Please excuse me if this next comment is seen as boring, or "un-cool" (It's a habit that I'm trying to break!), but I felt the need to counter a couple of comments that I've seen on this thread.
Any heating or cooking apparatus that relies on burning gas, oil, or solid fuel such as wood or coal, WILL produce carbon monoxide, basically because the combustion process will gradually take the available oxygen from the atmosphere.
If you have sufficient ventilation then this oxygen will be replaced as it burns, and all will be well. If you DON'T have adequate ventilation, then the oxygen level will be reduced to a level that will not support life... that means YOUR life and anyone else in the room or compartment.
To add to this problem (and as a previous poster has said) the carbon monoxide will make you feel drowsy. You may not even realise this, and simply drift off into your FINAL sleep. Even more worrying, you may get to a stage where you DO realise that you are being poisoned, but the amount of carbon monoxide that you've absorbed will have semi-paralysed you, so you have no option other than to lay there and wait until you lose consciousness, before you die.
Yes, you can get away with it for a short time if you're very careful, don't get distracted, and sometimes are just plain lucky (I've used a gas hob myself for heat at times), but you do have to be aware of the risks and plan for them.
Now I'm as much of a critic of Health & Safety Regs as (almost) anyone, and have seen how OTT parts of H&S have gone in recent years, but when it comes to basic life-threatening safety issues such as those mentioned in this topic, then I'm afraid that anyone who tries to play down the seriousness of the hazards has obviously never had to deal with the casualties caused by carbon monoxide.
As I've said before, most (but not all) of the casualties of carbon monoxide poisoning were not expecting to die on that particular day.
(Boring mode now switched off.... Normal service resumed!

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