|MadSci Network: Chemistry|
John, Flammability is a difficult parameter to find a definition for. The most definitive answer that I could find was at a website at the following address; http://www.science.smith.edu/safety/Chapter_V(d).htm In essence, the definitions supplied at this site refer to the flashpoints of specific substances to determite their flammability. I hope that this will be sufficient in answering your question. The following is an excerpt from that site which I thought to be relevant; CLASSES OF FLAMMABLE AND COMBUSTIBLE LIQUIDS BOILING POINT FLASH POINT CLASS oC (oF) oC (oF) EXAMPLES Flammable 1A <37.8 (100) <22.8 (73) ethyl ether, pentane Flammable 1B >37.8 (100) <22.8 (73) acetone, ethyl alcohol Flammable 1C -- 22.8< and <37.8 (100) butanol, isoamyl acetate Combustible 2 -- 37.8(100)< and <60(140) formalin, cyclohexanone Combustible 3A -- 60(140)< and <93.3(200) phenol, dichlorobenzene Combustible 3B -- >93.3(200) ethylene glycol, mineral oil Source: National Fire Protection Association, 1987. Flammable and Combustible Liquids Code, NFPA 30. There are a number of important definitions in the evaluation of fire hazard: Flammable Solid - a nonexplosive material that is capable of producing fire as a result of friction, water exposure, air exposure or retained heat from synthesis or processing, or when ignited burns so vigorously and persistently so as to create a hazard Flammable Gas - gases of which mixtures in air of 13 percent or less, by volume, form a flammable mixture; or the flammable range (explosive range) in air is wider than 12 percent regardless of the lower limit (U.S. Department of Transportation definition) Boiling point - the temperature at which the vapor of the liquid is in equilibrium with atmospheric pressure the lower the boiling point the greater the fire hazard Flash point - the minimum temperature at which a liquid gives off vapor in sufficient concentration to form an ignitable mixture with air near the surface of the liquid - also applies to certain solids that evaporate or volatilize : the lower the flashpoint the greater the fire hazard Auto-ignition Temperature - the minimum temperature which will initiate a self-sustained combustion of liquid, gas or solid in the absence of a spark or flame : the lower the autoignition temperature the greater the fire hazard Flammable or Explosion limits - the range of concentration of a gas or vapor in air, by volume percent in air, in which a fire or explosion can occur upon ignition in a confined area : the wider the range of the explosion limits and the lower the lower limit, the greater the fire hazard Vapor Density - the weight of a volume of pure vapor or gas compared to the weight of an equal volume of dry air at the same temperature and pressure: vapor densities greater than one indicate the vapor or gas is heavier than air Information on these physical characteristics of flammable chemicals is listed on manufacturer's container labels and on Material Safety Data Sheets. For a fire to occur, three conditions must be met: (1) for gases and vapors the concentration of the flammable gas or vapor must be between the lower and upper flammable limits, (2) an oxidizing agent (e.g., the air in the room or a chemical oxidizer) must be available, and (3) there must be a source of ignition or the material is at its auto-ignition temperature.
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