The Upper Explosive Limit (UEL) is the maximum concentration of a flammable gas or vapor in air that can ignite. Above the UEL, the mixture is too rich to burn due to insufficient oxygen for combustion.
The range between LEL and UEL defines the flammable range, which is the dangerous zone where ignition can occur. For methane, the UEL is approximately 15% by volume, creating a flammable range from 5% (LEL) to 15% (UEL).
The flammable range varies significantly between different gases. Below the LEL, the mixture is too lean to burn. Between LEL and UEL is the flammable range where ignition is possible. Above the UEL, the mixture is too rich to burn.
Understanding both LEL and UEL is essential for proper gas detection system design, setting appropriate alarm thresholds, and understanding explosion risks in different scenarios. The relationship between these limits determines the detection strategy.