Andy Fredericks on 1 3/4″ Handlines

“While many residential fires can be extinguished with only 90 gpm and certainly the skill

and tenacity of an experienced nozzleman should never be underestimated, 1 1/2-inch

hose offers no flow reserve for contingencies. In addition, the friction loss in 1 1/2-inch

hose can be significant, requiring a high pump discharge pressure (PDP) and severely

restricting handline length.

The use of 13/4″-inch hose, pioneered by the New York City Fire Department in the late

1960’s, overcame many of these limitations. Not only is the practical flow limit much

higher (about 200 gpm versus 125 gpm for 1 1/2-inch), the friction loss per length is much

more reasonable.

Consider the following example: A 150-foot, pre-connected, 1 1/2-inch handline with a 100

psi combination nozzle flowing 125 gpm will require a PDP of almost 160 psi. The same

flow with the same nozzle through 150 feet of 1 3/4″-inch hose will require a PDP of only

135 psi. At the same PDP used in the first example (160 psi), the 1 3/4″-inch handline will

deliver 165 gpm—a 24 percent increase in flow volume.

A more recent introduction is the 2-inch handline. While the practical flow limitation of 2-

inch hose is over 200 gpm, in reality there is a significant amount of “unused capacity.”

It has been suggested that actual fireground flows from 1 3/4″-inch hose average a paltry

110 gpm or less. The reason is that as flow increases, so does nozzle reaction.

Particularly for fire departments that employ 100 psi combination nozzles, reaction

forces will exceed levels that can be safely and effectively controlled by a single

firefighter at flows of only 130-140 gpm. The difference between potential and actual

flows is even more dramatic with 2-inch hose. Since the upper-end flows through a 2-

inch hose produce rather substantial nozzle reaction forces and make the line difficult to

bend, the nozzleman usually ends up screaming for less pressure or the nozzle is

partially closed in order to maintain control. As a result, 2-inch handlines often end up

delivering less than 50% of their potential capacity. In practical terms, 1 3/4″-inch hose is

just as effective, plus it costs less and is easier to handle” (Fredericks, 2000).

Reference: Fredericks, Andy, 2000 Fire Nuggets Magazine http://www.firenuggets.com

 

Tags:

Leave a Reply

Your email address will not be published. Required fields are marked *