Pros and Cons of Nitrox: What are they?

[Scubaguy62]

PADI still claims that it doesn't help recreational divers but their about the only ones and I think it's because they don't want to develop new tables. LOL

The wheel version of the RDP, and speaking only regarding planned ML dives, recognizes a minimum shallower depth, i.e, if the first depth is 120 fsw, the next shallower depth the diver can plan for is 80 fsw. I may be wrong in my perception Mike, but isn't that in esence a deep stop at 70% the max depth?

Rick

 

[ScubaRon]

As PDE divers are just volunteers from all over the place, I'm not sure what you would think the bias would be. The numbers just reflect the growing use of Nitrox in diving.

As an alternate possibility, the more recent survey is from a larger pool which should in theory provide more accurate numbers. Also, it's possible that there is a better understanding of Nitrox and it's proper use than previously, and thus less problems. It will be interesting to see the 2005 report.

Still not sure how 11% use and 13% injuries becomes a 20% higher accident rate.

Edit: I notice that of the 2001, 2002, 2003 and 2004 reports, three of them show Nitrox as the group with much lower accident rates. Only one year (2003, the one that you choose to quote from) shows Nitrox with (slightly) higher accident rates. Wonder where the bias is?

PDE is indeed based on volunteers, but it's data come heavily from a few sources (I don't have the exact numbers in front of me, so some of them may be little bit off):
- 2 companies (Aggressor and Nekton I believe) make up 25% or so of the dives.
- Dive professionals make up a pretty hefty percentage of PDE.
- Data from PDE sponsors like Suunto, Uwatec etc. will be overrepresented, while data from non-sponsors like Aeris, Oceanic, will be underrepresented.
- PDE data are worldwide.
The injury data are US residents only, but cover (almost) the entire dive population. So that's why I said there is likely some bias. By the way, this bias could go either way. What struck me about the PDE 2004 data was the IMO very high percentage (28% if I remember correctly) of Nitrox users. From looking around me I find it hard to believe that that is a national average.

I calculated the accident rate (2003) as follows:
nitrox rate: 12.7% / 11% = 1.155
air rate: 83% / 86% = 0.965
1.155 is 20% higher than 0.965 (again: numbers might be off a little)

 

[ScubaRon]

What device needs to be O2 clean? The Mares Surveyor Nitrox is non AI dive computer. I dive with an Aeris Atmos 2, and if I switch from nitrox to air, the gas mode will not set to "air," but will set from say 32% to 21%. Does the Surveyor Nitrox computer tells the diver to have the reg O2 clean if switching from nitrox to air? Mares computers are notorious for being overly conservative, so if it does, I'm not surprised.

My mistake: it's the SPG (and the hose) which are part of the Surveyor Console that the warning is for. The computer itself would never come into contact with nitrox and obviously does not need to be O2 cleaned.

Come to think about it, I have not seen the Mares Nitrox reg being advertised that much anymore, so I wonder if they still make them. If they don't, I wonder why!

They still mention the special nitrox version of some of their regs in the 2004 catalog, but it's in pretty small print.

 

[MikeFerrara]

The wheel version of the RDP, and speaking only regarding planned ML dives, recognizes a minimum shallower depth, i.e, if the first depth is 120 fsw, the next shallower depth the diver can plan for is 80 fsw. I may be wrong in my perception Mike, but isn't that in esence a deep stop at 70% the max depth?

Rick

No it's not the same thing. The weel considers each level of the multilevel dive as an "on-gassing" stage of the dive. The longer you stay down regarless of level your rep group continues to climb. You don't stop the clock until you begin a direct ascent to the surface (with safety stop of course). They're forcing you up shallow before giving you credit and even then you're pressure group doesn't drop until you leave the water. That's not the way it really works.

Now, if you run some profile with a decompression software (especially a bubble model or one that uses gradient factors) you'll see that above some depth you're off-gassing. Stopping deeper keeps bubbles under greater pressure which, all else being equal, keeps them smaller, with a thicker skin and higher internal pressure. The higher internal pressure especially when combined with increased PPO2 (decreased PN2) maximizes the gradient accross the bubble so we're off-gassing better while at the same time keeping the bubble small.

Looking at desolved gas, we're getting rid of the inert gas load slower.

That's not a very detailed explaination but the fact is that deeper stops and slower ascents are good for every one and I believe especially good for the recreational diver on a multi-dive, multi-day trip. Riding table NDL's or computer color zones, rushing up to safety stop depth and rushing from there to the surface is the worst thing you could do especially if you're breathing nitrogen that you don't have to have.

Many dives done by recreational divers are gas limited more so than time limited and often minimum surface intervals are set by the boat so the use of nitrox flat out reduces the nitrogen load. Add in slower ascents and deeper sops and the difference in loading/bubbling on surfacing can be dramatic.

When you consider tha real average ascent speed of recreational divers (especially the last and most critical part of the ascent) less N2 is a really really good thing.

Run it in some software and play with it yourself.

Hence the reason that many now believe that air is for tires. LOL. I don't know that I'd go that far but diving air over nitrox when you have a choice is silly.

 

[glbirch]

PDE is indeed based on volunteers, but it's data come heavily from a few sources (I don't have the exact numbers in front of me, so some of them may be little bit off):
- 2 companies (Aggressor and Nekton I believe) make up 25% or so of the dives.
- Dive professionals make up a pretty hefty percentage of PDE.
- Data from PDE sponsors like Suunto, Uwatec etc. will be overrepresented, while data from non-sponsors like Aeris, Oceanic, will be underrepresented.
- PDE data are worldwide.
The injury data are US residents only, but cover (almost) the entire dive population. So that's why I said there is likely some bias. By the way, this bias could go either way. What struck me about the PDE 2004 data was the IMO very high percentage (28% if I remember correctly) of Nitrox users. From looking around me I find it hard to believe that that is a national average.

