On a cold winter night, the person sleeping in a room with closed door and windows with a coal fire burning inside may die due to the excessive accumulation of:

Due to the burning of coal, the available oxygen gets depleted and it leads to incomplete burning of coal. Incomplete combustion of coal gives carbon monoxide gas. It is a very poisonous gas. It is dangerous to burn coal in a closed room. The carbon monoxide gas produced can kill persons sleeping in that closed room

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