Hazard Screening for Toxic Inhalation Scenarios

Screening level evaluation for toxic inhalation impacts of a chemical release poses significant challenges for the Process Safety specialist. A simple approach is to specify a concentration above which it is assumed that individuals could be seriously impacted for a specified exposure duration (and a concentration below which serious impacts would be unlikely). Lethality or probit models offer the best relationship for estimation of toxic inhalation impacts. However, these models are only available for a very limited number of chemicals. There are several useful measures available with Emergency Response Planning Guideline (ERPG) concentrations becoming an acceptable industry criteria for comparing inhalation toxicity in the absence of lethality or probit models.

Relating lethality at one hour exposure duration from published probit models to ERPG Level 3 concentration may provide a means for comparing potential toxic impacts for screening level hazard evaluation and risk analysis. As there is very significant variability in the relationship of ERPG concentration and lethality from the published models, a “conservative” correlation should be considered. Even with very high uncertainty, toxic hazards may be compared and prioritized to determine which hazard situations deserve further evaluation.