[en] The HEPA filter is an extremely effective means for removing fine (submicron) particulate matter from air and process offgases, so effective, in fact, that it is considered to be the best means for sterilizing air and is widely used for that purpose in laboratory and industrial biological operations, hospitals, and medical (e.g., cancer) research facilities. Even small defects in original installation or which may develop under operational or system upset conditions can degrade operability of the system. Therefore, careful attention to detail in system design and installation is essential to obtaining optimal, or even marginal performance from the filters; and searching and repeated testing are essential to maintaining that performance. Design, installation, and testing practices followed in present day DOE-sponsored nuclear facilities comply with these requirements; and it is fair to say that those facilities are capable of protecting the public from airborne releases of radioactivity, including particulate matter in the respirable size range