Which statement best explains the lower explosive limit for petroleum vapors?

Which statement best explains the lower explosive limit for petroleum vapors?

• A. Oxygen deficiency prevents ignition
• B. The mixture is too rich
• C. It is the point at which a vapor does not ignite because it's too lean
• D. It is the concentration at which the vapor will ignite only in the presence of a catalyst

Answer: (C)

The lower explosive limit is the minimum concentration of vapor in air that can support combustion with an ignition source. Below this limit, the mixture is too lean—there aren’t enough fuel molecules present to sustain a flame—even if oxygen is present. For petroleum vapors, there is a flammable range between the LEL and the upper explosive limit (UEL); within that range, ignition is possible. The statement describing the mixture as too lean captures this idea precisely. The other ideas—being oxygen-deficient, being too rich, or needing a catalyst—do not define the LEL.

The lower explosive limit is the minimum concentration of vapor in air that can support combustion with an ignition source. Below this limit, the mixture is too lean—there aren’t enough fuel molecules present to sustain a flame—even if oxygen is present. For petroleum vapors, there is a flammable range between the LEL and the upper explosive limit (UEL); within that range, ignition is possible. The statement describing the mixture as too lean captures this idea precisely. The other ideas—being oxygen-deficient, being too rich, or needing a catalyst—do not define the LEL.