Who DOESN'T analyze their gas?

I know most anyone reading this will happily post about how they always analyze their breathing gas... I don't want to hear from you (sorry)... I want to hear from the divers who don't analyze their gas. My wife and I have for years consistently, without miss, made analyzing our gas part of our gear-up routine. We do it together (she is always afraid I am going to whack the analyzer out of calibration so I must be babysat), mark our tanks, set our computers and then go for our dive. If we are diving on a boat we usually do it the night before in the garage, then pack up and go.
Recently I was diving with some new friends (off shore/boat spearfishing) and noticed they didn't analyze their gas. When I asked if they did, they simply said the shop they get it from just pumps 32% so there is nothing to worry about, and they went about the day as if nothing mattered. A couple of trips later they surfaced complaining of headaches, which we thought to be overexertion, but they worsened during the night accompanied by noxiousness the next morning. I became very concerned for them, as I didn't know whom they were getting gas from, so I analyzed their tanks for oxygen, and they were good. I then ordered a C0 analyzer, something I have been meaning to get for awhile now and anxiously awaited its delivery.
So, it got me thinking... every time I am somewhere like peacock or JB or wherever other divers are present, I cannot recall hardly ever seeing anyone pull out an analyzer and test their gas. We all were taught it is important, we all know the potential for gas mix-ups or incorrect fills or even the possibility of C0 contamination. Most basic Nitrox classes teach you that the correct practice is to analyze the gas at the shop at the time of pickup and that the fill should be logged at the fill station prior to departure. Of course in cave country, this isn't the case... you can get tanks slammed full of nitrox or other gas without showing a C-card and certainly without analyzing before departure. Enough said... back to my original inquiry... who DOESN'T analyze their gas? why?

I haven't been to a shop yet that did not have an O2 analyzer you could use. Yes and a lot of shops will make you analyze it and sign the log.. However a co2 analyzer isn't as readily available. And for some reason people don't tend to monitor or analyzes air. Even though there's the same potential for co2. I admit I don't monitor for co2. I wish I had a co2 monitor since the shops have the o2 monitor

Is this like asking, "If anyone here is dead, raise your hand?"

Hey, you said they were spearfishing. That's all you needed to know.

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Originally Posted by Seanmeboy

I haven't been to a shop yet that did not have an O2 analyzer you could use. Yes and a lot of shops will make you analyze it and sign the log.. However a co2 analyzer isn't as readily available. And for some reason people don't tend to monitor or analyzes air. Even though there's the same potential for co2. I admit I don't monitor for co2. I wish I had a co2 monitor since the shops have the o2 monitor

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Want to point out that it is CO (Carbon Monoxide), not CO2 (Carbon Dioxide) for which you measure. You can get the headache and nauseousness from breathing too fast on perfectly good gas, due to failure to properly breath and exchange CO2.

I often don't if I'm present while the tanks are being filled and I can see the in-line analyzer. But, Tri-mix I always analyze, I don't have a CO analyzer.
I find it comical when I see people mark their tanks to the .1 percent of O2, you don't think our recreational analyzers are that accurate do you?

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Originally Posted by a64pilot

I often don't if I'm present while the tanks are being filled and I can see the in-line analyzer. But, Tri-mix I always analyze, I don't have a CO analyzer.
I find it comical when I see people mark their tanks to the .1 percent of O2, you don't think our recreational analyzers are that accurate do you?

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Nor are the computers' place holders giving that level of accuracy. I guess it helps to remember to round up or down?

As far as rounding, another way is to never bust the floor for the mix, as in don't go deeper than 110 for 32%, but run air tables for conservatism. I do that for my Kids as I'm not real sure there has ever been any studies on Nitrox and younger people, applies probably for older, possibly overweight people as well?
Only way I can think of for an electrically driven compressor to get CO in it would be for the operator to use an incorrect oil, one that would burn at high compression temperatures? Of course I guess they could park a running lawnmower right beside the air intake, but other than that, where could the CO come from?

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Originally Posted by a64pilot

As far as rounding, another way is to never bust the floor for the mix, as in don't go deeper than 110 for 32%, but run air tables for conservatism. I do that for my Kids as I'm not real sure there has ever been any studies on Nitrox and younger people, applies probably for older, possibly overweight people as well?
Only way I can think of for an electrically driven compressor to get CO in it would be for the operator to use an incorrect oil, one that would burn at high compression temperatures? Of course I guess they could park a running lawnmower right beside the air intake, but other than that, where could the CO come from?

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There have been several problems overseas, with poorly maintained compressors and not carefully controlling what is around the air intake. Don't think there has been one in the US from a dive shop.

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Originally Posted by Jax

Don't think there has been one in the US from a dive shop.

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Think again. There have been several reports of serious injury from bad gas at USA dive shops.

