MONTE-CARLO UNCERTAINTY ANALYSIS OF A DIFFUSION-MODEL FOR THE ASSESSMENT OF HALOGEN GAS EXPOSURE DURING DOSING OF BROMINATORS

Monte Carlo simulation was incorporated into a diffusion-based exposur e assessment model for the estimation of worker exposure to halogen ga ses during dosing of 500-lb sacks of a bromine-based biocide (BCDMH) i nto brominators. Indoor and outdoor dosing scenarios were modeled for small and targe brominators. The diffusion model used describes a conc entration gradient of halogen as a function of distance and time from the source. instead of ascribing worst-case single point value estimat es to the variables used in the diffusion model, Monte Carlo simulatio n was used to describe a distribution of values for each appropriate m odel variable. Using a personal computer and Monte Carlo simulation so ftware, 10,000 iterations of the diffusion model were performed for fo ur different dosing scenarios using random and independent samples fro m the distributions entered. The corresponding output distributions of predicted exposures were then calculated and displayed graphically fo r each scenario. The results_of the Monte Carte simulation predict tha t outdoor dosing of either small or large brominators with BCDMH is hi ghly unlikely to result in an exceedance of the working occupational e xposure limit for total halogen. In most ambient wind speed conditions , diffusion prevents appreciable airborne exposure to workers in the i mmediate vicinity of the brominator, Although relatively uncommon, dos ing of brominators indoors in the assumed absence of local exhaust ven tilation may generate airborne concentrations of total halogen that ex ceed the working short-term occupational exposure limit. Although very limited and inconclusive, field trial monitoring of BCDMH transfer op erations indoors resulted in halogen concentrations well within the di stribution of concentrations predicted by the Monte Carlo simulation o f the diffusion model.