Analysis of Exposure Using a Logbook Method

Two principal problems are met when measuring long-term mean exposures at the workplace: (1) Sampling is often done from wide and skewed exposure distributions, which causes a certain risk for inaccurate estimations, when measurements are performed only on a single day or a few days. (2) Commonly, measurements of workers' exposures are performed by personal sampling, but action to reduce exposure frequently comprises alterations of the processes performed or their environments. A sampling strategy is therefore proposed which, at the expense of high precision (low random errors), could improve accuracy (reduce combined bias and random errors) when determining the long-term mean exposure to volatile chemicals for workers having shifting work patterns. The proposed logbook method measures the time and concentration components of the time-weighted average concentration (TWAC) separately. It consists of process logkeeping and process measurements (i.e., only one process is performed during the sampling period). The method makes possible a detailed analysis of exposure by which workers can be ranked after exposure and processes can be ranked after their contributions to workers' exposure. The method preserves information on the structure of exposure, whereas much information is lost when a day's exposure is summarized into one single value of the TWAC. Further, when costs and efficiency of engineering controls, substitution, education, and the like, are known, a cost-effective strategy for improving the working environment can be made and implemented based on quantitative exposure data. The practical application of the method is illustrated by measurements performed in two fiberglass-reinforced polyester facilities. The two facilities have similar buildings, engineering controls, working methods and materials, but differ in work organization. Analysis of exposure shows great differences between the two facilities in terms of long-term mean exposures and day-to-day variation of exposure. In both facilities, ranking processes after both exposure intensity and exposure duration is quite different from the order of processes ranked after intensity alone. Analyses of exposure are easily done in computer spreadsheets.