I got bad gas from a dive shop here in CENTRAL FLORIDA. It was reported and the problem was being worked on that day.

I analyze for PO2 three times: after it's filled, when I load it into the car for the trip, and when I put the reg on it. I only analyze once for CO, and that's when I get it home from the fill.

I never really thought about how bad gas could result in noxiousness, but now that you mention it...

I won't say that I've never dove an un analyzed tank, but I will say that it is stupid to dive one.

On a recent out of country dive trip, I was surprised that the shop employee wanted me to calibrate with an unmarked tank supposedly full of air next to the analyzer, not with ambient air. I was also amused to watch nitrox divers hook the analyzer reg up backwards to the tank, and also to write down to the .1...while I am sure they were horrified to watch me round up or down after calibrating to nasty old ambient air. To each their own--that's why I write my name on the tanks I intend to breathe.

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Originally Posted by Slüdge

I analyze for PO2 three times: after it's filled, when I load it into the car for the trip, and when I put the reg on it. I only analyze once for CO, and that's when I get it home from the fill.

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why analyze 3 times? the P02 will change after a fill as the old gas homogenizes with the new gas, but I had always been under the belief that as long as I analyze close to the actual dive or at least 24hrs after the fill, I would have the most accurate results. Of course I could understand analyzing at the dive shop to ensure you got the mix you intended.

I've only seen someone get sick from bad air once, long ago. The air had oil in it, or at least the tank had about a tablespoon of oil in it when we pulled the valve and looked. You could smell the oil, but of course you don't smell with your mouth so it wasn't noticed pre-dive. Don't think the oil would have been found with an analyzer.
Shops un-familar to me, I always analyze the gas.

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Originally Posted by kwinter

Think again. There have been several reports of serious injury from bad gas at USA dive shops.

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Originally Posted by bpcfire1

I got bad gas from a dive shop here in CENTRAL FLORIDA. It was reported and the problem was being worked on that day.

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Thanks for the correction, guys. I analyze for CO as a matter of procedure, but hadn't seen any stories.

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Originally Posted by IowaCaveDiver

under the belief that as long as I analyze close to the actual dive or at least 24hrs after the fill, I would have the most accurate results.

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After it's filled to make sure I got what I wanted. Before loading it into the car in case something has changed (after the mix has sat around awhile), so I have time to either run back up to the shop, or plan a stop at a local shop when I get to Florida. And then I analyze when I assemble the rig, just because. It only takes a minute.

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Originally Posted by JahJahwarrior

On a recent out of country dive trip, I was surprised that the shop employee wanted me to calibrate with an unmarked tank supposedly full of air next to the analyzer, not with ambient air.

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Calibrating to ambient air will usually give a reading that is at least 0.2% lower than calibrating to dry, room-temp air (as in an air tank); on a good "90-90" day you might be almost 1% off. That means the O2 percentage you are breathing is actually lower than what you think, if you calibrated to ambient air. that is conservative for MOD, not so for nitrogen uptake.
Attachment 9102
If you don't believe this, calibrate to the gas in an air tank, and then read the O2 percentage for ambient air.

I'm sure most of you folks already knew this, but I'm concerned when anyone says ambient air is the way to calibrate.

As to rounding, I round up to figure out MOD, and down to set my computer to add a touch of conservatism. And then I subtract 10 feet from my MOD for the actual dive. I like cushions.

With ambient air at least you know the o2 within a percentage point. +/-1% is good enough for anything scuba.

Calibrating off a tank of who knows what, you're shooting in the dark.

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Originally Posted by PfcAJ

With ambient air at least you know the o2 within a percentage point. +/-1% is good enough for anything scuba.

Calibrating off a tank of who knows what, you're shooting in the dark.

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Who ever said to calibrate off a tank of who knows what? Calibrate to a tank of air; it'll be dry, and not likely to be at 90 F.

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Originally Posted by a64pilot

I've only seen someone get sick from bad air once, long ago. The air had oil in it, or at least the tank had about a tablespoon of oil in it when we pulled the valve and looked. You could smell the oil, but of course you don't smell with your mouth so it wasn't noticed pre-dive. Don't think the oil would have been found with an analyzer.
Shops un-familar to me, I always analyze the gas.

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That is exactly what happened to me from renting a tank on a dive. There was so much oil that it left a film on the water when I free flowed my reg. I made it about 20ft and literally could taste this nasty taste. After calling the dive, and going to the shop where I got the tank, it was found that there were several tanks with oil including some others that were in use also.

I have had a situation from my job, where a bottle had some oil in it and after use for a bit I became very ill and had to be taken to the ER.

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Originally Posted by a64pilot

I find it comical when I see people mark their tanks to the .1 percent of O2, you don't think our recreational analyzers are that accurate do you?

