LeL

LEL stands for Lower Explosive Limit, a term used in fire safety and industrial hygiene to denote the lowest concentration of a combustible gas or vapor in air that can ignite and sustain a flame when an ignition source is present. The limit is expressed as a percentage of the gas or vapor by volume. Below the LEL, the mixture is too lean to support combustion, while concentrations above the Upper Explosive Limit (UEL) are too rich for ignition. The LEL varies among substances; for example, methane has an LEL of approximately 5 % by volume, whereas propane’s LEL is about 2.1 %.

Determining the LEL is essential for risk assessments, design of ventilation systems, and the implementation of safety protocols in environments such as chemical plants, refineries, mining operations, and confined spaces. Safety standards often require monitoring air for concentrations that approach a certain percentage of the LEL (commonly 10–20 %) to trigger corrective actions before hazardous conditions develop.

Measurement of LEL can be performed with portable explosive gas detectors that use catalytic or infrared sensors. These devices provide real‑time readings and alarms when concentrations exceed predefined thresholds. Proper calibration, regular maintenance, and training of personnel are critical to ensure reliable detection. Understanding and controlling LEL values helps prevent fires, explosions, and associated injuries or property damage.