Which CH4 level is within the acceptable limit?

Which CH4 level is within the acceptable limit?

• A. 12% LEL
• B. 9% LEL
• C. 15% LEL
• D. 20% LEL

Answer: (B)

Lower Explosive Limit tells you the smallest methane concentration in air that can ignite. Gas detectors often report readings as a percent of the LEL, so a higher percent means you’re closer to the point where ignition could occur. For safety, many procedures consider around 10% LEL as the practical upper limit for normal work; methane’s LEL is about 5% in air, so 100% LEL is 5% CH4 and 10% LEL is roughly 0.5% CH4. The reading at 9% LEL is below that 10% threshold, so it’s considered within an acceptable limit. The other readings—12%, 15%, and 20% LEL—are above the typical safety threshold and require attention, such as increased ventilation or stopping work until the area is brought down to safer levels.

Lower Explosive Limit tells you the smallest methane concentration in air that can ignite. Gas detectors often report readings as a percent of the LEL, so a higher percent means you’re closer to the point where ignition could occur. For safety, many procedures consider around 10% LEL as the practical upper limit for normal work; methane’s LEL is about 5% in air, so 100% LEL is 5% CH4 and 10% LEL is roughly 0.5% CH4. The reading at 9% LEL is below that 10% threshold, so it’s considered within an acceptable limit. The other readings—12%, 15%, and 20% LEL—are above the typical safety threshold and require attention, such as increased ventilation or stopping work until the area is brought down to safer levels.