The highest concentration (expressed in percent vapor or gas in the air by volume) of a substance that will burn or explode when an ignition source is present
US Department of Labor, Occupational Safety & Health Administration (OSHA), OSHA Office of Training and Education, Glossary of Terms, Construction Safety and Health Outreach Program, DC, USA 1996. http://www.osha.gov/doc/outreachtraining/htmlfiles /hazglos.html, Washington, (OSH - Amer) {516}