Alarm indicators at master alarm panels related to gas manifolds are used to indicate when or just before changeover from one header to the other.

• A. To regulate pressure
• B. To monitor temperature
• C. To log data
• D. To indicate changeover

Answer: (D)

The main idea here is that these alarm indicators are there to signal a switch between the two gas headers. In a dual-header manifold, one header is primary and the other is backup; when pressure or supply conditions trigger a changeover, the master alarm panel lights or sounds to alert staff that the system is shifting from one header to the other or will do so soon. This immediate notice helps ensure continuous gas supply, verify that the backup header is ready, and allow quick action if something isn’t switching correctly.

These indicators aren’t primarily for regulating pressure—pressure regulation is handled by regulators and the changeover valve system itself. They also aren’t mainly for monitoring temperature, which isn’t the function of the changeover alert. Likewise, while some systems may log events, the alarm indicator’s purpose is to indicate the changeover status, not to serve as a data logger.