Flammability Characteristics of Liquids and Vapors

Shock wave An abrupt pressure wave moving through a gas. A shock wave in open air is followed by a strong wind the combined shock wave and wind is called a blast wave. The pressure increase in the shock wave is so rapid that the process is mostly adiabatic. 

Overpressure The pressure on an object as a result of an impacting shock wave. 

The flash point and flammability limits are not fundamental properties but are defined only by the specific experimental apparatus and procedure used. 

Flammability characteristics of some important organic chemicals (liquids and gases) are provided in appendix B. 

The flash point temperature is one of the major quantities used to characterize the fire and explosion hazard of liquids. 

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Flash point is one of the most important fire safety characteristics and hence it is a very important consideration in solvent design. The flammability limit of a solvent is characterized by its flash point, which is the temperature at which the mixture of air and vapor above the liquid can be ignited (Mullin, 1961). It is the lowest point at which the vapor pressure of a liquid will produce a flammable mixture. The flash point of the solvent can be estimated using the following group contribution method (ICAS, 2003)... 

The lower flammable limit (LFL) or lower explosive limit (LEL) is the minimum concentration of vapor in air below which a flame is not propagated when an ignition source is present (61—64). Below this concentration, the mixture is considered too lean to bum. The lower flammable limit and the flash point of a flammable liquid are closely related by the liquid s vapor pressure characteristics. 

If the temperature of a liquid is below its flash point, flammable concentrations of vapor cannot exist, but conditions still can exist for flammability if mists or foams are formed. A suspension of finely divided drops of a flammable liquid in air has many of the characteristics of a flammable gas-air mixture and can bum or explode. A mist may be produced by condensation of a saturated vapor or by mechanical atomization. Normally, the diameter of drops in a condensed mist is less than 0.01mm, whereas in a mechanical spray it usually is greater than 0.1 mm. 

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