A Question for Nitrox Mavens

[joewr]

Hi,Gang,

Thanks for all the thoughtful answers and comments, but the question related to whether the various dive cert agencies were now teaching that EAN could be used for additional safety when diving by using air settings on one's dive computer?

During the Dark Ages when I did my EAN training, PADI only cited extended bottom times as the goal. In fact, they stressed using EAN tables and, not once, was using air tables for EAN diving mentioned.

So, I was wondering if there were a change in what was being taught and, if so, when such a change in "philosophy" came about?

joewr...looks like trip to the LDS is in the offing...and this space is still for lease...

 

[diverrex]

It's taught as an option for additional conservatism, not as its main purpose. Considering in the "old days" how many divers were taught or at least came away from class with the mistaken idea that diving Nitrox allowed you to take in less nitrogen and was therefore always safer than air in an absolute sense rather than being relative to how close you pushed Nitrox NDL I think it's a valid option to teach, if for no reason to help make the principles stick in their heads.

Almost every time I dive Nitrox I'll change to Nitrox settings on my computer even when the planned dive profile is well below air limits just because I want to know exactly where I am NDL wise and just in case I find something particularly interesting and want to extend bottom time past the plan. But if I'm going to Bonaire for the week diving with my wife and Nitrox is free and I know on a typcial dive I won't go past 70 feet and with a typical multilevel down and back up along the reef I'll be well within air NDL for a 60-70 minute dive and knowing my wife won't want to go past 70 minutes anyhow then I'll usually just leave my computer on air. If I'm diving the Hilma Hooker then I'll adjust to Nitrox settings.

 

[joewr]

The "old" PADI manual says Incidents of DCS are basically no more or less whether using Air or Nitrox, unless you use Nitrox and follow the Air tables. Uhhh.... yeah that makes sense.

Hi, TMHeimer!

How "old" is your PADI Manual? Mine is from the 1980's.

joewr...clearing the mind and this space...

 

[joewr]

It's taught as an option for additional conservatism, not as its main purpose. Considering in the "old days" how many divers were taught or at least came away from class with the mistaken idea that diving Nitrox allowed you to take in less nitrogen and was therefore always safer than air in an absolute sense rather than being relative to how close you pushed Nitrox NDL I think it's a valid option to teach, if for no reason to help make the principles stick in their heads.

Hi, from the Northern Part of Our Great State!

Speaking only with regard to the EAN training that I got in the "old days", we were taught that Nitrox just extended bottom times by lowering the nitrogen concentration in our tanks. However, the green/yellow/red zones were a direct reflection of the total absorbed nitrogen and that when one entered the yellow zone on either air or Nitrox, the nitrogen level was the virtually the same...it just took more breaths to get there with Nitrox.

We were never taught that using Nitrox allowed one to ignore nitrogen issues. In fact, we were taught that besides DCS, a Nitrox-user also had to pay attention to oxygen toxicity issues.

At any rate, I am learning that there is a new generation of divers who use Nitrox with a completely different "philosophy" than was taught to me.

joewr...nothing clever to add to this space just yet...

 

[MauiScubaSteve]

How "old" is your PADI Manual? Mine is from the 1980's.

joewr...clearing the mind and this space...

AFAIU, this Wikipedia "Nitrox History" is pretty accurate; my PADI Enriched Air Diver Manual is version 1.0, copyright '95.

In 1985 Dick Rutkowski, a former NOAA diving safety officer, formed IAND (International Association of Nitrox Divers) and began teaching nitrox use for recreational diving. This was considered dangerous by some, and met with heavy skepticism by the diving community.

In 1991, in a watershed moment, the annual DEMA show (held in Houston, Texas that year) banned nitrox training providers from the show. This created a backlash, and when DEMA relented, a number of organisations took the opportunity to present nitrox workshops outside the show. In 1992 BSAC banned its members from using nitrox.

In 1992 the name was changed to the International Association of Nitrox and Technical Divers (IANTD), the T being added when the European Association of Technical Divers (EATD) merged with IAND. In the early 1990s, the agencies teaching nitrox were not the main scuba agencies. New organizations, including Ed Betts' American Nitrox Divers International (ANDI) - which invented the term "Safe Air" for marketing purposes - and Bret Gilliam's Technical Diving International (TDI) gave scientific credence to nitrox.

Meanwhile, diving stores were finding a purely economic reason to offer nitrox: not only was an entire new course and certification needed to use it, but instead of cheap or free tank fills with compressed air, dive shops found they could charge premium amounts of money for custom-gas blending of nitrox to their ordinary moderately experienced divers. With the new dive computers which could be programmed to allow for the longer bottom-times and shorter residual nitrogen times which nitrox gave, the incentive for the sport diver to use the gas increased. An intersection of economics and scientific validity had occurred.

