Assessment of Methods Used to Measure Fume Hood Performance
Mulenga, Emmanuel M.
(University of Arizona)
Background:
Contaminants generated in laboratories or during industrial processes are often controlled through the use of fume hoods. Such hoods are generally constructed with nonflammable materials. Over the years, laboratory fume hoods have been designed to meet certain face velocity standards that lack a solid foundation that is supported by extensive experimental data. An air velocity traverse across the face of the hood represents the typical technique used today to assess hood performance in laboratory and industrial settings. Research by Caplan and Knutson (1982) revealed a number of parameters beyond hood face velocity that can have an even greater impact on hood performance. Their research forms the basis for a more complex method for assessing hood performance that has been recommended by the American Society of Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE). The method is based on using a tracer gas to measure actual leakage from a fume hood, as well as assessing parameters such as hood location and use patterns to further assess the potential for disruption of control velocities across the hood face. While the ASHRAE method has more scientific validity than the face velocity method, it appears to be much more complex and time consuming. A previous research project conducted by an industrial hygiene student at the University of Arizona (Scott, 1992) explored the possibility of expanding the standard face velocity method to include some of the parameters identified by Caplan that were shown to have substantial impact on hood performance
Objective:
The objective in this proposed research paper is to assess the three fume hood assessment methods (face velocity technique, ASHRAE tracer gas technique, and Scott method) used to measure fume hood performance and determine if modifications or a combination of the methods could provide a better basis for assessing hood performance. Some of the confounding factors expected to affect hood performance include 1) airflow velocity
2) type of hood design 3) location and velocities associated with general ventilation patterns in the room, 4) traffic in the vicinity of the hood face 5) amount and types of compounds being stored or used in the hood and 6) other experiments or production processes being conducted in the workspace.
Methodology:
A thorough description of each of the three hood assessment techniques (face velocity, ASHRAE, Scott) will be provided. A qualitative analysis of the strengths and limitations of each method will also be conducted. In addition, a comparative study of the application of the three methods to a minimum of five representative hoods at a semiconductor manufacturing site will be attempted. The cooperation of a semiconductor manufacturing facility in the Phoenix area will be required to accomplish this part of the proposed research.
Relevance and Expected Outcome:
At the end of this research project I hope to show the distinct differences that exist between three individual methods of testing lab hood performance, and to develop recommendations that could optimize hood performance by identifying the different parameters that need to be considered during hood installation and assessment. Consequently, even though hood designs differ, using a more comprehensive hood assessment technique could potentially maximize the capture and control of toxic chemicals before they reach the breathing zone of workers. This would minimize worker exposures to compounds, including occupational carcinogens, to the greatest extent possible by ensuring that hood performance can be traced to the most scientifically defensible information available.