The flash point of a flammable liquid is the lowest temperature at which it can form an ignitable mixture in air. Temperature is a physical property of a system that underlies the common notions of hot and cold something that is hotter generally has the greater temperature 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. The fire point of a Fuel is the temperature at which it will continue to burn after ignition for at least 5 seconds 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. Fuel is any material that is burned or altered in order to obtain energy

Mechanism

Every flammable liquid has a vapor pressure, which is a function of that liquid's temperature. Liquid is one of the principal States of matter. A liquid is a Fluid that has the particles loose and can freely form a distinct surface at the boundaries of Vapor pressure (also known as equilibrium vapor pressure or saturation vapor pressure) is the Pressure of a Vapor in equilibrium The Mathematical concept of a function expresses dependence between two quantities one of which is given (the independent variable, argument of the function Temperature is a physical property of a system that underlies the common notions of hot and cold something that is hotter generally has the greater 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. In Thermodynamics, a thermodynamic system is said to be in thermodynamic equilibrium when it is in thermal equilibrium Mechanical equilibrium, and Different flammable liquids require different concentrations 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. Flash point is basically the lowest temperature at which there is enough fuel vapour to ignite.

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 Fuel is the temperature at which it will continue to burn after ignition for at least 5 seconds Examples include Cleveland Open Cup (COC) and Pensky-Martens open cup. The main difference being that the former is heated from below, while the latter is heated from the sides as well as below.

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. In the Pensky-Martens closed cup flash point test, a Brass test cup is filled with a test specimen and fitted with a cover 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). Lower flammability limit (LFL usually expressed in volume per cent is the lower end of the concentration range of a flammable solvent at a given temperature and pressure for which air/vapor

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.

Methods for determining the flash point of a liquid are specified in many standards. For example, testing by the Pensky-Martens closed cup method is detailed in ASTM D93, IP34, ISO 2719, DIN 51758, JIS K2265 and AFNOR M07-019. Determination of flash point by the Closed Cup Equilibrium method is specified in ISO 1523:2002.

Examples of fuel flash points

Petrol (gasoline) is designed for use in an engine which is driven by a spark. Diesel or Diesel fuel (ˈdiːzəl in general is any Fuel used in Diesel engines The most common is a specific fractional distillate of petroleum Jet fuel is a type of Aviation fuel designed for use in Aircraft powered by gas-turbine engines. Kerosene, sometimes spelled kerosine in scientific and industrial usage is a Combustible Hydrocarbon liquid Biodiesel refers to a non-petroleum-based Diesel fuel consisting of short chain Alkyl ( Methyl or ethyl) Esters made by An engine is a mechanical device that produces some form of output from a given input The fuel should be premixed with air within its flammable limits and heated above its flash point, then ignited by the spark plug. A spark plug (also very rarely nowadays in British English: a sparking plug) is an electrical device that fits into the Cylinder The fuel should not preignite in the hot engine. Therefore, gasoline is required to have a low flash point and a high autoignition temperature. The autoignition temperature or kindling point of a substance is the lowest temperature at which it will spontaneously ignite in a normal atmosphere without an external

Diesel is designed for use in a high-compression engine. Diesel or Diesel fuel (ˈdiːzəl in general is any Fuel used in Diesel engines The most common is a specific fractional distillate of petroleum A diesel engine is an Internal combustion engine which operates using the Diesel cycle (named after Dr 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. A gas compressor is a mechanical device that increases the Pressure of a Gas by reducing its Volume. The autoignition temperature or kindling point of a substance is the lowest temperature at which it will spontaneously ignite in a normal atmosphere without an external There is no ignition source. Therefore, diesel is required to have a high flash point and a low autoignition temperature.

Diesel varies between 126°F and 204°F (52°C-96°C/WJ). Jet fuels also vary greatly. Both Jet A and jet A-1 have flash points between 100°F and 150°F (38°C-66°C/WJ), close to that of off the shelf kerosene. However, both Jet B and FP-4 have flash points between -10°F and +30°F (-23°C - -1°C/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. A material safety data sheet ( MSDS) is a form containing data regarding the properties of a particular substance

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)

Estimation of flash point data:

• L. Catoire et al. , Journal of Physical and Chemical Reference Data, Vol. 33, N°4, pp. 1083-1111 (2004)
• L. Catoire et al. , Journal of Physical and Chemical Reference Data, Vol. 35, N°1, pp. 9-14 (2006)

References

See also

• Fire point