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It may be comical but it lets my dive buddy know that I actually analyzed the tank rather just wrote down what I think it is. I see several advantages with no real downside.

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Originally Posted by tursiops

Who ever said to calibrate off a tank of who knows what? Calibrate to a tank of air; it'll be dry, and not likely to be at 90 F.

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Most shops I've been to have a tank of 'air' just sittin there. You really don't know whats in it. Could be air. Could be 24%. Could be somethin' goofy like 18%. Who knows? Calibrating with atmospheric air is always yields 21% +/- 1%.

I always mark to x.x% though. Easy to have a label requesting 50% get confused with an analysis for 50%. Writing '50.4%' works to eliminate confusion between the two options.

Some of the analyzers available today automatically compensate for temp and humidity. In S. Florida as a general rule, setting the analyzer to 20.6 will almost always be too close to cause any concern.

Not to mention any names, but ask Tienuts why he does/ does not analyze tanks.

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Originally Posted by PfcAJ

With ambient air at least you know the o2 within a percentage point. +/-1% is good enough for anything scuba.

Calibrating off a tank of who knows what, you're shooting in the dark.

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Unless you are somewhere where the ambient air is .17%. ;)

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Originally Posted by tursiops

Who ever said to calibrate off a tank of who knows what? ...

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JahJahwarrior did, and you quoted him. I would have to agree with JahJah, and wouldn't trust a tank of "who knows what", just because it was sitting at some shop, unmarked.

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Originally Posted by JahJahwarrior

...the shop employee wanted me to calibrate with an unmarked tank supposedly full of air next to the analyzer...

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Originally Posted by Jax

Unless you are somewhere where the ambient air is .17%. ;)

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And where exactly would that be?

.17% isn't enough to sustain life. And if you meant 17%, I can't think of a place on earth where you would be scuba diving and have a hypoxic situation around you. Even at altitude, where there is 'less oxygen', the proportions remain constant, just at lower pressure.

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Originally Posted by FW

JahJahwarrior did, and you quoted him. I would have to agree with JahJah, and wouldn't trust a tank of "who knows what", just because it was sitting at some shop, unmarked.

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You're right, I did quote him. I guess in the spirit of don't trust anyone or anything, I should assume that the tank of air sitting there for calibration purposes is not actually air. I guess I should also not believe the CO content is zero, that it is N2 mixed with the O2 and not CO2 in the "nitrox," and that the floor I'm standing on isn't going to give way and drop me into a pit underneath. Oh, wait, THAT actually happens... Hmmm.

http://www.cavediver.net/forum/showt...nalyze?p=51172

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Originally Posted by tursiops

Attachment 9102

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My Scubapro analyzer came with one of these cards, and I got a thermometer for the dive trailer that gives humidity, so that's what I do. (In the summer, 90°F with 90% relative humidity yields 20.0% FO2 in ambient air.)

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Originally Posted by PfcAJ

And where exactly would that be?

.17% isn't enough to sustain life. And if you meant 17%, I can't think of a place on earth where you would be scuba diving and have a hypoxic situation around you. Even at altitude, where there is 'less oxygen', the proportions remain constant, just at lower pressure.

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First, all O2 analyzers actually measure the PPO2, and convert it into a percentage.

Imagine my surprise firing up my "new to me" Predator to find it flashing a red 17 PPO2! I lived at 5000 feet at the time.

So, conversation with Shearwater: All "barometric pressures reported by weather agencies are normalized for the area.".

Now that I moved into town, my Petrel reports .18 . . . :)

BTW, the Army requires all transferees to have at least 80 days on station before administering a PT test, because it takes time to build the red blood cells to carry the required O2.

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Originally Posted by Slüdge

I got a thermometer for the dive trailer that gives humidity, so that's what I do. (In the summer, 90°F with 90% relative humidity yields 20.0% FO2 in ambient air.)

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A thermometer measures temperature...a hygrometer measures humidity...

Back to my rock...

Dive safe,

Celia

Okay, I got a combination thermometer/hygrometer for the dive trailer...

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Originally Posted by Jax

First, all O2 analyzers actually measure the PPO2, and convert it into a percentage.

Imagine my surprise firing up my "new to me" Predator to find it flashing a red 17 PPO2! I lived at 5000 feet at the time.

So, conversation with Shearwater: All "barometric pressures reported by weather agencies are normalized for the area.".

Now that I moved into town, my Petrel reports .18 . . . :)

BTW, the Army requires all transferees to have at least 80 days on station before administering a PT test, because it takes time to build the red blood cells to carry the required O2.

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Thats because you didn't calibrate it. The % (which is what we're discussing) is the same in all cases. 20.9%. Your ppo2 might be lower, but the % is the same.

http://www.analox.net/reference/RM-0...i_Altitude.pdf

Page 5 is the relevant info.

