What is the first step when shutting down a constant pressure relay?

The first step when shutting down a constant pressure relay is to start with the attack apparatus and work backward toward the source pumper. This approach is essential because the attack apparatus is typically operating under pressure to deliver water to the firefighting operation. By shutting down from the attack apparatus first, you ensure that the fire ground has the water supply it needs without interruption while you gradually isolate the relay.

This method also allows for the systematic and controlled removal of apparatus from the relay system, minimizing the risk of sudden drops in pressure which could potentially disrupt operations or affect firefighting efforts. Once the attack units are disconnected, you can move upstream toward the source pumper, ensuring that the relay remains effective throughout the shutdown process without impacting ongoing fire operations.

The other options do not follow the best practice for shutting down a constant pressure relay effectively, as they either risk collapsing the pressure needed for firefighting or do not prioritize the safety and operational efficiency required in such situations.