- Joined
- Dec 25, 2017
- Messages
- 141
Bottom Line Up Front:
Acetylene leaking from your left-open bottle can trigger a room-air CO alarm/monitor.
This is challenging to track down in the face of uncertainty as your CO alarm does not differentiate between actual CO and a number of other gasses that can cause interference. It is imperative that one always treat the CO alarm as indicating a real threat to your life.
Here is my recent experience (abridged):
In my 1000 square-foot stand-alone shop I found my ceiling-mounted garden variety CO alarm triggered. The only source of actual CO is the rooftop AC/gas heat package unit. I shut the heat off and opened doors to let in a chilly cross breeze. After a while I replaced the batteries and reset the CO monitor. Closed the shop, heat still off. About an hour later it went off again.
This second alarm was puzzling, but maybe some residual CO was loitering in the space. Or, maybe the CO alarm was broken or at end of life.
I did some reading about CO alarm levels. Many of them go off at 50 ppm. 50ppm is the 8 hour exposure limit.
Bought a second sensor from the orange big box store. This one is by Kidde and has a digital display of CO concentration in ppm. I placed that in my shop, which had been closed for a few hours, heat off. It soon displayed about 35 ppm!! (This is peeking at it from outside.) This was concerning. I opened the doors to the cross breeze. After a while (20 minutes??) the reading dropped to 0 (zero) ppm.
I closed the shop and did other stuff all day. When I returned home the CO reading was about 40 ppm!
Even though the heat had been off more than 24 hours, I shut off the gas to the building. Now I am reading about sources of false CO alarms. Many web sites discuss charging of lead-acid batteries as being implicated (one story is a golf cart being charged in a garage). Indeed, over-charging a battery can cause significant release of hydrogen gas, which will set off an alarm.
Well, I have 3 lead-acid batteries in there, always on battery maintainers. I shut off battery charging. Ventilated the space again. Closed it over night.
In the morning the reading was something like 45 ppm. The high-reading memory had stored about 110 ppm.
Well, more reading eventually revealed a few stories of acetylene bottles causing CO alarms. In one case a contractor had left an (I assume open) bottle in a basement where they were doing piping work.
As it turns out, just about a week ago I was educating myself about acetylene safety. That is when I discovered safe practices of never letting a bottle drop below 25 psi in the tank AND never using more than 15 psi in the hose. There are also limits on flow rate based on bottle size. (I’ll post separately about this if folks are interested.)
I had decided to mark my regulator gauges with a red Sharpie at 25 psi bottle pressure and 15 psi hose pressure. At the same time, I opened the tank valve to check the pressure in the tank.
So, now it dawns on me that I must have left the bottle valve open. I went out there, and sure enough found the open bottle valve and noticed the tank pressure was down about 100 psi from a week ago.
Now the scientist in me points the torch at the CO sensor snout and gives it a short dose of acetylene. Within a few minute that CO sensor pegged at 999ppm full scale.
I closed the acetylene bottle and put the OA rig outside. Ventilated the shop for a couple of hours. The CO sensor was still reading 999, well saturated. I closed the shop up, put the heat back ON, and did something else for the afternoon. That evening the CO sensor had come off saturation and was reading 0 (zero) ppm. I turned on the battery chargers. In the morning I still had 0 ppm. I put the OA setup with closed bottles back inside. Reading have stayed at 0 ppm.
So, a left-open bottle of acetylene caused the CO alarms and 3 days of worry, deduction, and shopping for a new rooftop package unit.
IMPORTANT FOLLOW-ON INFO (PLEASE READ):
I have since found a detailed writeup of cross contamination (interference) of various gasses with CO alarms. This shows clearly the VERY STRONG response of CO sensors to acetylene. The document also points out that MANY OF THESE GASSES POISON THE CO SENSOR. Thus, if you have exposed your CO alarm to acetylene it needs to be replaced.
