Abstract
The possibility of accidental industrial chemical releases has generated considerable recent attention. One area requiring research for emergency planning is the development of safe exposure concentrations for the public in the event of an inadvertent release. The United States Environmental Protection Agency (EPA) has established a list of extremely hazardous substances and suggested that the toxicity ranking for 92 hazardous materials could be based on the ‘immediately dangerous to life or health’ (IDLH) values developed by the National Institute for Occupational Safety and Health (NIOSH) and the Occupational Safety and Health Administration (OSHA). Eighty-four compounds with IDLU values for which published toxicologic data were available were reviewed to assess the appropriateness of applying such values to accidental release situations. When compared with 30-min animal median lethal concentrations(LC50s), 18 of the IDLHs reviewed were in the same range as lethal levels for animals. For 45 compounds the IDLH values were comparable to concentrations producing severe toxic effects (specifically, unconsciousness, incapacitation, or intolerable irritation). Where available, emergency planning guidelines for the military were compared to IDLHs, and in all 31 cases, the IDLHs exceeded the military exposure guidelines. Twenty compounds also were found to pose a potential cancer risk according to common regulatory guidelines, even under the assumption of a single, 30-min exposure at the IDLH concentration. In addition, the high degree of variability (four orders of magnitude) in the relationship of IDLH values to outcomes of lethality or severe toxicity suggests that the use of IDLH values as emergency planning guidelines for accidental releases is questionable. Furthermore, this review raises concerns about the adequacy of the IDLH values themselves to protect workers from exposure to acutely toxic compounds.