What is the flash point of a liquid?

The flash point of a liquid is defined as the lowest temperature at which the vapor of the liquid can ignite in the presence of an ignition source. This means that at this temperature, enough vapor is produced from the liquid to create a mixture that is combustible when it interacts with a flame or spark.

Understanding the flash point is crucial for fire and explosion investigations, as it helps in assessing the fire hazards associated with various liquids. Knowing a liquid's flash point enables investigators to determine the conditions under which a fire could start and to evaluate the risks in a given environment.

For example, if a liquid has a flash point of 100°F, it means that at temperatures below this, the liquid’s vapors will not ignite, whereas at or above this temperature, the vapors can be ignited under the right conditions.

Other options described include different thermal properties of liquids, such as boiling points and ignition temperatures, but these do not accurately define the specific point at which a liquid can produce sufficient vapor to ignite when exposed to an ignition source. Therefore, the correct definition of the flash point is the lowest temperature at which a liquid can support a flame.