Question 50Safety & Environmental - Assistant Engineer

70% to pass

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 _______________.

Athe detector is sampling a space in which 30 percent of the atmosphere is explosive

Ba flammable vapor concentration exists at the sample point, but it is too lean to burn

Can explosion is about to take place

Dthe detector sensor is sampling a space where the cargo vapor concentration is 30 percent by volume

AI Explanation

The correct answer is B) a flammable vapor concentration exists at the sample point, but it is too lean to burn. The reason this is the correct answer is that gas detection systems on LNG tankers are designed to activate an alarm when the cargo vapor concentration reaches 30% of the lower explosive limit (LEL). This means that the vapor concentration is high enough to be flammable, but still too lean to support combustion and cause an explosion. The alarm is intended to alert the crew that a potentially hazardous situation is developing, but an explosion is not imminent. The other answer choices are incorrect because: A) the atmosphere is not 30% explosive, just 30% of the LEL; C) an explosion is not about to take place; and D) the vapor concentration is not 30% by volume, but rather 30% of the LEL.

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