Fire Engineering Training Community

Where firefighters come to talk training

We responded to a CO alarm last week with an interesting outcome. We were dispatched at about 21:00 hrs. Upon arrival, the occupants of a 1 story ranch with basement reported that at approximately 02:00 that morning, their CO alarm went off. Thinking it was a bad battery, they disconnected it. They replaced the battery the following morning, and the alarm continued to activate. They then purchased an new CO detector, which aslo activated. (So much for that theory Darwin had).
Occupants reported no recent use of any appliances in the home and they had an oil fed furnace which had not been running recently due to warm temperatures. They did report recently having an in ground oil tank removed from the back yard because it had been leaking.
As soon as our crew made entry, they immediately detected readings above 60 ppm CO on the 1st floor. Readings in the basement were above 70 ppm CO. We turned off the furnace, vented the house, and took additional readings (9 ppm Co 1st floor, 17 ppm CO basement). Sealed the house up, waited 1/2 hour rechecked, and levels were at or near the original level. On the 2nd set of readings, it was noted that the highest readings were near the basement sump pump pit, and that they became more elevated whenever the pump kicked on. We had originally believed that CO or some substance mimicing it was being sucked into the house through ground water, possibly from decaying material or oil which had leaked from the tank. We called our County Haz Mat Coordinator in to take a look. Using a more sophisticated gas meter, he was able to pinpoint the problem to an overheating back up battery for the sump pump, which was disconnected and problem solved.
Hindsight being 20/20, we probably could have also diagnosed this problem with a T.I.C. But I wanted to share this unusual source of CO to remind everyone we need to think out of the box when the cause isn't immediately apparent and I have to ask, has anyone seen this before?

Views: 12010

Replies to This Discussion

We've seen it twice at the same occupancy. We were dispatched to a bank for an unusual odor. Using the multi-gas meter we detected elevated CO readings. After a long invest we determined that the source of the CO was the battery back-up for the bank's computer system. About 6 months later the same problem occurred at the same location.
There was an incident, possibly in Fire Engineering or perhaps Firehouse a few year ago, with a similiar call in Florida. It was to a total electric house, so things didnt add up. They were getting a Hyrodrogen reading on thier CO meter, thy hodrogen was being released by a charging battery.
We have seen this in at least 2 occassions over the last couple of years. We actually have made it a practice since then to ask the residents when we respond out for CO calls if they have a sump pump. We had readings over 60 in the 100ppm range and it was the sump pump. The sump pumps were both connected in both situations but were either clogged or werent functioning due to a fault with the pump itself which overheated the battery.
We had the exact situation last summer/fall. What you are seeing is the sulfur dioxide given off by the battery (I assume that battery was boiled dry) gasing off. This gas fools the 4 gas meter into thinking that it is CO. Caused us headaches for about 24 hours even to the point that we evacuated the owner for the night until we could get it figured out.
We had it right in the Fire Hall. On one of our apparatus the automatic charging system malfunctioned and was causing a battery to overcharge and off gas. The CO alarm activated and upon investigation found the problem with over 100 PPM near the truck.
We had this same situation occur in a Sam's Club with battery operated fork lifts. The battery had boiled off and gassed off sulfur dioxide.
We have a large retirement community in our city that is built around two golf courses. Most of the residents have electric golf carts that they keep hooked up to chargers in the garage. We have had numerous CO alarms due to the batteries drying up. Took us a while to figure this one out since most of the houses are all electric.
I have not experienced this but have been told about it by several different people in different departments. When the battery is full of water as it should be, it gives off hydrogen as it charges. Our CO meters are sensitive to hydrogen and will register it as CO. When the battery is dry, as it should not be, the battery and the wires will heat up giving off CO containing smoke and a burning odor.
I was not aware of that a dry battery would also give off sulfur dioxide. In any case, checking for a sump pump is a good idea when making a CO investigation.
This is one more example of how listening to other firefighters tell their stories makes us all more effective as firefighters.
Yes have seen this a least twice now. First was with a sump pump with a battery back up. The battery had ran dry on water. New owner did not even know back up system was there. Initially called us because household CO detector was alarming. WHen we entered found 60 PPM at front door. Exited and reentered on SCBA. FOund higher levels in part of basement with sump pump and highest levels over battery.

Second time was shortly after above. No levels around natural gas fixtures. Asked about battery back ups, etc. Owner advised no sump backup system but computer did have a battery backup UPS system. When checked there found high levels in area of UPS. Removed UP from house nothing else found.

Now make it part of the resident interview process when arrive on scene, as to what was being used, etc.
Yes, I had the son of a county fire marshal call me due to a co detector going off in his house. After investigation the highest readings were in the basement but there were no fuel fired sources there to cause the alarm. They called me for a couple of reasons, one we are good friends for the last 25 years but the main reason was they couldn't figure out what was causing the alarm. Well I am also the Hazmat program director for the N.C. state fire marshal's office and that is why he called me. After talking with them on the phone and asking a few questions I found out he had recently purchased an electric golf cart and he was charging it in his basement. This was the source of the alarm, but not due to co. The reason for the alarm is contamination of the sensor with acidic gas vapors produced while charging the cart. The co sensor uses an electochemical sensor that contains an electrolyte that is used to read co levels due to changes in the ph of the sensor causes a change in the electrical current through the sensor and that was percieved as elevated co levels. It only takes a very small amount of acid or base vapors to cause electrochemical sensors to give false readings.
Also had an instance where a golf cart in the garage was causing the homeowner's detector to go off
We saw something similar here in Raleigh earlier this year. A homeowner was recharging his golf cart battery (lead-acid) in the garage, with the door closed. Directly above the garage was the second story. A by-product when charging a battery of this type is hydrogen, which, being lighter than air, rose into the second story. The CO alarm activated due to cross-sensitivity of the sensor. It turns out that a reading of 100 ppm of hydrogen will read as 40 ppm of CO - thus activating an alarm. In addition, a concentration of hydrogen in the attic space will cause a change in the LEL readings on your monitors. Nothing to be too concerned about, the homeowners just need to be aware of the situation, and vent the area when charging the batteries.

Hope this helps.


Policy Page


Our contributors' posts are not vetted by the Fire Engineering technical board, and reflect the views and opinions of the individual authors. Anyone is welcome to participate.

For vetted content, please go to

Fire Engineering Editor in Chief Bobby Halton
We are excited to have you participate in our discussions and interactive forums. Before you begin posting, please take a moment to read our policy page. -- Bobby Halton

Be Alert for Spam
We actively monitor the community for spam, however some does slip through. Please use common sense and caution when clicking links. If you suspect you've been hit by spam, e-mail

FE Podcasts

Check out the most recent episode and schedule of

© 2022   Created by fireeng.   Powered by

Badges  |  Report an Issue  |  Terms of Service