High-Efficiency Particulate Air (HEPA) Systems

High-efficiency particulate air (HEPA) filters were developed in the early 1940s and used first by the Manhattan Project to contain the spread of airborne radioactive contaminants. Introduced commercially in the following decade, “HEPA filter” refers not to a specific filter design but to a specific level of efficiency, as defined by the Department of Energy (DOE) in the United States and the European Committee for Standardization in the European Union. The DOE standard defines a HEPA filter as one that removes at least 99.97 percent of airborne particles 0.3 micrometers in diameter (the Most Penetrating Particle Size, or MPPS). The European standard is similar, but defines five HEPA classes—H10 through H14—of increasing efficiency. In contrast, the typical pleated filter used in a home furnace in ...