What does the upper flammable limit refer to?

The upper flammable limit (UFL) refers specifically to the maximum concentration of vapor in the air that can support combustion. Beyond this limit, there is too much fuel (the vapor) in the mixture, and combustion cannot occur. This is a critical concept in fire safety and industrial hygiene, as knowing the UFL helps in assessing potential fire hazards in various environments.

In practical terms, when the concentration of combustible vapor exceeds the UFL, it results in a mixture that is too rich in fuel for ignition to take place, meaning that while the vapor may still be present, it cannot burn effectively. This understanding is essential for safety professionals who are tasked with evaluating and mitigating risks associated with flammable substances in the workplace. Knowledge of UFL helps in developing safe storage, handling, and exposure limits for substances that can pose a fire risk.