What is the upper flammable limit (UFL)?

The upper flammable limit (UFL) refers specifically to the maximum concentration of fuel vapor in the air that can ignite when exposed to an ignition source. If the concentration of fuel vapor exceeds this limit, there is not enough oxygen to support combustion, and the mixture cannot ignite. Understanding this concept is critical for safety and prevention in fire operations, as it helps firefighters recognize situations where there is a risk of ignition versus those that are too rich to ignite.

The UFL is often used in conjunction with the lower flammable limit (LFL) to determine the safe operating ranges for handling flammable materials. This knowledge is essential for assessing risks in environments where flammable gases or vapors may be present.