What is the flash point of a substance?

The flash point of a substance refers to the lowest temperature at which its vapors can ignite when exposed to an open flame or spark. This temperature is crucial because it indicates the potential for a substance to catch fire under specific conditions. When the vapor concentration is above a certain level and reaches this flash point, a flame can briefly flash, signaling that the substance is combustible.

Understanding the flash point is important for safety during storage, handling, and transportation of flammable materials. It helps determine appropriate safety measures and precautions.

In contrast, the other options describe different concepts: continuous ignition refers to a higher temperature known as the ignition point; the melting point describes the temperature at which a solid turns into a liquid; and the maximum safe temperature typically relates to operational limits for materials, not specifically to ignition. Therefore, option B is the correct definition of flash point.