At what maximum gas concentration must the fixed gas detection system on a LNG ship activate an audible and visual alarm?

Correct Answer: Option C — 30% by lower flammable limit

Under 46 CFR 154.1350, the fixed gas detection system on liquefied gas carriers must trigger audible and visual alarms before the gas concentration reaches 30% of the lower flammable limit (LFL) in monitored spaces. This ensures early warning of leaks before an explosive atmosphere can form.