Simplified methods of using probit analysis in consequence analysis

Ensuring personnel can safely shelter during a chemical release is critical. The probit function is useful in determining maximum safe sheltering time. Probits provide a link between probability of expected response and the exposure of a population to a specific event. Probit analysis can provide an estimate of the percentage of sheltered occupants with potential for adverse response to a chemical release. Probits can be used to estimate duration of exposure for probability of nuisance‐level response, loss of consciousness, or fatal exposures. Dispersion modeling tools provide data on predicted effects in response to long‐term exposure (typically 1 h). However, these tools do not define the maximum allowable exposure time for building occupants before loss of consciousness or fatalities are seen. This article provides methodology for estimating critical exposure duration. This article provides a methodology with existing MS Excel formulas in measuring probits to arrive at probability of response to a toxic release. While data on probit values for some chemicals is readily available, there is minimal guidance in the open literature on developing estimates of probit constants where they do not currently exist or are not published. This article presents a methodology for estimating probit constants based on toxicological data. © 2014 American Institute of Chemical Engineers Process Saf Prog 34: 58–63, 2015