22/03/2026
LEL (Lower Explosive Limit) is the minimum concentration of gas in air that can ignite.
UEL (Upper Explosive Limit) is the maximum concentration of gas in air that can ignite.
Gas can explode when its concentration is between LEL and UEL.
Below LEL: too lean (not enough gas).
Above UEL: too rich (not enough oxygen).
Interview answer: "Gas is explosive when its concentration is between the Lower Explosive Limit (LEL) and Upper Explosive Limit (UEL)." ⚠️