Scientific Study of Nitrox and Air use

[Lee Bell]

In an exhaustive study, lasting over 40 years and involving thousands of
hours of diving, the relationship between air, nitrox and DCS is finally
clarified. Study results are as follows:

- Diving air, as air, within the limits of air tables, is completely safe.
In thousands of test dives, at depths covering the entire range normally
referred to as "recreational limits," absolutely no incidents of DCS were
noted.

- Diving air, as air, within the limits of pre gradient bubble computers is
almost completely safe. In thousands of test dives, at depths covering the
entire range normally referred to as "recreational limits," only one
suspected incident of DCS was noted. Incidents aggregate less than one .05
percent (.0005), a statistically insignificant number of suspected
incidents. It should be noted that the one suspected incident occurred at
the extreme limit of recreational depths and at extreme limit of the
computer's recommended profiles. In light of other results, it is likely
that at least one, and perhaps more, manufacturers of early dive computers,
failed to correctly identify the point at which some DCS risk occurs.

- Diving air, as air, within the limits of more conservative modern
computers, is completely safe. Absolutely no incidents of DCS were noted.
It is further noted that the profile responsible for the one suspected
incident of DCS experienced with an older computer, was not within profiles
recommended by modern computers. It is likely that safeguards added to even
the least conservative of modern computers have adequately addressed issues
with older, less conservative models.

- Diving nitrox, as nitrox, within the limits of modern nitrox capable
computers, is completely safe. Absolutely no incidents of DCS were noted.

Researcher's note:
1. No data is available for dives using nitrox, using nitrox tables. For
information on this subject, users are directed to studies performed by
other research groups including WKPP, GUE, DIR and Magilla.
2. Due to budget constraints, no data is available for diving nitrox as air.
Since diving air as air and nitrox as nitrox, researchers concluded that
there is no cost benefit to this practice. Rumors that the practice is
"safer" or "more conservative" are made moot by the fact that it is simply
not possible to be safer than 100% safe.

Lee Bell 2006-08-04

[ben bradlee]

LOL

[Chris]

Post by Lee Bell
In an exhaustive study, lasting over 40 years and involving thousands of
hours of diving, the relationship between air, nitrox and DCS is finally

These data are interesting, but, you fail to mention what organization
performed this scientific study... more info please.

cheers,
Chris

[Greg Mossman]

Post by Chris

Post by Lee Bell
In an exhaustive study, lasting over 40 years and involving thousands of
hours of diving, the relationship between air, nitrox and DCS is finally

These data are interesting, but, you fail to mention what organization
performed this scientific study... more info please.

It was a government-funded study, no doubt.

[Lee Bell]

Post by Greg Mossman

Post by Chris
These data are interesting, but, you fail to mention what organization
performed this scientific study... more info please.

NAUI, SSI and TDI were represented.

Post by Greg Mossman
It was a government-funded study, no doubt.

Funded entirely with private funds, no advertising, endorsements or
commercial contributions involved.

Lee

[Chris]

Post by Lee Bell
NAUI, SSI and TDI were represented.
Funded entirely with private funds, no advertising, endorsements or
commercial contributions involved.

Could you (or someone else) please provide an official source for this
study? I mean no disrespect, nor do I question the validity of your
statements - for my own reasons I'd very much like to have the actual
document of this study, rather than what "some guy on the internet"
said about some study.

cheers,
Chris

[Greg Mossman]

Post by Chris

Post by Lee Bell
NAUI, SSI and TDI were represented.
Funded entirely with private funds, no advertising, endorsements or
commercial contributions involved.

Could you (or someone else) please provide an official source for this
study? I mean no disrespect, nor do I question the validity of your
statements - for my own reasons I'd very much like to have the actual
document of this study, rather than what "some guy on the internet"
said about some study.

Yeah, like how do you know someone didn't just make it up?

[Lee Bell]

Post by Greg Mossman

Post by Chris

Post by Lee Bell
NAUI, SSI and TDI were represented.
Funded entirely with private funds, no advertising, endorsements or
commercial contributions involved.

Could you (or someone else) please provide an official source for this
study? I mean no disrespect, nor do I question the validity of your
statements - for my own reasons I'd very much like to have the actual
document of this study, rather than what "some guy on the internet"
said about some study.

Yeah, like how do you know someone didn't just make it up?

You read the official source. Perhaps you'd like to post the results of
your own study. How many times have you been bent diving air as air? How
many times diving nitrox as nitrox? How many times diving nitrox as air?
Since you're positive that one is more dangerous than the other, surely you
have something to back your position up . . . or was it, perhaps, something
someone just made up?

Lee

[Limey]

Post by Lee Bell

Post by Greg Mossman

Post by Chris

Post by Lee Bell
NAUI, SSI and TDI were represented.
Funded entirely with private funds, no advertising, endorsements or
commercial contributions involved.

Could you (or someone else) please provide an official source for this
study? I mean no disrespect, nor do I question the validity of your
statements - for my own reasons I'd very much like to have the actual
document of this study, rather than what "some guy on the internet"
said about some study.

Yeah, like how do you know someone didn't just make it up?

You read the official source. Perhaps you'd like to post the results of
your own study. How many times have you been bent diving air as air? How
many times diving nitrox as nitrox? How many times diving nitrox as air?
Since you're positive that one is more dangerous than the other, surely
you have something to back your position up . . . or was it, perhaps,
something someone just made up?

After a day of diving in Boynton Beach, Florida I once held a conch shell to
my ear and could clearly hear the ocean.......though thinking about it I was
standing on the beach at the time.

LD.

[mike gray]

Post by Greg Mossman

Post by Chris

Post by Lee Bell
NAUI, SSI and TDI were represented.
Funded entirely with private funds, no advertising, endorsements or
commercial contributions involved.

Could you (or someone else) please provide an official source for this
study? I mean no disrespect, nor do I question the validity of your
statements - for my own reasons I'd very much like to have the actual
document of this study, rather than what "some guy on the internet"
said about some study.

Yeah, like how do you know someone didn't just make it up?

Actually, this whole argument boils down to one simple question:
within the tables, is the risk curve flat or does it have a
slope >0.

The phenomenon of undeserved hits, which has been studied by
many, always ends up being random, i.e. incidence without
corelation to profile. There is therefore only one answer, that
the curve is flat.

some older studies, using older tables, did indeed show a
cluster at the upper time/depth limits (where, btw, Lee got his
hit) resulting in revised tables with the limits moved left of
the increase in incidence.

To my knowledge, there have been no table revisions from any
source post WW II that were not based entirely on statistics,
completly ignoring doppler studies, chamber studies, or any high
tech scientific mishmash. (Yes, new tables have been developed,
but they are either curiosities or developed for extreme profiles.)

[Ron]

Post by mike gray
within the tables, is the risk curve flat or does it have a
slope >0.

And that's your own problem in a nutshell. You've oversimplified
the risk evaluation to meaningless noise.

You're making the following unspoken assumptions:
o The tables are good for everybody, regarless of
any physiological or environmental conditions
(e.g.: age, weight, fitness, pre- and post-dive
exercise, dehydration, etc.)
o In practice, people aren't adjusting their maximum
limits due to the conditions above.
o The idea that lack of an observable correlation
to profile in decompression hits means that
they're entirely random. You've completely
neglected any external conditions that might make
the normal profile a bad idea.
o That "the tables" you speak of are all identical.
o That people are diving the tables to near the limits
(If they're not, then the limits of the tables are
immaterial in terms of data gathering on bends).

Post by mike gray
To my knowledge, there have been no table revisions from any
source post WW II that were not based entirely on statistics,
completly ignoring doppler studies, chamber studies, or any high

At least you have a disclaimer in the above. DCIEM tables were
done with doppler studies. They tend to be more conservative
than the NAUI/PADI/etc. tables. I've found the DCIEM tables
to be readily available in the U.S.

BTW: You keep claiming that it's more dangerous to dive
air tables on Nitrox. There has never been a death due
to oxygen toxicity during the entire history of recreational
Nitrox use. By your own logic, that means that Nitrox
does not add any danger.

[mike gray]

Post by Ron

Post by mike gray
within the tables, is the risk curve flat or does it have a
slope >0.

And that's your own problem in a nutshell. You've oversimplified
the risk evaluation to meaningless noise.
o The tables are good for everybody, regarless of
any physiological or environmental conditions
(e.g.: age, weight, fitness, pre- and post-dive
exercise, dehydration, etc.)

Within the recreational tables, that's true.

Post by Ron
o In practice, people aren't adjusting their maximum
limits due to the conditions above.

And don't need to.

Post by Ron
o The idea that lack of an observable correlation
to profile in decompression hits means that
they're entirely random. You've completely
neglected any external conditions that might make
the normal profile a bad idea.

All external conditions are also random.

