However, combined with other tests such as viscosity, viscosity index, and specific gravity, the flash point can help reveal both the quality of the crude oil from which the lubricant was derived and the quality of the refining process. Originally, the flash point was developed for the purpose of determining the fire hazard of fuels and oils being stored or transported. Using Flash Point to Detect and Quantify Fuel Dilution As the name implies, the fire point is the temperature at which a sustained flame results (longer than four seconds). Continued heating of the oil (typically 50-75° F above the flash point temperature) will cause the “fire point” to be reached. When a small flame (ignition source) is applied to the oil’s surface this vaporous mixture will burn momentarily and then extinguish if the critical temperature has been reached. The flash point temperature of an oil corresponds roughly to a vapor pressure of 3-5 mm Hg. The oil flashes because a flammable mixture results when it is heated sufficiently, causing vapors to emerge and mix with oxygen in the air. The oil is said to have “flashed” when a flame appears and instantaneously propagates itself over the entire surface. This is an important property of fire-resistant hydraulic fluids in EHC systems on steam turbines.Īccording to ASTM, which first standardized the test in 1924, the flash point is the lowest temperature at which an ignition source causes the vapors of the specimen (lubricant) to ignite under specified conditions. However, the flash point should not be confused with the auto ignition temperature (AIT), which is the temperature (typically 360 degrees C or 650 to 700 degrees F for mineral oils) at which the oil vapor will combust spontaneously without an ignition source. The flash point and the slightly higher fire point are covered by ASTM D92 and D93.

The flash point (typically 225 degrees C or 440 degrees F for mineral oils) is an indication of the safety hazards of a lubricant with respect to fire and explosion. The flash point is the lowest temperature at which the vapor above the oil sample will momentarily ignite or flash when an ignition source is passed over it. The lab analyst can deploy information about a used oil’s flash point to troubleshoot such problems as thermal failure, gamma radiation, solvent contamination, mixed (or wrong) oils, and antifreeze contamination. Most commonly used as a quick pass/fail test for fuel dilution, more applications have surfaced in recent years. And, because of its low cost, simplicity and versatility, the test is popular among the used oil analysis community as well. Like viscosity, the flash point test has always been a standard part of a lubricant’s specification.

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