2. Civil air defense works, also known as civil air defense fortifications, refer to underground protective buildings built separately for wartime protection of personnel and materials, civil air defense command and medical rescue, and basements built in combination with ground buildings that can be used for air defense in wartime. Civil air defense project is an important facility to guard against sudden enemy attacks, effectively cover personnel and materials, and preserve war potential; It is an engineering guarantee for persisting in urban fighting and supporting the anti-aggression war for a long time until victory.
3. Explosion-proof wave valve is one of the important protective devices to ensure the survival of personnel in the tunnel of position engineering. It is installed at the head of the tunnel air intake and exhaust system. Usually the valve is opened and the tunnel is normally ventilated; In the event of a nuclear attack, the quick closing of the valve can prevent shock waves and radioactive dust from entering the tunnel through the vent pipe.