American Safe Room manufactures a double acting blast valve and two types of overpressure valve.

Blast valves install on the inside wall or ceiling of your shelter right over the air intake and outflow pipes. They allow low pressure air to move through them, either in or out of the shelter. When a high pressure wave comes over your shelter from a nearby detonation, the blast valves will automatically shut, protecting the air filter and the occupants from this pressure wave. Following the pressure wave will be a vacuum as the atmosphere is blown outward from the point of detonation. The valves will shut automatically when this vacuum hits.

Without blast valves protecting your shelter, you would first get a high pressure impulse coming through your ventilation pipes and then the air in your shelter would be at least partially sucked out through the same pipes. Any underground shelter with a decent blast door needs blast valves. You either have blast protection, or you don't.

Overpressure valves install on the air outflow blast valve to meter the outgoing air. They work with the filter to create and maintain overpressure. We have two types of overpressure valves: static and adjustable.

The adjustable overpressure valve should have a differential pressure gauge installed in the shelter to display the overpressure. This gauge requires a sampling tube to penetrate the wall or ceiling to sample the outside air pressure. We can also mount this gauge right on the inside of the blast door using a built in sampling tube.