HEPA Filter Performance under Adverse Conditions

摘要

High efficiency particulate air (HEPA) filters are commonly employed to control particulate matter (PM) emissions from radioactive materials management or treatment processes. Public concern has grown concerning HEPA filter use and monitoring. Of particular interest is the performance of HEPA filters under conditions which may be conducive to filter failure. To this end, a study was conducted evaluating HEPA filter performance under a variety of challenge conditions. Filters were challenged under a variety of conditions that can arise in Department of Energy (DOE) applications such as: low or high RH, controlled (inorganic PM < 30 mg/m3) and uncontrolled challenge (smoke > 30 mg/m3), and filters with physically damaged media or seals (I.e., leaks). Reported findings correlate filter function as measured by traditional (differential pressure) techniques in comparison with simultaneous instrumental determination of up and down stream PM concentrations. Additionally, emission rates and failure signatures will be discussed for filters that have either failed or exceeded their usable lifetime. Testing has included challenging filters with both water soluble and insoluble inorganic salts. Filter loading was monitored using differential pressure, and filter performance was evaluated by comparison of up versus downstream concentrations of PM. Measurements of PM concentrations were made both up and down stream of the filter using EPA Method 5i, electrical low pressure impactors (ELPI), differential mobility analyzer/condensation particle counters (DMA/CPC), diffusion battery/condensation particle counters, and condensation particle counters (CPC). This array of instrumentation allowed for simultaneous determination of the up and downstream particle number densities, particle size distributions, and filtering efficiencies as a function of time and challenge PM.