Please use the search function, there's a lot of threads around incl. where users tested CO concentrations. I don't have all links, I need to use the search, too.
Regarding opening the door, yes some CO will vanish the question is will it build up again, you'd need to do tests if you want to know it. I Personally would go inside a little earlier. Regarding the temperature it will depend on summer/winter.
There are reports from succesful / unsuccessful attempts. I do not have personal evidence, because obviously I'm still alive and I did not test the CO method on myself yet, that will be the last thing I'm gonna do here in this world.
But how don't the bottom of it melt with coals? I mean the metal buckets for that are made for ashes and used coals gets so hot that it will burn anything from its bottom if there is no wooden thing underneath it (they are made for empting cold or warm ashes from fireplaces and burn from bottom...
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