Post by Ron
o That "the tables" you speak of are all identical.

No, the recreational tables are nit identical. But they all are
so conservative as to eliminate virtually all risk.

Post by Ron
o That people are diving the tables to near the limits
(If they're not, then the limits of the tables are
immaterial in terms of data gathering on bends).

As I said before, the limits have been moved so far to the left
in modern recreational tables that "diving near the limits" is
well within the actual limits.

Post by Ron

Post by mike gray
To my knowledge, there have been no table revisions from any
source post WW II that were not based entirely on statistics,
completly ignoring doppler studies, chamber studies, or any high

At least you have a disclaimer in the above. DCIEM tables were
done with doppler studies. They tend to be more conservative
than the NAUI/PADI/etc. tables. I've found the DCIEM tables
to be readily available in the U.S.

One of a few dozen tables, all of which are so far to the left
as to be identical in practice.

Post by Ron
BTW: You keep claiming that it's more dangerous to dive
air tables on Nitrox. There has never been a death due
to oxygen toxicity during the entire history of recreational
Nitrox use. By your own logic, that means that Nitrox
does not add any danger.

Ahhhh, but the lifetime exposure is still in our futures.

BTW, no one has ever died from oxtox. There have been quite a
few that drowned as a result, however.

[-hh]

Post by mike gray

Post by Ron

Post by mike gray
within the tables, is the risk curve flat or does it have a
slope >0.

And that's your own problem in a nutshell. You've oversimplified
the risk evaluation to meaningless noise.

Unfortunately, all of the "undeserved hits" incidences do indicate that
there is indeed an element of noise within the activity risk.

Post by mike gray

Post by Ron
o The tables are good for everybody, regarless of
any physiological or environmental conditions
(e.g.: age, weight, fitness, pre- and post-dive
exercise, dehydration, etc.)

Within the recreational tables, that's true.

Simply illustrations of some of the variables which might someday
explain the incidences of 'undeserved' hits.

Post by mike gray

Post by Ron
o That "the tables" you speak of are all identical.

No, the recreational tables are nit identical. But they all are
so conservative as to eliminate virtually all risk.

Here's an example of how much the tables have changed:

Loading Image...

Note that this table allows a no-stop profile to 100fsw for 25 minutes,
and only requires a 3 minute stop at 10fsw for 30 minutes at 100fsw.

BTW, this table uses a 90ft/min descent rate, a 60ft/min ascent rate,
and bottom time is defined as start of dive to leaving the bottom (ie,
the ascent time is not included).

Finally, note which well-known recreational Agency's name is printed in
the top right corner.

Post by mike gray

Post by Ron
o That people are diving the tables to near the limits
(If they're not, then the limits of the tables are
immaterial in terms of data gathering on bends).

As I said before, the limits have been moved so far to the left
in modern recreational tables that "diving near the limits" is
well within the actual limits.

As per the above table, versus what many dive computers use these days
for their 100fsw no-stop limit and with the popular adoption of the 3-5
minute "safety" stop, I think it is safe to say that the evidence
clearly shows that the popular 100fsw bottom time limit has been
effectively reduced by (at least) roughly 50%.

Post by mike gray

Post by Ron
BTW: You keep claiming that it's more dangerous to dive
air tables on Nitrox. There has never been a death due
to oxygen toxicity during the entire history of recreational
Nitrox use. By your own logic, that means that Nitrox
does not add any danger.

Ahhhh, but the lifetime exposure is still in our futures.

Plus, there have certainly been errors made by tank jockies in
identifying the PPO2 content, both high and low.

Do note that if a tank that's supposed to be (ie, marked) 32% or 36%
but erroneously contains air (21%) and a diver then gets bent because
he dived to Nitrox limits, this is indeed a Nitrox-attributable dive
accident.

Post by mike gray
BTW, no one has ever died from oxtox. There have been quite a
few that drowned as a result, however.

As well as injuries that were the result of erroneous PPO2 markings.


-hh

[Lee Bell]

Post by -hh
Plus, there have certainly been errors made by tank jockies in
identifying the PPO2 content, both high and low.

Not relevant.

Post by -hh
Do note that if a tank that's supposed to be (ie, marked) 32% or 36%
but erroneously contains air (21%) and a diver then gets bent because
he dived to Nitrox limits, this is indeed a Nitrox-attributable dive
accident.

If anything, it's an air attribuatable accident. In fact, however, it's
neither. It's the fault of the diver who was taught to, and should have,
checked his gas before he dove it. Having been involved in exactly that
situation, it's fair for me to judge that it was my own damned fault.

Lee

[Scott]

Post by Lee Bell
If anything, it's an air attribuatable accident. In fact, however, it's
neither. It's the fault of the diver who was taught to, and should have,
checked his gas before he dove it. Having been involved in exactly that
situation, it's fair for me to judge that it was my own damned fault.

I couldnt begin to guess how much gas I have blended over the years, and it
never ceases to amaze me that people who dive nitrox or trimix not only dont
own an O2 analyzer and use it, but are willing to dive whatever it is I say
they have, which makes me ultra paranoid. I calibrate the analyzer on air
every time, even if I just filled three tanks simultaneously with the
continuous blender, the analyzer gets calibrated to air in between each
tank.

99% of the time, people dont even watch me analyze their gas, they just take
my word for it, and go dive.

I have had people bring in bottles and tell me that there is 32 in it, and
to just "top it off with 32", and then pre-fill analysis tells me they had
no idea what they were diving.

Last week I analyzed one that was allegedly 32% that measured 42%. When I
told the diver, he all but called me a liar. Only after I calibrated,
measured two seperate bottles of air and nitrox, then his, did he believe me
and understand that not only could he be dead, but that he should buy and
use his own analyzer.

No table in the known universe can accomodate stupidity or arrogance.

[mike gray]

Post by Scott

Post by Lee Bell
If anything, it's an air attribuatable accident. In fact, however, it's
neither. It's the fault of the diver who was taught to, and should have,
checked his gas before he dove it. Having been involved in exactly that
situation, it's fair for me to judge that it was my own damned fault.

I couldnt begin to guess how much gas I have blended over the years, and it
never ceases to amaze me that people who dive nitrox or trimix not only dont
own an O2 analyzer and use it, but are willing to dive whatever it is I say
they have, which makes me ultra paranoid. I calibrate the analyzer on air
every time, even if I just filled three tanks simultaneously with the
continuous blender, the analyzer gets calibrated to air in between each
tank.
99% of the time, people dont even watch me analyze their gas, they just take
my word for it, and go dive.
I have had people bring in bottles and tell me that there is 32 in it, and
to just "top it off with 32", and then pre-fill analysis tells me they had
no idea what they were diving.
Last week I analyzed one that was allegedly 32% that measured 42%. When I
told the diver, he all but called me a liar. Only after I calibrated,
measured two seperate bottles of air and nitrox, then his, did he believe me
and understand that not only could he be dead, but that he should buy and
use his own analyzer.
No table in the known universe can accomodate stupidity or arrogance.

Amen.

[Lee Bell]

Post by Scott
No table in the known universe can accomodate stupidity or arrogance.

Or complacency. You don't have to be stupid, or arrogant, to make a mistake
like failing to check the gas you're breathing. You only have to be
complacent.

In my deserved hit, I looked right at an in line analyzer that read 32%, an
analyzer that happened to be the same kind I own. Since I had tested the
first couple of tanks and found them spot on (membrane system), I got
complacent. I wasn't complacent enough not to look at all, but I was
complacent enough not to test every tank myself, after the gas was in the
tank. As you probably recall, I later noticed whips attached to tanks
marked for air at the same time they were hooked to tanks marked for 32%.
The in line gauge still read 32%, but it was not in line with the gas being
pumped . . . air.

The issue was not, however, whether I was breathing nitrox as air or nitrox
as nitrox, but whether I followed the procedures for either. I didn't. Had
I done so, the odds of getting bent would have been the same, breathing
nitrox as air would not have gotten me bent. Breathing nitrox as nitrox,
would not have gotten me bent. Breathing air as nitrox did.

Lee

[Scott]

Post by Lee Bell

Post by Scott
No table in the known universe can accomodate stupidity or arrogance.

Or complacency. You don't have to be stupid, or arrogant, to make a mistake
like failing to check the gas you're breathing. You only have to be
complacent.
In my deserved hit, I looked right at an in line analyzer that read 32%, an
analyzer that happened to be the same kind I own. Since I had tested the
first couple of tanks and found them spot on (membrane system), I got
complacent. I wasn't complacent enough not to look at all, but I was
complacent enough not to test every tank myself, after the gas was in the
tank. As you probably recall, I later noticed whips attached to tanks
marked for air at the same time they were hooked to tanks marked for 32%.
The in line gauge still read 32%, but it was not in line with the gas being
pumped . . . air.
The issue was not, however, whether I was breathing nitrox as air or nitrox
as nitrox, but whether I followed the procedures for either. I didn't.

