What is the definition of flashpoint?

• A. Minimum temperature at which fuel ignites
• B. Temperature of maximum vapor pressure
• C. Temperature at which solvent evaporates
• D. Minimum temperature at which sufficient vapors are present for an ignitable mixture

Answer: (D)

Flashpoint is the lowest temperature at which a liquid can produce enough vapor to form an ignitable mixture with air, so that an ignition source could cause a fire if one is present. Below this temperature, there isn’t enough vapor in the air to sustain ignition even if a spark or flame is nearby. This concept is different from the autoignition temperature (which is the temperature at which a substance will ignite without any ignition source) and from the boiling point (the temperature at which a liquid boils away), or from the idea of maximum vapor pressure, which isn’t about forming an ignitable mixture. Therefore, the statement about the minimum temperature at which sufficient vapors are present for an ignitable mixture best captures the definition of flashpoint.