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CO is venting out the roof or there are gas fired RTU on a building. Can the flue gases, specifically CO get back into the building. Obviously CO2 is heavier than air so that is not a question. But what about CO. It is always listed as slightly lighter than air which means at the same temperature it is lighter than air and if it is hotter it is even lighter.
But what about CO when it gets cold? Years ago I was researching some information on different gases and found an article that stated that because CO contains carbon, it can get heavier than air, especially below 32 degrees. Therefore if equipment is making high levels of CO and it is on the roof or going out the roof, it can easily re-enter the building through fresh air intakes or other vents or openings. This explains why CO is found on the opposite side of the building that the equipment may be on. I had to evacuate a commercial boiler room years ago because CO was coming down off the roof and back into the boiler room through the combustion air grilles.
I am thinking of all the RTU that might have been covered up by the recent blizzard on the East Coast and wondered how many CO poisoning are occurring that are going undetected?