The L.E.L. of a flammable or combustible liquid is the:

• A. Lowest Efficiency Level
• B. Lower Exposure Label
• C. Lower Explosive Limit
• D. Lowest Evaporation Limit

Answer: (C)

The concept being tested is the minimum vapor concentration needed for ignition. The lower explosive limit (L.E.L.) is the smallest amount of flammable vapor that, when mixed with air, can ignite if an ignition source is present. If the vapor concentration is below this limit, the mixture is too lean to ignite; if it’s between the L.E.L. and the upper explosive limit (UEL), ignition is possible under the right conditions.

That’s why Lower Explosive Limit is the best choice. The other phrases don’t describe flammability limits: efficiency, exposure labeling, or an evaporation-based limit aren’t used to define when a flammable mixture can ignite.