Analysis of the Basis for Immediately Dangerous to Life or Health (IDLH) Concentrations. A. Maier, J. Zhao, K. Poirier, and H. Ahlers, Toxicology Excellence for Risk Assessment, Cincinnati, OH; and National Institute for Occupational Safety and Health, Cincinnati, OH
Immediately Dangerous to Life or Health (IDLH) concentrations are airborne levels that upon exposure are likely to result in death or immediate or delayed permanent adverse health effects, or are likely to prevent escape from the exposure. These values are frequently used in an occupational setting to define respiratory equipment requirements and in the evaluation of procedures for entering exposure areas. A critical review was conducted of the human health and animal toxicity data upon which 15 of the IDLH concentrations were derived. The analysis was conducted to determine the appropriateness of the existing IDLH values with an emphasis on the strength of the supporting data. Of the 15 substance reviewed, the existing data appeared to include studies with adequate descriptions for six of the 15 substances. The critical effect for the IDLH concentrations was lethality for four substances, eye or respiratory irritation for five substances, and central nervous system effects for six substances. Based on the weight of the evidence, two values were viewed as insufficiently protective, seven as reasonably protective, two as conservative, and four values had data gaps which precluded a judgment. This analysis provides a framework for evaluating the adequacy of the supporting data for additional IDLH values and highlights the continued need for high quality acute toxicity data for substances commonly encountered in occupational environments.
Project Supported by the National Institute for Occupational Safety and Health.
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