What is %LEL?
The Lower Explosive Limit (LEL) is the lowest concentration of a flammable gas/vapour in air that can ignite. Gas detectors often display %LEL:
%LEL = (Measured %vol ÷ LEL %vol) × 100
Many permits require hot work only when readings are well below 10% LEL (site rules vary).
LEL / Flammable Mixture Calculator
Flammable gas · %LEL
Convert a measured concentration to % of Lower Explosive Limit for gas testing and hot-work checks.
Formula: %LEL = (Measured %vol ÷ LEL %vol) × 100
- Match meter calibration gas to the hazard.
- O₂ and toxic gases still need separate checks.
- Site hot-work %LEL limits override teaching bands.
Frequently asked questions
Where do I get LEL %vol?
From the SDS or gas tables — e.g. methane ≈ 5%vol, propane ≈ 2.1%vol. Use the gas your meter is calibrated for.
ppm input?
Convert ppm ÷ 10,000 to %vol first, or enter %vol directly.
Mixture of gases?
LEL for mixtures needs a specialist method — do not average casually.
Is 0% LEL “safe”?
It means below the flammable range for that sensor path — still control ignition sources and re-test.
