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The flash point of a flammable
Flammability

Flammability is defined at how easily something will burn or ignite, causing fire or combustion. The degree of difficulty required to cause the combustion of a substance is subject to quantification through fire testing....
 liquid is the lowest temperature
Temperature

In physics, temperature is a physical property of a Physical system that underlies the common notions of hot and cold; something that feels hotter generally has the greater temperature....
 at which it can form an ignitable mixture in air. At this temperature the vapour may cease to burn when the source of ignition is removed. A slightly higher temperature, the fire point
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. At the flash point, a lower temperature, a substance will ignite, but vapor might not be produced at a rate to sustain the fire....
, is defined as the temperature at which the vapour continues to burn after being ignited. Neither of these parameters is related to the temperatures of the ignition source or of the burning liquid, which are much higher.






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The flash point of a flammable
Flammability

Flammability is defined at how easily something will burn or ignite, causing fire or combustion. The degree of difficulty required to cause the combustion of a substance is subject to quantification through fire testing....
 liquid is the lowest temperature
Temperature

In physics, temperature is a physical property of a Physical system that underlies the common notions of hot and cold; something that feels hotter generally has the greater temperature....
 at which it can form an ignitable mixture in air. At this temperature the vapour may cease to burn when the source of ignition is removed. A slightly higher temperature, the fire point
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. At the flash point, a lower temperature, a substance will ignite, but vapor might not be produced at a rate to sustain the fire....
, is defined as the temperature at which the vapour continues to burn after being ignited. Neither of these parameters is 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.

Mechanism


Every flammable liquid
Liquid

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 its bulk material....
 has a vapour pressure, which is a function
Function (mathematics)

The mathematical concept of a function expresses dependence between two quantities, one of which is known and the other which is produced. A function associates a single output to each input element drawn from a fixed Set , such as the real numbers , although different inputs may have the same output....
 of that liquid's temperature
Temperature

In physics, temperature is a physical property of a Physical system that underlies the common notions of hot and cold; something that feels hotter generally has the greater temperature....
. As the temperature increases, the vapour pressure increases. As the vapour pressure increases, the concentration of evaporated flammable liquid in the air increases. Hence, temperature determines the concentration of evaporated flammable liquid in the air.

Each flammable liquid requires a different concentration of its vapour in air to sustain combustion. The flash point of a flammable liquid is the lowest temperature at which there can be enough flammable vapour to ignite, when an ignition source is applied.

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
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. At the flash point, a lower temperature, a substance will ignite, but vapor might not be produced at a rate to sustain the fire....
. 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 vapours 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 vapour pressure reaches the lower flammable limit
Lower flammable limit

Lower flammability limit , 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 mixtures can ignite....
 (LFL).

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 Small Scale closed cup method is detailed in ASTM D3828 and D3278, EN ISO 3679 and 3680, and IP 523 and 524.

Examples of flash points



Gasoline
Gasoline

File:GasCan.jpgGasoline or petrol is a petroleum-derived liquid mixture, primarily used as fuel in internal combustion engines.It consists mostly of aliphatic hydrocarbons, enhanced with iso-octane or the aromatic hydrocarbons toluene and benzene to increase its octane rating....
 (petrol) is designed for use in an engine
Engine

An engine is a mechanical device that produces some form of output from a given input.An engine whose purpose is to produce kinetic energy output from a fuel is called a Wiktionary:prime mover; alternatively, a motor is a device which produces kinetic energy from a preprocessed "fuel" ....
 which is driven by a spark
Spark

A spark is a small airborne ember or particle of red-hot matter.Spark may also refer to:In science:* An electric spark, usually with a flash and a sharp noise, may be:...
. The fuel should be premixed with air within its flammable limits and heated above its flash point, then ignited by the spark plug
Spark plug

A spark plug is an electrical device that fits into the cylinder head of some internal combustion engines and ignites compressed Particulate gasoline by means of an electric spark....
. The fuel should not preignite in the hot engine. Therefore, gasoline is required to have a low flash point and a high autoignition temperature
Autoignition temperature

The autoignition temperature or kindling point of a substance is the lowest temperature at which it will Spontaneous combustion in a normal atmosphere without an external source of ignition, such as a flame or spark....
.

Diesel
Diesel

Diesel or diesel fuel in general is any fuel used in diesel engines. The most common is a specific fractional distillation of petroleum fuel oil, but alternatives that are not derived from petroleum, such as biodiesel, biomass to liquid or gas to liquid diesel, are increasingly being developed and adopted....
 is designed for use in a high-compression engine
Diesel engine

A diesel engine is an internal combustion engine which operates using the diesel cycle . Diesel engines have the highest thermal efficiency compared to any internal combustion or external combustion engine....
. Air is compressed
Gas compressor

A gas compressor is a mechanical device that increases the pressure of a gas by reducing its volume.Compressors are similar to pumps: both increase the pressure on a fluid and both can transport the fluid through a pipe ....
 until it has been heated above the autoignition temperature
Autoignition temperature

The autoignition temperature or kindling point of a substance is the lowest temperature at which it will Spontaneous combustion in a normal atmosphere without an external source of ignition, such as a flame or spark....
 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 flash points vary 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)


Standardization

Flash points of substances are measured according to standard test methods. These test methods define the apparatus required to carry out the measurement, key test parameters, the procedure for the operator or automated apparatus to follow, and the precision of the test method. Standard test methods are written and controlled by a number of national and international committees and organizations. The three main bodies are the CEN / ISO Joint Working Group on Flash Point (JWG-FP), ASTM D02.8B Flammability Section and the Energy Institute's TMS SC-B-4 Flammability Panel.

Sources of data

Flash point data are found in many physical property data collections as well as Material Safety Data Sheet
Material safety data sheet

A material safety data sheet is a form containing data regarding the properties of a particular substance. An important component of product stewardship and workplace safety, it is intended to provide workers and emergency personnel with procedures for handling or working with that substance in a safe manner, and includes information such...
s (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.

Two of the most reliable data collections:

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


  • NFPA
    NFPA

    NFPA may refer to:* National Fire Protection Association** NFPA 704, National Fire Protection Association Fire Diamond* National Food Processors Association...
     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)


See also

  • Autoignition temperature
    Autoignition temperature

    The autoignition temperature or kindling point of a substance is the lowest temperature at which it will Spontaneous combustion in a normal atmosphere without an external source of ignition, such as a flame or spark....
  • Fire point
    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. At the flash point, a lower temperature, a substance will ignite, but vapor might not be produced at a rate to sustain the fire....