What does the Lower Explosive Limit (LEL) indicate?

The Lower Explosive Limit (LEL) indicates the lowest concentration of vapors necessary for ignition in an atmosphere. This measurement is critical in understanding explosive limits because it defines the minimum amount of flammable gas or vapor that must be present in the air for a fire or explosion to occur if an ignition source is introduced.

When the concentration of these vapors is below the LEL, the mixture is too lean to ignite, meaning that there aren't enough fuel vapors present to sustain a combustion reaction. Therefore, having knowledge of the LEL is essential for safety protocols when handling hazardous materials, as it helps prevent situations where fire or explosion could occur due to ignitable concentrations of vapor.

Other responses provide related but distinct information about different aspects of explosive hazards, but the LEL specifically identifies that crucial threshold of vapor concentration needed for ignition.