Flashpoint

Flashpoint is the lowest temperature at which a liquid gives off enough vapor to form an ignitable mixture with air near the liquid surface. At or above this temperature, the vapor may ignite briefly if an ignition source is present; below it, the vapor is not sufficient to sustain combustion. The concept is distinct from the ignition temperature, which is the temperature at which the mixture will ignite in air with a source, and from the fire point, which is the temperature at which the vapor continues to burn after ignition.

Flash point is determined under standardized test conditions using either open-cup or closed-cup methods. Open-cup tests, such as the Cleveland open cup, generally yield lower flash points because vapors escape more readily, while closed-cup tests, such as Pensky-Martens and TAG closed cup, confine vapors and usually yield higher results. Tests are conducted at ambient pressure, typically 1 atmosphere, and may specify a test temperature increment and an ignition source.

The measured flash point informs safety classification, storage, and handling of liquids and is a key parameter in regulatory schemes governing the transport and labeling of hazardous materials. In many jurisdictions, liquids are defined as flammable or combustible based on their flash point, with specific thresholds varying by regulation. Factors such as temperature, pressure, air composition, sample contamination, and vapor pressure influence measured values and can differ between methods.

In addition to its technical use, flashpoint is sometimes employed metaphorically to denote a moment at which a conflict or crisis could rapidly escalate.