Had

Post by Lee Bell
I done so, the odds of getting bent would have been the same, breathing
nitrox as air would not have gotten me bent. Breathing nitrox as nitrox,
would not have gotten me bent. Breathing air as nitrox did.

Dont get me wrong, I am not calling you any name whatsoever.

If you really want to see the death rate of complacency, just look at
rebreather fatalities.

[Lee Bell]

Post by Scott
Dont get me wrong, I am not calling you any name whatsoever.

You've never called me a name I didn't deserve.

Post by Scott
If you really want to see the death rate of complacency, just look at
rebreather fatalities.

Precisely why I don't use a rebreather.

I had a long discussion about rebreathers in a UK forum, where people
actually wish to own and dive the Yellow Box of Death (Buddy Inspiration).
When it was all said and done, my conclusion was that UK divers are more
cautious about their diving than I'm ever likely to be and that, if I could
not be consistent and careful, anal if you prefer, I should not be using a
closed circuit, computer controlled rebreather. So far, so good.

Speaking of which, I'll never forget the post about the guy who, when his
inspiration gave him a predive alarm, banged the computer module on
something hard to get it to stop. I learned from his mistake. He didn't
get a chance to.

Lee

[Carl Nisarel]

Post by Scott
I couldnt begin to guess how much gas I have blended over the
years,

That's because you're too lazy, sloppy, and stupid to properly
maintain records.

[Some Random Dude]

Post by Scott
No table in the known universe can accomodate stupidity or arrogance.

Darwins table. in only two parts. either in the gene pool or out of
the gene pool.

[Limey]

Post by Scott

Post by Lee Bell
If anything, it's an air attribuatable accident. In fact, however, it's
neither. It's the fault of the diver who was taught to, and should have,
checked his gas before he dove it. Having been involved in exactly that
situation, it's fair for me to judge that it was my own damned fault.

I couldnt begin to guess how much gas I have blended over the years, and it
never ceases to amaze me that people who dive nitrox or trimix not only dont
own an O2 analyzer and use it, but are willing to dive whatever it is I say
they have, which makes me ultra paranoid. I calibrate the analyzer on air
every time, even if I just filled three tanks simultaneously with the
continuous blender, the analyzer gets calibrated to air in between each
tank.

If I don't recalibrate the analyzer I use every time, I'd get different
readings every time, I'm sure. Don't have enough experience with analyzers
to know if that's normal, or if it's because it's a well used dive shop
owned analyzer.....but even after mixing my own gas, I always recalibrate
and check it twice.

Post by Scott
99% of the time, people dont even watch me analyze their gas, they just take
my word for it, and go dive.
I have had people bring in bottles and tell me that there is 32 in it, and
to just "top it off with 32", and then pre-fill analysis tells me they had
no idea what they were diving.
Last week I analyzed one that was allegedly 32% that measured 42%. When I
told the diver, he all but called me a liar. Only after I calibrated,
measured two seperate bottles of air and nitrox, then his, did he believe me
and understand that not only could he be dead, but that he should buy and
use his own analyzer.
No table in the known universe can accomodate stupidity or arrogance.

Here, here.

LD.

[Scott]

Post by Limey
If I don't recalibrate the analyzer I use every time, I'd get different
readings every time, I'm sure. Don't have enough experience with analyzers
to know if that's normal, or if it's because it's a well used dive shop
owned analyzer.....but even after mixing my own gas, I always recalibrate
and check it twice.

O2 analyzers are basically oxygen powered batteries.

An analyzer simply reads the voltage produced by the analyzer; the more O2,
the more voltage, and displays the result as a percent rather than a
voltage.

They are sensitive to temperature, humidity and length of exposure to O2.
Every now and then, I expose ours to pure he and pure O2 to see what the
swing is, and to see the degredation of the cell.

Teledyne R22D's are as good as they get, with thermistors and hydrophobic
membranes, but they still vary a great deal with length of exposure to O2,
temperature and humidity.

[Limey]

Post by Scott

Post by Limey
If I don't recalibrate the analyzer I use every time, I'd get different
readings every time, I'm sure. Don't have enough experience with analyzers
to know if that's normal, or if it's because it's a well used dive shop
owned analyzer.....but even after mixing my own gas, I always recalibrate
and check it twice.

O2 analyzers are basically oxygen powered batteries.
An analyzer simply reads the voltage produced by the analyzer; the more O2,
the more voltage, and displays the result as a percent rather than a
voltage.
They are sensitive to temperature, humidity and length of exposure to O2.
Every now and then, I expose ours to pure he and pure O2 to see what the
swing is, and to see the degredation of the cell.
Teledyne R22D's are as good as they get, with thermistors and hydrophobic
membranes, but they still vary a great deal with length of exposure to O2,
temperature and humidity.

Hmmm, good to know. I only get by there on Mondays but I'll make a point to
see if I get 100% on the O2 bottle after I calibrate it to 21%. Speaking of,
all this now has me wondering how close it is, since I usually just
calibrate by using ambient air in the shop.....of course the doors are
usually open but it is inside a fill station after all. Still, I'm sure it's
not a significant difference than outside air. The nitrox tanks are drained
outside before being brought in.

LD.

[-hh]

Post by Lee Bell

Post by -hh
Plus, there have certainly been errors made by tank jockies in
identifying the PPO2 content, both high and low.

Not relevant.

No?

Incorrectly high PPO2 increases OxTox risks.
Incorrectly low PPO2 increases (Narcosis and) DCS risks.

Post by Lee Bell

Post by -hh
Do note that if a tank that's supposed to be (ie, marked) 32% or 36%
but erroneously contains air (21%) and a diver then gets bent because
he dived to Nitrox limits, this is indeed a Nitrox-attributable dive
accident.

If anything, it's an air attribuatable accident. In fact, however, it's
neither. It's the fault of the diver who was taught to, and should have,
checked his gas before he dove it. Having been involved in exactly that
situation, it's fair for me to judge that it was my own damned fault.

Yes, it was basic human error, but my point was that the only reason
that the error could only have existed was because there is "mucking
around" with the PPO2 content via Nitrox, whereas PPO2 manipulatioin
isn't done when diving Plain Old Air (POA), so its harder to get it
wrong.

Any time there is a process step added, there is the potential for it
to be done wrong, which results in increased risks. Redundent checks
are one way to offset some, but its always hard to beat KISS.


-hh

[Lee Bell]

Post by Lee Bell

Post by -hh
Plus, there have certainly been errors made by tank jockies in
identifying the PPO2 content, both high and low.

Not relevant.

No?

No. If standard procedure is to check your gas, which it is, then what the
tank jockey does is not relevant. The mistake was not a nitrox related one
but, rather, a failure by the diver himself. This thread, which has not
morphed yet, is about the relative risks, or benefits, of breathing nitrox
as if it were air. I think it's important to keep that separated from the
risks of the diver's failure to follow procedures he/she knows are
important, like checking the gas. The failure of the diver to check the gas
he's breathing is no more a nitrox issue than the failure of a diver to
ensure his tank is full at the start of his dive.

Yes, it was basic human error, but my point was that the only reason that
the error could only have existed was because there is
"mucking around" with the PPO2 content via Nitrox, whereas PPO2
manipulatioin isn't done when diving Plain Old Air (POA),
so its harder to get it wrong.

By this logic, all diving accidents are compressor errors since, without
compressors mucking around with gas pressure, there would be no diving
accidents. Ok, so this is a bit extreme, but it illustrates the point.
Taking someone else's word for what you're breathing, is a mistake that the
diver, himself, could have and should have controlled. Failing to check is
exactly the same mistake whether you're breathing nitrox as air or as
nitrox.

If you'd like to start a new thead called "risk of assuming your gas is
air/nitrox/trimis without testing it" I'm game, but it ought to be a really
short discussion.

Any time there is a process step added, there is the potential for it to
be done wrong, which results in increased risks.

You bet, but we're talking about risks directly related to breathing nitrox
as air versus breathing nitrox as nitrox. Other risks aren't relevant to
that particular issue.

Redundent checks are one way to offset some, but its always hard to beat
KISS.

Which would be to stay out of the water altogether. Anything else requires
certain fundamental elements to be safe.

Lee

[-hh]

Post by Lee Bell

Post by Lee Bell

Post by -hh
Plus, there have certainly been errors made by tank jockies in
identifying the PPO2 content, both high and low.

Not relevant.

No?

No. If standard procedure is to check your gas, which it is, then what the
tank jockey does is not relevant. The mistake was not a nitrox related one
but, rather, a failure by the diver himself.

