Flash point

Flash point

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 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 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 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. 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. 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 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 flash points

Gasoline (Petrol) 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.

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 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)

ources 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.

Two of the most reliable data collections:

Sicherheitstechnische Kenngrößen. Band 1: Brennbare Flüssigkeiten und Gase. Elisabeth Brandes andWolfgang 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)

ee also

*Autoignition temperature
*Fire point

References


Wikimedia Foundation. 2010.

Игры ⚽ Поможем написать реферат

Look at other dictionaries:

  • Flash Point — Données clés Réalisation Wilson Yip Scénario Szeto Kam Yuen Nicholl Tang Acteurs principaux Donnie Yen Louis Koo Collin Chou Lui Leung Wai Fan Bingbing Pays d’origine …   Wikipédia en Français

  • Flash point — n. 1. the lowest temperature at which the vapors given off by a volatile liquid exposed to air will burst into flame when approached by a flame. Also called {flashing point}. [PJC] 2. That point in time or that degree of provocation at which som …   The Collaborative International Dictionary of English

  • flash point — flash′ point or flash′point n. 1) chem. the lowest temperature at which a liquid in a specified apparatus will give off sufficient vapor to ignite momentarily on application of a flame 2) cvb a point or stage at which an event or situation… …   From formal English to slang

  • flash point — [n] crucial moment breaking point, crisis, critical moment, hour of decision, moment of truth, turning point, zero hour; concept 674 …   New thesaurus

  • flash point — n. 1. the lowest temperature at which a volatile solid or the vapor of a liquid will flash when exposed to a brief flame under certain conditions 2. a critical moment at which someone or something bursts forth into activity or existence …   English World dictionary

  • flash point — noun 1. point at which something is ready to blow up • Syn: ↑flashpoint • Hypernyms: ↑criticality 2. the lowest temperature at which the vapor of a combustible liquid can be ignited in air • Syn: ↑flashpoint • …   Useful english dictionary

  • flash point — 1. Also, flashing point. Physical Chem. the lowest temperature at which a liquid in a specified apparatus will give off sufficient vapor to ignite momentarily on application of a flame. 2. a critical point or stage at which something or someone… …   Universalium

  • flash point — Flashing Flash ing, n. 1. (Engineering) The creation of an artifical flood by the sudden letting in of a body of water; called also {flushing}. [1913 Webster] 2. (Arch.) Pieces of metal, built into the joints of a wall, so as to lap over the edge …   The Collaborative International Dictionary of English

  • Flash Point — Filmdaten Deutscher Titel Flash Point Originaltitel Dou fo sin / Dao huo xian …   Deutsch Wikipedia

  • flash point — [1] The point in the temperature range at which a given oil (especially diesel oil) in vapor form will ignite and flash into flame. The higher the flash point, the better the lubricating quality of the oil. The temperature at which the vapor… …   Dictionary of automotive terms

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”