For volatile materials, which term describes the temperature at which the liquid develops sufficient vapor pressure to form a vapor-air mixture capable of ignition after external energy input?

For volatile materials, which term describes the temperature at which the liquid develops sufficient vapor pressure to form a vapor-air mixture capable of ignition after external energy input?

• A. Transition point
• B. Autoignition temperature
• C. Flame point
• D. Flash point

Answer: (D)

The concept being tested is the temperature at which a volatile liquid can form an ignitable vapor in air only when an external energy input is present. That temperature is the flash point. It is defined as the lowest temperature at which the liquid gives off enough vapor to form an ignitable mixture with air near the liquid surface, so an ignition source can cause combustion. Below this temperature, there isn’t enough vapor to ignite; above it, ignition is possible when an external spark or flame is introduced. Autoignition temperature describes ignition without any external energy input, which is a different scenario and occurs at a higher temperature. The flame point isn’t the standard term used here, and transition point isn’t a recognized term in this context.

The concept being tested is the temperature at which a volatile liquid can form an ignitable vapor in air only when an external energy input is present. That temperature is the flash point. It is defined as the lowest temperature at which the liquid gives off enough vapor to form an ignitable mixture with air near the liquid surface, so an ignition source can cause combustion. Below this temperature, there isn’t enough vapor to ignite; above it, ignition is possible when an external spark or flame is introduced.

Autoignition temperature describes ignition without any external energy input, which is a different scenario and occurs at a higher temperature. The flame point isn’t the standard term used here, and transition point isn’t a recognized term in this context.