With air, the gas check is for Pressure.
With Nitrox, the gas check is both Pressure and PPO2.

Hence, more opportunities for error, thus, greater risk even when
absolutely all other risks are absolutely equal.

Post by Lee Bell
... The failure of the diver to check the gas
he's breathing is no more a nitrox issue than the failure of a diver to
ensure his tank is full at the start of his dive.
From a holistic system approach, every possible {risk/failure mode} has

to be accounted for, and typically then organized into one of the
catagorical "bins". Since diving with air never really had to check
PPO2, why should it be put into the "air" bin?

Post by Lee Bell
By this logic, all diving accidents are compressor errors since, without
compressors mucking around with gas pressure, there would be no diving
accidents. Ok, so this is a bit extreme, but it illustrates the point.

It does, for in a Root Cause analysis there's a lot of options for
organizing your risk/failure nodes, and thus, what ends up where.
However, what they all have in common is that in the end, every
possible option has to go *somewhere* in each and every one of them.

Post by Lee Bell
Taking someone else's word for what you're breathing, is a mistake that the
diver, himself, could have and should have controlled. Failing to check is
exactly the same mistake whether you're breathing nitrox as air or as
nitrox.

Particularly true when we're receiving gas from a station that's
capable of pumping both.

And while an air/Nitrox station is increasingly common today, it wasn't
always so: we don't really have to go back all that many years to when
the Rec choices for gas were "just air" and the only question was
contamination. It was from this historical perspective that I chose to
"bin" the PPO2 content error risk as being Nitrox-attributable, versus
what had traditionally been the "air-only" Recreational diving risks.

Post by Lee Bell

Any time there is a process step added, there is the potential for it to
be done wrong, which results in increased risks.

You bet, but we're talking about risks directly related to breathing nitrox
as air versus breathing nitrox as nitrox. Other risks aren't relevant to
that particular issue.

Depends on your altitude: there's risks at the tank jockey fill
station from possible exposure to high pressure, high-PP Oxygen, such
as an Oxygen fire. These have to be "binned" someplace too, plus we
need to answer the question of risk transfers between participants.

For an example of risk transfer, if we were to come up with some "magic
mix" that reduces diver fatalities by 30 per year, but the fatality
rate of diveshop tank jockeys goes up by 30 per year, has "diving"
become more or less dangerous? The answer kind of depends on if you're
a diver, a tank jockey, or an outside industry observer.

Post by Lee Bell

Redundent checks are one way to offset some, but its always hard to beat
KISS.

Which would be to stay out of the water altogether. Anything else requires
certain fundamental elements to be safe.

Another one from Appalachia:

"Mother, may I go out to swim?"
"Yes, my darling daughter,
But hang your clothes on a hickory limb,
And don't go near the water."



-hh

[Lee Bell]

Post by -hh
With air, the gas check is for Pressure.
With Nitrox, the gas check is both Pressure and PPO2.

I purchase my gas at a shop that will tell you quite clearly that they don't
do air fills. They do, however, do 21% fills. I test every tank of gas I
use for both pressure and O2 content. If you look back only a few days,
you'll find that I'm not the only one that checks 21% fills.

Post by -hh
Hence, more opportunities for error, thus, greater risk even when
absolutely all other risks are absolutely equal.

For shops that bank 21% and other nitrox and trimix, the error mechanism is
the same regardless of the gas you ask for and the need to test is the same.
Air fills are only lower risk when obtained from shops that are not equipped
to do other types of fills.

Post by -hh

Post by Lee Bell
From a holistic system approach, every possible {risk/failure mode} has

to be accounted for, and typically then organized into one of the
catagorical "bins". Since diving with air never really had to check
PPO2, why should it be put into the "air" bin?

I agree that all risks need to be considered. See my comments above
regarding why the same risks apply to most air fills as apply to most nitrox
fills.

Also, please understand that the only point I've tried to make is that the
use of nitrox according to air standards is no safer, from a DCS standpoint,
than using nitrox as nitrox provided you abide by all the standards of
whichever gas you are using. Mistakes unrelated to that specific issue
certainly can cause problems, but that's true no matter what you breathe, no
matter how you breathe it.

Post by -hh

Post by Lee Bell
By this logic, all diving accidents are compressor errors since, without
compressors mucking around with gas pressure, there would be no diving
accidents. Ok, so this is a bit extreme, but it illustrates the point.

It does, for in a Root Cause analysis there's a lot of options for
organizing your risk/failure nodes, and thus, what ends up where.
However, what they all have in common is that in the end, every
possible option has to go *somewhere* in each and every one of them.

Only in the holistic approach. We, at least I, am still talking about a
single issue, the relative safety of nitrox breathed as air versus nitrox
breathed as nitrox. Originally, I was even willing to forget about the
OxTox issue, at least until one of the proponents of the safety of using
nitrox that way demonstrated that he didn't know the MOD of the gases he was
discussing.

Post by -hh

Post by Lee Bell
Taking someone else's word for what you're breathing, is a mistake that the
diver, himself, could have and should have controlled. Failing to check is
exactly the same mistake whether you're breathing nitrox as air or as
nitrox.

Particularly true when we're receiving gas from a station that's
capable of pumping both.

If I'd seen this earlier, I'd have saved some typing time.

Post by -hh
And while an air/Nitrox station is increasingly common today, it wasn't
always so: we don't really have to go back all that many years to when
the Rec choices for gas were "just air" and the only question was
contamination. It was from this historical perspective that I chose to
"bin" the PPO2 content error risk as being Nitrox-attributable, versus
what had traditionally been the "air-only" Recreational diving risks.

Post by Lee Bell

Any time there is a process step added, there is the potential for it to
be done wrong, which results in increased risks.

You bet, but we're talking about risks directly related to breathing nitrox
as air versus breathing nitrox as nitrox. Other risks aren't relevant to
that particular issue.

Depends on your altitude: there's risks at the tank jockey fill
station from possible exposure to high pressure, high-PP Oxygen, such
as an Oxygen fire. These have to be "binned" someplace too, plus we
need to answer the question of risk transfers between participants.

They need to be considered in an overall study of diving related risks.
They don't need to be considered in this discussion.

Post by -hh
For an example of risk transfer, if we were to come up with some "magic
mix" that reduces diver fatalities by 30 per year, but the fatality
rate of diveshop tank jockeys goes up by 30 per year, has "diving"
become more or less dangerous? The answer kind of depends on if you're
a diver, a tank jockey, or an outside industry observer.

Not unless the tank jockeys were diving at the time they died.

Lee

[n***@all.please.net]

Post by Lee Bell
Taking someone else's word for what you're breathing, is a mistake that
the diver, himself, could have and should have controlled. Failing to
check is exactly the same mistake whether you're breathing nitrox as air
or as nitrox.

What proportion of "air" tanks have you checked with an O2 meter?

[Lee Bell]

Post by n***@all.please.net

Post by Lee Bell
Taking someone else's word for what you're breathing, is a mistake that
the diver, himself, could have and should have controlled. Failing to
check is exactly the same mistake whether you're breathing nitrox as air
or as nitrox.

What proportion of "air" tanks have you checked with an O2 meter?

Back when I used air exclusively, I didn't check any of them. These days,
most of my dives are done on nitrox and the few that aren't are filled by a
shop that specializes in nitrox and trimix. Since the chance for error at
the shop I frequent is the same for air as it is for any other gas purchased
there, I check them too. It's just as easy to check all my tanks as some of
them.

I didn't used to check my air fills. The shops I used in the past did
partial pressure fills and my tanks have always been filled while I watched.
It would be hard to fail to notice someone first putting oxygen in them and
then topping them off with air. I felt relatively comfortable that they
were, in fact, filled with air. These days, I'm a bit more careful than
that, particularly since the only times I use air any more is when I'm
planning a dive beyond the depths where nitrox is practical and/or safe.

FWIW, I get my tanks filled and tested by the shop I buy my gas from. I
test them using the shop's analyzer. If my test and theirs don't agree, we
resolve the difference before I leave the shop. When I get the tanks home,
I check the pressure, which has stabilized by that point, and the O2
content, and replace the shop's contents sticker with my own. I use yellow
duct tape and a black marker. When I'm ready to go diving, I look for those
yellow tanks. Any tank that does not have my label on it, gets tested for
both pressure and O2 percentage before it, even those that I think contain
air. When I set up for a dive, one of the first things I do is remove that
duct tape. Because I have 12 tank that may contain anything from 21 to 50%
oxygen, I make a real effort to ensure I know what is in the one I plan on
using that day.

Lee

[n***@all.please.net]

Post by Lee Bell

Post by n***@all.please.net

Post by Lee Bell
Taking someone else's word for what you're breathing, is a mistake that
the diver, himself, could have and should have controlled. Failing to
check is exactly the same mistake whether you're breathing nitrox as air
or as nitrox.

