Testing Air Quality

[Web Monkey]

Hi All,

I'm curious how you guys test the quality of the gas for filling tanks?
What do you test for and at what levels?

Best Max

I get all my air from places I trust.

The actual analysis is done by a lab (as was mentioned), but the analysis is a lot like a VIP. It only proves that the air was good (or not) at the time the analysis was performed.

Some shops have been known to have their air intake in areas with intermittent pollution (like the parking lot), which would make the air just fine, or horribly toxic depending on what was going on near the air intake while the compressor was running.

If you want to be reasonably certain of getting good air, buy it from a place that has testing from a real lab, posts the results, and who you trust to not do anything dumb.

Terry

 

[rjack321]

CO2 is always tested for in breathing air. We actually had a sample fail CSA standards because CO2 was over the 500ppm allowable. It turned out not opening the window when running the compressor (inlet inside dive shop) was the cause but the standard for CSA is 500ppm and Grade E breathing air is 1000ppm we were 725ppm

In line, real time? That would be a rarity.

At a lab, sure its SOP.

 

[rjack321]

I'm surprised that there doesn't exist a piece of equipment that can test CO2, O2, CO and Humidity?
Something inline / realtime, that can give the operator realtime feedback as to what goes in the tank? It just seems to make sense to me. A lot of factors can change from the time a sample is taken and sent to a lab and the results are returned. Also, a lot of tanks can be filled in the same amount of time.
Am I missing something here?

Those monitors are all available. But you'd be missing total hydrocarbons - probably one of the most important.

You'd idea of an all in one unit is a good one, getting it calibrated might be a slight issue. Although CO2 and CO calibration standards are pretty cheap. Getting the industry to buy into it would be difficult. There's limited knowledge of breathing gas contaminants. Most compressor manufacturers don't know much either. Bauer being the notable exception.

 

[Mad_Max]

I really appreciate the time and input from everyone as I try and understand all of this.
So far I don't see any "show stoppers" for a design of something to measure most of these things "real time" in a flow thru "manner".

A couple of things that I don't understand:
Which total hydrocarbons would you want to screen for?
What level of humidity would you want to check for and at what resolution? I'm not sure why you test for humidity? I would have thought that because the air is compressed, it's already dry?

 

[rjack321]

total volatile hydrocarbons = thousands of potential chemicals. All the BTEX compounds, phthalates, solvents like acetone, true volatiles like styrene and vinyl chloride. The list is pretty substantial. These things are narcotic, potentially toxic esp. under higher PP, and sometimes carcinogenic.

There are broad spectrum analyzers like an FID, but they are coarse measures and I'm not sure they get down into the low/sub ppm range. GC-MS is SOP nowadays.

Compressed air is only really dry dry when it expands. In the compressed state its 5-20% RH typically. Moisture is an indicator of how good your filters are working and if they are spent. Its also critical to have a very low dew point for ice diving. The grade E limit is 24 ppm water.

 

[omar]

For a real time inline gas analyzer for scuba shops you would probably need a unit that could detect and provide sufficient resoultion to demonstrate that air is meeting CGA Grade E air.

CGA GRADE E AIR
Carbon Monoxide <2ppm
Carbon Dioxide <500ppm
Dew point -50º
Gaseous Hydrocarbons <25ppm
Condensed Hydrocarbons <.1ppm
Particulate Matter <2 microns

 

[rjack321]

And for nitrox those limits go down to 2ppm for CO and 0.05ppm condensed hydrocarbons if I recall correctly.

9.9ppm CO is really unacceptable in my book - regardless of the CGA standard.

 

[Mad_Max]

I think all of that is doable, I'm just not sure if it's worth the effort to build and sell something like this?
Assuming calibration wasn't an issue, for something like what we're talking about here; what price do you think the market could bear?

 

[Surface Tension]

The most common source of hydrocarbon contamination is the compressor oil.

Moisture is usually monitored to signal when the filter dessicant is shot and needs to be replaced.

A good filtration system should be removing normal amounts of these contaminates. If you think there is a risk of CO, you add hypcolite to the filter stack.

If you are seeing the contaminates in your final air it's more a syptom of a sick filter rather than bad intake air.

I monitor O2 in the final air because I continuous blend nitrox. Other than that I have a color indicating humidity strip to let me know when to replace my filter cartridge.

Dave

 

[ageddiver]

Here is a real-time monitor for RH, CO2 and CO we use for indoor air quality monitoring where I work - also works great for my compressor http://www.tsi.com/Product.aspx?Pid=19
Unfortunately it requires periodic calibrations with gases that make it impractical for the average joe. For breathing gas you don't need a GC-MS analysis for VOC's - you're only interested in the total. You'd only use the lab instrument if you needed to know exactly what organic compounds were there, for example if trying to locate the source. I use a small device (again from work) that will measure part per billion levels. Costs about $4K.
When I analyze I routinely see CO at <1ppm (non-detectable), RH at 2% (very dry), CO2 at around 350ppm (normal outdoor levels), and total VOC's at background (outdoor) levels.

I'd recommend Drager tubes for anyone wanting to analyze compressor air and with no access to other testing equipment. You have to buy a pump that will pull a measured amount of air through the tubes, but you'll get a pretty accurate measurement by watching color changes in the tubes, and they come for measuring just about anything.