NIOSH Updates Methodology for Setting IDLH Values

A NIOSH Current Intelligence Bulletin (CIB) released Nov. 1 describes the agency's updated method for determining immediately dangerous to life or health (IDLH) values. NIOSH defines an IDLH condition as "one that poses a threat of exposure to airborne contaminants when that exposure is likely to cause death or immediate or delayed permanent adverse health effects or prevent escape from such an environment." According to Current Intelligence Bulletin 66: Derivation of Immediately Dangerous to Life or Health (IDLH) Values, IDLH values represent a maximum level above which workers should not be exposed without highly reliable respiratory protection. The values are also intended to ensure that workers can escape from IDLH conditions even if their respiratory protection fails.

CIB 66 presents NIOSH's most recent update of the scientific rationale and methodology used to derive IDLH values. The methodology incorporates the guidelines and procedures used for the development of acute exposure guideline levels (AEGLs), which are levels below which adverse health effects are not likely to occur. According to NIOSH, the AEGL methodology helps ensure that IDLH values are derived according to validated scientific rationale.

The document compares IDLH values to other short-term exposure limits and discusses criteria for determining IDLH values and the use of uncertainty factors.

IDLH values were first developed in the 1970s as an element of the NIOSH Respirator Selection Logic. CIB 66 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.

CIB 66 can be downloaded from the NIOSH website

Ralph Stuart

secretary**At_Symbol_Here**dchas.org

Secretary

Division of Chemical Health and Safety

American Chemical Society