No, I don’t work for the Fire Department, but I am a public servant, so take this as free safety advice. Smart home owners use CO detectors, while those of us who think we’re smart don’t give them much thought until something scary happens.
In my case over a week ago, I noticed a “burnt” smell emanating from my utilities room. I went in and found that the top of my hot water heater was over heating like Dante’s Inferno, and so assumed something was wrong with the heater. Not so. Professionals came and found the heater was perfectly fine. What they did find was that a bunch of sheet-rock had collapsed in the chimney, preventing gasses from escaping, backdrafting back down onto the water heater and into my home, which included carbon monoxide. Someone else in my condominium area had a similar problem only a few months ago, and almost died for it. Thanks to the prompt professional responses, my chimney was cleaned that day; the heat and hot water swiftly restored. I was advised to get a CO detector — as if I needed persuading. Hell, I bought two. I chose a digital-display model (see above), which should read “0” most of the time, allowing for the occasional 1-30 PPM which, according to the instructions manual, “can often occur in normal everyday conditions”. When the display reads higher than 30, the alarm goes off. You can buy other alarms which trigger at 50. And according to some wisdom, healthy adults can tolerate up to 70 PPMs if the exposure isn’t long-term.
I wish I could have seen the PPM readings before my gas was shut off and the chimney cleaned. Because I apprehended the problem right away, and threw open all my sliding windows (in my living room and bedroom), I didn’t get sick. But I’ve no idea how much CO was in my home, especially my utilities room. My plumber guessed, based on the amount of sheet-rock taking up the chimney — there was one piece in particular that was almost completely blocking the passage — that it could have been anywhere between 100-600 PPMs in the utilities room with the door closed. Some fraction of that would have seeped into the rest of my home, and obviously if left unfixed, over time, even more.
Before last week, I didn’t know what “PPM”s were. “Parts per million” means the number of CO molecules in every million molecules of air (so, for example, 100 PPM of carbon monoxide means that for every 999,900 molecules of air, there are 100 molecules of CO). Here is the danger chart. A recent study found that the average peak CO levels during home alarm incidents was 452 PPMs.