Bioenvironmental Engineering Apprentice (BEA) Block 2 Practice Test

Which statement correctly describes the ignition potential of gas concentrations relative to LEL and UEL?

Concentrations above UEL do not ignite.

Concentrations below LEL cannot ignite.

Concentrations between LEL and UEL can ignite under proper ignition sources.

Gas ignition depends on the mixture being in the flammable range, defined by LEL and UEL. When the fuel concentration is between these limits, the air–fuel mix can ignite if there’s a source of ignition present. If the concentration is below the lower limit, the mix is too lean to ignite; if it’s above the upper limit, the mix is too rich to sustain combustion. Ignition also requires an adequate ignition source and proper mixing with air. So, mixtures within the LEL–UEL range can ignite with the right ignition source.

Ignition is independent of concentration.