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DEMONSTRATION OF SPLIT-FLOW VENTILATION AND RECIR CULATION AS FLOW-REDUCTION METHODS IN AN AIR FORCE PAINT SPRAY BOOTH - VOLUME I. MAIN REPORT, APPENDICES A-C
Citation:
Hughes, S., J. Ayer, AND R. Sutay. DEMONSTRATION OF SPLIT-FLOW VENTILATION AND RECIR CULATION AS FLOW-REDUCTION METHODS IN AN AIR FORCE PAINT SPRAY BOOTH - VOLUME I. MAIN REPORT, APPENDICES A-C. U.S. Environmental Protection Agency, Washington, D.C., EPA/600/R-94/214a (NTIS ADA-286807), 1994.
Impact/Purpose:
information
Description:
During a series of painting operations in a horizontal-flow paint spray booth at Travis AFB, CA, baseline concentrations of four classes of toxic airborne pollutants were measured at 24 locations across a plane immediately forward of the exhaust filters, in the exhaust duct, and inside and outside the respirator in the painter's breathing zone. The resulting data were analyzed and used to design a modified ventilation system that (1) separates a portion of the exhaust exiting the lower portion of the booth, which contains a concentration of toxic pollutants greater than the average at the exhaust plane (split-flow) and (2) provides an option to return the flow from the upper portion of the exhaust to the intake plenum for mixing with fresh air and recirculation through the booth (recirculation). After critical review by cognizant Air Force offices and an experimental demonstration showing that a flame ionization detector monitoring the air entering the booth is able to detect excursions above the equivalent exposure limit for the solvents in the paint, the exhaust duct was reconfigured for split-flow and recirculating ventilation. A volunteer painter was briefed on the increased risk of exposure during recirculation and on the purposes and possible benefits of this study. He then signed an informed consent form before participating in the recirculation tests. A series of tests generally equivalent to the baseline series was conducted during split-flow and recirculating ventilation, and three tests were performed during only split-flow ventilation. Data from the two sets of test show that pollutants concentrate toward the bottom of the booth during ordinary painting operations; that local processes associated with circulation near the paint spray gun contribute far more to the net exposure to the painter than do toxic pollutants in the recirculated air stream; and that, under well-ventilated conditions, including split-flow and recirculation of a large fraction of the exhaust air, equivalent exposures to airborne toxic pollutants (calculated as the sum of 8-hour, time-weighted concentrations of toxicants divided by their Permissible Exposure Limits) should not exceed 0.25 in the intake air. An economic analysis of costs to implement thermal or catalytic incineration, with and without flow reduction by split-flow and recirculating technologies, projects substantial savings, such that the payback periods for inclusion of flow reduction technology during installation of the control device are about 1 year. The recirculation of air in the paint spray booth did not result in an increase in air contaminants that would exceed the capability of proper respiratory protection. The magnitude of the incremental increase in exposure derives primarily from particulates in the recirculated air. This is defined by the particulate removal efficiency of the particulate controls, which can be compromised by improper maintenance. However, with proper design, installation, and maintenance, the increment to risk is normally less than the round-off errors in the calculation of net job-related risk. Because the cost benefit is obtained at an increase of risk of exposure to painters, the acceptability of this cost-benefit trade-off will have to be resolved by industrial hygiene functions at both policy and local levels before this advance can be implemented at Air Force installations.