What is the lower limit of flammability in air, as a percent of vapor in air/gas mixture?

The lower limit of flammability, also known as the lower explosive limit (LEL), indicates the minimum concentration of a vapor in an air mixture required for combustion to occur. In practical terms, this means that below this concentration, the mixture is too lean to ignite.

The correct percentage marked as 2.15% suggests that at this level, the concentration of the flammable vapor in air is sufficient for a flame to propagate if there’s an ignition source. Understanding this concept is crucial in safety practices, particularly in environments where flammable materials are handled.

Other options presented either indicate concentrations that are too low or too high to sustain a flammable mixture with air, demonstrating the importance of knowing precise measurements in hazardous material handling to prevent accidents.