Question

Why should we not sleep in a closed room where coal fire is burning?

Answer 1

Because the smoke from the fire will fill up the room and enter your lungs, and you can die.

Answer 2

Incomplete products of combustion, including carbon monoxide, will accumulate in the closed room and if you sleep long enough, you won’t wake up. Ever. Even with the fire place vented through a chimney, it’s rare that at least some of the products aren’t released into a closed room. The coal fired fire place should not be in the same room you sleep in.