“Exposure assessment is the process of estimating or measuring the magnitude, frequency and duration of exposure to an agent, along with the number and characteristics of the population exposed”. (US EPA) Results of exposure assessment help industrial hygienists understand exposure level of workers and design the required control measures to protect workers. Also, it could be used for exposure-response in epidemiologic study. Exposure assessment involves industrial hygiene sampling and analysis and estimating true level of occupational exposure.
2. Uncertainty and variability in exposure assessment
Uncertainty in occupational exposure assessment cause imprecise estimation of true exposure. Two 2 major sources of uncertainty are: natural variability and the lack of knowledge or fundamental ignorance. (Bullock and Ignacio, 2006; Keil et al, 2009; US EPA, 2008)
2.1 Natural variability or Type I uncertainty plays a big role in occupational exposure assessment since it causes heterogeneity and large variability as well as lognormal distribution and autocorrelation in occupational exposure data. Natural variability cannot be eliminated but can be characterized, quantified and minimized by proper industrial hygiene sampling strategies and statistical methods. Examples of natural variability in occupational exposure assessment are: variability between workers such as breathing rate or height of workers; variability between work days or working shift such as cycle of production, rate of production; variability of work environment such as air movement, ventilation rates, chemicals emission rate, difference of temperature; and variation in time. (Bullock and Ignacio, 2006; Keil et al, 2009; US EPA2008)
2.2 The lack of knowledge or Type II uncertainty results from limitation of knowledge in occupational exposure assessment. Example of this type of...