Patent ID: 7484668

Claim:
A building protection system for a building having an inlet air duct with an inlet damper in the inlet air duct operable to regulate an inlet air stream entering the building and passing through the inlet air duct, a return air duct with a return damper in the return air duct operable to regulate a return air stream, and a fan system operable to circulate a mixture of the inlet air stream and the return air stream in the building, the building protection system comprising: a chemical sensor system operable to detect one or more chemical contaminants, the chemical sensor system being disposed in the inlet air duct upstream of the inlet damper; a chemical sensor system operable to detect the one or more chemical contaminants, the chemical sensor system being disposed in the return air duct upstream of the return damper; a radiological sensor system operable to detect one or more radioactive contaminants, the radiological sensor system being disposed in the inlet air duct upstream of the inlet damper; a radiological sensor system operable to detect the one or more radioactive contaminants, the radiological sensor system being disposed in the return air duct upstream of the return damper; and a control system connected to the sensor systems, the fan system and the dampers, the control system being operable to close the dampers and to turn off the fan system whenever any of the chemical sensor systems detect at least a predetermined level of one or more of the one or more chemical contaminants or whenever any of the radiological sensor systems detect one or more of the one or more radioactive contaminants; wherein the fan system includes a brake mechanism connected to the control system which is operable to brake rotations of said fan system in response to a signal from said control system whereby an existing positive air pressure upstream of said fan system will diminish and result in a back flow of an air stream upstream of the fan system.