Which statement defines the flash point?

Which statement defines the flash point?

• A. The temperature at which a liquid ignites spontaneously
• B. The temperature at which a liquid forms a combustible air mixture after ignition from an external energy source
• C. The temperature at which a liquid boils at standard pressure
• D. The temperature at which a liquid develops enough vapor to form an ignitable mixture with air

Answer: (D)

Flash point is the temperature at which a liquid begins to emit enough vapor to form an ignitable mixture with air in the presence of an ignition source. Below this temperature, the vapor concentration is too low to ignite; at or above it, a spark or flame can ignite the vapors. This is different from the boiling point, which is about vaporization of the liquid itself, and from autoignition, which is ignition that happens without any external ignition source. The given statement captures the idea that enough vapor must be produced to form an ignitable mixture with air, which is what defines the flash point.

Flash point is the temperature at which a liquid begins to emit enough vapor to form an ignitable mixture with air in the presence of an ignition source. Below this temperature, the vapor concentration is too low to ignite; at or above it, a spark or flame can ignite the vapors. This is different from the boiling point, which is about vaporization of the liquid itself, and from autoignition, which is ignition that happens without any external ignition source. The given statement captures the idea that enough vapor must be produced to form an ignitable mixture with air, which is what defines the flash point.