What is the purpose of a PGD in this detector system?

• A. To continuously monitor CH4 at the failed detector location
• B. To monitor oxygen levels only
• C. To trigger automatic ventilation shut down
• D. To measure CO2

Answer: (A)

A PGD is used to provide methane monitoring at the location of a failed detector, ensuring continuous CH4 data where the fixed detector is not functioning. This is crucial because CH4 levels directly affect explosion risk and ventilation decisions, so keeping an ongoing reading at that spot keeps safety response timely even when a detector is out of service. It isn’t primarily about monitoring oxygen, nor about measuring CO2, and the PGD itself doesn’t automatically shut the ventilation off—the data it provides supports safety actions taken by the broader system.