Sources of CO in compressed air

[SCUBA_Phil]

Another source of CO is the filter stack itself. This source is very small and only happens under the right circumstances. Here is my experience. I have a 7 cuft/min electric compressor. The filter (LF) is rated for 20 hours @ 70F. This measurement was taken with ~11 hours on the filter. I had just bought a Analox CO tester and started to test my tanks (including my bank bottles). Every thing tested 000 PPM CO. I had not run the compressor in 4 weeks and decided to test the residual air in the line. It measured 25 PPM CO. I blew down the line and started the compressor. The new air was measuring 000 PPM. A call to the manufacture cleared up what happened. If you don't run the compressor for a while and the pressure drops in the filter stack, the cartridge will release CO. I do not have any sources of CO near the compressor. My guess is that the nominal CO in the air gets removed by the filter stack, but then it can be released. In my case, once the filter stack is under pressure, it produces grade E air with no CO detectable. I now check it at start up and and the end. The reality of my findings is that this is a very small amount of CO. If I did not detect it, is would have amounted to ~0.5 cuft and would have been diluted by the remaining grade E air. Lesson learned for me: monitor the CO levels while running the compressor! Note: I have my PMV set at 2000 PSI

 

[Stoo]

And my life is worth more than the $150 it costs to buy a CO analyzer.

I purchased an Analox CO analyzer recently, but oddly, I haven't found the "definitive word" on what level of CO is deemed acceptable, if any. Analoz says check with your "local authorities" (Huh?), I wrote to DAN, but they never responded...

Is there a common value that is widely accepted...?

 

[swamp diver]

I purchased an Analox CO analyzer recently, but oddly, I haven't found the "definitive word" on what level of CO is deemed acceptable, if any. Analoz says check with your "local authorities" (Huh?), I wrote to DAN, but they never responded...

Is there a common value that is widely accepted...?

Why don't you use what is listed in the most recent Canadian Standards Association (CSA) commercial dive standard 275.2 (2011)?

For air and nitrox the maximum CO permitted is 3 ppm and for trimix it is 1 ppm. Of course if you are running a catalyst bed and have CO monitoring on the compressor as required by the standard you're CO level will always be < 1 ppm.

Some jurisdictions allow higher amounts but this is often because the local compressed breathing air standard has not been updated for years in order to reflect the most recent science on the topic of CO toxicity.

The Brits also allow only 3 ppm for air diving, the Euros allow 15 ppm but this will likely drop to 5 ppm in the next version, and the Americans allow 10 ppm (CGA Grade E). The US fire services though whose standard committee updates their document every 4 years now allow a maximum CO exposure for fire fighters at 1 atmosphere of 5 ppm.

If you are older (>50) or on any sort of BP or diabetes medication I'd certainly stick to the 3 ppm maximum that the Brits and Canadians adhere to. If younger and with no health problems you could problem get away with 5 ppm for air diving, but the bottom line is that there really should be no CO in the compressed air from a properly maintained compressor and seeing any CO > 1 ppm should be a red flag to remain vigilante at that fill station.

 

[Dive-aholic]

I purchased an Analox CO analyzer recently, but oddly, I haven't found the "definitive word" on what level of CO is deemed acceptable, if any. Analoz says check with your "local authorities" (Huh?), I wrote to DAN, but they never responded...

Is there a common value that is widely accepted...?

Industry standard seems to be 10 ppm for grade E scuba air and 3 ppm for oxygen compatible scuba air. Personally, I have zero tolerance for my own compressors. For travel, I go with the 10 ppm. However, if I get a positive reading the dive op hears about it.

 

[Scared Silly]

I am with Swamp Diver 3ppm is my limit.

If I get a reading of 1 ppm I do not worry, if I get a reading of 2 ppm I tell the dive op and watch for other cylinders. If none found I will take it as an outlier (i.e. hot compressor, last bottle of the day). If 3ppm I reject the cylinder, will not dive it, and of course alert the dive op.

 

[Stoo]

Thanks folks... I'm not concerned "here" as all the shops I use do have inline CO monitors and zero tolerance. The reason for my question (and the reason I bought the analyzer) is for testing gas when I am away. I'm off to a fairly remote location in Belize in a couple of weeks, and while I have no reason to doubt the quality of the air, it ain't like it's a big deal to take this thing...

 

[JayScuba]

I believe the main source of lethal CO contamination in Scuba air is when a compressor has not been properly maintained for quite some time, and the rings on the pistons allow compressor oil to pass into the compression chamber. Then the oil then ignites essentially the same way as a diesel engine, from the heat of compression. In this case, the compressor needs to be re-built. Since CO is odorless and tasteless, you will never know unless you test.

In my experience, funky tasting air is generally a result of either bad 4^th stage air filter and or bad water separator, ie not drained or auto drain is malfunctioning. It has nothing to do with CO.
Most gasoline compressors have the intake filter right near the compressor fan and the engine exhaust on the other side of the compressor so exhaust is blown away from the intake filter and the intake filter gets very fresh air. Obviously if this is inside, you may have a problem, but who runs a gas compressor inside??
A good compressor has pressure gauges for each stage. If the pressure of any of these gauges drops significantly from when the compressor is new, you potentially have bad rings and a potential for CO. You need to rebuild.

A good dive shop tests their air every quarter so they are quite safe. Also there are many systems for checking CO inline. I expect most dive shops use these.
Personally, I have a portable CO tester that I use when I travel to Mexico and the Caribbean. Compressor oil is expensive and these guys run on shoestring budgets, so they may not spend all the money needed to properly maintain compressors.

 

[victorzamora]

.....all the shops I use do have inline CO monitors and zero tolerance.....

So did the fill station I used in Mx for caves. I still found CO according to my analyzer. They found out about it (I told them and then showed them) and they apparently started a pretty hefty investigation. It was a low reading (3ppm), and I did the dive anyway, but I informed them. Another fill station with the same setup/policy showed 6ppm for OW dives. They heard about it, looked into it, and we all believe it may have been exhaust from the boat....but they checked their sensors multiple times as well.

 

[Stoo]

So did the fill station I used in Mx for caves. I still found CO according to my analyzer.

I guess the inline analyzer is great, but it doesn't "fix" bad air. If nobody is checking the CO monitor, then it's perfectly plausible that you could get a raunchy fill...

 

[victorzamora]

I guess the inline analyzer is great, but it doesn't "fix" bad air. If nobody is checking the CO monitor, then it's perfectly plausible that you could get a raunchy fill...

.....or that technology fails and can't be trusted explicitly. Multiple levels of confirmation are the only thing that will convince me.