Underground survival bunkers require a well-planned air and filtration system to circulate fresh air inside the unit. The recommended system depends on the size and location of the bunker, as well as the depth at which it is buried. A combination of vents, pipes, valves and filters often work together to provide the bunker with an adequate source of fresh and renewable air.
A small underground bunker needs at least two vents to deliver enough fresh air for survival and cooling. If the bunker is located near the surface, standard air vents may offer the most cost-effective solution, but a bunker buried deeper requires proper piping to route the outside air above the ground into the vents beneath the surface. A galvanized steel material that is strong enough to withstand movements beneath the earth's surface is recommended for all piping.
All above-ground vents are typically concealed to prevent disclosure of the underground bunker's location. Rocks, shrubs or flowers may hide the vents or a creative design may disguise them. Pressure valves are often integrated into the air systems of bunkers that are buried deeper than 30 feet. These valves prevent damage in the case of over-pressurization. A reliable filtration system is recommended inside the bunker, especially if the bunker houses several occupants. Store an adequate supply of replacement filters in the bunker as well.