What is the upper explosive limit of natural gas (methane)?

What is the upper explosive limit of natural gas (methane)?

• A. 10%
• B. 17%
• C. 15%
• D. 20%

Answer: (B)

The upper explosive limit represents the highest concentration of methane in air that can still sustain a flame. Beyond this point, the mixture becomes too rich in fuel and not enough oxygen remains to support combustion, so ignition cannot propagate. For methane, this upper limit is in the high-teens by volume in air. Many safety references list it around 15%, but a commonly cited value is about 17%. That’s why the option near the upper bound is considered the best answer: it identifies the highest concentration at which methane–air mixtures can still ignite. Concentrations well below that can ignite if ignited, while concentrations above it are too fuel-rich to support combustion.

The upper explosive limit represents the highest concentration of methane in air that can still sustain a flame. Beyond this point, the mixture becomes too rich in fuel and not enough oxygen remains to support combustion, so ignition cannot propagate.

For methane, this upper limit is in the high-teens by volume in air. Many safety references list it around 15%, but a commonly cited value is about 17%. That’s why the option near the upper bound is considered the best answer: it identifies the highest concentration at which methane–air mixtures can still ignite. Concentrations well below that can ignite if ignited, while concentrations above it are too fuel-rich to support combustion.