Fire Hose, Water Supply, and Fire Streams
Hose and water supply
Know hose sizes and their jobs: 1¾-inch attack lines, 2½-inch attack and medium supply lines, and large-diameter hose for supply. Couplings may be threaded, Storz, or quarter-turn. Hose loads - minuteman, triple layer, accordion, horseshoe - are selected by the space and the speed needed. Hydrant types matter: dry-barrel hydrants drain when closed and suit freezing climates, while wet-barrel hydrants stay charged where freezing is not a concern. Static, residual, and flow pressures describe supply capacity; a large drop from static to residual signals limited supply.
Pump pressure and streams
Pump discharge pressure equals nozzle pressure plus friction loss plus appliance loss plus elevation change. Elevation costs about 0.5 psi per foot gained and adds about 0.5 psi per foot lost. Solid bore and fog nozzles behave differently: solid bore converts pressure to reach and penetration, fog produces a protective curtain and absorbs heat but is easily disrupted by wind. Nozzle reaction grows with pressure and tip size - a real safety consideration on ladders and roofs.
Traps
Most errors are arithmetic and omission: forgetting appliance loss, ignoring elevation, or adding elevation when the line goes downhill. Another favorite mixes up the 25 percent static-to-residual rule of thumb for inadequate supply.
Rule of thumb
PDP = NP + FL + appliance loss + elevation - write it out and fill in every term before you answer.