When is the second pump called off while refueling in a Type 4 system?

The correct answer is based on the operational protocols for safe and effective refueling in a Type 4 system. Specifically, the second pump is called off when the flow is maintained above 700 gallons per minute (gpm) for 15 seconds. This guideline ensures that the system is efficiently utilizing the pumps and that there is adequate flow rate for the refueling operation, which minimizes downtime and enhances safety.

Maintaining a flow rate above this threshold for a specified duration helps to confirm that the system is stable and that the primary pump can manage the flow alone without risking an inadequate supply. If flow were allowed to drop too low, it could lead to operational inefficiencies or complications during the refueling process. Thus, monitoring the flow and confirming consistent rates over a brief period is crucial for ensuring smooth operations.

In comparison, the other potential scenarios do not align with established operational protocols. Calling off the second pump based on flow rates that are either too low or not adequately sustained would not provide the necessary assurance for safe refueling operations.