Expert Judgement and Lethal Toxicity of Inhaled Chemicals

The application of formal expert judgement for assessing quantitative data of the toxicity of large amounts of inhaled chemical substances after a potential major hazards incident is described. In this particular application, the expert assessments were used to derive probit relations for the acute lethal effects of five hazardous substances: ammonia, acrylonitrile, hydrogen fluoride, sulphur trioxide and azinphos-methyl. The purpose of the study was to develop a protocol for selecting experts and the elicitation and analysis of expert assessments, to apply this protocol to generate probit relations for representative substances, and to evaluate the overall performance of the protocol. The use of formal expert judgement includes quantitative estimates of variables, calibration of experts and representation of uncertainty on the variables. This enables analysts to optimize combined experts' assessments for establishing quantitative results for further use in probit relations. Twenty-seven experts, distributed over the five substances, gave medians and 90% central confidence bands of the lethal dose-response relations under several conditions. The calculated dose-response relations are shown and compared to existing probit relations with respect to its impact on risk assessment outputs. The calculated relations can be applied in quantitative risk assessments, for example, under the Dutch law on major hazards installations. The scientific and practical efforts and costs of using the expert judgement technique are described.