Small-diameter fire hose (3/4- 1 inch), often carried on booster reel, preconnected to pump of an engine (and the booster tank) for putting out small fires near the truck without having to connect to a fire hydrant; easily recovered with a motorized reel. Also known as "red line" for the common red rubberized outer layer. Booster hose is also used for High Pressure Fog (HPF) applications