A blast valve is used to protect a shelter, such as a fallout shelter or bunker, from the effects of sudden outside air pressure changes.
An overpressure valve is a one way check valve that installs on the wall of your shelter or safe room.
The overpressure valve is normally closed and will not open unless the air pressure inside the shelter is slightly greater than the outside air pressure. It opens when the air filtration system is turned on.
