API Publ 4644:1997 pdf download

API Publ 4644:1997 pdf download.A METHODOLOGY FOR ESTTMATING INCREMENTAL BENZENE EXPOSURES AND RISKS ASSOCIATED WITH GLYCOL DEHYDRATORS.
The US. Environmental Protection Agency (EPA) is currently evaluating potential applicability criteria for glycol dehydrator air emission controls. To assist this evaluation, the American Petroleum Institute (API) commissioned TRJ Environmental, Inc. (TRJ) to develop a methodology to estimate benzene exposures and associated risks under representative emission conditions.
The EPA assisted in this research effort by performing a series of dispersion model runs using emission parameters suggested by API and meteorological data representing 348 weather stations in the United States. TRJ performed a series of statistical analyses on the results of these runs which indicated that the distribution of ambient (outdoor) benzene concentrations produced by an operating glycol dehydrator unit could be estimated as a function of benzene emission rate, vent velocity, vent diameter, land use (urban or rural), and source-to-receptor distance. Equations based on the statistical analyses were incorporated into a spreadsheet model capable of plotting outdoor concentration vs. distance’ for specified emission scenarios and concentration percentiles.
In addition to the spreadsheet model, a Monte Carlo routine for estimating lifetime cancer risk as a function of the estimated benzene concentration distribution was aLso developed. The entire process (spreadsheet program and Monte Carlo routine) was incorporated into a PC-based model called SimRisk. SimRisk generates a lifetime risk distribution that accounts for four factors that affect benzene exposure (residential occupancy period, time spent indoors and outdoors at the home location, indoor/outdoor ratio for benzene concentration, and breathing rate). The lifetime risk distribution is specific to benzene emission rate, vent velocity, vent diameter, land use (urban or rural), and source-to-receptor distance.
A simplified version of SimRisk was developed that can be used to estimate the 50th and 95th percentile values of lifetime risk solely as a function of benzene emission rate, source-to-receptor distance, and Land use. This simplified risk model could be incorporated into control applicability criteria for glycol dehydrator vent emissions. To determine the applicability of controls to a specific unit, the analyst would use a simple graph or lookup table obtained from the model to determine the minimum source-to- residence distance associated with a specified lifetime cancer risk, lithe actual distance from the glycol dehydrator unit to the nearest residence exceeds this minimum distance, the analyst could assume that the glycol dehydrator unit requires no further emission controls. If, however, the actual distance from the glycol dehydrator unit to the nearest residence is equal to or less than this minimum distance, then the source may be subject to additional controls.
This model is applicable only to glycol dehydrators operating under a specific set of conditions and should not be used outside of the following ranges.