Evaluation of Glass Fiber Hepa Filters as a Function of Media Velocity

The Department of Energy currently employs high-efficiency particulate air (HEPA) filters in a variety of applications, such as particulate matter removal from ventilation air and treatment of off-gasses from storage or remediation of mixed wastes. Section FC of the ASME AG-1 Code addresses glass fiber HEPA filters and restricts the media velocity to a maximum of 5 ft/min. Advances in filtration media technology now allow glass fiber HEPA filters to function at significantly higher velocities and still achieve HEPA performance. However, no rigorous testing has been performed that can provide policymakers with data needed to determine optimal operating conditions with respect to media velocity. Of particular interest is the removal of ultrafine (< 100 nm) particulate. Because ultrafine particles are removed by a diffusive capture mechanism, increasing media velocity would result in shorter residence times within the media matrix. Therefore, it is highly unlikely that higher media velocities for HEPA filters will be allowed without data to demonstrate the effect of media velocity on removal of particles in the smaller size range. In order to address this issue, static testing has been conducted to generate performance related data and a range of dynamic testing has provided data regarding filter lifetimes, loading characteristics, changes in filtering efficiency and the most penetrating particle size over time. Results of this testing will be provided to the ASME AG-1 FC Committee for consideration in future versions of the HEPA standard.