Another two stories to back up your case:
When I started teaching, I moved into a bedsit in a big Victorian house in Sheffield and immediately redecorated it. As the nights got colder, I found that I was suffering from lots of headaches and drowsiness when I was in the bedsit. On a couple of occasions I passed out on my bed (without the aid of any alcohol!). When I came round later I felt really ill but getting outside, for a walk in the fresh air, seemed to help quite a bit.
Them, while sitting in my bedsit, I read an inquest report in the local newspaper. A man had died of carbon monoxide poisoning and a gas expert had reported told the inquest that the classic signs of of a blocked flue were present within the flat, i.e. the enamel was pealing from the top of the gas fire and there was a sooty build up, all around the room, at the foot of the walls.
I looked at my gas fire and saw that the enamel was pealing from the top of the gas fire. I looked around at my recently redecorated walls and saw a dark, sooty line running all around the room. I doubt that anyone has ever turned a gas fire off as quickly as I did that evening!
Second one:
About 20 years ago, a friend invited me to stay with her family in a holiday camp chalet over the Christmas period. In order to avoid feeding the coin meter in the chalet, to heat the place, she took a portable gas heater with her (which she'd picked up cheaply in a car boot sale). We very quickly all started to experience headaches and drowsiness and I told her that she'd have to stop using the heater. She refused to believe that there was any real risk and we had a big row about it. It was only when I told her that I wasn't prepared to risk her 10-year-old son's safety and that I would take him away to somewhere safe [whether she agreed or not], that she decided to relent.