Shearwater says it is operating exactly as it ought.

So do you think you're breathing 17-18% oxygen?

17% O2 at sea level will easily support life, you won't be performing as well during your Marathon, but you won't die either.
What I don't know is at what percent O2 won't support life at seal level pressure, but think it would be a very variable number.
I suspect this knowing Ferry pilots that regularly fly at 18,000 ft. without supplemental O2 and don't even get a headache doing so, I suspect I would go un-conscious trying that.

I don't know how credible this is, but it says available oxygen in the air in Denver is 18%.

http://www.faqs.org/sports-science/Mo-Pl/Oxygen.html

On the o2 analyzer they issue at me at work it is .1 6 alarm

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Originally Posted by Slüdge

I don't know how credible this is, but it says available oxygen in the air in Denver is 18%.

http://www.faqs.org/sports-science/Mo-Pl/Oxygen.html

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That's flat out wrong. The pO2 may well be .18, but that does not mean the %O2 is 18%

Sigh. Science.

What gas makes up the balance if its 18% oxygen in Denver?

I find it interesting that divers (allegedly) understand that at if one is breathing air at 33ft, the ppo2 is .42, and the inspired gas fraction (fo2) is still .21. But the same rules appear not to apply in the other direction?

Less pressure = less ppo2. More pressure = higher ppo2. Same percentage in all cases.

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Originally Posted by Slüdge

I don't know how credible this is, but it says available oxygen in the air in Denver is 18%.

http://www.faqs.org/sports-science/Mo-Pl/Oxygen.html

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It's wrong. PfcAJ is exactly right. The percentage is 20.9, it is only the PPO2 that has dropped to .18 at altitude (which you can call 18% of sea level pressure...but your are not at sea level). But what is causing the problem for the athletes is that each breath has fewer oxygen molecules in it, compared to how many at sea level. So they are breathing a gas that is 20.9% O2, but that gas has fewer O2 molecules than the athlete is used to in a breath...in fact 18/20.9 as much, so the athlete feels O2 starved...as if the percentage of O2 were lower. Turns out we function on PPO2, not percentage O2.....

Last time I played in Denver both my o2 analyzer and computers read 18 percent o2. In reality it's .18 ATA ppo. The stage at the PAC keeps full k bottles of aviator grade o2 on both stage left and right for cast and crew. I was there 8 weeks and never fully acclimated.

I remember when I was in Colorado City working on a film years ago I had to get the carb on my old Land Rover adjusted due to some of the off-roading in higher elevations.
One time it stalled out on Mosquito Pass near Leadville and that was a bit concerning due to the multiple thousand feet drop near my driver's side tires.

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Originally Posted by a64pilot

I often don't if I'm present while the tanks are being filled and I can see the in-line analyzer. But, Tri-mix I always analyze, I don't have a CO analyzer.
I find it comical when I see people mark their tanks to the .1 percent of O2, you don't think our recreational analyzers are that accurate do you?

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Labels written to the 0.X percent mean that's what it was actually analyzed at. A label of say "18/45" just says that's what's supposed to be in there. Some of us have 3-6 sets of doubles and its helpful to know what's in what even if its not yet verified for diving.

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Originally Posted by tursiops

It's wrong. PfcAJ is exactly right. The percentage is 20.9, it is only the PPO2 that has dropped to .18 at altitude (which you can call 18% of sea level pressure...but your are not at sea level). But what is causing the problem for the athletes is that each breath has fewer oxygen molecules in it, compared to how many at sea level. So they are breathing a gas that is 20.9% O2, but that gas has fewer O2 molecules than the athlete is used to in a breath...in fact 18/20.9 as much, so the athlete feels O2 starved...as if the percentage of O2 were lower. Turns out we function on PPO2, not percentage O2.....

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Correct. And just to take it a step further, I wonder if there are any stats about EXPIRED pO2 at altitude. At sea level we inspire pO2 of 0.21 and expire about 0.16. We metabolize about 25% of the O2 molecules we inhale. But at altitude where the pO2 is 0.18, we still need to metabolize the same number of molecules. Since there are fewer in each breath, we use a greater percentage of the ones available. Hence our expired pO2 should drop more than at sea level. I don't know what the numbers would be, but maybe expired air in Denver is about 0.11? This is probably the same logic that on SCR our loop FO2 doesn't drop that much at depth compared to at the surface.

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Originally Posted by PfcAJ

Sigh. Science....

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I think it is more an issue of semantics than science :-)

What I've always wondered is what happens to very active divers blood count? Specifically the red blood cell count? People acclimatize to high altitudes by their bodies increasing the amount of red blood cells, I think it can as much as double.
What happens to people that spend a lot of time in high PO2? Does their red blood cell count drop? I'm talking people that spend say four or more hours diving at least five days a week, not weekend warriors like me.

