Abstract: A building protection system includes chemical sensor systems to detect chemicals in inlet and return air; radiological sensor systems to detect radioactive materials in the inlet and return air; and a control system (a) to signal a building control system to close dampers and to turn off a fan system when more than predetermined levels of a chemical or radioactive material is detected and (b) to issue reports.

Abstract: An improved building protection system in a building having an inlet air duct for bringing an atmospheric air steam into the building, a damper in such air duct operable to regulate atmospheric air stream passing through the duct, a return air duct with a damper in such duct operable to regulate the return air stream mixed with the inlet air stream and a fan system means operable to suck an atmospheric air stream into the air duct and the return air stream into a return duct, an improved building protection system employing paired sensors for the same toxic agent in the ducts, logic means monitoring the outputs of the paired sensors operable to determine the parity of such outputs, logic means monitoring the outputs of the paired sensor operable to indicate the presence of such toxic agent and control means connected to the logic means operable to shut down the building's HVAC system only when the outputs have substantial parity and presence of such toxic agent is detected by said sensors.