Fire attack: Hose size matters

Taking a too small hose to a big fire will compromise the initial attack and set off a chain of other bad fireground events

Last month we looked at the dominos that can be created when advancing a hose line improperly and the issues that can arise with that. This month we will look at the issue of selecting the correct size hose line.

There are three standard sized hose lines that the fire service uses as a front line attack line: 1½, 1¾ and 2½ inch. These three common-size lines are used for the majority of fire knock down and suppression.

The remaining times may involve large master streams or deck guns. The issue with selecting the correct size line is the amount of water that can be delivered from that hose line. Select the wrong size in the beginning, and the operation will not go as planned.

The selection of the hose line is the first domino being lined up leading to a much bigger problem.

Doing what's familiar
Firefighters tend to fall back upon habits that they may have developed over time due to upon repetition and familiarity. One habit that most firefighters fall back on is with the 1½- or 1¾-inch hose line.

These sizes always seem to be the first hose lines pulled off for the any offensive fire attack. While the 1½- or 1¾-inch hose line does provide ample water delivery for most of our everyday fires, it falls short when it comes to large fires that require large volumes of water.

The hose coupling diameter of a 1½- and a 1¾-inch are the same, they only differ with the diameter of the hose jacket. So when there is water flowing through a 1¾-inch hose line, it still has to travel through a 1½-inch coupling at every 50 or 100 feet.

This small reduction in the hose coupling diameter adds some friction loss overall, but the amount is inconsequential in comparison to the amount of water that can be delivered at a lower operating pressure with a 1¾-inch hose line.

Water to match the fire
The size of the structure, the fire and fuel load being dealt with and the size of the fire, will dictate what size hose line to be pulled off first and used for effective water delivery. The general rule that most firefighters can remember is small fire equals small water and big fire equals big water.

Small water refers to your basic 1½- or 1¾-inch hose lines; the big water refers to the 2½-inch hose line.

With a 1½-inch nozzle, the average water delivery rate can be between 150 to 200 gpm. With a 2½-inch nozzle, the water delivery rates can be increased with minimal increase in pump pressure. The average water delivery rates are between 200 and 325 gpm.

This increase in water delivery may be what is needed to achieve a quick and effective knockdown of a large fire. In the accompanying video, you will see examples of where the first hose line pulled off is the wrong size based upon the size of structure and the fuel load present.

Make sure to not handicap yourself by pulling off the wrong size line. 

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