Fan death is a South Korean urban legend which states that an electric fan, if left running overnight in a closed room, can cause the death (by suffocation, poisoning, or hypothermia) of those inside.
"The fan uses up the oxygen in the room and creates fatal levels of carbon dioxide. There is no actual conversion of oxygen to carbon dioxide happening; unlike a candle, the electric motor in a fan does not alter the chemical composition of the air (apart from creating some ozone if the motor uses brushes, and outgassing from the materials)"