What is the formula to calculate the Elevation Pressure (EP)?

The formula to calculate Elevation Pressure (EP) is based on the understanding that for every story in a building, the pressure decreases due to the height of the water column. The generally accepted rule is that each story above ground level reduces the available pressure by approximately 5 psi.

When using the first option, subtracting 1 from the number of stories acknowledges that the pressure at the ground level is not affected in the way that the upper floors are. Therefore, multiplying the number of stories minus one by 5 psi directly gives the amount of pressure loss due to the height of the building.

This formula reflects the physical principles of fluid dynamics, where the height of the water column directly impacts the pressure experienced at various points in a system. Thus, applying this knowledge leads us to the conclusion that the correct option effectively captures how elevation influences pressure in firefighting applications.