Methods of testing HEPA filters with short upstream approaches

The design of an air cleaning system to be used in a high gamma radiation field presented unique problems for in-place Dioctyl phthalate (DOP) leak testing. The design required remotely changeable HEPA (High Efficiency Particulates Air) filters in a throw-away, stainless steel housing, located underground in a stainless steel-lined concrete pit. The conventional approach of providing ten duct diameters of upstream mixing for the dispersion of testing the second filter stage in the system. To establish aerosol (DOP) injection ports that could provide mixing in accordance with ANSI N510-80, a full-scale housing was built. The housing and components were built of plexiglas to view the DOP streams. A series of tests were designed in which the following factors were varied: (1) aerosol distributors, (2) aerosol distributor locations, (3) baffle design, and (4) baffle location. DOP concentration measurements were taken immediately upstream of the filters. The uniformity score, as determined by ANSI N510-80, was defined as the larger of maximum minus average divided by average, or average minus minimum divided by the average values of DOP concentration. Three tests met the uniformity score requirement of 0.20, but all three had ten duct diameters of upstream mixing. The type of aerosol distributor,more » duct length, and flow rate were found to most affect the uniformity score. 5 figs.« less