The OSHA respiratory protection standards require a full facepiece pressure demand SCBA or a combination full facepiece pressure demand supplied-air respirator with auxiliary self-contained air supply for employee use in IDLH atmospheres.

NIOSH Seeks Comments on New IDLH Process

The agency is conducting a public review of the draft Current Intelligence Bulletin, titled Derivation of Immediately Dangerous to Life and Health (IDLH) Values.

NIOSH is asking for comments by March 15 about its draft Current Intelligence Bulletin, Derivation of Immediately Dangerous to Life and Health (IDLH) Values, and said it may decide later to hold a public meeting in Cincinnati or online.

The draft document and instructions for submitting comments are available at Submissions and other information will be available at the NIOSH Docket Office, 4676 Columbia Parkway, Room 111, in Cincinnati or at the NIOSH Web page,, under docket number NIOSH 156. For information, contact G. Scott Dotson at NIOSH's Robert A. Taft Laboratories, 513-533-8540.

NIOSH and OSHA developed occupational health standards together in 1074 for substances for which OSHA had permissible exposure limits at the time. This joint effort was called the Standards Completion Program, and Immediately Dangerous to Life and Health (IDLH) values were determined for each chemical as part of the respirator selection process for each draft technical standard, according to NIOSH's Jan. 24 announcement.

"Since the establishment of the original IDLH values in 1974, NIOSH has continued to review the available scientific data to improve the protocol used to derive the acute exposure guidelines, in addition to the chemical-specific IDLH values," it states. "This draft CIB represents the most recent update of the scientific rationale and process used to derive IDLH values based on health effects considerations determined through a critical assessment of the toxicology and human health effects data.

"The new process relies on a weight-of-evidence approach based on scientific judgment for establishing IDLH values that allows for the critical evaluation of the quality and consistency of the scientific data, and in extrapolation from the available data to the IDLH value. The weight-of-evidence approach refers to the critical examination of all the available data from diverse lines of evidence and the derivation of a scientific interpretation based on the collective body of data including its relevance, quality and reported results. Guidelines are presented to aid in the selection of the critical adverse effect, a point of departure (POD) or the point on the dose-response curve from which dose extrapolation is initiated, and applying default uncertainty factors (UFs) to derive the IDLH value. Conceptually, the derivation process presented in this CIB is similar to that used in other risk assessment applications including the process steps of:

  • Hazard characterization,
  • Identification of critical adverse effects,
  • Identification of a POD,
  • Application of an appropriate UF based on the study and POD, and
  • Determination of the final risk value."

The draft bulletin includes a discussion of the strategy used to identify relevant data, the scheme used to prioritize and select chemicals for which an IDLH value will be established, and an overview of the analysis applied by NIOSH to develop a scientifically-based approach for the selection of the UFs. Appendix A of the draft gives an example: an IDLH value for vinyl acetate (CAS 108-50-4) that is based on the new process.

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