Aluminum 80s versus larger steel tanks

[Mike]

More bottom time means exceeding NDL's. Not what a dive op wants to have to deel with when toting a croud of vacation divers for a 2 tank dive.

There are at least 3 diver operations in Cozumel who have figured out how to overcome your list of impossibles, it's probably not a coincidence that they also happen to be 3 of the most highly rated/regarded shops. One of the rules of at least one of them is nobody dives without a computer, they also employ other procedures which they've developed to make it all safe and possible. In regard to NDL, if you haven't dived there yet, the dives are typically multi-level not square dive profiles.

 

[halocline]

I have speculated about a rise in the incidence of DCS in Cozumel if the larger tanks become commonly used. Hopefully it won't happen but I would not rule it out. Larger tanks in Coz does mean many inexperienced divers going deeper and staying down longer, which eventually is likely to cause some extra cases of DCS, computer use or not. It all depends on diver behavior. I suppose nitrox use in the bigger tanks could help as well.

 

[Ron Lee]

More bottom time means exceeding NDL's. Not what a dive op wants to have to deel with when toting a croud of vacation divers for a 2 tank dive.

Would it be a correct assumption that you have never dove with a Cozumel dive op who uses 120 cu ft tanks?

 

[boulderjohn]

More bottom time means exceeding NDL's.

I suppose nitrox use in the bigger tanks could help as well.

I'm trying to remember the last time I did a recreational dive in Cozumel that was not on nitrox. It may have been way back when I was still using the operator that insisted I could only use it on the second dive because it was too dangerous to use it on the first dive.

 

[macado]

I have speculated about a rise in the incidence of DCS in Cozumel if the larger tanks become commonly used. Hopefully it won't happen but I would not rule it out. Larger tanks in Coz does mean many inexperienced divers going deeper and staying down longer, which eventually is likely to cause some extra cases of DCS, computer use or not. It all depends on diver behavior. I suppose nitrox use in the bigger tanks could help as well.

It would be very interesting to see these statistics or ratio of divers with DCS incidents with operators with steel tanks vs. AL80s. My understanding is that there are some operators that use the typical AL80 that have much higher rate of DCS incidents but I don't know if that is true.

A lot of people automatically have the assumption that diving Nitrox = safer/less DCS hits/less nitrogen exposure. This is far from the truth especially if people are doing long aggressive profiles on Nitrox and hitting their NDLs. Just as easy to get bent on nitrox as it is air.

 

[boulderjohn]

Just as easy to get bent on nitrox as it is air.

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.

 

[gopbroek]

It would be very interesting to see these statistics or ratio of divers with DCS incidents with operators with steel tanks vs. AL80s. My understanding is that there are some operators that use the typical AL80 that have much higher rate of DCS incidents but I don't know if that is true.

A lot of people automatically have the assumption that diving Nitrox = safer/less DCS hits/less nitrogen exposure. This is far from the truth especially if people are doing long aggressive profiles on Nitrox and hitting their NDLs. Just as easy to get bent on nitrox as it is air.

I do not think there are any true statistics on DCS for any major dive destination; it’s not good for business. Any numbers I believe would be anecdotal but due to the sheer number of divers in Cozumel I think it is probably pretty low. Reading some of the other threads concerning ambulances hijacking DCS (real or suspect) cases off the points (kind of like the old movie Mother, Jugs & Speed) I get the impression that there used to be a primary chamber downtown and then several others were recently built for profit and there is now an over capacity problem.

Regardless of tank size or mixture, DC’s have become cheap and common. I think that the common use of dive computers has really lowered the rate of DCS worldwide. The other thing is common sense, if you ride the NDL aggressively, regardless of tank size or mixture, you increase your risks (NDL is NDL no matter what the O2 content). At the very least you should do a long tail out at 15’ to off gas as much as possible, I like about 10 minutes minimum or longer, hanging off a SMB, if there is anything other than the abyss to see I will go down to minimal gas. I see this as one of the benefits of a ‘dive your tank’ operation, but that is my preference, others may feel more comfortable with a pure up and out as a group operation.

 

[redacted]

A lot of people automatically have the assumption that diving Nitrox = safer/less DCS hits/less nitrogen exposure. This is far from the truth especially if people are doing long aggressive profiles on Nitrox and hitting their NDLs. Just as easy to get bent on nitrox as it is air.

I agree that such an "automatic assumption" may be dangerous. But, if you think about it, Nitrox in Cozumel is most used by divers conducting air dive profiles so you don't have to assume it is safer. You can easily REASON that it is reducing nitrogen exposure. With the instances of DCS so low overall, the effect on DCS in Cozumel is probably indistinguishable.

 

[Skittl1321]

Nitrox in Cozumel is most used by divers conducting air dive profiles so you don't have to assume it is safer.

So then, it won't increase your bottom time, and you'll still likely reach your NDL before you can use a larger tank... the argument being made in this thread is that if you dive nitrox you get longer bottom times. You can't get longer bottom times and increased safety (with an air profile). One or the other.

Most people who dive nitrox in Cozumel are probably using it on 80s (because most people in Cozumel dive 80s)- so not hitting the NDLs for nitrox; but if everyone were to be on 120s, I think a lot more divers would be hitting the NDLs for nitrox due to the extended dives.

 

[nimoh]

So then, it won't increase your bottom time, and you'll still likely reach your NDL before you can use a larger tank... the argument being made in this thread is that if you dive nitrox you get longer bottom times. You can't get longer bottom times and increased safety (with an air profile). One or the other.

actually you can get both. The more you increase your bottom time, the less you increase your safety, and vice-versa. However, if you increase your bottom time by a little bit, you are still increasing your safety (with respect to NDL).

Take an 70' dive for 35 minutes. You would be within 5 minutes of your NDL.

Same 70' on EAN32 but for 45 minutes. You have a longer bottom time but are now 10 minutes from your NDL.