What proportion of "air" tanks have you checked with an O2 meter?

Back when I used air exclusively, I didn't check any of them.
I didn't used to check my air fills.

The short answer is: You don't know.

[Dennis (Icarus)]

Post by n***@all.please.net

Post by Lee Bell

Post by n***@all.please.net

Post by Lee Bell
Taking someone else's word for what you're breathing, is a mistake that
the diver, himself, could have and should have controlled. Failing to
check is exactly the same mistake whether you're breathing nitrox as air
or as nitrox.

What proportion of "air" tanks have you checked with an O2 meter?

Back when I used air exclusively, I didn't check any of them.
I didn't used to check my air fills.

The short answer is: You don't know.

And the accurate answer is what he gave.

Dennis.

[Limey]

Post by n***@all.please.net

Post by Lee Bell

Post by n***@all.please.net

Post by Lee Bell
Taking someone else's word for what you're breathing, is a mistake that
the diver, himself, could have and should have controlled. Failing to
check is exactly the same mistake whether you're breathing nitrox as air
or as nitrox.

What proportion of "air" tanks have you checked with an O2 meter?

Back when I used air exclusively, I didn't check any of them.
I didn't used to check my air fills.

The short answer is: You don't know.

Only if you can't read.

[Lee Bell]

I'm about to go to bed. Tomorrow through Thursday, I'll be out diving
nitrox, as nitrox . . . a lot. I'll be using nitrox because it lets me do
the number of dives I want each day. I'm a lot more worried about sharks
that want my catch and the 5-7 foot waves NOAA is predicting than I am about
the risk of DCS, at least now that I've learned that I need to check every
tank I use to be sure I know what is in it before I breathe it.

My final word, at least for now, is that it's good to be conservative, but
best to understand what the real costs and benefits of what you chose are.
If you were to chose to cut your dive short by a few minutes, no problem.
If you were to chose, as I do, to do multiple deep stops, slow your ascent
and extend your safety stop, no problem. I just think that cutting a dive
you could do safely on nitrox roughly in half by using it as though it is
air is just plain crazy.

YMMV

Lee

PS: My Oceanic computer allows 24 minutes at 90 feet on air and 46 minutes
at 90 feet on 36%.

[Greg Mossman]

Post by Lee Bell
PS: My Oceanic computer allows 24 minutes at 90 feet on air and 46
minutes at 90 feet on 36%.

Suunto allows me 22 min on air, 38 min on 36%. It gives me 6 min at 150' on
air.

[Limey]

Post by Lee Bell
If you'd like to start a new thead called "risk of assuming your gas is
air/nitrox/trimis without testing it" I'm game, but it ought to be a
really short discussion.

Yup, and it was almost discussed last time I checked in when somebody was
mentioning the death of Audry Mestre. If you don't check the contents of yer
own tanks for scuba, meaning pressures *and* mixes, then I'm afraid you gets
whats ya gets.

LD.

[Ron]

Post by mike gray
BTW, no one has ever died from oxtox. There have been quite a
few that drowned as a result, however.

I hadn't heard about that. Any pointers to reports?

[Scott]

Post by Ron

Post by mike gray
BTW, no one has ever died from oxtox. There have been quite a
few that drowned as a result, however.

I hadn't heard about that. Any pointers to reports?

You are kidding, right?

Drowning is the cause of death in almost all SCUBA related fatal oxtox
events.

Convulsions make you spit out your reg and aspirate water.

A few divers have survived the convulsions, and smoe due to wearing a FFM.

[Al Wells]

In article <***@4ax.com>, ***@see.below
says...

Post by Ron
At least you have a disclaimer in the above. DCIEM tables were
done with doppler studies. They tend to be more conservative
than the NAUI/PADI/etc. tables. I've found the DCIEM tables
to be readily available in the U.S.

According to Peter Bennett, studies done on divers using the DCIEM
tables produced exactly the same rate of DCS as the PADI tables -
aprroximately 0.04%, leading him to believe that the tables are as safe
as they can be, and that the unexplained DCS was perhaps related to the
ascent rate. I don't know how the later studies on that went.

[JOF]

Post by mike gray
The phenomenon of undeserved hits, which has been studied by
many, always ends up being random, i.e. incidence without
corelation to profile. There is therefore only one answer, that
the curve is flat.

Are you saying the Lee Bell Curve is flat?

JF

[mike gray]

Post by JOF

Post by mike gray
The phenomenon of undeserved hits, which has been studied by
many, always ends up being random, i.e. incidence without
corelation to profile. There is therefore only one answer, that
the curve is flat.

Are you saying the Lee Bell Curve is flat?
JF

Yes.

[JOF]

Post by JOF

Post by mike gray
The phenomenon of undeserved hits, which has been studied by
many, always ends up being random, i.e. incidence without
corelation to profile. There is therefore only one answer, that
the curve is flat.

Are you saying the Lee Bell Curve is flat?

Yes.

So much for a break on the mark then.

JF

[Lee Bell]

Post by Chris

Post by Lee Bell
NAUI, SSI and TDI were represented.
Funded entirely with private funds, no advertising, endorsements or
commercial contributions involved.

Could you (or someone else) please provide an official source for this
study? I mean no disrespect, nor do I question the validity of your
statements - for my own reasons I'd very much like to have the actual
document of this study, rather than what "some guy on the internet"
said about some study.

You read the original. It wasn't something said by someone about some
study, it was the direct results of the study conducted by the person that
presented it.

Lee

[Chris]

Post by Lee Bell
You read the original. It wasn't something said by someone about some
study, it was the direct results of the study conducted by the person that
presented it.

Oh, OK. That's a horse of a different color then. The way this material
was presented, I thought this was a real scientific study, not simply
the results of one diver over the course of time. While I'm sure these
data are correct for the unknown diver that presented the material to
you, the scientific method of this study cannot be documented and
therefor it would be improper and dangerous for me (or anyone else) to
extrapolate these data to apply to themselves.

Thanks for the clarification.

cheers,
Chris

[Lee Bell]

Post by Chris
Oh, OK. That's a horse of a different color then. The way this material
was presented, I thought this was a real scientific study, not simply
the results of one diver over the course of time.

It was a real scientific study. It was a test of the specific conditions
under discussion, enough times to be statistically significant, carefully
controlled and even more carefully observed. Just because you don't
recognize, or know about, my scientific credentials, does not make the study
any less scientific.

Post by Chris
While I'm sure these data are correct for the unknown diver that presented
the material to you, the scientific method of this study
cannot be documented and therefor it would be improper and dangerous for
me (or anyone else) to extrapolate these data to
apply to themselves.

Let's try this again. I'm the guy that did the thousands of hours of dives
over more than 40 years. I'm the guy that had the tanks filled, knows what
was in them, planned the dives and measured the depths and times. This is
not guesswork, it's specific, detailed, scientific and accurate, right down
to the single case of DCS at the limits of one of the old style computers, a
computer I still have.

If you can't draw conclusions from the information, that's you're problem.
The data is accurate and reflects on exactly the issues being addressed.
Unless you have comparable experience or information to the contrary,
information as easily traced to its source as mine is, I suggest you think
twice about denying the validity of its results.

Lee

[n***@all.please.net]

Post by Lee Bell

Post by Chris
Oh, OK. That's a horse of a different color then. The way this material
was presented, I thought this was a real scientific study, not simply
the results of one diver over the course of time.

It was a real scientific study. It was a test of the specific conditions
under discussion, enough times to be statistically significant, carefully
controlled and even more carefully observed. Just because you don't
recognize, or know about, my scientific credentials, does not make the study
any less scientific.

Post by Chris
While I'm sure these data are correct for the unknown diver that presented
the material to you, the scientific method of this study
cannot be documented and therefor it would be improper and dangerous for
me (or anyone else) to extrapolate these data to
apply to themselves.

Let's try this again. I'm the guy that did the thousands of hours of dives
over more than 40 years. I'm the guy that had the tanks filled, knows what
was in them, planned the dives and measured the depths and times. This is
not guesswork, it's specific, detailed, scientific and accurate, right down
to the single case of DCS at the limits of one of the old style computers, a
computer I still have.
If you can't draw conclusions from the information, that's you're problem.
The data is accurate and reflects on exactly the issues being addressed.
Unless you have comparable experience or information to the contrary,
information as easily traced to its source as mine is, I suggest you think
twice about denying the validity of its results.

Try to publish it in a reviewed journal if you want to see how credible it
is.

[Lee Bell]

Post by n***@all.please.net
Try to publish it in a reviewed journal if you want to see how credible it
is.

I already know how credible it is. I live it.

[n***@all.please.net]

Post by Lee Bell

Post by n***@all.please.net
Try to publish it in a reviewed journal if you want to see how credible it
is.

