EHM (Extremely Hazardous Material) : Such materials are listed in Attachment V. They are orders of magnitude more hazardous than those listed as High Hazard Substances
Environmental Health & Safety, Glossary of Common Laboratory Safety and Hygiene Terms, Columbia University in the City of New York, USA 2008. http://ehs.columbia.edu/Glossary.html, (Lab Sfty and Hyg - Amer) {57}