Definition(s)
Upper Flammable Limit
The maximum concentration of a flammable vapor in air (or other oxidant) above which propagation of flame does not occur on contact with an ignition source. The UFL is usually expressed as a volume percentage of the vapor in air Sometimes called the upper explosive limit (UEL). In popular terms, a mixture containing a percentage of flammable vapor above the UFL is too “rich” to burn.
Source: API Standards 2217A, Guidelines for Safe Work in Inert Confined Spaces in the Petroleum and Petrochemical Industries, Fourth Edition, July 2009. Global Standards
Upper Flammable Limit (UFL)
The maximum concentration of a vapor in air (or other oxidant) above which propagation of flame does not occur on contact with an ignition source. The upper flammable limit is usually expressed as a volume percentage of the vapor in air. Sometimes called the Upper Explosive Limit (UEL). In popular terms, a mixture containing a percentage of flammable vapor above the UFL is too “rich” to burn and one below the LFL is too “lean” to burn.
API RP 2201, Safe Hot Tapping Practices in the Petroleum & Petrochemical Industries, Fifth Edition, July 2003 (Reaffirmed October 2010), Global Standards
API RP 2009, Safe Welding, Cutting, and Hot Work Practices in the Petroleum and Petrochemical Industries, Seventh Edition, February 2002 (Reaffirmed, March 2012), Global Standards
Upper Flammable Limit (Gas Properties)
Volume fraction of flammable gas or vapour in air above, which an explosive gas atmosphere does not form, expressed as a percentage (see IEC 60079-20).
NOTE This is also known as upper explosive limit (UEL).
Source: IEC 60079-29-1, Explosive atmospheres – Part 29-1: Gas detectors – Performance requirements of detectors for flammable gases. Global Standards