Hood efficiencies of vapor degreasers under operating conditions.
Conroy LM; Prodans RS; Lachman M; Yu X; Wadden RA; Franke JE; Scheff PA
School of Public Health, Environmental and Occupational Health Sciences, University of Illinois at Chicago, Chicago, Illinois 1994 Nov; :1-27
The capture efficiency of local exhaust hoods used to control vapor degreasing tanks during normal operations was measured and compared with American Conference of Governmental Industrial Hygienists (ACGIH) design criteria of 1988. Hood efficiency was determined by measuring concentration of degreaser solvent in the workplace and local exhaust ventilation (LEV) ducts. Measured workplace concentration was translated to a mass emission rate in the workspace using a mass balance model, and calculating the LEV capture efficiency as the ratio of exhaust mass flow rate to total (exhaust and workspace) mass flow rate. The 15 degreasers evaluated were located in 12 private industrial settings, including metal fabricators, electronics manufacturers, and electroplaters. Trichloroethylene (79016) was used in 12 degreasers. Methyl- chloroform (71556), perchloroethylene (127184), and methylene- chloride (75092) were used in the other three applications. The degreasers were operated at an average of 104% of the design airflow. Average fugitive emissions ranged from 0.002 grams/second (g/s) to 0.972g/s. Average capture efficiency ranged from 9% to 99%. The relationship between measured hood capture efficiency and hood exhaust flow rate had a correlation coefficient of 0.073. Hood capture efficiency was highly variable, and the ACGIH hood design parameter did not predict hood performance. Hood capture efficiency best correlated with hood face velocity with a correlation coefficient of 0.449. The authors conclude that the ACGIH recommended flow of 0.25 cubic meters/second/square meter of tank surface is sometimes inadequate; it is not possible to predict conditions where the recommended flow will be adequate.
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