Evaluation of a proposed velocity equation for improved exothermic process control.
McKernan-JL; Ellenbecker-MJ; Holcroft-CA; Petersen-MR
Ann Occup Hyg 2007 Jun; 51(4):357-369
Exothermic or heated processes create potentially unsafe work environments for an estimated 5-10 million American workers each year. Excessive heat and process contaminants have the potential to cause adverse health effects in exposed workers. Owing to the potential hazards, engineering controls are recommended for these processes. Our understanding of heat transfer and meteorological theories, and their applications for engineering controls have evolved since seminal work was published by Hemeon in 1955. These refined theories were reviewed and used to develop a proposed equation to estimate buoyant plume mean velocity. Mean velocity is a key parameter used to estimate the plume volumetric flow required for controlling effluents from exothermic processes. Subsequent to developing the proposed equation, plume velocity data were collected with a thermal anemometer for a model exothermic process in the laboratory, and an actual exothermic process in the field. Laboratory and field results were then compared to solutions provided by the proposed, American Conference of Governmental Industrial Hygienists (ACGIH), and Hemeon mean velocity equations. To determine which equation most closely matched the laboratory and field data, either t-tests or Wilcoxon Signed Rank tests were conducted (based on examination of data normality) to determine the difference between collected data and solutions from the proposed, ACGIH, and Hemeon equations. Median differences and P-values from Wilcoxon Signed Rank tests (nonparametric) indicate that the ACGIH mean velocity equation provides significantly different estimates from the laboratory and the field mean velocity data. However, the proposed and Hemeon equation provided solutions that were not significantly different from the collected data. These results were unexpected due to the similar developmental backgrounds between the ACGIH and Hemeon equations. Findings indicate that radiant heat flux is an important consideration when using horizontal plate heat transfer equations to estimate plume mean velocity over the range of parameters investigated. Results indicate that the mean velocity equation currently recommended by ACGIH is not as accurate as either the proposed or Hemeon equations over the range of parameters investigated.
Models; Computer-models; Mathematical-models; Air-flow; Ventilation; Ventilation-systems; Ventilation-hoods; Exhaust-hoods; Exhaust-ventilation; Engineering-controls; Control-technology;
Author Keywords: engineering controls; hot process; local exhaust ventilation
John L. McKernan, National Institute for Occupational Safety and Health, Division of Surveillance, Hazard Evaluation and Field Studies, 4676 Columbia Parkway, MS-R14, Cincinnati, OH 45226, USA.
Annals of Occupational Hygiene