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In-Depth Survey Report: Evaluation of Local Exhaust Ventilation Systems for the 010 Culling System at United States Postal Service, Merrifield Processing and Distribution Center, Merrifield, Virginia [2003-06]
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2003/06/01
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Description:Researchers from the National Institute for Occupational Safety and Health (NIOSH) conducted an evaluation of the Ventilation/Filtration System (VFS) developed for the United States Postal Service (USPS) mail processing equipment-the 010 Culling System. The VFS was developed and installed by a private contractor hired by the USPS to reduce the potential for employee exposure to harmful substances that could be contained in mail pieces processed by the equipment. This effort is in response to the 2001 terrorist attacks that used the mail as a delivery system for anthrax. NIOSH was asked to assist the USPS in evaluating controls for this and other mail processing equipment. Evaluations were based on a variety of tests including: tracer gas (TG) experiments, air velocity measurements and smoke release observations to evaluate contaminant capture efficiency
and simultaneous particle count experiments upstream and downstream of the VFS filtration to evaluate system filtration efficiency. The experiments showed that, with few exceptions, the system meets or exceeds minimum contaminant capture requirements and that contaminant filtration capabilities meet or exceed 99.97%. However, testing did reveal poor contaminant capture efficiency at Flats Ejector # 1 (about 28%). Based on these results as discussed in this report, the following recommendations are made to further improve the control of potential contaminants by this mail sorting system. Both Flats Ejectors should be permanently modified to maximize smoke capture and TG capture efficiency. Although smoke release observations suggest adequate contaminant capture at the Left-Hand Loose Mail Distribution System (LMDS) Hamper Dump, it is recommended that the gap to the side of the slotted intake be sealed. This action may also increase contaminant capture velocities at the face of the curtain. USPS Engineering should consider elimination of the exhaust at the LL-I0 and LL-6 areas. Since these areas are enclosed, workers should be adequately protected as long as the chute underneath is controlled by the Advanced Facer Canceller System (AFCS) VFS. Although TG experiments suggest adequate capture efficiencies at the Dual Pass Rough Cull (DPRC) waterfall area, there are several open knock-outs in walls in this area that should be sealed to maximize VFS effectiveness. The USPS and its vendors should consider redirection of the exhaust plumes from the air handling units as they may interfere with proper contaminant capture of the 010 Culling System VFS, DPRC VFS and AFCS VFS which are in the plumes. Proper balance of the Left-Hand side of the LMDS System with the Right-Hand side could alleviate disparities in Hamper Dump contaminant capture velocities and Hand Culling Station TG capture efficiencies. The skirt added by the vendor during testing to the SC-2 bypass chute should be made permanent, and similar modifications should be made to the SC-1 bypass chute. To ensure optimal filtration system performance, the USPS and its vendors should take steps to guarantee that filters are changed often enough to be operating within prescribed parameters and that filters are protected from physical damage. Moreover, such steps should be taken prior to further testing of filtration system efficiency. Proper and regular maintenance of the filtration component of the VFS unit is essential for effective filtration. Work procedures for maintenance should be designed with this in mind and should be closely followed. Further testing to investigate why computations for some areas indicate capture efficiency greater than 100% is warranted. Therefore, future NIOSH testing should include making individual TG experiments longer in length.
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Pages in Document:1-16
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NIOSHTIC Number:nn:20023096
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NTIS Accession Number:PB2004-104527
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Citation:Cincinnati, OH: U.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, EPHB 279-14a2, 2003 Jun;:1-16;
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Federal Fiscal Year:2003
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Peer Reviewed:False
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End Date:20050930
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[PDF-404.21 KB]