To calculate the available water using the 10-20-30 rule, it's important to understand the relationship between static pressure, residual pressure, and flow rate. The 10-20-30 rule provides a methodology for determining the amount of water available by assessing the pressures involved during firefighting operations.
In this scenario, the static pressure is 75 psi, and the residual pressure when flowing is 60 psi. By subtracting the residual pressure from the static pressure, you determine the available pressure that can still contribute to water flow, which is needed to ensure an effective firefighting strategy.
Here's the breakdown:
The difference between the static and residual pressures is 15 psi (75 psi - 60 psi). This drop indicates how much pressure is lost during the flow.
According to the 10-20-30 rule, the minimum residual pressure while flowing should be maintained above 20 psi for effective operation. This means that 15 psi of loss is acceptable since you still have 60 psi residual pressure remaining.
You are flowing 700 gallons at this point.
When applying the 10-20-30 rule, it indicates that the total available water can be approximated by taking the flowing gallons as the base.