Aluminum 80s versus larger steel tanks

[MMM]

I would still be willing to bet that with enough widespread use of bigger tanks in Cozumel, eventually DCS incidence would rise. Currently it's just a few dive ops offering these tanks to a relatively low number of divers.

It's just a guess here, but I think if you developed a table tallying the numbers of divers hitting the chambers in Cozumel divided between the 3 companies offering large steel tanks and the rest of the aluminum 80s, it would be disproportionately heavy on the latter side...even factoring in the ratios of people diving steel and aluminum. Dave is the only steel operator posting here but maybe he could give some indication of the percentage of his divers that end up in the chamber. I suspect it's pretty low.

 

[Mossman]

It's just a guess here, but I think if you developed a table tallying the numbers of divers hitting the chambers in Cozumel divided between the 3 companies offering large steel tanks and the rest of the aluminum 80s, it would be disproportionately heavy on the latter side...even factoring in the ratios of people diving steel and aluminum. Dave is the only steel operator posting here but maybe he could give some indication of the percentage of his divers that end up in the chamber. I suspect it's pretty low.

I want to agree with you. The steel 120 ops seems to cater to experienced divers with the other perks they offer, not just the bigger tanks. For instance, the huge camera tank on the Jewfish is not going to make a big difference to the guy off a Carnival boat carrying his disposable u/w camera.

But then I recall the lady who got into deco on my last trip with LU who thought her computer was broken because she had no idea what the display was reading. I don't believe she would have gotten into deco doing the same dive on an AL80 as her air consumption rate didn't seem so great. Fortunately she was diving a Suunto, so the mandatory deco was only 'virtually' mandatory, but I can see halocline's point. Even on nitrox, I get into deco plenty with my Suunto when diving a 120 - the difference is that I do my stop(s).

 

[MMM]

Did she end up in the chamber? If not, then she would not be captured in my theoretical survey above.

But then I recall the lady who got into deco on my last trip with LU who thought her computer was broken because she had no idea what the display was reading.

 

[Dave Dillehay]

My guess is that we have 2-3 per year that exhibit signs of bends, skin rash is the most telling symptom. Keeping in mind that if one goes to a chamber doc they almost always will be treated out of an abundance of caution--and my unskilled guess is that less than half are actually bent.

On the other hand we serve many more divers than the others with high capacity tanks, probably 4 times as much, but by keeping groups at 6 or less, the DM can more closely monitor each diver and our two hour surface interval helps as well.

It is my belief that we average less than most alum 80 dive shops on a per capita basis. You may be able to count the reasons.


Dave Dillehay
Aldora Divers

 

[nimoh]

I want to agree with you. The steel 120 ops seems to cater to experienced divers with the other perks they offer, not just the bigger tanks. For instance, the huge camera tank on the Jewfish is not going to make a big difference to the guy off a Carnival boat carrying his disposable u/w camera.

But then I recall the lady who got into deco on my last trip with LU who thought her computer was broken because she had no idea what the display was reading. I don't believe she would have gotten into deco doing the same dive on an AL80 as her air consumption rate didn't seem so great. Fortunately she was diving a Suunto, so the mandatory deco was only 'virtually' mandatory, but I can see halocline's point. Even on nitrox, I get into deco plenty with my Suunto when diving a 120 - the difference is that I do my stop(s).

Perhaps getting bent would have been good for her. After 5 hours in the chamber, she would probably never dive again relying on a computer that she didn't know how to use. I wonder what her next incident will be given that this one was no big deal?

 

[macado]

That depends upon the mix, depth, and time. You are also assuming that the nitrox user will get as close to the NDLs for nitrox as the air user gets on air. If so, that is true. On the other hand, I use nitrox very frequently, and I am usually nowhere in the vicinity of the NDLs for the dives I do, while the people diving air on the same dive have to be pretty darn close to those NDLs.

Yes, very true. Sorry I meant to say my statement was more along the lines of if you dive nitrox very close to NDLs then it's really not much more conservative than diving air and going close to NDLs.

I don't consider my usage of nitrox very conservative since when I dive in Cozumel i'm generally hitting or exceeding my NDLs with nitrox.

 

[boulderjohn]

My guess is that we have 2-3 per year that exhibit signs of bends, skin rash is the most telling symptom. Keeping in mind that if one goes to a chamber doc they almost always will be treated out of an abundance of caution--and my unskilled guess is that less than half are actually bent.

In an entirely unrelated thread, some documents were posted related to this. One of the points made in one of the documents from DAN was that a large number of people are regularly treated with chamber rides even though they do not have DCS. In many of those cases, a truly qualified physician making the initial diagnosis should have known the difference. The thread was not at all about Cozumel, so my statement should not be considered a reflection of the qualifications of the people there.

 

[halocline]

I would not assume that if the big steel tanks are eventually used by more dive ops and by a more widespread group of divers, all the dive ops will follow Aldora's practices to offset the potential increase in risk in using bigger tanks to extend depth/bottom time.

That's the potential problem with the use of these tanks. Right now, the AL80 is somewhat of a limiter in terms of going into deco; a 120 is 50% more air....

 

[Lorenzoid]

I would not assume that if the big steel tanks are eventually used by more dive ops and by a more widespread group of divers, ....

This seems unlikely in the first place, since so many divers are looking mainly for economy and will not be inclined to use dive ops whose fees then factor in the increased costs of dealing with steel tanks. I suspect steel tanks will continue to remain a niche offering by just a few dive ops.

But I agree with your speculation. For the unwashed masses, steel tanks would be an invitation to difficulties.

 

[boulderjohn]

I am beginning to lose track of who has said what in this thread.

I am getting sense that the general drift is that there is no advantage to steel 120s because you don't get any longer bottom times than with an AL 80, and if you do use them, you have a higher risk of DCS because of the increased bottom times. Or am I misreading this?