Abstract: An air flow filter device includes a housing having at least two openings therein, a stationary air filter, such as an HEPA filter, disposed within the housing, and a one-way air flow valve disposed within the housing in parallel with the filter. The valve is positioned such that sufficient air flowing into the housing from the one opening closes the valve so that such air flows through the filter in order to exit through the other opening, and such that sufficient air entering the housing from the other opening opens the valve so that the air flows through the valve in order to exit through the one opening. In this manner, air may be circulated in both directions without escape of contaminants, such as asbestos fibers, into the environment.