What term defines the minimum concentration of fuel vapor and air that supports combustion?

The term that defines the minimum concentration of fuel vapor and air that supports combustion is indeed the "lower flammable limit." This concept is critical in understanding fire safety and prevention. The lower flammable limit (LFL) refers to the lowest concentration of a vapor in air below which propagation of flame does not occur. Below this concentration, there is not enough fuel present to sustain a flame. Therefore, knowing the LFL is crucial for firefighting and storage of flammable materials, as it helps prevent situations where a fire could ignite.

In contrast, the upper flammable limit refers to the maximum concentration of fuel vapor in air above which combustion cannot occur due to a lack of sufficient oxygen. The combustion threshold, while sometimes discussed in terms of ignition, is not a standard term used to define flammable limits. The fire point is a temperature at which enough vapor is produced to support combustion, but it does not specifically define the concentration of those vapors. Understanding these terms and their significance helps improve safety measures in dealing with combustible materials.