What does IDLH stand for? 

IDLH

IDLH is an acronym for Immediately Dangerous to Life or Health, and is defined by the US National Institute for Occupational Safety and Health as exposure to airborne contaminants that is "likely to cause death or immediate or delayed permanent adverse health effects or prevent escape from such an environment." Examples include smoke or other poisonous gases at sufficiently high concentrations. The OSHA regulation defines the term as "an atmosphere that poses an immediate threat to life, would cause irreversible adverse health effects, or would impair an individual's ability to escape from a dangerous atmosphere." IDLH values are often used to guide the selection of breathing apparatus that are made available to workers or firefighters in specific situations. The NIOSH definition does not include oxygen deficiency although atmosphere-supplying breathing apparatus is also required. Examples include high altitudes and unventilated, confined spaces. The OSHA definition is arguably broad enough to include oxygen-deficient circumstances in the absence of "airborne contaminants," as well as many other chemical, thermal, or pneumatic hazards to life or health. It also uses the broader term "impair", rather than "prevent", with respect to the ability to escape. For example, blinding but non-toxic smoke could be considered IDLH under the OSHA definition if it would impair the ability to escape a "dangerous" but not life-threatening atmosphere.

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