Thread: Acetylene incidents
06-19-2009, 12:41 PM #1
- Join Date
- Jan 2004
My dept has had 2 incidents on the last year where we where dispatched to a c/o alarm sounding. On both occasions it was discovered that contractors where using a acetylene torch that was leaking. Our 4 gas meter was detecing C/O but the detector was not acting normal. I have read that Acetylene is extremely flamable. Should we purchase a meter for Acetylene? Could I get some advice on how to handle this type of situation
06-19-2009, 03:32 PM #2
CO sensors are sensitive to a number of other gases including Acetylene. We mostly run into hydrogen from charging batteries, but you can look up quite a few others. The tricky thing is that the concentrations are very low, so it doesn't show up as a percentage of the LEL, but will show up in the PPM range. A separate meter is not really necessary, but if you buy a new one, look for a 4 gas that measures flammable gases starting in the PPM range and then moving into LEL.
06-19-2009, 06:49 PM #3
Acetylene has a LEL of 2.5% and a UEL of 100%. It is never too rich to burn.
It also has a IP of 11.40, so most PIDs aren't going to detect it.
Here are a couple of references:
If you're going to see these situations often, a detection method (colorimetric tubes maybe?) would be a good idea. Some HAZMAT training wouldn't hurt either.
Last edited by EFD840; 06-19-2009 at 06:51 PM.
06-19-2009, 08:19 PM #4
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- Jan 2004
Last edited by BHFF22; 06-19-2009 at 11:18 PM.
06-29-2009, 12:35 PM #5
- Join Date
- May 2009
- Livonia, MI
I know the writer over at the Incident Commander responded to you by email, but I thought I'd post the response here in case anyone else was curious.
We went to our favorite, GfG Instrumentation, to get a direct answer from a manufacturer.
"A CO sensor will respond to some hydrocarbons as well as hydrogen.
As far as hydrogen goes there are special sensors available that have a much smaller cross sensitivity.
Two common hydrocarbons that with cause the CO sensor to respond are Ethylene and Acetylene, both with an approximately 50% cross sensitivity factor.
This means that a 100 PPM concentration of acetylene in air will result in a reading of about 50 PPM on the CO channel.
Acetylene has a lower explosive limit of 2.5%/vol (25,000 PPM). and an LEL sensor calibrated to a methane scale will provide a 90% relative response to acetylene.
This means that a 100% LEL concentration of acetylene will result in a 90% reading on the LEL channel.
In other words a 1% LEL reading caused by acetylene means that the actual concentration is 1.11% LEL or 277 PPM C2H2.
A concentration of 277 PPM C2H2 will result in a reading on the CO channel of roughly 140 PPM.
Depending on the gas detector used the typical lowest reading on the LEL channel is either 1 or 2% LEL, thus may not respond before the concentration is over 500 PPM where the CO sensor at this point will be reading 250 PPM.
A CO sensor does not get damaged by moderate exposure to LEL concentration of C2H2, however, it may take a long time for the sensor to clear and in some cases the exposure may cause a permanent baseline shift.
Such baseline shift can generally be corrected by performing a zero calibration after the sensor has fully cleared.
Finally, I cannot stress enough the importance of frequent verification of sensor accuracy.
This is true more so for the LEL sensor than any other because certain common compounds and damage the sensor and as a consequence can cause it to fail to responds sufficiently to combustible gases."
In addition from http://incidentcommander.blogspot.com/ 's writer:
"Larsí answer is very similar to believe on the topic, with the caveat that different brands sometimes have slightly different cross-over issues between gases. The majority of sensors in field use (save infrared, PIDs, paramagnetic, FIDs and a few other rare ones) are provided by either CitiCell or Figaro, although there are several more recent intrusions into the market from India and Korea. What Iím saying is that CitiCell still most likely provides the detectors cells for the catalytic bead your Lumidor is probably using.
So, there may be slight differences in cross-over for the LEL sensor your using between CO and acetylene, and the cross-over for the same regarding the house CO alarm, but there is always cross-over potential.
This all leads me to believe that you were right to be concerned about acetylene and its associated flammability issues."
Hope this helps anyone else who may have run into the same issue.
09-09-2009, 07:59 AM #6
Industrial scientific reports that 100ppm of acetylene across a CO sensor responds at 140ppm. The response is not linear! I can get a hit with my pid on acetylene at room temperature...why? Acetylene is disolved in acetone ( i forget the term after 20 years) acetone vp180mmHg, ip 10.16eV.....relative response and cross sensitivity both important as flammability and toxicity the point is to protect yourself and others given the tools with limitations both technical and cranial...lolExcuse me while I FART. Find A Recent Text.
10-03-2009, 03:33 AM #7
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- Dec 2008
- Great State of Texas
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