LEL and UEL refer to which property of gases?

• A. Carcinogenic potential
• B. Explosive limits
• C. Volatility
• D. Corrosiveness

Answer: (B)

LEL and UEL describe the flammability range of a gas in air, i.e., the explosive limits. The lower explosive limit is the minimum concentration of a flammable gas in air that can ignite and sustain combustion; below this level the mixture is too lean to burn. The upper explosive limit is the maximum concentration at which ignition is still possible; above this level the mixture is too rich to burn. Between these two values, the gas-air mixture is combustible. For example, methane is flammable in air roughly between 5% and 15%; outside that range it won’t ignite. Gas detectors often report concentration as a percent of the lower explosive limit to quickly convey how close the environment is to a combustible range. This concept is distinct from carcinogenic potential, volatility, or corrosiveness.