IDLH (Immediately Dangerous To Life or Health) 2 :
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. [air quality]
CoTradeCo Glossary of Critical Industrial Safety Terms and Other Important Words, Abbreviations and Acronyms, La Quinta, CA., USA 2010. https://cotradeco.com/pages/52-glossary-of-critica l-terms-abbreviations-ratings-regulations, (IndS - Amer) {36}