Flash Point vs. Fire Point

Difference between Flash Point and Fire Point

Flammable liquids produce vapor pressure which rises according to the degree of hotness of the surrounding environs. The amount of the vaporized liquid in air is directly proportional to the atmospheric pressure of the surrounding air. A different flammable liquid burns at different amount of air pressure depending on individual characteristics. The lowest temperature at which a flammable liquid produces enough mixture to ignite is called Flash point. However at this point if the source of fire is eliminated the liquid will stop burning. On the other hand Fire point is the point at which this liquid will continue burning even if the source of fire is eliminated. Both of these characteristics of flammable liquid are independent of the source of ignition.

Essentially flash point therefore means that it is the point at which the vapors of the liquid will ignite when there is a source of ignition. These two factors play an important role during the transportation of liquids fuels. They can determine the hazard that can be brought about by the carried liquid. Liquids with flash point of less than 60.5 are called flammable liquids whereas those with more than this are said to be combustible.

The gasoline that is employed in the vehicle industry must be heated to obtain its flash point. It is then mixed with air before its combustion takes place. Petrol has a low Flash point and auto ignition. These are the features that make it very flammable. Diesel which does not require an ignition source has a high flash point and a very minimal auto ignition point.

The point at which the vapors of the flammable liquid present in the air continue to ignite is called the fire point. This happens even if the source of detonation is not present. Thought the vapors from the same liquid may be burning at some few minutes, this cannot make the liquid to continue burning. This point of the liquid is known as the flash point. Flammable liquids have a lower flash point than the fire point.  This shows that the liquid vapors can be ignited at a low temperature but not continue if the source of fire is eliminated.

In a Nut Shell

  • For any flammable liquid, its vapor pressure maximizes with increase in temperature.
  • Flash point is the lower point at which the vapors of a liquid ignite but stops on removal of an ignition source.
  • Fire Point is basically a point above the flash point on which burning continues on removal of the ignition source.

Then we may conclude that in lost flammable liquids the fire point is higher than the flash point by a margin of 10 degrees.