August 17, 2023

NIOSH Requests Technical Review of Draft IDLH Value Profile for HCl

A draft IDLH (immediately dangerous to life or health) value profile for the chemical hydrogen chloride (HCl), which is used in a range of industrial processes, is available from NIOSH for technical review and public comment. According to the agency, HCl also forms during the burning of plastics and other chemical substrates. NIOSH’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 profile summarizes the technical data associated with acute inhalation exposures to HCl.

The NIOSH Pocket Guide to Chemical Hazards describes HCl as a “colorless to slightly yellow gas with a pungent, irritating odor.” The draft profile for HCl lists an IDLH value of 45 ppm (70 mg/m3), which is lower than the previous IDLH value of 50 ppm and is based on research published in 1988 that identified an LC50 value for HCl gas exposure of 1,341 ppm from guinea pigs. LC50 values indicate the concentration of a substance that kills half of exposed test animals. To calculate the IDLH of 45 ppm, “[a]n uncertainty factor (UF) of 30 was applied to estimate the risk of severe injury or death in a workplace emergency,” the draft profile explains.

As part of the technical review of the new draft document, NIOSH asks reviewers to consider whether the IDLH value profile clearly outlines the health hazards associated with acute exposures to HCl and whether the rationale behind the IDLH value derivation is clearly explained. Comments are due by Oct. 10, 2023. Further details, including instructions for submitting comments, can be found on 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​.​​​​​​

Related: The article “Decision Time” from the March 2018 Synergist discusses exposure models for emergency response. Part of the article focuses on a hydrochloric acid release as an example to inform tips for emergency dispersion modeling.