IDLH Values: NIOSH’s Measure of Air That Is Immediately Dangerous to Life or Health

Exposure to chemicals at work has long been known to threaten workers' lives and health. A short, intense exposure to high concentrations of some airborne chemicals can quickly overwhelm a worker, causing anything from eye and respiratory irritation to severe, irreversible harm, an inability to escape, and in extreme cases death.

What IDLH values are

The National Institute for Occupational Safety and Health's Immediately Dangerous to Life or Health (IDLH) values describe these high-risk exposure concentrations and conditions. They are part of the respirator selection criteria first developed in the mid-1970s, and they serve two purposes:

1. to make sure a worker can escape from a contaminated environment if their respiratory protection fails;
2. to mark the maximum level above which only a highly reliable breathing apparatus, giving the greatest protection, is permitted.

How they've evolved

The original IDLH values date from the 1970s and were revised in 1994. Since then, NIOSH has continued to review scientific data and to research methods for developing acute exposure guidelines. How values are now derived is set out in NIOSH Current Intelligence Bulletin 66, Derivation of Immediately Dangerous to Life or Health Values (DHHS (NIOSH) Publication Number 2014-100).

The table of values

NIOSH publishes IDLH values for several hundred substances, each with its CAS number. It aims to re-evaluate every one under the Bulletin 66 criteria; until then, the list mixes values based on the 1994 revised criteria and on Bulletin 66, so it matters which criteria produced a given value. Where an entry has more than one IDLH value, the one based on Bulletin 66 is current NIOSH policy.

Values are given in parts per million (ppm) or milligrams per cubic metre (mg/m³). Some are capped at 10% of the lower explosive limit, marked [10% LEL]. A few familiar examples:

The full list is on the NIOSH IDLH page.

Sources

Based on "Immediately Dangerous to Life or Health (IDLH) Values," National Institute for Occupational Safety and Health, Centers for Disease Control and Prevention; a work of the United States government in the public domain. The explanation of the table and the example values were missing from the imported page and are taken from the page as published.