Three dead and one in recompression chamber in Italy, Tuscany

[boulderjohn]

Yes I recall the care needed to produce nitrox now, after reading your post.

I did not want to complicate the first post by giving too much detail, but I figure someone is going to come in to correct me, so I will add that there would be a difference in the oxygen level of nitrox if the air being used is contaminated, with the degree depending upon hos the nitrox is being made. It would be a very small amount, though, and the degree to which it could be detected would be diminished by the percentage of pure oxygen in the mix. Any lessened degree of oxygen in the air would be better detected by putting an oxygen analyzer on a tank containing nothing but the undiluted potentially contaminated air.

 

[gianaameri]

Sorry guys, but there is just no way you can detect CO with an O2 analyser (and won't go in the technicalities).

Lesson learnt here is that those who sell gas should test it with a CO analyser before releasing it to the end-user.

It would be prudent for the end-user to test the tanks as well with a CO analyser (since it is not done as a matter of course by Dive Shops and in any event why trust the Dive Shop with your own life???).

Two suppliers:

EII CO Carbon Monoxide Analyzer: Analox - Looking after the air you breathe.

http://www.temc.it/en/diving/de-ox-safe-carbon-monoxide-analyzer

 

[TN-Steve]

Could we? Not trying to sharpshoot you, but I think you overlooked something. With the CO aren't we looking at something like parts per million, so even a high concentration , say 100 PPM maps to a very tiny fraction of the overall percentage. I'm not familiar with the O2 testers used, but from what I've seen, it looks like they, at most, read to 1 or maybe 2 decimal points. 100 PPM should work out to 0.001%. (and I may have 1 too few "0"s).

I'm not sure that we could pick up the CO content unless it was so high that it would be a significant portion of the gas, say 2-3%.

If I'm wrong, please let me know, like I said, not trying to sharpshoot you, just doesn't compute in my brain.

Steve

I did not want to complicate the first post by giving too much detail, but I figure someone is going to come in to correct me, so I will add that there would be a difference in the oxygen level of nitrox if the air being used is contaminated, with the degree depending upon hos the nitrox is being made. It would be a very small amount, though, and the degree to which it could be detected would be diminished by the percentage of pure oxygen in the mix. Any lessened degree of oxygen in the air would be better detected by putting an oxygen analyzer on a tank containing nothing but the undiluted potentially contaminated air.

 

[boulderjohn]

Could we? Not trying to sharpshoot you, but I think you overlooked something. With the CO aren't we looking at something like parts per million, so even a high concentration , say 100 PPM maps to a very tiny fraction of the overall percentage. I'm not familiar with the O2 testers used, but from what I've seen, it looks like they, at most, read to 1 or maybe 2 decimal points. 100 PPM should work out to 0.001%. (and I may have 1 too few "0"s).

I'm not sure that we could pick up the CO content unless it was so high that it would be a significant portion of the gas, say 2-3%.

If I'm wrong, please let me know, like I said, not trying to sharpshoot you, just doesn't compute in my brain.

Steve

That's why I said it would be a very small amount. I was adding to my earlier point that it would not be detectable given the normal range of an oxygen meter. I should have been more emphatic about that--sorry.

 

[TN-Steve]

That's why I said it would be a very small amount. I was adding to my earlier point that it would not be detectable given the normal range of an oxygen meter. I should have been more emphatic about that--sorry.

Ah...my bad. That's what I get for not always checking earlier posts. I didn't think that was where you were going, and now I know that you weren't...

Thanks

Steve

 

[Pearlman]

Pearlman,
I do not believe using NITROX would solve the issue.
Nitrox is done by continuosly mixing Oxy and air and then going into the compressor, loading oxy in the tanks and then air or using a Nitrox unit removing nitrogen from air and then going into the high pressure compressor.

Since the CO most of the time comes from high pressure compressor overheating and burning lubricating oil, you would end up with CO laced NITROX in the tank.


As DandyDon says test it or dive on hope!

Fabio

OK. From a chemistry perspective - CO and O2 won't mix, is that correct? So you can have 32% O2 in a tank and also some CO ?

I guess my confusion stems from a lack of understanding of this.

P

 

[tbone1004]

Pearlman, it's more of the way they are mixed. 1ppm is .0001% O2 sensors are not sensitive enough to detect that, and more importantly, due to the way nitrox is blended, you see a variation of around 1% in O2 percentage regularly. CO analyzer is the only way to test for it.

 

[boulderjohn]

OK. From a chemistry perspective - CO and O2 won't mix, is that correct? So you can have 32% O2 in a tank and also some CO ?

I guess my confusion stems from a lack of understanding of this.

P

Of course.

Nitrox is made in several different ways. All ways include a compressor with an air intake. If the intake brings in contaminated air to the mixing process, then the nitrox will be contaminated. If the compressor creates its own CO (as described above), it will get into the final mix.

 

[fsardone]

Pearlman, it's more of the way they are mixed. 1ppm is .0001% O2 sensors are not sensitive enough to detect that, and more importantly, due to the way nitrox is blended, you see a variation of around 1% in O2 percentage regularly. CO analyzer is the only way to test for it.

This is now becoming a tech diving/gas blending thread, but given the outcome of the incident I feel it appropriate. Even because you do not need to be tech diving to have benefit from understanding gases and how they interact with your body.

I am in Europe and I will be referring to BS EN12021 which is the standard for breathable air which says that breathable air should not contain more than 15 ppm of CO.

I can already hear DandyDon scream out loud "too much" and he is right. I will explain why.

If you look up CO intoxication you will see that 100 ppm are able to give significative clinical symptoms of CO poisoning but this is at 1 bar. 100 ppm is 0,01% (I did check my exponents ) which using the dalton law gives me a ppCO 0,01 bar (ppO2 at that point would be 0,21 bar). You will remember that physiological effects of gas are function of partial pressure and not concentration. That is why 21% of oxy is ok on surface but when I dive to 80 meters I dive 15% oxy (or even less): to keep ppO2 within limits.

Now if I have a tank containing 15ppm CO (0,0015%) and I dive to 56 meters (sorry metric is easier) which is 6.6 bar my ppCO is again 0,01 bar which is enough to give me clinical symptoms (ppO2 in air is 1,386 bar!). Add this to the fact you might be diving air (like the victims) because you are not trimix certified or it is too expensive or is not available and you have the narcotic effect of high ppN2. So double jeopardy incapacitated by Nitrogen and by CO intoxication.

So even if a compressor is certified to stay within standards (BS EN 12021) it might be not enough for deep diving and deep diving might be as little as 40 meters (5 bar) in air or 60/70 in Trimix (since you are using 30-50% helium even if air from compressor was 15ppm you are using about half of it, while the rest is made up with helium/oxygen so you end up with 7-8 ppm). Fact is the standard is made for scuba and surface breathing apparatus but not taking into the account those crazy people diving way past the recreational limits like myself. Those need to be able to take care of themselves .

Hope this is of use.

I will join DandyDon Crusade DAN Europe is now carrying a CO analyser in their shop (available from Sep 14).

Fabio

 

[gianaameri]

I cannot see any reason for accepting any CO in SCUBA gases as an end-user.

It just should not be there.

If you get any, buy your gas elsewhere.