A threat detection system includes a facility including at least three separate rooms located in the facility and a positive pressure zone located external to the facility. A ventilation system is coupled to the at least three separate rooms. A first room is located in the facility, wherein the first room includes a first room pressure zone that is negative with respect to the positive pressure zone external to the facility. A second room is located in the facility and connected to the first room, wherein the second room includes a second room pressure zone that is negative with respect to the first room pressure zone. A third room is located in the facility and connected to the second room, wherein the third room includes a third room pressure zone that is negative with respect to the positive pressure zone external to the facility and positive with respect to the second room pressure zone, whereby the first room pressure zone, the second room pressure zone, and the third room pressure zone result in air within the facility or entering the facility to flow into the second room.