Review of Inspection and Testing of Installed High-Efficiency Particulate Air Filters at ORNL

High-efficiency filters are indispensable elements in the contamination control programs of most atomic energy installations. These filters, if in good condition, will remove 0.3-μm particles from an air stream with an efficiency of 99.97% minimum. In the United States it is standard procedure to measure the efficiency of new filters by determining the efficiency with which they remove a 0.3-μm particle diameter monodisperse aerosol of DOP from an air stream. This test is used by filter manufacturers and other quality assurance laboratories. The use of pretested high-efficiency filters alone does not ensure that the system in which they are installed will have a comparable efficiency. Experience has clearly demonstrated that systems should be assumed to be inefficient until an in-place test shows the contrary to be true. Routine in-place testing of high-efficiency filter systems was initiated at Oak Ridge National Laboratory in mid-1962. The in-place test method adopted by the Laboratory is patterned after the standard test used to measure the efficiency of new filter units. The principal difference is that the DOP aerosol used for the in- place test is polydisperse with an average particle diameter slightly larger than 0.3 μm. Though the basic in-place test has remained unchanged, six years of experience has resulted in refinement and standardization of techniques which permit wider application of the in-place test and more economical testing. To facilitate the in-place testing of all ORNL high-efficiency filter systems, as required by Laboratory policy, a computer program was instituted in mid-1965. This program provides automatic advance notification to cognizant management and operating personnel when systems are scheduled for test. Similarly, test results are reported automatically. The paper discusses- (1) the computer program; (2) present practice at ORNL with regard to in-place testing policy, techniques, and equipment, and (3) the effect that six years of in-place testing has had on the overall problem of contamination control. (author)