SB Forum--Bad Air Incident

[aa3jy]

Copied from the SB forum...though not cave related but content has bearing here..
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"Bad air originating in tank and not compressor
I posted this in response to a thread talking about sources of CO in breathing gas but decided to post in the Accidents and Incidents Forum as the results could have been serious:

I have just returned from a trip to the Caribbean and I am really glad that I took my Analox CO analyzer there. The resort has always provided clean air and just recently installed a new compressor and bought new steel tanks. First day of diving I tested my own tank and as expected it read 0 ppm. I gave the analyzer to my son to test his own tank. He called out and said his tank was reading 75 ppm so I assumed he had done something wrong and upset the calibration. I re-calibrated it to ambient air and then went to show him what he did wrong. Meter read 81 ppm which I thought was damned near impossible so I tested my own tank again and every other tank that was set up for the divers. Sure enough none of the other tanks registered more than 1 ppm. Tested my son's tank yet again and it still read 81 ppm, replaced his tank with a new one and set the contaminated tank to drain. When the interior of the tank was inspected they found 3" of seawater and a great deal of rust, somehow the tank had drained and had must of taken on seawater when being swum in from the boat. Hate to think of what would have happened if my son had used the tank. It also goes to show that an inline tester on the compressor would not have prevented this incident. I have vowed to test every tank that I, my son or my dive buddies dives regardless of the reliability of the source. I am sure that the other divers that were present will be in the market for an CO analyzer."

[Sludge]

I have vowed to test every tank that I, my son or my dive buddies dives regardless of the reliability of the source.

[Greenwood_60]

Interesting. How does salt water cause 81 ppm of CO?

[nakatomi]

Wow, that is so awesome you caught that one!!

[mbaker]

Interesting. How does salt water cause 81 ppm of CO?

I am not a chemist and would also like to know the answer to this question. Possibilty exists that perhaps the rusting of the cylinder cause build up of CO or yet another gas that the analyzers sensor reacted to? Sadly I have not yet seen any of the manufacturers chime in on any threads related to CO analyzers in attempt to clarify any questions people have posted regarding readings straying from zero with higher oxygen content and so forth. I get the feeling that nobody knows the answers......

[nakatomi]

This is not the first time I have heard that CO may be the result of a chemical reaction of partial pressure blending in a rusty tank.

About the analyzer readings, mine works great and is very reliable. While I've heard that newer models of the Sensorcon may possibly show a higher ppm reading under pressure, I am sure with a proper flow rate (I think 50liter per minute) the reading will be fine.

If in doubt about the proper readings, you could always buy a calibration gas, which is not all that expensive. The 10ppm version for the Analox works great with all analyzers.

[mbaker]

http://www.cavediver.net/forum/showt...light=analyzer

Look back on this thread.

[nakatomi]

Interesting Mike. The Sensorcon reads 0ppm on O2, which I also analyze every time. Same with the Analox that I borrowed from Rob before I got my own analyzer.

[Rhino]

Not wanting to rehash the old thread (you can access the link in this thread contained in a previous post), below is a link to the Analox bump gas for illustration. Just to clarify for the uninitiated, bump gas is not intended for "calibration." According to Analox, with their 10 ppm bump gas, if you get a reading above 5 with bump testing, then you're analyzer is good to go to test breathing gas. Frankly, when I asked an Anolox employee about using their bump gas, the rep explained that for bump testing the "breath hold and blow test" was fine (telling me that I could save my money instead of buying their bump gas).

http://www.analox.net/proddetail.php...ctid=95&ref=22

[skip]

Interesting. How does salt water cause 81 ppm of CO?

Yes, how is that? Something to do with rusting? But where does the Carbon come from? Sources might be: Wrong lube used after O2 cleaning, from stuff in the salt water, or filling with "dirty" air that had not filtered all the carbon. Rusting would not do it. Iron Oxide. Reduces O2 for sure, but does not increase CO unless there was X amount of CO to start with and O2 is removed; CO stays the same in absolute amount, but now a bigger partial percentage. ??

skip