HOW TO CONVERT LEL TO PPM

If we use methane (CH4) as an example, the LEL (lower explosive level) of methane is generally considered to be 5% by volume (5% By Vol). That means the mixture is too lean to burn if there is less than 5% methane present. But at 5%, we can burn or explode if there is an ignition source.

So we call 5% by vol methane the same as 100% LEL.

"5% methane is 100% of the explosive concentration."

• 100% LEL = 5% methane = 50,000 ppm methane
• 10% LEL = 0.5% methane = 5000 ppm methane
• 1% LEL = 0.05% methane = 500 ppm methane

Thumb rule for dummies

• Multiply the LEL percentage number by 10,000 to get PPM.
• To convert from PPM to an LEL percentage, divide the PPM by 10,000.