Definition(s)
Flammable (Explosive) Limits
The lower and upper percentages by volume of concentration of gas in a gas-air mixture that will form an ignitable mixture (reference NFPA 497).
API RP 500, Recommended Practice for Classification of Locations for Electrical Installations at Petroleum Facilities Classified as Class I, Division 1 and Division 2, Third Edition, December 2012, Global Standards