FLASH POINT AND FIRE POINT

FLASH POINT

The flash point of an oil is the lowest temperature at which it gives off vapors that will ignite for a moment when a small flame is brought near it.

FIRE POINT

The fire point of an oil is the lowest temperature at which the vapors of the oil burn continuously
for at least 5 seconds when a flame is brought near it .

MEASURING FLASH POINT

There are two basic types of flash point measurement: open cup and closed cup.

In open cup devices the sample is contained in an open cup which is heated, and at intervals a flame is brought over the surface. The measured flash point will actually vary with the height of the flame above the liquid surface, and at sufficient height the measured flash point temperature will coincide with the fire pont.The best known example is the Cleveland Open Cup (COC).

There are two types of Closed cup testers: non-equilibrium, such as Pensky-Martens where the vapours above the liquid are not in temperature equilibrium with the liquid, and equilibrium, such as Small Scale (commonly known as Setaflash) where the vapors are deemed to be in temperature equilibrium with the liquid. In both these types the cups are sealed with a lid through which the ignition source can be introduced. Closed cup testers normally give lower values for the flash point than Open cup (typically 5-10 °C) and are a better approximation to the temperature at which the vapor pressure reaches the lower flammable limit.

The flash point is an empirical measurement rather than a fundamental physical parameter. The measured value will vary with equipment and test protocol variations, including temperature ramp rate (in automated testers), time allowed for the sample to equilibrate, sample volume and whether the sample is stirred.