A Probabilistic Health Risk Assessment Screening Tool forSources of Volatile and Gaseous Toxic AirPollutant Emissions

摘要

A generalized method has been developed to provide realistic probabilistic screening-levelestimates of long-term health risks associated with inhalation of emissions from industrial orcommercial facilities. The product is a set of look-up tables that identify the level of cancerand/or non-cancer risk as a function of distance for various probability thresholds. Once a tablehas been tailored to a specific industrial sector, it could be used in variety of contexts, such ascharacterizing risk for existing facilities, determining the collective risk of nearby facilities, orfinding an appropriate site for a new facility. The probabilistic method accounts for two majorsources of variability in inhalation risk assessment, dispersion climatology and personalexposure. The step-wise approach used to develop the screening tool is described and anexample application is presented. In the initial step, engineering judgment and experience,together with established emission factors, are used to develop generic physical parameters andemissions for model facilities for an industrial category. Long-term dispersion modeling usingAERMOD is conducted for the model facility using unit emissions and over 100 sets ofmeteorological data representing the range of dispersion climatology throughout the U.S.Statistical distributions are then fit to the sets of modeled ambient concentrations as a function ofdistance for each model facility. U.S. EPA dose-response factors are then applied using acharacteristic profile of HAP emissions for the model facility to develop toxicity-weightedemissions, which when multiplied by the modeled unit concentrations result in upper-limit modelestimates of individual risk (assuming a person is continuously exposed at fixed location over astandard 70-year lifetime). Realistic risk probabilities are then generated from these upper-limitestimates by applying SimRisk, a probabilistic computer program that incorporates typicalvariations in human activity patterns. The method is demonstrated with an example application.