Abstract
In-place filter testing is a widely accepted practice for assuring performance of high-efficiency particulate air (HEPA) filter systems. American Society of Mechanical Engineers (ASME) standards address aspects of uncertainty in in-place filter test results through limits on spatial variation of test aerosol concentration and flow velocity. This article augments the standards by developing an approximate expression for test result uncertainty. The expression uses concentration, flow velocity, and penetration heterogeneities as indices of spatial variation. The uncertainty expression is used to evaluate testing of a hypothetical HEPA filter system meeting requirements of the standards and of an operating field HEPA filter system. At a performance acceptance limit of 5×10−4 penetration, uncertainty in tests on the standard system is just over the inferred ASME system acceptance limit of 6.7%. Uncertainty for field system tests is more than twice the limit. The uncertainty expression is used to determine limits on test results that assure compliance with system performance acceptance limits and to evaluate options for modifying the field system. The approach presented here provides a potential mechanism to economically establish a correspondence between tests on qualified nonstandard systems and requirements of the standards. The correspondence assures that tests on the nonstandard systems provide performance assurance equivalent to tests on fully compliant systems. Nonstandard systems that pass these tests can be reasonably expected to meet the same health and environmental protection requirements as fully compliant systems.