IDLH (Immediately Dangerous to Life or Health) designates an atmospheric concentration of a hazardous substance that presents an immediate threat to life, can cause irreversible health effects, or significantly impairs an individual's ability to escape from a hazardous environment. Not to be confused with permissible exposure limits, IDLH values are critical in the context of incident command systems (ICS) and the establishment of hot, warm, and cold zones during hazardous materials incidents. In hazmat and CBRN operations, it is often referenced alongside scene control concepts such as Hot, Warm, and Cold Zones and decontamination corridors to clarify operational boundaries.
Category context: Hazardous materials, decon, isolation zones, UN/ERG concepts, and CBRN terminology.