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Neither flash point nor fire point depends directly on the ignition source temperature, but ignition source temperature is far higher than either the flash or fire point, and can increase the temperature of fuel above the usual ambient temperature to facilitate ignition.
The autoignition temperature or self-ignition temperature, often called spontaneous ignition temperature or minimum ignition temperature (or shortly ignition temperature) and formerly also known as kindling point, of a substance is the lowest temperature at which it spontaneously ignites in a normal atmosphere without an external source of ignition, such as a flame or spark. [1]
The fire point, or combustion point, of a fuel is the lowest temperature at which the liquid fuel will continue to burn for at least five seconds after ignition by an open flame of standard dimension. [1] At the flash point, a lower temperature, a substance will ignite briefly, but vapour might not be produced at a rate to sustain the fire ...
Flashover occurs when the majority of the exposed surfaces in a space are heated to their autoignition temperature and emit flammable gases (see also flash point). Flashover normally occurs at 500 °C (932 °F) or 590 °C (1,100 °F) for ordinary combustibles and an incident heat flux at floor level of 20 kilowatts per square metre (2.5 hp/sq ft).
The technical definitions vary between countries so the United Nations created the Globally Harmonized System of Classification and Labeling of Chemicals, which defines the flash point temperature of flammable liquids as between 0 and 140 °F (60 °C) and combustible liquids between 140 °F (60 °C) and 200 °F (93 °C).
This allows the development of an equilibrium between the liquid and the air volume. The ignition source is directed into the cup at regular intervals with simultaneous interruption of stirring. The test concludes upon observation of a flash that spreads throughout the inside of the cup. The corresponding temperature is the liquid's flash point.
The lowest temperature at which a small test flame passing over the surface of the liquid causes the vapor to ignite is considered the chemical's flash point. This apparatus may also be used to determine the chemical's fire point which is considered to have been reached when the application of the test flame produces at least five continuous ...
Flash point Minimum ignition energy (mJ) @ proportion in air at which achieved [a] [4] Autoignition temperature Lower Upper Acetaldehyde: 4.0 57.0 IA −39 °C 0.37 175 °C Acetic acid (glacial) 4 19.9 II 39–43 °C 463 °C Acetic anhydride: II 54 °C Acetone: 2.6–3 12.8–13 IB −17 °C 1.15 @ 4.5% 465 °C, 485 °C [5] Acetonitrile: IB 2 °C