Group C – Technical Review of Three (3) Draft IDLH Value Profiles

Federal Register Notice: Federal Register Notice [PDF – 261 KB] – Final

Federal Register Notice: Federal Register Notice [PDF – 192 KB]

Background Information: 

Information about IDLH Value Profiles

In 2013, NIOSH published Current Intelligence Bulletin (CIB) 66 – Derivation of Immediately Dangerous to Life or Health (IDLH) Values [NIOSH 2014-100]. Since the establishment of the IDLH values in the 1970s, NIOSH has continued to review available scientific data to improve the protocol used to derive acute exposure guidelines, in addition to the chemical-specific IDLH values. The information presented in this CIB represents the most recent update of the scientific rationale and the methodology (hereby referred to as the IDLH methodology) used to derive IDLH values. The primary objectives of this document are to:

1. Provide a brief history of the development of IDLH values
2. Update the scientific bases and risk assessment methodology used to derive IDLH values from quality data
3. Provide transparency behind the rationale and derivation process for IDLH values
4. Demonstrate how scientifically credible IDLH values can be derived from available data resources.

The IDLH methodology outlined in this CIB reflects the modern principles and under­standing in the fields of risk assessment, toxicology, and occupational health and provides the scientific rationale for the derivation of IDLH values based on contemporary risk as­sessment practices. According to this protocol, IDLH values are based on health effects con­siderations determined through a critical assessment of the toxicology and human health effects data. This approach ensures that the IDLH values reflect an airborne concentration of a substance that represents a high-risk situation that may endanger workers’ lives or health. Relevant airborne concentrations are typically addressed through the characteriza­tion of inhalation exposures; however, airborne chemicals can also contribute to toxicity through other exposure routes, such as the skin and eyes. In this document, airborne con­centrations are referred to as acute inhalation limits or guidelines to adhere to commonly used nomenclature.

The emphasis on health effects is consistent with both the traditional use of IDLH values as a component of the respirator selection logic and the growing applications of IDLH values in risk management plans for non-routine work practices governing operations in high-risk environments (e.g., confined spaces) and the development of emergency preparedness plans. Incorporated in the IDLH methodol­ogy are the standing guidelines and procedures used for the development of community-based acute exposure limits called Acute Exposure Guideline Levels (AEGLs). The inclusion of the AEGL methodology has helped ensure that the health-based IDLH values derived with use of the guidance provided in this document are based on validated scientific rationale.

The IDLH methodology is based on a weight-of-evidence approach that applies scientific judgment for critical evaluation of the quality and consistency of scientific data and ex­trapolation from the available data to the IDLH value. The weight-of-evidence approach refers to critical examination of all available data from diverse lines of evidence and the derivation of a scientific interpretation on the basis of the collective body of data, includ­ing its relevance, quality, and reported results. This is in contrast to a purely hierarchical or strength-of-evidence approach, which relies on rigid decision criteria for selecting a critical adverse effect, a point of departure (POD), or the point on the dose–response curve from which dose extrapolation is initiated and for applying default uncertainty factors (UFs) to derive the IDLH value. Conceptually, the derivation process for IDLH values is similar to that used in other risk-assessment applications, including these steps:

1. Hazard characterization
2. Identification of critical adverse effects
3. Identification of a POD
4. Application of appropriate UFs, based on the study and POD
5. Determination of the final risk value