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Originally Posted by FW

I think it is more an issue of semantics than science :-)

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"Sigh" semantics

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Originally Posted by a64pilot

What I've always wondered is what happens to very active divers blood count? Specifically the red blood cell count? People acclimatize to high altitudes by their bodies increasing the amount of red blood cells, I think it can as much as double.
What happens to people that spend a lot of time in high PO2? Does their red blood cell count drop? I'm talking people that spend say four or more hours diving at least five days a week, not weekend warriors like me.

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"Doc, I need to figure out if I have cancer or I'm just overexposed to nitrox."

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Originally Posted by jj1987

"Doc, I need to figure out if I have cancer or I'm just overexposed to nitrox."

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I'm no Doc, and I didn't stay in any motel last night, but isn't it white cell count they look at with some forms of cancer?
Somebody has to know the answer, it's just too easy a thing to check to have not been checked?

LOL, you guys are hilarious.

PfcAJ asks the right question. Suddenly because altitude is higher, we're breathing 18% O2 and 82% Nitrogen? Do the trees not work as well up there converting CO2 into O2? Now, if someone had said the O2 content in Detroit was less than 21% that would be believable. :)

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Originally Posted by a64pilot

What I've always wondered is what happens to very active divers blood count? Specifically the red blood cell count? People acclimatize to high altitudes by their bodies increasing the amount of red blood cells, I think it can as much as double.
What happens to people that spend a lot of time in high PO2? Does their red blood cell count drop? I'm talking people that spend say four or more hours diving at least five days a week, not weekend warriors like me.

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http://www.ncbi.nlm.nih.gov/pubmed/11908696

In saturation divers, there is a significant drop in blood numbers. I did not find any abstracts for rec or tec divers.

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Originally Posted by gschaut

http://www.ncbi.nlm.nih.gov/pubmed/11908696

In saturation divers, there is a significant drop in blood numbers. I did not find any abstracts for rec or tec divers.

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2nded

Physiologically it makes perfect sense as well. People with chronic respiratory problems are another interesting situation. Frequently copd patients will have an elevated hgb/hct from chronic hypoxia, provided they don't have renal disease as well(kidneys are involved in epo production which is needed to stim rbc proliferation).

Sent from my HTC PH39100 using Tapatalk 2

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Originally Posted by a64pilot

I'm no Doc, and I didn't stay in any motel last night, but isn't it white cell count they look at with some forms of cancer?
Somebody has to know the answer, it's just too easy a thing to check to have not been checked?

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Maybe, depends on what kind of cancer. You can get a cancer originating from literally ANY cell type in the body. The difference in types of cancer is which cell type it originated from. The human body is essentially a highly effective socialist regime with the central nervous center pulling societies strings. Every once in a while a certain cell line may say #### this ####, I'm going rogue. Most of the time the body recognizes this and kills the rogue before it has time to proliferate.

Sent from my HTC PH39100 using Tapatalk 2

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Originally Posted by CaveMD

Maybe, depends on what kind of cancer. You can get a cancer originating from literally ANY cell type in the body. The difference in types of cancer is which cell type it originated from. The human body is essentially a highly effective socialist regime with the central nervous center pulling societies strings. Every once in a while a certain cell line may say #### this ####, I'm going rogue. Most of the time the body recognizes this and kills the rogue before it has time to proliferate.

Sent from my HTC PH39100 using Tapatalk 2

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Love this description. Kind like Egypt.

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Originally Posted by a64pilot

I'm no Doc, and I didn't stay in any motel last night, but isn't it white cell count they look at with some forms of cancer?

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It's called leukemia

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Originally Posted by Superlyte27

LOL, you guys are hilarious.

PfcAJ asks the right question. Suddenly because altitude is higher, we're breathing 18% O2 and 82% Nitrogen? Do the trees not work as well up there converting CO2 into O2? Now, if someone had said the O2 content in Detroit was less than 21% that would be believable. :)

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No, the problem is that Oxygen analizers DO NOT measure PERCENTAGE of oxygen. Even though that is the value displayed.

Oxygen analizers measure the PARTIAL PRESSURE IN ATMOSPHERES of oxygen.

At 3,000' above sea level, the TOTAL air pressure is about 850 mBar. Or about 85% of sea level air pressure.

At sea level, 21% oxygen is equal to 210 mBar Partial Pressure. BUT... at 3,000', 21% oxygen is only 185 mBar Partial Pressure.

So the oxygen analizer reads 18.5% instead of 21%.

This is why we have to calibrate the O2 analizer every time it's used. Altitude, Temperature and Humidity ALL affect the PPO2 in the atmosphere.

Each analizer has a calibration chart for Temp and Humidity. Sea level (or near sea level) altitude is assumed. If you are doing "altitude" diving, you can either use math to calibrate the difference in PPO2 caused by air pressure.

