idea that 120s would have made that ill-fated dive better, I also don't know that 120s will make people engage in risky habits.

 

[Mossman]

and stay hydrated, don't drink too much and get plenty of sleep?

One out of three ain't bad. I stay well hydrated

Again, nitrox mitigates the other factors. Having less nitrogen saturated into the tissues means less risk of desaturation issues, even if there aren't any statistics to prove it.

What we need is a dive boat that will give us pure O2 to breathe on our SIs and on the boat ride home. You'd think Aldora could offer that sort of thing for an extra $10-20/day.

 

[mikeycanuk]

Out of our 20 dives with the 120's our NDL's were never an issue, ever. We didn't go that deep mainly due to our 12 yr olds depth restriction. I like the fact our logbooks went from 45 min dives to 70-80-88 mins. For all the hassle of getting 3 sets of gear ready in the am to the 45 mins after of washing wetsuits, soaking computers, scrubbing masks and doing laundry after the dives are over- we are essentially getting 3 dives for the hassle of 2 (let's not forget the boat rides). I don't get getting in more dives later in the day, I'm usually a few beers in and no way I'm cleaning anything else, riding yet again on a boat.

I always thought more air was better, but Cozumel must be an exception I guess, more air now = DCS!?! Madness!

To each their own but 275+ posts is a lot, even for this forum.


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[Mossman]

For all the hassle of getting 3 sets of gear ready in the am to the 45 mins after of washing wetsuits, soaking computers, scrubbing masks and doing laundry after the dives are over-

Huh? Wow, that does sound like a hassle.

Fortunately I use a dive op that washes my wetsuit, I leave my mask on the boat to be rinsed along with the rest of the gear, I "soak" my computer (the wrist part) in my post-dive shower, and I do my laundry when I get back home. To me, that is a vacation!

 

[Ron Lee]

This is incredibly presumptuous to make a statement that using a 120 would have made what they did safer. For all we know, using a 120 may have made them reason they had plenty of air and go even deeper.

If you're just making stuff up, it would be just as easy to say that in the general population a 120 is going to encourage riskier behavior because divers think they have enough air to handle a problem scenario. Maybe some people who wouldn't go to Devil's Throat get more confident due to more air, but then, due to their inexperience they freak out at depth and in a swim through. More air isn't going to help someone who is spitting out a regulator in panic. And I absolutely think that people get over confident and these things happen.

But just like you have no idea that 120s would have made that ill-fated dive better, I also don't know that 120s will make people engage in risky habits.

I said that they might have fared better. Imagine that instead of using 80 cu ft tanks (and one 100 cu ft if my memory is correct) that it went bad at the same point. To my knowledge no one who is still alive has given truthful accounting of the dive. So again from memory let us assume that at some depth...perhaps it was 250-300', the woman got below the two men. It matters not at this point whether it was an 80, 100 or 120 cu ft tank.

The Mexican divemaster goes after her and they reach some unspecified depth before starting back up. At this point having the 120 cu ft tank versus an 80 cu ft tank does/may make a difference. They have 50% more air at the start and it is reasonable to assume that they would have significantly more air starting up than using an AL80 tank.

That extra air means more air to do deco related stops on the way up. I am not well-versed on gas usage for a dive like this and whether they had enough air to make deep stops on the way up to prevent DCS issues....or even if making those stops makes the ultimate DCS event more survivable than not making them, but I sure would rather have the air to do what makes sense than rocket to the surface because air is low.

 

[boulderjohn]

I said that they might have fared better. Imagine that instead of using 80 cu ft tanks (and one 100 cu ft if my memory is correct) that it went bad at the same point. To my knowledge no one who is still alive has given truthful accounting of the dive. So again from memory let us assume that at some depth...perhaps it was 250-300', the woman got below the two men. It matters not at this point whether it was an 80, 100 or 120 cu ft tank.

The Mexican divemaster goes after her and they reach some unspecified depth before starting back up. At this point having the 120 cu ft tank versus an 80 cu ft tank does/may make a difference. They have 50% more air at the start and it is reasonable to assume that they would have significantly more air starting up than using an AL80 tank.

That extra air means more air to do deco related stops on the way up. I am not well-versed on gas usage for a dive like this and whether they had enough air to make deep stops on the way up to prevent DCS issues....or even if making those stops makes the ultimate DCS event more survivable than not making them, but I sure would rather have the air to do what makes sense than rocket to the surface because air is low.

Diving with more air would have made a really bad idea a little better. It is true that all might have lived if they had had just a bit more air, but doing the same dive on 120s is still a bad idea.

But you bring up a good point.

A lot of people talk about having sufficient gas reserves to deal with any emergency that happens at depth, and most of those people believe that an AL 80 does not supply sufficient reserves to deal effectively with emergencies on dives below 100 feet, and anyone doing such a dive with such a tank should make the bottom time much shorter than the NDL for that dive for the "just in case" factor.

 

[Mike]

This is incredibly presumptuous to make a statement that using a 120 would have made what they did safer. For all we know, using a 120 may have made them reason they had plenty of air and go even deeper.

It's not presumptious at all, if you know the details of the incident there was no going deeper on purpose because of a tank size, she had already gone too far on an 80 and lost mental control and had no control of her depth, and that was that, Gabi went after her to bring her back from the depths, the benefits of having more air would have been to Gabi and the air share they were on during the ascent, not for her, she already was out of control on an 80.

Personally I'd just give up on the continuous grasping at straws of attempting to come up with why less air is better on dives. The ultimate diving tank would be a tank with infinite supply, to try to say otherwise is just being contrarian for the sake of being so.

---------- Post added May 21st, 2014 at 07:02 PM ----------

I always thought more air was better, but Cozumel must be an exception I guess, more air now = DCS!?! Madness!

Madness is a good description.

Hey, I think we should work on passing a law on hookah diving, that there needs to be a timer set on their compressors, infinite air supply for them is just plain wrong. I'm not sure why it's wrong, but I'm sure there are some here that given enough time would come up with at least a half dozen reasons. There is just no way that any diver should have unlimited air, it must be limited!

 

[cvchief]

I always thought more air was better, but Cozumel must be an exception I guess, more air now = DCS!?! Madness!

It does seem like the facts are getting spun a bit.

I used to use a fatty 100AL on air. As my air consumption improved, I found that I constantly bumped into deco on air, because I was staying longer at depth. I could not use the entire tank on the profile without adding deco stops or going up. The bigger tank ran me into deco and, I would assume, raised my risk of DCS. As 100AL nitrox was not available, I moved to 80 nitrox and never get very close to deco. Additionally the fillers never fully fill 100AL. So I was already 10% short. On a 120 air, I would bust the crap outta NDL, I would guess. So in some fashion, bigger tanks would increase my DCS risk on the same profile. So apples to apples, yea maybe the risk is greater?

Of course if I dove 120s, I would dive only nitrox, just like 80s. ( I feel less tired and the air is sweeter. Have at that one....) And I would imagine, with time limited dives and larger surface intervals, I might be further from the limits anyway. So it is really apples to oranges.

So pick apples to apples or oranges to apples and argue whichever side you want.

By the by, 70 some minutes today on Gardens and French on that sweet 36. Lovely!