Which statement is true regarding lower explosive limits (LEL)?

The statement that a fuel vapor will not ignite at levels below the lower explosive limit (LEL) is accurate. The LEL defines the minimum concentration of a vapor in air that is needed for the mixture to be capable of igniting and sustaining combustion. If the concentration of vapor is below this limit, the mixture is too lean to support combustion, meaning that there are not enough fuel molecules present to create a flammable or explosive reaction with oxygen.

Understanding this concept is critical for safety in firefighting and hazardous materials response. Firefighters need to be aware of LEL values for various fuels to assess risks in their operations, ensuring they do not enter environments where the concentration of flammable vapors is too low, which can lead to misjudgments about the presence and potential risk of fire or explosion.