Immediately dangerous to life or health (IDLH) means any condition that would interfere with an individual’s ability to escape unaided from a permit space and that poses a threat to life or that would cause irreversible adverse health effects.NOTE: Some materials -hydrogen fluoride gas and cadmium vapor, for example -may produce immediate transient effects that, even if severe, may pass without medical attention, but are followed by sudden, possibly fatal collapse 12-72 hours after exposure. The victim “feels normal” after recovery from transient effects until collapse. Such materials in hazardous quantities are considered to be “immediately” dangerous to life or health.