I already know how credible it is.

If so, how does it generalise?

[Lee Bell]

Post by n***@all.please.net
If so, how does it generalise?

It generalizes about as well as any other study involving thousands of hours
or testing. At some point, you either conclude that the lack of a problem
event means your tables are good enough or you don't. If you do, then enjoy
your diving.

If you don't, find another hobby. If you can't trust the tables and an
exceptionally long history of testing, then you have no basis for accepting
any combination of gas, depth and time as safe.

Lee

[Ed]

I think DAN would disagree.... I have read dozens of stories in the DAN
magazine about people getting bent while following the tables,
computers, etc. We all know the risks, mitigate them to meet our risk
profile and hopefully live to dive another day. Myself, I dive a
very conservative Nitrox computer... I also carry an air computer in
case I have to go to the PONY and also as a backup.(Never needed it yet)
I may go to the limits of my current Nitrox Mix but I try to
mitigate my risk by following the deco stops of my air computer. To
conservative?? maybe...but it has worked for me since computers were
cheap enough to own several.

Post by Lee Bell

Post by n***@all.please.net
If so, how does it generalise?

It generalizes about as well as any other study involving thousands of hours
or testing. At some point, you either conclude that the lack of a problem
event means your tables are good enough or you don't. If you do, then enjoy
your diving.
If you don't, find another hobby. If you can't trust the tables and an
exceptionally long history of testing, then you have no basis for accepting
any combination of gas, depth and time as safe.
Lee

[Lee Bell]

Post by Ed
I think DAN would disagree.... I have read dozens of stories in the DAN
magazine about people getting bent while following the tables, computers,
etc.

Then you need to think again. First, DAN wasn't there for any of the
reported dives. Second, they have a vested interest in having you believe
that you're likely to get bent even if abide by the tables. How much
insurance do you think they would sell if everyone knew that all they had to
do to stay safe is stay within the tables?

Before you say it, no, I'm not suggesting DAN is lying. I'm suggesting that
DAN simply choses not to question what they're told by others.

Finally, nobody said that there aren't unexplained hits. What we said is
that they really are unexplained and that they are, as near as anyone can
tell, the same no matter what gas, or gas tables are being used.

Post by Ed
We all know the risks . . .

Actually, it's pretty clear we don't all know the risks. At least one
person here did not know what the MOD was for various gases that he was
advocating be used like air. At least one other person here stated that
there had never been an OxTox death, something that is only true if you
somehow decide that drowning during OxTox convulsions is not OxTox related.

Nobody here has spoken against diving conservatively. Nobody here has
spoken against cutting your dive short because you feel safer, even on
nitrox, if you don't dive it to the limit. All we've said is, no matter how
conservative you chose to be, dive air like air, nitrox like nitrox, heliox
like heliox and trimix like trimix.

Post by Ed
Myself, I dive a very conservative Nitrox computer... I also carry an air
computer in case I have to go to the PONY and also as a backup.(Never
needed it yet)

Your air computer is a complete waste. It backs up nothing. It can't
account for the nitrox you were breathing at the beginning of the dive. If
you want to carry a backup for a nitrox computer, carry a second nitrox
computer.

Post by Ed
I may go to the limits of my current Nitrox Mix but I try to mitigate my
risk by following the deco stops of my air computer. To conservative??
maybe...but it has worked for me since computers were cheap enough to own
several.

Not too conservative. More like too ignorant. Ignorance can be cured. You
can't dive nitrox to the limit if you follow the deco stops of your air
computer. The concepts are mutually exclusive.

Lee

[Ron]

Post by Lee Bell
Nobody here has spoken against diving conservatively. Nobody here has
spoken against cutting your dive short because you feel safer, even on
nitrox, if you don't dive it to the limit. All we've said is, no matter how
conservative you chose to be, dive air like air, nitrox like nitrox, heliox
like heliox and trimix like trimix.

Although, it strikes me as ironic. The very thing you're
counseling against (diving nitrox, within the MOD, using
air tables for extra conservatism) would have prevented
your bends incident.
Diving nitrox on air tables is safe, as there is no instance
where the air table specifies less time than the nitrox table.
That's not true for all profiles when you're using heliox or
trimix.

[-hh]

Post by Ron
Although, it strikes me as ironic. The very thing you're
counseling against (diving nitrox, within the MOD, using
air tables for extra conservatism) would have prevented
your bends incident.

I would not be so confident.

There have been people who have gotten DCS hits on profiles as

Post by Ron
Diving nitrox on air tables is safe, as there is no instance
where the air table specifies less time than the nitrox table.

When you only look at half of a question, you only get half of the
answer.

Here, DCS risk is only 'half the question'.

Consider a dive on that old PADI table that I already posted: it
allows depths to 140fsw. On 36% Nitrox, that would be a 1.9 PPO2.

Still feeling that DCS is the >only< risk to worry about?


Note that old table also permits bottom times of up to 20 minutes at
140fsw on air. After 6 minutes @ 10ft, you surfaced as an "I" (old
lettering system) Residual Nitrogen level for planning repetitive
dives.



-hh

[mike gray]

I'm gone for two weeks.

Someone hold up my end, please.

[Ron]

Post by -hh
Consider a dive on that old PADI table that I already posted: it
allows depths to 140fsw. On 36% Nitrox, that would be a 1.9 PPO2.
Still feeling that DCS is the >only< risk to worry about?

Have you stopped beating your wife?

I never said or felt that DCS is the *only* risk to be
concerned with. In fact, I said, and you quoted:
"(diving nitrox, WITHIN THE MOD, using
air tables for extra conservatism)"
Emphasis added, so that maybe you can notice it this time.

[-hh]

Post by Ron
I never said or felt that DCS is the *only* risk to be
"(diving nitrox, WITHIN THE MOD, using
air tables for extra conservatism)"
Emphasis added, so that maybe you can notice it this time.

You first wrote:

"Although, it strikes me as ironic. The very thing you're
counseling against (diving nitrox, within the MOD, using
air tables for extra conservatism) would have prevented
your bends incident."

...which was in context of the profiles that Lee did, and got bent on.


After a <CR> to end the paragraph, you then went on to make a much more
broad statement:

"Diving nitrox on air tables is safe, as there is no instance
where the air table specifies less time than the nitrox table."

Note the absence of any other qualifiers here than "on air tables".

Perhaps you intended for this statement to have more qualifiers such as
the MOD but it was not what you wrote.


And this would appear to be even more clear when you went on to say:

"That's not true for all profiles when you're using heliox or
trimix."

...which we all know are mixes suited for deep diving. But the air
table is deep enough.


Plus, there is the little problem of people well within the limits who
have gotten "undeserved hits", with air or nitrox.


This is not the first time that this topic has been discussed. From
past conversations, we know that Peter Bennett, developer of the DCIEM
tables found that the DCS risk profile tailed out into a flat line at
0.04% incidence. Supposedly, it made him a bit perturbed :-)

Bennett was previously known to been doing a study at UNC to see if he
could lower this apparently profile independent (ie, 'flat') 0.04%
incidence risk rate, through slower ascent rates. Not sure if he found
anything or if it has been published yet.


FWIW, my personal opinion is that it is likely a manifestation of the
uncontrolled risk from PFO's. If you look at the following paper from
Bennet et al,

http://www.smw.ch/docs/pdf200x/2001/25/smw-09706.pdf

...which states:

"Some divers try to decrease the amount of nitrogen load by using
special nitrogen-oxygen mixtures ("nitrox"), with 40% oxygen and
60% nitrogen as typical example. The reduced nitrogen content
compared to air decreases the probability of bubble formation,
but 40% oxygen in the breathing gas carries the double risk of
oxygen toxicity. These are all but theoretical considerations, and
no prospective clinical trial has ever been conducted to establish
their utility in daily routine for the prevention of decompression
events in the presence of a cardiac right-to-left shunt."


Emphasis on the "....no prospective clinical trial has ever been
conducted to establish their utility..." statement.

PFO's occur in ~25% of the Adult population. Since most people don't
even know that they have one, their presence is generally independent
of the dive profile. As such, it is a quite plausible causal attribute
to the "flat" 0.04% incidence rate of 'undeserved' hits.



You also might want to try finding the USN's Statistically based
Decompression Tables (Weathersby, P.K., S.S. Survanshi, R.Y. Nishi and
E.D. Thalmann. "Statistically Bases Decompression Tables VII:
Selection and Treatment of Primary Air and N2-O2 Data". Joint Report
NSMRL (#1182) and NMRI (#92-85), US Navy, 18 September 1992), which
will tell you what each of the lines represent on this chart:

http://www.huntzinger.com/dive/usn_risk.pdf



-hh

[Greg Mossman]

Post by -hh
http://www.smw.ch/docs/pdf200x/2001/25/smw-09706.pdf

In the Summary:

"The use of special nitrogen-oxygen mixtures ("nitrox", 60% nitrogen and 40%
oxygen as the typical example) decreases the probability of nitrogen
narcosis and probably bubble formation, at the cost of increased risk of
oxygen toxicity."

