June 22, 2023

Draft IDLH Value Profiles for Hydrogen Bromide, Hydrogen Iodide Published

Today, NIOSH published draft IDLH (immediately dangerous to life or health) value profiles for two chemicals: hydrogen bromide, which is used as a solvent and organic catalyst, and hydrogen iodide, a substance used primarily as a reducing agent. The agency’s IDLH values are established to ensure workers’ ability to escape from a contaminated environment in the event that their respiratory protection equipment fails. IDLH values are also intended to represent a maximum level above which workers should not be exposed without highly reliable respiratory protection. The draft profiles summarize the technical data associated with acute inhalation exposures to hydrogen bromide and hydrogen iodide.

NIOSH describes both chemicals as “corrosive, nonflammable [gases] with an acrid, irritating odor.” Hydrogen bromide is colorless, whereas hydrogen iodide can be colorless to yellow or brown. The draft profile for hydrogen bromide lists an IDLH value of 35 ppm (116 mg/m3), which is higher than the previous IDLH value of 30 ppm. NIOSH’s new draft profile for hydrogen iodide lists an IDLH value of 35 ppm (183 mg/m3), a value the agency says is based on the lethality of the “closely related” hydrogen bromide.

“Lethal concentrations of halogen acid vapors cause severe dyspnea and respiratory distress,” the draft profile for hydrogen iodide explains. “The immediate effects and potency of [hydrogen iodide] is expected to be similar to [hydrogen bromide] and hydrogen chloride (HCl) gases.”

NIOSH requests technical review of the new draft documents. The agency asks reviewers to consider whether the IDLH value profiles clearly outline the health hazards associated with acute exposures to each chemical and whether the rationale behind the IDLH value derivation is clearly explained. Comments are due by Aug. 21, 2023. Further details, including instructions for submitting comments, can be found on Regulations.gov or in the Federal Register.

The NIOSH method for determining IDLH values is described in Current Intelligence Bulletin 66: Derivation of Immediately Dangerous to Life or Health (IDLH) Values, or CIB 66. The document notes that occupational health and safety professionals have incorporated IDLH values into risk management plans for operations in high-risk environments such as confined spaces, and in guidance for emergency responders. For more information on IDLH values, visit the NIOSH website​.​​​​​​