4. Case study for chemical exposure assessment
As a case study an assessment of six competing process routes for manufacturing methyl methacrylate (MMA) is presented. The routes are acetone cyanohydrin based route (ACH), ethylene via propionaldehyde based route (C2/PA), ethylene via methyl propionate based route (C2/MP), propylene based route (C3), isobutylene based route (i-C4), and tertiary butyl alcohol based route (TBA). For more details about the processes, see Rahman et al. (2005).
4.1. Analysis on wind distribution data
For estimating the worker potential exposure at real wind conditions, wind distribution data in a seaside location in Finland was used in the case study. The data for 2007 consisting of almost 9000 measurements at 25 m height from surface. The highest probability of the wind speed in that year falls between 3 and 4 m/s at 25 m. First, the wind speeds at 1.5 m above ground level are estimated based on the data at 25 m height. The friction coefficient value of 0.20 is applied in Eq. (4). Then, using Eqs. (1), (2) and (3) the Weibull parameters were estimated by regression; the shape parameter β was found to be 2.29 and the scale parameter α is 2.1 m/s at 1.5 m height. The annual wind distribution at 1.5 m height is shown in Fig. 1. The corresponding cumulative distribution is presented in Fig. 2.