Question

why are we advised never to sleep in a room with a burninf candle

Answer 1

We know that to burn a fire we need to have oxygen along with the material itself.

So, in a room mostly the oxygen spilling system that is windows and doors are mostly found closed. Hence, if a candle in burnt in a room that candle will surely use all oxygen present in that room.

Means lack of oxygen. Which is not good thing. This create serious problem of suffocation, so we need to avoid to sleep in a room with a burning candle.

Answer 2

We are advised never to sleep in a room with burning coal fire in it because the burning of coal emits carbon dioxide in the air which is harmful for us. Also, the incomplete combustion of coal can emit carbon monoxide which is a very harmful gas