OR... you can just bring an tank of "bump gas" (known value, pre-calibrated gas) with you to calibrate your analizer.

The last couple of analizers I have used were hooked to the low pressure port on a scuba reg. with a pre set amount of gas flowing through it at 130 to 150 psi. I would think this will negate the altitude effect and display the proper cal. So at sea level it will (should) read 20.9 and at 5000 ft it should read around 18 when reading the ambient air, but when you hook it to a tank with air it will (should) read 20.9 and just as at sea level it will read what ever nitrox mix was mixed and installed into the tanks.....

My 2c

so if a Egyptian with leukemia and a socialist spinial cord analizes his gas in Denver then it's 18% before he passes out from screaming **** *** **** in arabic which in English translates to **** *** ****.

when im in cave country I dont usually analyze the banked nitrox fills but always my trimix fills even if its banked.Up north here most shops have air fills only and if im getting 2-3 tanks filled i will usually only check one,, i guess now ill start using the analyzers i own a little more.

I have a couple of analyzers. I find that one (oxycheq expedition) that I hook to the bc hose with a flow restrictor and cap on the sensor interesting. If I remove the flow cap and calibrate ambient air in the house (climatized and not too much humidity) then calibrate using the cap and restrictor from a tank of air the readings are off more than I would expect from just a change in humidity since the temps of the ambient air and tank (which has been stored inside the home) are are essentially the same. I attribute it to a slight pressure increase in the flow cap, hence raising the PO2 for the tank/flowcap scenario. Tanks will always test about .6% higher when calibrated with the flow cap on an air tank as opposed to calibrating with the sensor exposed to air directly. I have an Oxycheq E'lCheapo that acts more like the expedition with the cap off.
Not a deal breaker, If I calibrate the expedition using ambient air I just set it to 20.5 ish to meet somewhere in the middle.

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Originally Posted by scubadude

I have a couple of analyzers. I find that one (oxycheq expedition) that I hook to the bc hose with a flow restrictor and cap on the sensor interesting. If I remove the flow cap and calibrate ambient air in the house (climatized and not too much humidity) then calibrate using the cap and restrictor from a tank of air the readings are off more than I would expect from just a change in humidity since the temps of the ambient air and tank (which has been stored inside the home) are are essentially the same. I attribute it to a slight pressure increase in the flow cap, hence raising the PO2 for the tank/flowcap scenario. Tanks will always test about .6% higher when calibrated with the flow cap on an air tank as opposed to calibrating with the sensor exposed to air directly. I have an Oxycheq E'lCheapo that acts more like the expedition with the cap off.
Not a deal breaker, If I calibrate the expedition using ambient air I just set it to 20.5 ish to meet somewhere in the middle.

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Sounds like you need to turn down the tank knob and lower the flowrate when using the flowcap. Too much flow will indeed raise the apparent PP but there is no need for that much flow.

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Originally Posted by JTB

when im in cave country I dont usually analyze the banked nitrox fills but always my trimix fills even if its banked.Up north here most shops have air fills only and if im getting 2-3 tanks filled i will usually only check one,, i guess now ill start using the analyzers i own a little more.

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I'm glad you've come to that conclusion, but story time for those who haven't...

I've seen 3 cases over the last 2 years or so where someone I know or myself has gotten a fill where the o2 percentage was WAY off from what they expect (as in 40% or so when expecting 32%). The shops were all cave shops where this happened, and no it wasn't the same shop each time.

None of us would go cave diving without a guideline, even though we stand some chance to recover from that, following flow, scratch marks, reading the cave, etc. A hyperoxic event is almost always unrecoverable.

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Originally Posted by tursiops

Sounds like you need to turn down the tank knob and lower the flowrate when using the flowcap. Too much flow will indeed raise the apparent PP but there is no need for that much flow.

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When using the flow cap there is always a flow restrictor between the cap and the first stage, so the flow is the same regardless of where the knob on the tank is, unless of course it is off :)
The restrictor was part of the analyzer package, so I just assume it give the needed flow, maybe not though.

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Originally Posted by scubadude

I have a couple of analyzers. I find that one (oxycheq expedition) that I hook to the bc hose with a flow restrictor and cap on the sensor interesting. If I remove the flow cap and calibrate ambient air in the house (climatized and not too much humidity) then calibrate using the cap and restrictor from a tank of air the readings are off more than I would expect from just a change in humidity since the temps of the ambient air and tank (which has been stored inside the home) are are essentially the same. I attribute it to a slight pressure increase in the flow cap, hence raising the PO2 for the tank/flowcap scenario. Tanks will always test about .6% higher when calibrated with the flow cap on an air tank as opposed to calibrating with the sensor exposed to air directly. I have an Oxycheq E'lCheapo that acts more like the expedition with the cap off.
Not a deal breaker, If I calibrate the expedition using ambient air I just set it to 20.5 ish to meet somewhere in the middle.

