Flash Point vs Fire Point
All flammable liquids have a vapor pressure that increases with its temperature. The concentration of evaporated liquid in the air increases with increase in vapor pressure. Different flammable liquids require different concentrations in the air to sustain combustion. Flash point of a flammable liquid is defined as the lowest temperature at which it can form an ignitable mixture in air. However, the vapor stops to burn if the source of ignition is removed. Fire point, which is a slightly higher temperature, is the temperature at which vapors of the flammable liquid continue to burn after being ignited even after the source of ignition is removed. Both the flash point and fire point have no relation to the temperature of the source of ignition.
Flash point is the minimum temperature when there is sufficient concentration of vapors of the flammable liquid in air to sustain burning when there is a source of ignition. Flash point and fire point are two important characteristics of liquid fuels that decide their transportation as they define fire hazards of these flammable liquids. It is unanimously agreed that liquids with a flash point less than 60.5 degrees centigrade or 37.8 degrees centigrade are flammable, while liquids having flash points higher than these limits are called combustible liquids.
Gasoline (petrol) is used as a fuel in automobiles. It need to be preheated above its flash point and mixed with air before a spark from spark plug causes it to burn. Petrol needs to have a low flashpoint and high auto-ignition temperature. On the other hand, there is no ignition source in the case of diesel and hence it requires having a high flash point and a low auto-ignition point.
Fire point is the temperature at which the vapors of the flammable liquid present in air continue to burn after removal of source of ignition. If fire propagates for at least 5 seconds, it is said to be the fire point of the liquid. Though the vapors of the liquid are ignited at a lower temperature called flash point, they are not sufficient in quantity to sustain burning. In general, fire points can be taken as 10 degrees higher than flash points of flammable liquids.
Flash Point vs Fire Point
• Every flammable liquid has a vapor pressure that increases with an increase in temperature.
• The lowest temperature at which there is enough concentration of vapors in air to ignite the liquid is called its flash point. However, vapors cease to burn if the source of ignition is removed.
• Fire point is slightly higher temperature at which these vapors continue to propagate and burn after removal of source of ignition
• In general fire point is taken to be 10 degrees higher than flash point of flammable liquids.