NIOSH recently announced the availability of final Immediately Dangerous to Life or Health value profiles for four chemicals: acetonitrile, chloroacetonitrile, methacrylonitrile, and nitrogen dioxide. Each profile summarizes the health hazards of acute exposures to high airborne concentrations of a chemical and discusses the rationale for the chemical’s proposed IDLH value. According to NIOSH, an IDLH value, which is based on a 30-minute exposure duration, is the maximum level above which only a highly reliable breathing apparatus that provides “maximum worker protection” is permitted.

The new IDLH value for acetonitrile is 137 ppm (230 mg/m³). Chloroacetonitrile’s IDLH value is 14 ppm (23 mg/m³), and the IDLH value for methacrylonitrile is set at 4.0 ppm (11 mg/m³). The IDLH value for nitrogen dioxide, 13 ppm (24 mg/m³), is based on a lowest observed adverse effect level of 30 ppm for respiratory irritation and severe cough in volunteers following a 70-minute exposure.

“Duration adjustment resulted in the calculation of a 30-minute equivalent LOAEL of 38 ppm,” NIOSH’s IDLH value profile for nitrogen dioxide explains. “A composite uncertainty factor of 3 was applied to account for human variability yielding an IDLH value of 13 ppm for nitrogen dioxide.”

The new documents are available on NIOSH’s .

IDLH values are established to ensure workers’ ability to escape without loss of life or immediate or delayed irreversible health effects and to prevent severe eye or respiratory irritation or other reactions that would hinder escape.