Which statement correctly defines the flash point of a liquid?

Which statement correctly defines the flash point of a liquid?

• A. Minimum temperature at which a liquid gives off enough vapors to form an ignitable mixture with air near the surface of the liquid.
• B. A temperature at which the liquid will ignite without an ignition source.
• C. Temperature at which a liquid boils.
• D. The temperature at which a vapor is heavier than air.

Answer: (A)

The flash point is the lowest temperature at which a liquid can release enough vapors to form an ignitable mixture with air at or near the surface of the liquid. When the liquid reaches this temperature, an ignition source can cause combustion of the vapors; below it, there isn’t enough vapor to ignite. This is different from the boiling point, which is about when the liquid becomes vapor throughout, and from the autoignition temperature, which is the temperature at which the vapor-air mix will ignite without any flame or spark. The idea of a vapor being heavier than air is about density, not the ignition threshold.

The flash point is the lowest temperature at which a liquid can release enough vapors to form an ignitable mixture with air at or near the surface of the liquid. When the liquid reaches this temperature, an ignition source can cause combustion of the vapors; below it, there isn’t enough vapor to ignite. This is different from the boiling point, which is about when the liquid becomes vapor throughout, and from the autoignition temperature, which is the temperature at which the vapor-air mix will ignite without any flame or spark. The idea of a vapor being heavier than air is about density, not the ignition threshold.