Tankers carrying cryogenic cargoes, such as LNG, are fitted with gas detector systems which are designed to activate an alarm at 30% of the lower explosive limit. If an LNG gas detector alarm sounds, this means __________.

Correct Answer: Option B — a flammable vapor concentration exists at the sample point, but it is too lean to burn

Lower Explosive Limit (LEL) represents the minimum concentration of vapor in air capable of ignition. At 30% LEL, the mixture is too lean to support combustion. This safety margin provides early warning to personnel that flammable vapors are present before the atmosphere reaches a combustible state.