Flammable and Combustible Liquids

DOE-HDBK-1015/2-93 Hazards of Chemicals and Gases FLAMMABLE AND COMBUSTIBLE LIQUIDS Rev. 0 CH-05 Page 31 IC - Those liquids having flash points at or above 73 F and below 100 F. Class II - Those liquids having flash points at or above 100 F and below 140 F. Class III - Those liquids having flash points above 140 F. IIIA - Those liquids having flash points at or above 140 F and below 200 F. IIIB - Those liquids having flash points above 200 F. Flammable and combustible liquids vaporize to form flammable mixtures when they are stored in open containers, when they leak or are spilled, or when heated. The hazard that exists from these mixtures is largely dependent upon the flash point of the liquid, the concentration of the mixture, and the potential of a source of ignition at a temperature sufficient to cause the mixture to burst into flame. Since it is the vapor-air mixture formed from the evaporation of the liquid that poses the hazard, exposures of large liquid surface areas and sources of heat should be avoided or prevented during handling or storage of these liquids. Some of the commonly used terms associated with flammable and combustible liquids are provided below. Auto-Ignition Temperature - The minimum temperature at which a flammable mixture will ignite from its own heat source or contact with a heated surface without necessity of a spark or flame. Flash Point - The minimum temperature at which a liquid gives off vapor in sufficient concentration to form an ignitible mixture with air near the surface of the liquid (under controlled test conditions). Flammable Limits - The minimum concentration of vapor in air below which propagation of flame does not occur on contact with a source of ignition. This is known as the lower flammable limit (LFL). There is also a maximum concentration of vapor or gas in air above which propagation of flame will not occur. This is called the upper flammable limit (UFL). Flammable Range - The difference between the lower and upper flammable limits, expressed in percentage of vapor or gas in air by volume. Also known as the explosive range. Propagation of Flame - The spread of flame through the entire volume of the flammable mixture from a single source of ignition.