What is the lower explosive limit of methane?

What is the lower explosive limit of methane?

• A. 1%
• B. 3%
• C. 5%
• D. 7%

Answer: (C)

In flammability terms, the lower explosive limit is the minimum methane concentration in the air that can sustain a flame once ignited. For methane, this lean limit is about 5 percent by volume in air. Below this, mixtures are too lean to ignite; between about 5 and 15 percent methane in air, flames can propagate, with 15 percent as the upper limit. So the correct value is 5 percent. The other options fall outside the LEL: 1% and 3% are too lean, while 7% is within the flammable range but not the minimum.

In flammability terms, the lower explosive limit is the minimum methane concentration in the air that can sustain a flame once ignited. For methane, this lean limit is about 5 percent by volume in air. Below this, mixtures are too lean to ignite; between about 5 and 15 percent methane in air, flames can propagate, with 15 percent as the upper limit. So the correct value is 5 percent. The other options fall outside the LEL: 1% and 3% are too lean, while 7% is within the flammable range but not the minimum.