Immediately dangerous to life or health; any atmosphere that poses an immediate hazard to life or produces immediate, irreversible debilitating effects
University of Maine, Department of Chemistry, Glossary of Safety Terms and Acronyms, Orono, ME, USA 2009. http://www.business.govt.nz/worksafe/tools-resourc es/glossary-of-terms-and-acronyms/a-to-b, (ChemSfty - Amer) {503}