Factors Influencing the Performance and Lifetime of Fibrous Glass and Metal Media HEPA Filters

High efficiency particulate air (HEPA) filters are used in a variety of nuclear applications as final air treatment units. The design of air filtration systems in nuclear facilities that will function well requires a significant amount of knowledge about the challenge conditions that these filters will be exposed to. Additionally, risk assessments conducted as a review of these systems need also to be based on knowledge of filter challenge parameters during upset conditions that may be used as design basis conditions. This paper presents a summary of findings of factors that influence the performance lifetime of conventional fibrous glass media filters. These factors include aerosol challenge (particle size distributions and mass concentrations), media velocities, wetting conditions, and changes in gas density. These data are correlated to design considerations for new systems and to process upset conditions used in risk assessments, particularly those involving fires. Data from filter testing activities are also compared to filter loading models and to literature information regarding aerosol emission rates from combustion of various materials. Additional data are provided relating the performance of metal media HEPA filters under conditions that exceed maximum ranges for fibrous glass filters. These discussions focus on selection factors between these two categories of filter units.