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More likely that the .006 error is due to humidity. Normal room air has moisture content, a "properly filled" tank of air has a moisture content of near zero (dew point -60 or lower). So the room air shows a slightly lower O2 content due to "normal" humidity.

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Originally Posted by scubadude

When using the flow cap there is always a flow restrictor between the cap and the first stage, so the flow is the same regardless of where the knob on the tank is, unless of course it is off :)
The restrictor was part of the analyzer package, so I just assume it give the needed flow, maybe not though.

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Check your assumption: run the analyser with the knob up high, then low, then almost off. Should be the same gas, but the analysis will drop. The "flow cap" mostly just protects the analyser's sensor so you don't blow it out. Best practice is turning the flow on first, feeling that it is only just barely on, then putting the flow cap against the valve.

Who DOESN"T analyze their gas, you ask? Why Chuck Norris does not. Oxygen gets Chuck Norris poisoning, not the other way around.

I did check the assumption this way; Turn on the tank, the 1st stage is pressurized and the output to the BC hose is the 1st stage IP regardless of where the tank knob is set (unless off), then to the flow restrictor (which sees the IP only) then to the flow cap over the sensor. I can crack the tank valve open which pressures up all HP and LP hoses on the setup, then turn off the tank and the O2 reading stays the same as the pressure in all the hoses depletes to a point that affects the IP, then at that point is when a change in the O2 reading will occur. The bleed down takes tens of seconds to finish depending on the hoses on the reg setup. So the flow is stable no matter where the tank knob is until IP is affected.

The O2 reading change I was referring to above is .06 not .006, not sure if the humid diff would account for a whole .06, but I guess I could look that up somewhere.

Sorry if I hijacked the thread, just thought since we were on that topic, someone may have experienced the same thing.

On topic: I have personally witnessed a FullCave/Instructor that was diving with a group of request air instead of ean32 at one of the big cave shops in order to make some short dives with us, to save $ on fills I guess, since the dives were to be short. The air diver never tested the tanks since air was ordered. The rest of us ordered ean32. The result was we all got an ean32 fill. One of the group noted that the tanks seemed to all be filled together at the same time. Once the air tanks was tested it came in around 30%.

It might not be completely the same but it's a funny story. We drove up to the Pike Peak visitor center, it is at about 14,000. my wife and I walked all around the area checking out things with no ill effect. Her Daughter was about 11 at the time took ten steps out of the car and just about passed out. The point being different people are effected differently and all of our data is Guidelines and must be verified independently for you.

@scubadude
Sorry, man, ignore almost everything I said to you! I misunderstood your setup. I thought you were blowing air directly from the tank valve onto the cap on the analyzer; I missed that you were using a BC hose with a flow-restrictor on it.

The info you are looking for is in post #17 in this thread. It's pretty easy to get 0.6% error from the humidity in the room.

There are four main sources of error in the analysis: temp, humidity, barometric pressure, and flow rate onto the sensor. Calibrating to a tank of room temp air takes care of the first three; the flow restrictor takes care of the fourth.

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Originally Posted by tursiops

Who ever said to calibrate off a tank of who knows what? Calibrate to a tank of air; it'll be dry, and not likely to be at 90 F.

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The other day I analyzed a tank that I thought was air. It was supposed to be air. The fill station where it came from only has air. We're not supposed to put anything but air inside of any of the tanks in our dive locker.

It had 26% in it.

Apparently, someone borrowed some of the tanks, filled them with nitrox somewhere else, and dove them. Then returned them without properly marking them.

I think the people that are calibrating on ambient air are probably onto something.

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Originally Posted by kensuf

I think the people that are calibrating on ambient air are probably onto something.

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Nope Spelodiver and Geschaut (sp?) have it right, only way to calibrate anything is with a known standard, one where all the variables are controlled

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Originally Posted by a64pilot

Nope Spelodiver and Geschaut (sp?) have it right, only way to calibrate anything is with a known standard, one where all the variables are controlled

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True, but the "known standard" should be marked as such.

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Originally Posted by FW

True, but the "known standard" should be marked as such.

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Absolutely but at some point that tank had an analizer put on it. So when and how was that tank analized? Most shops I deal with in the great white north have tanks that are only for calibration purposes and are certified to be 20.8 when their fill station is certified. I know the folks and trust them but I still double check with my O2/He analizer and my Co analizer because mistakes happen and it's my life.

I always analyze my gas at the dive shops so when I get to the dive site, I just pull my tanks out and go.

This way you can fix any mistakes made while there instead of waiting until you get to your dive destination only to realize your gas is the wrong mix or bad gas.

Every shop has an analyzer. If they don't... you really don't want to be doing business with them.

