In an inert gas system, high pressure alarms are set in the main vapor collection line to cause an audible and visual alarm if the pressure reaches a certain level. What is the percentage of the lowest relief valve setting at which the alarm must sound?

Correct Answer: Option C — 90%

Under 46 CFR 39.2005, the high-pressure alarm in a vapor control system must be set to activate at a pressure no higher than 90 percent of the lowest pressure relief valve setting, providing early warning before physical pressure relief occurs.