Upper Bound on the Threshold Crossing Probability for Short-Time Exposure Dosage with Implications for the Assessment of Hazard from Toxic Vapors

摘要

The effects of most toxic substances (e.g., chemical and biological warfare agents) are cumulative in the sense that the response of the biological receptor (e.g., human lung) is dependent on the concentration of the noxious vapor integrated over the total exposure time, i.e., the total exposure dosage. An upper bound on the threshold crossing probability of the random dosage field produced by the instantaneous or short-term release of a passive scalar (contaminant) into the turbulent atmospheric boundary layer is obtained. This bound is constructed by developing a model for the nonstationary stochastic process representing the fluctuations in the concentration of the contaminant as observed at some fixed receptor downwind of the source (i.e., the point of release of the scalar). The implications of this bound for the evaluation of the hazard posed by the release of toxic substances into the atmosphere is discussed. Here, it is emphasized that the neglect of fluctuations in the dosage can lead to significant underestimation of the risk of exposure to the toxic substance. Furthermore, it is speculated that the nature as well as the magnitude of the concentration fluctuations will have considerable impact on the protection levels that are provided by the current individual and collective protection equipment such as mask cannisters or filters and protective suits. Canada. (aw)