As for calibrating the tester, I always remove the caps, wave it around back and forth in the air and adjust from there.
After a test or two, the gasses get trapped inside the cap and cause it to read incorrectly, so every few tanks, I take the cap back off and let it "air out" so it reads ambient air again.

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Originally Posted by a64pilot

Nope Spelodiver and Geschaut (sp?) have it right, only way to calibrate anything is with a known standard, one where all the variables are controlled

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http://www.brandtinst.com/Gasco/Gasc..._Cylinder.html

In the fire dept, we use small cylinders of known, certified gas content (bump gas) to test and calibrate our gas meters. Granted, we are metering for different gas values than diving. But the principal is the same.

For diving, I usually just calibrate my O2 meter to both ambient air (with temperature/humidity compensation table), then recheck the meter on a 100% oxygen gas supply at the fill station. If the values I get on the meter are close to 100% on the O2 source, I presume that the O2 meter is properly calibrated. The odds of having BOTH a meter calibration error on my O2 meter AND the shop's Oxygen tanks contaminated with less than 100% oxygen (to the EXACT same level as the meter error) are small enough I can live with it.

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Originally Posted by corvettejoe

Every shop has an analyzer. If they don't... you really don't want to be doing business with them.

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Every cave country shop has an O2 analyzer... Amigos is the only one I've personally seen with a CO2 analyser for customers to use. Which other cave shops have CO2 analysers for customers to use?

I looked at the linked abstract, and I'd really like to know what units they were using. If they were using grams/deciliter, which is the usual in the US, the reduction is enormous and frankly unbelievable. If they were using grams/liter, it was about an 8% reduction, which is honestly still a bit surprising, but more reasonable.

The difference in magnitude of effect between hypoxia and hyperoxia is easy to understand if you understand the dynamics of oxygen in the blood. It isn't dissolved . . . it's carried on hemoglobin. At sea level, breathing air with normal lungs, hemoglobin is between 99 and 100% saturated; raising the inspired ppO2 results in very little additional oxygen content in the blood, as oxygen is very poorly soluble in plasma. On the other hand, lowering the inspired ppO2 results in very little content change at first, but once you hit a threshold, the content falls very fast, as the hemoglobin is desaturated. Poor oxygen content is what stimulates the kidneys to release the hormone that causes red blood cells to be made. The process is not instant, which is why Jax mentioned the waiting period for exercising testing at altitude.

The lack of change in O2 content is why I wouldn't expect to see a big change in red cell count with prolonged hyperoxia. Apparently there is some effect, but if the units are what I suspect, it's pretty small. (In contrast, the hematocrit can go up 25% or more in chronic hypoxia.)

Oh, and I label my tanks to the .1% . . . it makes sure I know I've actually analyzed the tank, and not labeled it for desired content.

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Originally Posted by Greenwood_60

Every cave country shop has an O2 analyzer... Amigos is the only one I've personally seen with a CO2 analyser for customers to use. Which other cave shops have CO2 analysers for customers to use?

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Should that read "CO analyser"?

Ugh, yeah. My mistake.

Pretty sure I have used a CO analyzer at Cave Country Dive Shop. If it is not sitting out and available, just ask and I'm sure the staff will be happy to provide it for your use.

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Originally Posted by cavman

Pretty sure I have used a CO analyzer at Cave Country Dive Shop. If it is not sitting out and available, just ask and I'm sure the staff will be happy to provide it for your use.

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I can confirm that Cave Country has a CO meter, I have seen tanks analyzed while I was getting fills.

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Originally Posted by amphipod06

A thermometer measures temperature...a hygrometer measures humidity...

Back to my rock...

Dive safe,
Ч
Celia

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Actually a thermometer and some water is pretty much all you need to find out what the ambient humidity is.

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Originally Posted by Greenwood_60

Every cave country shop has an O2 analyzer... Amigos is the only one I've personally seen with a CO2 analyser for customers to use. Which other cave shops have CO2 analysers for customers to use?

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That would be good to know! Since I've been made aware of the dangers of CO, I've been using my buddy's analyzer mostly and just never checked at the shops I use to see if they have one.
It's on my Christmas list this year to get my own analyzers though.

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Originally Posted by Greenwood_60

Every cave country shop has an O2 analyzer... Amigos is the only one I've personally seen with a CO2 analyser for customers to use. Which other cave shops have CO2 analysers for customers to use?

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given heightened awareness of CO analyzing over the past couple years, I was very surprised I couldn't get my hands on one at either CE or DO on our way to peacock.... I had just dove the day before with the guys that had the symptoms of possible bad gas (the initial reason for this thread) and really wanted to test their tanks. No luck at either location so I bit the bullet and ordered one from Edd. Thankfully the tanks tested clean, so at this point we decided it was probably just over exertion.