Development of a HEPA filter with high structural strength and high resistance to the effects of humidity and acid

HEPA-filters may be subject to considerable stresses during operation in nuclear installations, particularly in the case of an accident. The state of the art of filter media technology presently allows the utilization of only glass-fiber filter paper in manufacture of HEPA-filters. A newly-developed filter medium made of synthetic micro-fiber nonwoven material, including the production process, the filtration and the material characteristics, in particular with respect to the resistance to hydrofluoric acid and high moisture is described. The HEPA-filter units manufactured with such filter media have satisfactorily passed structural tests under both high air velocities and high differential pressure as well as tests under extended exposure to high relative humidity and fog conditions