For dives with a hard bottom less than the MOD of the nitrox mix, there's
practically a zero risk of oxygen toxicity when diving recreational
profiles. Diving nitrox on air tables for these divers is certainly safer
than diving air.

Oxygen toxicity for recreational dives on deeper water sites is only a
concern for inattentive divers. Those same divers are just as likely to run
a deco obligation and get into trouble with DCS as well. The threat of
oxygen toxicity as compared with the dangers of DCS for recreational
profiles by attentive divers is a red herring.

[Brooklyn]

Post by Greg Mossman
For dives with a hard bottom less than the MOD of the nitrox mix, there's
practically a zero risk of oxygen toxicity when diving recreational
profiles. Diving nitrox on air tables for these divers is certainly safer
than diving air.

Did someone say you're a lawyer?

Diving nitrox on air tables (.0004 probability of DCS) is certainly
safer than diving air (.0004 probability of DCS)?

Can you give us just a rough estimate of how much less .0004 is than
.0004?

Dive Brooklyn, the birthplace of scuba.

[Greg Mossman]

Post by Brooklyn
Did someone say you're a lawyer?

I know when to assert the 5th.

Post by Brooklyn
Diving nitrox on air tables (.0004 probability of DCS) is certainly
safer than diving air (.0004 probability of DCS)?

.0004 may be the probability of DCS for the general population. Individual
subpopulations may bear a higher risk and that risk is doubtlessly reduced
by diving nitrox to air tables.

For instance, the birth control pill might have an overall efficacy rate of
99%, but it's 100% certain I won't get pregnant.

Post by Brooklyn
Can you give us just a rough estimate of how much less .0004 is than
.0004?
Dive Brooklyn, the birthplace of scuba.

Dive L.A., the birthplace of scuba instruction.

[someone had to start teaching it after all the Brooklynese started dropping
like flies on a NY summer day]

["Magilla"]

Post by Greg Mossman
.0004 may be the probability of DCS for the general population.
Individual subpopulations may bear a higher risk and that risk is
doubtlessly reduced by diving nitrox to air tables.

You'd probably make them half happy by just saying use the damn Nitrox
tables, and back off the NDLs. Same thing, in reality.

Then ask them if getting comatose drunk is what you're trying to avoid,
is just getting plastered on a regular basis without passing out healthy?

Oops, sorry, bad example, wrong crowd <evil grin>.

Curtis

[Greg Mossman]

Post by "Magilla"
Then ask them if getting comatose drunk is what you're trying to avoid,
is just getting plastered on a regular basis without passing out healthy?

You can't get bent if you don't get wet, but look at all the fun you're
missing by staying dry.

["Magilla"]

Post by Greg Mossman

Post by "Magilla"
Then ask them if getting comatose drunk is what you're trying to
avoid, is just getting plastered on a regular basis without passing out
healthy?

You can't get bent if you don't get wet, but look at all the fun you're
missing by staying dry.

And just who is staying dry?

Damn Greg, I'd have thought the lawyer would have caught the real
analogy. ;-)

Curtis

[mike gray]

Post by Greg Mossman

Post by Brooklyn
Dive Brooklyn, the birthplace of scuba.

Dive L.A., the birthplace of scuba instruction.

LA was kinda late. Le Prieur was teaching scuba in the '20s.

[-hh]

Post by Greg Mossman
For dives with a hard bottom less than the MOD of the nitrox mix, there's
practically a zero risk of oxygen toxicity when diving recreational
profiles.

Yes, and for divers having similarly good practices and staying within
the No-Deco limits, there's also practically a zero risk of DCS when
diving recreational profiles...approx 0.04%

So in a nutshell the question is if "half of zero" really is better
than "zero".

Post by Greg Mossman
The threat of oxygen toxicity as compared with the dangers of
DCS for recreational profiles by attentive divers is a red herring.

Any time you try to divide something by zero, you're going to get
dramatic-looking answers which are fundamentally misleading: when two
risks are very small, examining the ratio between them is the red
herring. So do all the 'Herring Halving' you wish ... you're not
really changing the risks.


And the pragmatic question is even if it did achieve "half a zero", is
it significant enough to be worth paying an extra $8/tank for?


-hh

[Greg Mossman]

Post by -hh
Yes, and for divers having similarly good practices and staying within
the No-Deco limits, there's also practically a zero risk of DCS when
diving recreational profiles...approx 0.04%
So in a nutshell the question is if "half of zero" really is better
than "zero".

I think the better question is whether 0.04% is really zero.

If 0.04% is zero, 0.08% is twice zero and would still be zero. However,
that defense won't work very well, say, in a DUI case when you try to
convince the judge that you're not really drunk because you only blew a
0.08% on the Breathalyzer and that's really just zero because it's merely
twice zero.

Post by -hh
And the pragmatic question is even if it did achieve "half a zero", is
it significant enough to be worth paying an extra $8/tank for?

What price to put on the all saved lives? I dunno. Ask Ford. Ask
Firestone. If I had my way, I'd sue whoever invented air for product
liability. Maybe we can sue the dive shops for continuing to carry the
crap. It's like selling unfiltered cigarettes.

Plus you have all the collateral benefits, some real, some imaginary. There
may be less narcosis, if oxygen isn't as or more narcotic than nitrogen.
You may experience less fatigue, possibly due to reduced microbubble
formation, possibly from the oxygen "high". At the least, there's a placebo
effect. On liveaboard trips when I'm diving unlimited nitrox, I always stay
up later than anyone diving air and manage to metabolize more alcohol as
well, and still manage to be one of the first up in the morning. At home,
when I breathe mere air, I can never keep up that sort of behavior for long.

[-hh]

Post by Greg Mossman

Post by -hh
So in a nutshell the question is if "half of zero" really is
better than "zero".

I think the better question is whether 0.04% is really zero.

We currently can't lower the risk below 0.04%. That's what makes it
effectively zero.

And considering that we know that 25% of the Adult population has a PFO
which IIRC has roughly 4x the DCS risk, this means that we're aware of
a subpopulation with roughly a 0.20% risk, yet because no Rec Agency
requires a diving candidate to undergo a PFO screening test as part of
their pre-certification medical, the "Accepted Industry Practice" is
choosing to ignore this demonstrably higher risk. YMMV on if you agree
with them, but DAN has stated that this PFO-attributable condition is
an acceptably "small" (relative) risk in diving.

Post by Greg Mossman
If 0.04% is zero, 0.08% is twice zero and would still be zero. However,
that defense won't work very well, say, in a DUI case when you try to
convince the judge that you're not really drunk because you only blew a
0.08% on the Breathalyzer and that's really just zero because it's merely
twice zero.

The fallacy in this example is twofold. First, we're talking about
trying to reduce risk, not increasing it. Second, in the case of
alcohol, it is possible to consume some small amount and have a blood
alcohol that's below 0.04%, but with diving, if we proverbially even
stick a toe in the water, its a step function to an activity risk floor
of 0.04%.

We aren't (yet) capable of reducing this "background noise" without
effectively total cessation of diving activity, whereas even an
alcoholic can safely eat a vanilla cupcake, and "zero" DWI's are due to
the driver's consumption of 2 TSP/4hrs of cough syrup.

Post by Greg Mossman

Post by -hh
And the pragmatic question is even if it did achieve "half
a zero", is it significant enough to be worth paying an
extra $8/tank for?

What price to put on the all saved lives? I dunno.

Cross that bridge once we come to it, for the road we're on might not
even lead us there.

Post by Greg Mossman
If I had my way, I'd sue whoever invented air for product liability.

Don't worry, you'll get to meet Him, eventually, to plead your case:
we pretty well know that air is toxic to human life, although it has a
half-life of 74 years (as per most life insurance companies :-)

Post by Greg Mossman
Plus you have all the collateral benefits, some real, some imaginary.

You should have said collateral "effects", for they're not all
necessarily beneficial: if nothing else, spending the extra money for
Nitrox means less cash remaining for booze :-)

And yes, the effects encompass both the physiological and psychological
realms, which in Humans can be very difficult to quantitatively
partition, particularly when the test subject's motivation levels are
an uncontrolled variable.


-hh

[Greg Mossman]

Post by -hh
You should have said collateral "effects", for they're not all
necessarily beneficial: if nothing else, spending the extra money for
Nitrox means less cash remaining for booze :-)

That's why I love Aggressors: $100 for unlimited nitrox and the booze is
free.

