What is the residual pressure in the scenario?

In firefighting and hydrant flow discussions, residual pressure refers to the pressure remaining in a water distribution system after water flow has commenced. It is typically measured in pounds per square inch (psi) and is crucial for determining the adequacy of water supply for firefighting operations.

The correct answer indicates a residual pressure of 70 psi, which suggests it is below the maximum operational pressure but still within an effective range to deliver water to the hoses and equipment. This pressure is critical because it affects the flow rate and performance of the firefighting equipment; a sufficient residual pressure means the system can continue to supply water effectively to combat a fire while maintaining effective operation of the nozzles and other equipment being used.

Higher pressures, such as those represented by other options, may seem beneficial but often exceed practical operational limits for firefighting scenarios, potentially causing damage to hoses and fittings or excessive flow rates that are difficult to manage. Therefore, a residual pressure of 70 psi would typically be seen as providing a good balance between adequate supply and operational safety.