In 1993 Skin Diver magazine, the leading recreational diving publication at the time, published a three part series arguing that nitrox was unsafe for sport divers.[21] Against this trend, in 1992 NAUI became the first existing major sport diver training agency to sanction nitrox.

In 1993 Dive Rite manufactured the first nitrox compatible dive computer, called the Bridge.[22]

In 1996, the Professional Association of Diving Instructors (PADI) announced full educational support for nitrox.[17] While other main line scuba organizations had announced their support of nitrox earlier,[23] it was PADI's endorsement that put nitrox over the top as a standard sport diving "option."[24]

emphasis added by me

On page 4 of said '95 PADI Enriched Air Diver Manual there is this paragraph beginning...ending with;

Because you absorb less nitrogen using enriched air, you might expect that using enriched air within normal air no decompression limits would substantially improve your safety. This probably isn't true. The DCI incidence rate is already so low that it's unlikely that simply reducing nitrogen can produce a "meaningful safety" improvement. Although there's been no experimental study of this, statistical estimates suggest that using enriched air within normal air limits only reduces the incidence rate a fraction of a percent....

.... It should be noted that some divers feel that "any" mathematical risk reduction, no matter how minimal, still makes it worth using enriched air on dives that they could expect to make safely with air. As long as enriched air procedures are followed, there are no added safety concerns with this personal choice.

 

[drrich2]

Joewr:

I certified in Nitrox back around early '07 or so, if memory serves. As for the mindset of nitrox divers these days, and drawing on the impressions of others noted on this forum, I think that with many users there's a sense that as long as you don't pass the MOD for your mix, or do multiple repetitive dives near it, then your 'oxygen clock' isn't likely to get into a dangerous cumulative exposure. Now, how accurate that is I don't know off-hand, but when I took the course, the issue of oxygen toxicity was indeed taught, but when I looked at the issue back then, it was hard to see where I'd likely run into issues with it.

That said, my main repetitive diving with nitrox is done on Bonaire trips where the only tank I get is 80 cf, and I'm a big guy whose dive time is usually 40 - 50 minutes, part of that spent in the shallows at the end of the dive. Someone who had a much longer dive time on an 80 cf tank, liked to dive deep & dove 5 times per day a few days running might be in a different situation. I haven't tried to figure that one out, since it doesn't apply to me.

I'd be interested to hear how often others run into oxygen build-up as a 'rate limiting factor' in their dive frequency or duration in the real world.

Richard.

 

[Mossman]

I'd be interested to hear how often others run into oxygen build-up as a 'rate limiting factor' in their dive frequency or duration in the real world.

That requires too much time at high ppO2, probably not achievable within NDC limits at 32% on a single tank, but with a larger tank, a richer mix, I suppose it's eventually possible. More practical to worry about it for tech dives or especially rebreathers.

 

[RonFrank]

I did a live aboard where we were doing 5 hours of diving a day. We dove air and our BT was not a problem. The first dive of the day we generally did our deepest dive, but the profiles allowed for us to have enjoyable multi level dives. Keep in mind the folks running the show are also divers, so the way we were diving was no accident. Most people did not bother with nitrox.

One of the places where Nitrox was important was the FL coast where the dives were relatively flat and deepish. Think Jupiter. Nitrox there made a lot of sense. The couple of folks not on Nitrox were spending a lot of time sitting on the boat. We were doing EANX36.

BTW, O2 buildup is not an issue multi-day. We did 4 dives a day (4 hrs+) for 6 days and O2 was not an issue. Two dives were generally max 100'+. Not sure if this can become an issue for the DM's in Coz.

 

[TMHeimer]

Hi, TMHeimer!

How "old" is your PADI Manual? Mine is from the 1980's.

joewr...clearing the mind and this space...

It's just the -'95-'04 one (took the course in '06). The quote is actually: "Using enriched air nitrox may have a tangible safety benefit for a dive that pushes the air no decompression limits".

 

[boulderjohn]

As far as getting a safety factor by diving nitrox but using air tables, Halemano's second quote is the key one. If you are diving air within the NDL's, the odds of getting DCS are, I believe, something like a hundredth of a percent. If you dive nitrox to gain a safety advantage, then you are indeed getting a safety advantage, but the amount you have reduced those odds is close to immeasurable. It would be like driving 54 mph in a 55 mph speed zone on a clear road in order to gain a safety advantage.

As far as the concern with cumulative O2 loading--pulmonary oxygen toxicity--if you play with the numbers there you will see that it takes a tremendous amount of exposure to get anywhere close to the limits. Even divers using nitrox for 5 dives a day on a liveaboard are not likely to get close.

Technical divers who are pushing the MODs for extended periods on the deep part of the dive, using 50% on the earlier parts of the ascent, and finishing off on pure O2 have a hard time getting close to the limits, even with repeated dives on the same day.