[Limey]

Post by Greg Mossman

Post by -hh
You should have said collateral "effects", for they're not all
necessarily beneficial: if nothing else, spending the extra money for
Nitrox means less cash remaining for booze :-)

That's why I love Aggressors: $100 for unlimited nitrox and the booze is
free.

Dayum, why have they been keeping this kind of intel from ME?

LD.

[Chris Guynn]

Post by Limey

Post by Greg Mossman
That's why I love Aggressors: $100 for unlimited nitrox and the booze is
free.

Dayum, why have they been keeping this kind of intel from ME?
LD.

Probably because they're hoping to be able to stay in business.

[Limey]

Post by Chris Guynn

Post by Limey

Post by Greg Mossman
That's why I love Aggressors: $100 for unlimited nitrox and the booze

is

Post by Limey

Post by Greg Mossman
free.

Dayum, why have they been keeping this kind of intel from ME?

Probably because they're hoping to be able to stay in business.

Chris, you're on to me!

LD.

[Lee Bell]

Post by Ron
Although, it strikes me as ironic. The very thing you're
counseling against (diving nitrox, within the MOD, using
air tables for extra conservatism) would have prevented
your bends incident.

Yes, but not for the reasons you think. I could not have done the dive
safely on air. I would have avoided getting bent because I would have been
sitting on the boat instead of diving. By the way, I'm not counseling
against anything. I'm simply saying that those that use nitrox based on air
tables get a poor return on their money. They neither get the increased
dive time/shorter surface interval I get, nor the increased safety they
believe they are getting.

Post by Ron
Diving nitrox on air tables is safe, as there is no instance
where the air table specifies less time than the nitrox table.

There are, however, both depths and times (separately) that air tables allow
that nitrox tables don't..

Lee

[Ron]

Post by Lee Bell
I'm simply saying that those that use nitrox based on air
tables get a poor return on their money. They neither get the increased
dive time/shorter surface interval I get, nor the increased safety they
believe they are getting.

Maybe so. Or maybe it helps to avoid long-term
problems.

Reports of cognitive dysfunction and damage
to the liver, retina, and heart of the diver
with no history of decompression sickness are
now emerging. Because these symptoms may
occur gradually and away from the dive site,
prudent physicians should be aware of the
signs and symptoms related to adverse events
of diving in order to minimize the morbidity
and mortality they can cause.
http://www.scuba-doc.com/LTE.htm

Whether extra conservatism can address the
long-term problem remains speculative, since
I'm aware of no good scientific studies on this.

[mike gray]

Post by Ron
Whether extra conservatism can address the
long-term problem remains speculative, since
I'm aware of no good scientific studies on this.

Other than DAN and NEDU, I don't have any either.

[mike gray]

Post by mike gray

Post by Ron
Whether extra conservatism can address the
long-term problem remains speculative, since
I'm aware of no good scientific studies on this.

Other than DAN and NEDU, I don't have any either.

And, of course, DCIEM, but they're Canadian.

[n***@all.please.net]

Post by Lee Bell

Post by n***@all.please.net
If so, how does it generalise?

It generalizes about as well as any other study involving thousands of hours
or testing.

Let's not confuse Lee with Science; _cience is his game.

[ben bradlee]

Post by n***@all.please.net
Try to publish it in a reviewed journal if you want to see how credible it
is.

One needs not to fully understand the studies, findings, results, and
recommendations published on rec.scuba before knowing with absolute
certainty where such studies, findings, results, and recommendations belong.

Credibility is credibility - this is rec.scuba.

[Carl Nisarel]

Post by ben bradlee
Credibility is credibility - this is rec.scuba.

IOW, no credibility.

[ben bradlee]

Post by Carl Nisarel

Post by ben bradlee
Credibility is credibility - this is rec.scuba.

IOW, no credibility.

It's one man's opinion. It was apparent to me that Lee's post was a story.
Maybe it's a true story. Maybe it current memories clouded by the shades of
time. Maybe it's strung together aspirations. It's of little importance
what it is, but it was a cute story. The problem with much (I claim most)
of what you read on rec.scuba is that is just opinion. Three or four guys
agree and it becomes fact. If one stepping into rec.scuba doesn't know that
the bullshit is flying, he or she could very well believe what is said and
get hurt.

Let me explain it another way. There are things that people know. Your
knowledge, 2 + 2 = 4, etc. There are things that people don't know. You
say, "I don't know" because it's the truth. Then there is a third
category: Things we don't know we don't know. Here you're confronted with,
or providing, information about a subject that you don't know enough to
determine you don't know. Most of rec.scuba is don't know we don't know.
People providing buckets of information from a thimble full of reserves.
This is rec.scuba.

[Carl Nisarel]

Post by Lee Bell
I'm the guy that did the thousands of hours of dives
over more than 40 years.

N=1

[Chris]

Post by Lee Bell
It was a real scientific study.

Nope. Calling a posting "scientific" doesn't make it that. One subject
in the study, that defined the study and operated it. There's nothing
scientific about that - it's too subjective.

Post by Lee Bell
Let's try this again. I'm the guy that did the thousands of hours of dives
over more than 40 years. I'm the guy that had the tanks filled, knows what

Let's<sic> do. It's still a one person study - that's all. No dive
table from any organization has ever based their data on one diver for
a very good reason - it's statistically useless information.

Post by Lee Bell
If you can't draw conclusions from the information, that's you're problem.

I did draw a conclusion - the only valid conclusion available to me.
This is not a scientific study. If you don't like my conclusion, that's
your problem<g>.

Post by Lee Bell
Unless you have comparable experience or information to the contrary,
information as easily traced to its source as mine is, I suggest you think
twice about denying the validity of its results.

Since you didn't notice it before, I'll repeat it again: I never
questioned the validity of your data (and said so multiple times). Only
the labeling of that data as a "scientific study". I suggest you think
twice about misrepresenting data as a scientific study. It dilutes the
importance of studies that do bother with those pesky details required
by all scientific studies (the scientific method).

cheers,
Chris

[Lee Bell]

Post by Chris

Post by Lee Bell
It was a real scientific study.

Nope. Calling a posting "scientific" doesn't make it that. One subject
in the study, that defined the study and operated it. There's nothing
scientific about that - it's too subjective.

I didn't call the post scientific. I called the study scientific. There's
nothing subjective about it. I did the dives and recorded the results.
Nothing subjective about it.

Post by Chris
Let's<sic> do. It's still a one person study - that's all. No dive
table from any organization has ever based their data on one diver for
a very good reason - it's statistically useless information.

Actually, it's not one diver. More than 30 years worth of those dives was
done with an assortment of buddies. They didn't get bent either.

Post by Chris

Post by Lee Bell
If you can't draw conclusions from the information, that's you're problem.

I did draw a conclusion - the only valid conclusion available to me.
This is not a scientific study. If you don't like my conclusion, that's
your problem<g>.

OK with me. Spend your money for no benefit. You'll have plenty of time to
think about it sitting on the boat while Mike, I and others are still
enjoying our dives.

Lee

[n***@all.please.net]

Post by Lee Bell

Post by Chris

Post by Lee Bell
It was a real scientific study.

Nope. Calling a posting "scientific" doesn't make it that. One subject
in the study, that defined the study and operated it. There's nothing
scientific about that - it's too subjective.

I didn't call the post scientific. I called the study scientific. There's
nothing subjective about it. I did the dives and recorded the results.
Nothing subjective about it.

Post by Chris
Let's<sic> do. It's still a one person study - that's all. No dive
table from any organization has ever based their data on one diver for
a very good reason - it's statistically useless information.

Actually, it's not one diver. More than 30 years worth of those dives was
done with an assortment of buddies. They didn't get bent either.

The story changes...

[Limey]

Post by Lee Bell

Post by Greg Mossman

Post by Chris
These data are interesting, but, you fail to mention what organization
performed this scientific study... more info please.

NAUI, SSI and TDI were represented.

Post by Greg Mossman
It was a government-funded study, no doubt.

Funded entirely with private funds, no advertising, endorsements or
commercial contributions involved.

As self-appointed commercial manager for the next study group, we are
working feverishly to obtain Captain Morgan's as Official Sponsor.

LD.

[Grumman-581]

Post by Chris
These data are interesting, but, you fail to mention what organization
performed this scientific study... more info please.

Darwin, of course...

[Lee Bell]

Post by Grumman-581

Post by Chris
These data are interesting, but, you fail to mention what organization
performed this scientific study... more info please.

Darwin, of course...

Unquestionably involved.

[Dennis (Icarus)]

Post by Chris

Post by Lee Bell
In an exhaustive study, lasting over 40 years and involving thousands of
hours of diving, the relationship between air, nitrox and DCS is finally

These data are interesting, but, you fail to mention what organization
performed this scientific study... more info please.

I suspect it was Bell Labs.

:-)

Dennis