What is residual pressure in the context of a fire hydrant?

Residual pressure in the context of a fire hydrant refers to the pressure that remains in the water distribution system while water is actively flowing from the hydrant. This pressure is crucial for determining the available flow rate during firefighting operations. It indicates how much water can be supplied to the hydrant and assesses the performance of the water supply system under operational conditions.

Monitoring residual pressure helps firefighters understand the effectiveness of the water supply and can influence the tactics used during firefighting efforts. For example, if the residual pressure is too low, it may indicate potential issues in the water supply network or insufficient water for the demands of the fire suppression.

The other options do not accurately describe residual pressure. The buildup of pressure in the hydrant when not in use is more indicative of static pressure. Pressure inside the fire truck is unrelated to the pressures discussed in this context. Likewise, the pressure detected when a hose is detached refers to what's commonly known as residual or drain-down pressure, which is a different scenario. Thus, the correct interpretation pertains to the pressure available in the system when water is flowing.