In environments with combustible gas hazards, it is important to know long before the gas concentration reaches the LEL. Typical safety standards require that a gas detection unit give warnings at 10 - 20% of the LEL. Do not confuse the alarm level with the volume of gas required to reach the LEL. For example: Methane has an LEL of 5% by volume in air. For a gas detector to give an alarm at 10% of the LEL, it must trigger when it detects 0.5% by volume. The detector for this application would most likely be calibrated for the range from 0% to 5% gas by volume, but display the reading as 0 - 100% LEL.