A sturdily constructed bomb shelter can save you from the initial blast of a nuclear attack, only for you to die a short while later from contaminated air. The solution is to add an NBC air filter to your bomb shelter. These filters are designed to protect you against nuclear, biological, and chemical toxins in the air. In addition, they also protect against carbon dioxide build-up in your emergency shelter.
Maintaining a true air-tight seal is nearly impossible. Because of this, NBC air filters utilize overpressure. Overpressure systems ensure that the air pressure inside your facility is higher than the air pressure outside your facility. This ensures that air will flow out of your shelter, but not in to your shelter.
A large explosion will push air out in front of it. This high-pressure blast wave can destroy buildings, overturn cars, and kill people. It can also damage your NBC air filter. Behind this blast wave is a vaccum wave of low-pressure which creates similar damage with the opposite force.
Add a blast value to your air intake and air outlet pipes. These blast valves should be bi-directional, to protect against both high-pressure and low-pressure waves.
These valves should be equipped with a lock-down mechanism. A lock-down mechanism will enable you to manually close the valves to protect your shelter in the event of a fire or other threat.
Overpressure Relief Valve
The overpressure relief valve allows air to safely escape from your shelter, without allowing any air to flow back into your shelter.
Manual Air Pump
An NBC air filter requires power to operate. This power is usually 115v or 230v wall power, but any large scale attack is likely to take out the power grid. Because of this, most NBC air filters use a 12v battery backup. Batteries do not last forever though, so a manual hand or foot operated air pump is an important addition to an NBC air filtration system.