At the scene of a fire, a pump operator uses the difference between two types of pressure to determine how many more attack lines or appliances could be operated from the available water supply. What are these two types of pressure?

The correct answer involves understanding the concepts of static and residual pressure, which are crucial in assessing a water supply's capabilities during firefighting operations. Static pressure refers to the water pressure in the system when no water is flowing; it represents the maximum potential pressure available in the water supply system, typically measured in pounds per square inch (psi). This pressure is important for understanding the total amount of water that can be drawn from a hydrant or reservoir when no appliances are in use.

Residual pressure, on the other hand, refers to the pressure in the system while water is flowing and being used by attack lines or appliances. This value shows the pressure remaining in the system after water has been drawn off and indicates how much more water can be used without dropping below an acceptable pressure level.

By comparing these two pressures, the pump operator can determine how many additional attack lines or appliances can be operated safely without compromising the water supply. If the residual pressure remains sufficiently high while flow is established, additional lines can be added. If the residual pressure drops significantly, it may indicate that the existing supply is inadequate for further demands, ensuring firefighters understand the limitations of their water source and adjust their attack strategy accordingly.