I calculated the accident rate (2003) as follows:
nitrox rate: 12.7% / 11% = 1.155
air rate: 83% / 86% = 0.965
1.155 is 20% higher than 0.965 (again: numbers might be off a little)

If we assume this is a valid method of calculating relative safety, then the 2001 report shows that Nitrox is 200% safer for accidents, and 1600% safer for fatalites. 75% and 400% safer in the 2002 report, and also similarly safer for the 2004 report. Quick and dirty math, so I could be off slightly as well.

The national average is probably not as high as the 24% in the report. The live-aboards have started offering Nitrox, which is likely weighing the report a little heavy on that end as I suspect those users are breating N2 more that 24% of the time. I know last time I was on an Agressor I was using N2 on about half the dives (if I recall correctly), and many of the other divers were as well.

 

[MikeFerrara]

PDE is indeed based on volunteers, but it's data come heavily from a few sources (I don't have the exact numbers in front of me, so some of them may be little bit off):
- 2 companies (Aggressor and Nekton I believe) make up 25% or so of the dives.
- Dive professionals make up a pretty hefty percentage of PDE.
- Data from PDE sponsors like Suunto, Uwatec etc. will be overrepresented, while data from non-sponsors like Aeris, Oceanic, will be underrepresented.
- PDE data are worldwide.
The injury data are US residents only, but cover (almost) the entire dive population. So that's why I said there is likely some bias. By the way, this bias could go either way. What struck me about the PDE 2004 data was the IMO very high percentage (28% if I remember correctly) of Nitrox users. From looking around me I find it hard to believe that that is a national average.

I calculated the accident rate (2003) as follows:
nitrox rate: 12.7% / 11% = 1.155
air rate: 83% / 86% = 0.965
1.155 is 20% higher than 0.965 (again: numbers might be off a little)

i don't think that you're arguement (or your math) is statistically valid. What were the accidents. You haven't done anything at all to show that the nitrox cause or was even related to the accidents you're refering to.

since by definition all the PDE divers are diving with computers (correct?) you could just as easily blame the brand or model of computer. You could blame the resort the boat or whatever. you need to show a statistical correlation and significance of the relationship between the nitrox and the injuries.

Most diving injuries (other than medical problems) are cause by poor skills (per the DAN report). Rapid ascents andthings like that are what's hurting divers when we see figures like rapid ascents are reported in sisty something percent of the dives that result in fatality or that buoyancy control problems are reported in fourtysomething percent of the dives that result in injury.

It aint the nitrox. I do believe that the lack of understanding of decompression theory could have a significant effect though.

 

[ScubaRon]

since by definition all the PDE divers are diving with computers (correct?) you could just as easily blame the brand or model of computer. You could blame the resort the boat or whatever. you need to show a statistical correlation and significance of the relationship between the nitrox and the injuries.

That was exactly my point.

You seem to think that I am arguing that nitrox is unsafe. That is not true. As I stated earlier "I personally believe that Nitrox, when used properly is as safe as air".

 

[glbirch]

That was exactly my point.

You seem to think that I am arguing that nitrox is unsafe. That is not true. As I stated earlier "I personally believe that Nitrox, when used properly is as safe as air".

Earlier quote:

The only advantage of Nitrox is a longer bottom time. Contrary to what some dive shops tell you Nitrox is not proven to be safer than air. Although it reduced the chances of DCS somewhat, it also introduces other risks (oxygen toxicity being the main one) and the overall accident rate of Nitrox divers is significantly higher than that of air divers. This does not necessarily mean that Nitrox would be unsafer either: Nitrox is probably more often used by (tec) divers who do higher risk dives.

That didn't seem to be your point when you made this comment, which I disagree with. Or am I misreading something?

 

[ScubaRon]

That didn't seem to be your point when you made this comment, which I disagree with. Or am I misreading something?

My original point was that I have not seem any proof that nitrox was SAFER than air. I still feel that way.

I emphasize this point, because there are several dive instructors in my area whose main selling technique seems to be to tell every novice OW diver that they must take a nitrox course, because it makes diving soo much safer. As a result you have all these novice divers paying for nitrox on their 45ft monthly dive and feeling oh-so safe with 0 buoyancy skills. I despise that selling technique and think that people should be told the pro's and the con's, so than can make their own decision...like we're doing in this thread.

I have never claimed not do I believe that Nitrox would be unsafer than air if used properly.

 

[glbirch]

My original point was that I have not seem any proof that nitrox was SAFER than air. I still feel that way.

I emphasize this point, because there are several dive instructors in my area whose main selling technique seems to be to tell every novice OW diver that they must take a nitrox course, because it makes diving soo much safer. As a result you have all these novice divers paying for nitrox on their 45ft monthly dive and feeling oh-so safe with 0 buoyancy skills. I despise that selling technique and think that people should be told the pro's and the con's, so than can make their own decision...like we're doing in this thread.

I have never claimed not do I believe that Nitrox would be unsafer than air if used properly.

Well, there's a growing body of evidence that suggests that (all else being equal) Nitrox reduces the possibility of DCI. I'm not sure what you would consider adequate proof.

I doubt I would ever tell someone not to take a Nitrox course, but to take advantage of someone's lack of knowledge and/or experience to sell them something they may or may not need is not a practice I agree with. Certainly someone should be informed of the benefits and risks so that they can make a proper decision.

However, if you're going to carefully choose only the data that supports your opinion and then state it as a fact supported by that data (which you seem to have done earlier in this thread) I don't think that's any better.