The cross contamination document is linked here and also attached as a PDF.
https://braschenvtech.com/wp-content/uploads/2020/06/Cross-Contamination.pdf
Acetylene leaking from your left-open bottle can trigger a room-air CO alarm/monitor.
This is challenging to track down in the face of uncertainty as your CO alarm does not differentiate between actual CO and a number of other gasses that can cause interference. It is imperative that one always treat the CO alarm as indicating a real threat to your life.
Here is my recent experience (abridged):
In my 1000 square-foot stand-alone shop I found my ceiling-mounted garden variety CO alarm triggered. The only source of actual CO is the rooftop AC/gas heat package unit. I shut the heat off and opened doors to let in a chilly cross breeze. After a while I replaced the batteries and reset the CO monitor. Closed the shop, heat still off. About an hour later it went off again.
This second alarm was puzzling, but maybe some residual CO was loitering in the space. Or, maybe the CO alarm was broken or at end of life.
I did some reading about CO alarm levels. Many of them go off at 50 ppm. 50ppm is the 8 hour exposure limit.
Bought a second sensor from the orange big box store. This one is by Kidde and has a digital display of CO concentration in ppm. I placed that in my shop, which had been closed for a few hours, heat off. It soon displayed about 35 ppm!! (This is peeking at it from outside.) This was concerning. I opened the doors to the cross breeze. After a while (20 minutes??) the reading dropped to 0 (zero) ppm.
I closed the shop and did other stuff all day. When I returned home the CO reading was about 40 ppm!
Even though the heat had been off more than 24 hours, I shut off the gas to the building. Now I am reading about sources of false CO alarms. Many web sites discuss charging of lead-acid batteries as being implicated (one story is a golf cart being charged in a garage). Indeed, over-charging a battery can cause significant release of hydrogen gas, which will set off an alarm.
Well, I have 3 lead-acid batteries in there, always on battery maintainers. I shut off battery charging. Ventilated the space again. Closed it over night.
In the morning the reading was something like 45 ppm. The high-reading memory had stored about 110 ppm.
Well, more reading eventually revealed a few stories of acetylene bottles causing CO alarms. In one case a contractor had left an (I assume open) bottle in a basement where they were doing piping work.
As it turns out, just about a week ago I was educating myself about acetylene safety. That is when I discovered safe practices of never letting a bottle drop below 25 psi in the tank AND never using more than 15 psi in the hose. There are also limits on flow rate based on bottle size. (I’ll post separately about this if folks are interested.)
I had decided to mark my regulator gauges with a red Sharpie at 25 psi bottle pressure and 15 psi hose pressure. At the same time, I opened the tank valve to check the pressure in the tank.
So, now it dawns on me that I must have left the bottle valve open. I went out there, and sure enough found the open bottle valve and noticed the tank pressure was down about 100 psi from a week ago.
Now the scientist in me points the torch at the CO sensor snout and gives it a short dose of acetylene. Within a few minute that CO sensor pegged at 999ppm full scale.
I closed the acetylene bottle and put the OA rig outside. Ventilated the shop for a couple of hours. The CO sensor was still reading 999, well saturated. I closed the shop up, put the heat back ON, and did something else for the afternoon. That evening the CO sensor had come off saturation and was reading 0 (zero) ppm. I turned on the battery chargers. In the morning I still had 0 ppm. I put the OA setup with closed bottles back inside. Reading have stayed at 0 ppm.
So, a left-open bottle of acetylene caused the CO alarms and 3 days of worry, deduction, and shopping for a new rooftop package unit.
IMPORTANT FOLLOW-ON INFO (PLEASE READ):
I have since found a detailed writeup of cross contamination (interference) of various gasses with CO alarms. This shows clearly the VERY STRONG response of CO sensors to acetylene. The document also points out that MANY OF THESE GASSES POISON THE CO SENSOR. Thus, if you have exposed your CO alarm to acetylene it needs to be replaced.
The cross contamination document is linked here and also attached as a PDF.
https://braschenvtech.com/wp-content/uploads/2020/06/Cross-Contamination.pdf
