Characteristics of Flammable Liquids
Flammable liquids are always covered with a layer of vapors. When mixed with air and contacted by an ignition source, it is the vapor, not the liquid which burns. The fuel vapor and oxygen provide two sides of the fire triangle. A flammable liquid is usually more dangerous when temperatures are high because more vapors are generated.

Four terms are commonly used with flammable liquids:

The lowest temperature at which a liquid gives off enough vapors to form a flammable mixture with air.

The lowest temperature at which the vapor-air mixture will continue to burn after it is ignited. This is generally a few degrees above the flash point.

The temperature at which a mixture of flammable vapor and air will ignite without a spark or flame. This term is also applied to the temperature of a hot surface which will ignite flammable vapors. The temperature varies with the type of surface.

The range between the smallest and largest amounts of vapor in a given quantity of air which will explode or burn when ignited. The amount is usually expressed in percentages. For instance, carbon disulfide has an explosive range of one to 50 percent. If air contains more than one or less than 50 parts of carbon disulfide vapor, the mixture can explode or burn.