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%

Safety regulations mandate that high-pressure alarms in the inert gas main must be set to activate at 90% of the lowest relief valve setting. This provides a critical buffer, allowing the crew to take corrective action before the relief valves lift and potentially vent inert gas to the atmosphere.