Handbook of Chemical Health and Safety. Alaimo RJ, ed., New York: Oxford University Press, Incorporated, 2001 Mar; :102-129
As discussed in Hewett (see Chapter 15), industrial hygiene exposure assessments come in three varieties: qualitative, semiquantitative, and quantitative. Quantitative surveys, which involve the measurement of current worker exposure using personal sampling equipment or direct reading instruments, are often necessary for initial or baseline evaluations. Furthermore, periodic sampling and occasional audits are necessary for validating earlier assessments and for detecting upward trends in exposure. Consequently, an industrial hygienist is often faced with questions regarding the collection, analysis, interpretation, and management of occupational exposure data. Hewett described the rationale behind exposure monitoring and covered data collection and data management. The purpose of this chapter is to suggest appropriate procedures for analyzing and criteria for interpreting exposure data. As discussed in Hewett, exposure-monitoring programs must be designed and tailored for a wide variety of work environments. But first, as noted by Roach in 1967. "[it] is important that hygienic standards should not be given widely different interpretations." We should also agree that the goal of an effective exposure-monitoring program is to routinely and accurately characterize the exposure profile of each worker. It is less critical that we adopt identical or similar data analysis and interpretation procedures. There are numerous data analysis techniques - parametric and nonparametric - that will yield similar decisions regarding the acceptability of the work environment. Regardless of the number of measurements collected or the sophistication of the analysis technique, there is always a role for professional judgment and common sense. The procedures presented here emphasize the calculation of the point estimate of a relevant exposure parameter, and in addition the 95% lower confidence limit (LCL) and the 95% upper confidence limit (UCL). Taken together, these confidence limits comprise a 90% confidence interval for the true parameter. The advantage of this interval estimate is that it can readily be used to gauge (a) the accuracy of our point estimate of the true parameter, and (b) the acceptability of the work environment by comparing the LCL or UCL to an exposure limit or other relevant criterion. These procedures are consistent with those recommended by the Exposure Assessment Strategies Committee (EASC), of the American Industrial Hygiene Association (AIHA) and the Comite Europeen de Normalisation (CEN). Each worker should expect a work environment devoid of unreasonable risks. Our goal is to protect each individual worker, but limited resources usually compel industrial hygienists to (a) aggregate workers into exposure groups; (b) determine which exposure groups warrant priority attention; and (c) evaluate the "exposure profile" of each exposure group in order of priority. Consequently, our data collection strategies (see Hewett), and data analysis and interpretation procedures must be designed so that our conclusions regarding the exposure group are reasonably predictive of the exposures experienced by each member of the group.