A FIX FOR THE USEPA's RMP~*COMP MODEL

摘要

The U.S. Environmental Protection Agency (EPA) Risk Management Program and Plan (RMP) Rule was issued on June 20, 1996, which required the implementation of the Risk Management Program by June 21, 1999 for the existing facilities. Hazard assessment is one of the main components of the RMP, which includes an estimate of possible release quantities for worst-case and alternative release scenarios and estimation of toxic endpoint distances. This analysis is more commonly known as offsite consequence analysis (OCA). EPA developed the RMP OCA Guidance Document to assist the facilities subject to RMP rule in performing the offsite consequence analysis for the worst-case as well as the alternative release scenarios. This document also provides guidance in estimating the evaporation rates from liquid pools at various temperatures and the toxic endpoint distances for the accidental releases of toxic substances. Guidance for similar analysis for common water solutions of toxic substances is also provided in this OCA guidance document. The EPA has also developed the RMP~*Comp Electronic Tool for performing the offsite consequence analysis. This is a computerized tool and is supposed to reproduce the results obtained using the RMP OCA guidance document. However, a review of the results of offsite consequence analysis performed for the worst-case release scenarios for common water solutions released in diked areas indicated that the dike option does not work properly (over-predicts toxic endpoint distances) if the common water solution release temperature is higher than 77 deg F (25°C). A review of the maximum temperatures recorded during the last three years in the various cities in USA indicated that maximum temperatures were higher than 77 deg F in most of the cites. Thus, the RMP*Comp Electronic Tool cannot be used to estimate the toxic endpoint distances for worst-case release scenarios involving common water solutions in most parts of the country. A further review of the RMP~*Comp Electronic Tool outputs indicated that this problem can be fixed quickly. In addition to fixing the RMP~*Comp Electronic Tool, a hybrid approach can be followed for estimating the toxic endpoint distances for worst-case release scenarios for common water solutions. This hybrid approach for aqueous ammonia involves the following steps: (1) use the RMP~*Comp Electronic Tool for estimating the evaporation rates at 77 deg F with and without dike, (2) calculate the ratio of these two evaporation rates, (3) estimate the release rate at the temperature higher than 77 deg F, (4) correct this evaporation rate for the diked condition using the ratio estimated in step 2, and (5) estimate the toxic endpoint distance using the Table 10 in the OCA guidance document. The details of this approach are presented in the paper.