What term is used to define the percentage of a flammable substance in the air that will burn when in contact with an ignition source?

The term used to define the percentage of a flammable substance in the air that will burn upon contact with an ignition source is known as the flammable/explosive limit. This concept is crucial in fire safety and prevention as it identifies the concentration ranges of vapors in the air that can ignite and cause an explosion when exposed to an ignition source, such as a flame or spark.

The flammable/explosive limit consists of two components: the lower flammable limit (LFL) where the concentration is too low to ignite, and the upper flammable limit (UFL) where it is too rich to burn. Understanding these limits helps in assessing risks and ensuring safe handling and storage of flammable materials, making it a critical factor in fire safety protocols.