Lesson Learned Statement:Facility management should assess a facility's High Efficiency Particulate Air (HEPA) ventilation system configuration against the testing method used to challenge and measure that system's performance.
Discussion:On September 12, 1995, the facility manager for Lockheed Martin Energy Systems/Oak Ridge National Laboratory (LMES/ORNL) Building 3525 found that air from a contaminated room was bypassing a HEPA ventilation filter. The air leaked through a room process drain line connected through a common header to a drain in the downstream side of the filter housing. Quality inspectors had been assigned to perform a semiannual, in-place leak test of HEPA filters for the Charging Area of Building 3525. With the filter fan running, they dispersed test aerosol in the Charging Area with a smoke generator and measured the quantity of aerosol on the upstream and downstream sides of the filter. Test personnel did not inject aerosol dispersant into the upstream part of the duct because they wanted to minimize the number of test personnel and equipment entering a contaminated area. Maintenance mechanics had replaced the HEPA filters immediately before the inspectors performed the test in an effort to increase airflow through the Charging Area. After replacement, the new filters failed to meet the 99.95% aerosol filter efficiency requirement. The mechanics suspected the filters were improperly seated, so they retightened the filters and recaulked the seams on the filter housing. They unsuccessfully retested the reseated filters. During causal evaluation of the failed leak tests, the manager found an open process drain on the downstream side of the filter housing and a closed drain on the upstream side. Mechanics again replaced the filters, recaulked the seams, and sealed the upstream side drain plug. Believing the downstream drain line was the culprit, the manager directed the mechanics to leave the downstream drain unsealed. The manager requested two tests be performed to verify his hypothesis. First, the test aerosol was injected directly into the filter duct. Second, the Charging Area was filled with aerosol. The first test met the filter efficiency requirement; the second did not. On this basis, the manager concluded that the downstream process drain allowed a portion of the aerosol to pass from the Charging Area downstream to the filter outlet, aided by the pressure differential between the filter housing outlet and the Charging Area.
Analysis:Mechanics plugged the drain and completed the test successfully. Radiological operations (suspended during HEPA filter testing) resumed. Management determined that the leak through the downstream process drain line had been present for many years. Post-incident radiological surveys downstream of the HEPA filter detected no fan outlet contamination. Facility management evaluated the incident. They identified the DIRECT CAUSE as an equipment/material problem. Previously, mechanics and facility management had been unaware of the faulty ventilation system configuration. Earlier in-place tests injected the challenge aerosol directly into the upstream side of the filter system and did not challenge the (unknown) bypass route. The September 12, 1995, test filled the entire Charging Area with aerosol and discovered the bypass. Management identified the ROOT CAUSE of the occurrence as a work organization and planning deficiency. Neither the ORNL support organization performing the testing nor facility management had knowledge that the in-place test was inadequate. The Building 3525 facility was constructed in the 1960s. Subsequent changes in management and management practices contributed to the occurrence. Proper application of established conduct of operations policies contributed to the discovery of the problem.
Recommended Actions:Facility management should assess a facility's HEPA ventilation system configuration against the testing method used to challenge and measure that system's performance. If it is unclear whether or not filter bypass leakage is possible, management should perform a baseline system bypass test. This incident shows that bypass leakage may occur through dampers, ducts, conduits, floor drains, pipe penetrations, etc. from within an associated room or ventilation system.
Originator:Lockheed Martin Energy Research, Inc Oak Ridge National Lab (C. E. Devore, 423-576-7713)
Contact:Claretta J. Sullivan, (423)241-3134
Name Of Authorized Derivative Classifier:n/a
Name Of Reviewing Official:
Priority Descriptor:Blue / Information
References:Occurrence Report ORO--MMES-X10METCER-1995-0010 U.S. Department of Energy, Operating Experience Weekly Summary #95-38.
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DOE Function / Work Categories:Conduct of Operations - General
Environmental Protection - General
Personal Injury / Exposure - Airborne Materials
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