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?