The flash point of a flammable liquid is the lowest temperature at which it can form an ignitable mixture in air. At this temperature the vapor may cease to burn when the source of ignition is removed. A slightly higher temperature, the fire point, is defined as the temperature at which the vapor continues to burn after being ignited. Neither of these parameters are related to the temperatures of the ignition source or of the burning liquid, which are much higher. The flash point is often used as one descriptive characteristic of liquid fuel, but it is also used to describe liquids that are not used intentionally as fuels. Flash point may refer to: Flash point, a scientific attribute, the temperature at which a liquid can ignite Flash Point (film), a 2007 film starring Donnie Yen and Louis Koo Flashpoint (politics), an area or dispute that has a strong possibility of developing into a war Flashpoint (album), a live... Fig. ... The fire point of a substance is the temperature at which it will combust and continue to burn of its own accord, that means the evaporation rate is high enough so new vapor-air mixture is produced at least at the same rate as it is burned. ... For information on the band, see Fuel (band). ...

Mechanism

Every flammable liquid has a vapor pressure, which is a function of that liquid's temperature. As the temperature increases, the vapor pressure increases. As the vapor pressure increases, the concentration of evaporated flammable liquid in the air increases. Hence, temperature determines the concentration of evaporated flammable liquid in the air under equilibrium conditions. Different flammable liquids require different concentrations of the fuel in air to sustain combustion. The flash point is that minimum temperature at which there is a sufficient concentration of evaporated fuel in the air for combustion to propagate after an ignition source has been introduced. A liquid will usually assume the shape of its container A liquid is one of the main states of matter. ... In chemistry and physics, Vapor pressure is the pressure of a vapor in equilibrium with its non-vapor phases. ... Graph of example function, The mathematical concept of a function expresses the intuitive idea of deterministic dependence between two quantities, one of which is viewed as primary (the independent variable, argument of the function, or its input) and the other as secondary (the value of the function, or output). A... Fig. ... In thermodynamics, a thermodynamic system is said to be in thermodynamic equilibrium when it is in thermal equilibrium, mechanical equilibrium, and chemical equilibrium. ...

Measuring flash points

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 (hence the name) 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 point. The fire point of a substance is the temperature at which it will combust and continue to burn of its own accord, that means the evaporation rate is high enough so new vapor-air mixture is produced at least at the same rate as it is burned. ...

Closed cup testers, of which the Pensky-Martens closed cup is one example, are sealed with a lid through which the ignition source can be introduced periodically. The vapour above the liquid is assumed to be in reasonable equilibrium with the liquid. Closed cup testers give lower values for the flash point (typically 5-10 K) and are a better approximation to the temperature at which the vapour pressure reaches the Lower Flammable Limit (LFL).

The flash point is an experimental 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 equilibriate, sample volume and whether the sample is stirred. The testers and protocols are specified in standards such as DIN 51758, ASTM 93, and Determination of flash point: Closed cup equilibrium method (ISO 1523:2002).

Examples of fuel flash points

Petrol (gasoline) is designed for use in an engine which is driven by a spark. The fuel should be premixed with air within its flammable limits and heated above its flash point, then ignited by the spark plug. The fuel should not preignite in the hot engine. Therefore, gasoline is required to have a low flash point and a high autoignition temperature. Gasoline or petrol is a petroleum-derived liquid mixture consisting mostly of hydrocarbons and enhanced with benzene or iso-octane to increase octane ratings, primarily used as fuel in internal combustion engines. ... Diesel or diesel fuel (IPA: ; voiced “s” because of its eponym) is a specific fractional distillate of fuel oil (mostly petroleum) that is used as fuel in a diesel engine invented by German engineer Rudolf Diesel. ... Kerosene or kerosine, also called paraffin oil or paraffin in British usage (not to be confused with the waxy solid also called paraffin wax or just paraffin) is a flammable hydrocarbon liquid. ... Gasoline, as it is known in North America, or petrol, in many Commonwealth countries (sometimes also called motor spirit) is a petroleum-derived liquid mixture consisting primarily of hydrocarbons, used as fuel in internal combustion engines. ... An engine in the broadest sense, is something that produces an output effect from a given input. ... Look up Spark in Wiktionary, the free dictionary. ... This article or section should include material from Spark gap A spark plug is an electrical device that fits into the cylinder head of some internal combustion engines and ignites compressed aerosol gasoline by means of an electric spark. ... The autoignition temperature, or the ignition temperature of a substance is the lowest temperature at which a chemical will spontaneously ignite in a normal atmosphere, without an external source of ignition, such as a flame or spark. ...

Diesel is designed for use in a high-compression engine. Air is compressed until it has been heated above the autoignition temperature of diesel; then the fuel is injected as a high-pressure spray, keeping the fuel-air mix within the flammable limits of diesel. There is no ignition source. Therefore, diesel is required to have a high flash point and a low autoignition temperature. Diesel or diesel fuel (IPA: ; voiced “s” because of its eponym) is a specific fractional distillate of fuel oil (mostly petroleum) that is used as fuel in a diesel engine invented by German engineer Rudolf Diesel. ... This article does not cite any references or sources. ... A gas compressor is a mechanical device that increases the pressure of a gas by reducing its volume. ... The autoignition temperature, or the ignition temperature of a substance is the lowest temperature at which a chemical will spontaneously ignite in a normal atmosphere, without an external source of ignition, such as a flame or spark. ...

Diesel varies between 126F and 204F (52C-96C/WJ). Jet fuels also vary a lot. Jet A and jet A-1 have a FP between 100F and 150F (38C-66C/WJ), close to that of off the shelf kerosene. However, both Jet B and FP-4 have a FP between -10F and +30F (-23C/-1C/WJ)

Sources of data

Flash point data are found in many physical property data collections as well as Material Safety Data Sheets (MSDS) however not all data sources are equal, and the usefulness of the data depends on the method (specifically open or closed cup) which is not always specified. An example MSDS in a US format provides guidance for handling a hazardous substance and information on its composition and properties. ...

Two of the most reliable data collections:

Sicherheitstechnische Kenngrößen. Band 1: Brennbare Flüssigkeiten und Gase. Elisabeth Brandes and Wolfgang Möller, Wirtschaftsverlag NW (2003), ISBN 3-89701-745-8

NFPA 325, Fire Hazard Properties of Flammable Liquids, Gases and volatile solids, 1994; contained within NFPA Guide to Hazardous Materials (13th Ed), ISBN 0-87765-473-5

Another useful compilation of data can be found on the CONCAWE website under Product Dossiers (http://www.concawe.be)

See also

• Fire point