Water-Flow Myths

"Whether it's department SOPs, SOGs or just the word from the old-timers, we in the fire service have rules that govern the way we do things, especially when it comes to moving water. Some of these rules were established years ago, and others are more recent... The problem is, some of these rules can prevent us from doing things better."

Note:

"All techniques and operations discussed in this article as new alternative methods are directly in line with manufacturers' recommendations for their equipment and have been used safely and successfully on the fireground."

--Paul Shapiro

Myth #1

The 2 1/2" discharge on a pumper cannot support large-diameter hose (LDH) because of its low-flow capabilities.

Reality #1

A large-diameter discharge is the most efficient way to flow large volumes of water through LDH. If your apparatus doesn't have a large-diameter discharge, you can still accomplish large-flow operations with a 2 1/2" discharge. You should be able to achieve 1,000-gpm flows at a respectable RPM range. Paul recommends using the side 2 1/2" discharge, with no bends in the set-up.

Myth #2

Laying an LDH supply line is like taking the hydrant to the fire or laying an above-the-ground water main.

Reality #2

This myth leads you to believe that you don't need to do anything...just lay the hose and it will deliver all the available water. But the truth is, as good as LDH is, you still need to use your pumper and effective hose lays. In one test, 500 feet of 5" LDH connected directly to the hydrant produced a flow of 1,150 gpm. Then a pumper was positioned at the hydrant, and the LDH connected to the pumper. The flow was almost doubled, producing 2,100 gpm. Many departments would have settled for the 1,150 gpm, never considering the flow they were missing.

Myth #3

A deluge gun (portable monitor) with 2 1/2" inlets must be connected with 2 1/2" or 3" supply lines.

Reality #3

An adaptor will allow you to connect LDH directly to the deluge gun. Flow tests show that the LDH produced 1,000 gpm with 20 psi less engine pressure than using a combination of LDH and 3" hose.

Myth #4

If only a 2 1/2" port on the hydrant is available, don't use LDH because the hydrant can't support it.

Reality #4

Rule of thumb: The 2 1/2" port will flow only 20% less than the large port on the hydrant when using LDH. If you need it, use it!

Myth #5

You can't use LDH on a weak hydrant system.

Reality #5

In fact, it's just the opposite. If you face a weak hydrant system, LDH is the best choice. A weak hydrant system will probably lack good hydrant pressure, so you should use the supply hose with the lowest friction loss to make up for the wak hydrant pressure. Five-inch hose has less friction loss than 2 1/2" or 3" hose.

Myth #6

Two short pieces of 3" hose from a hydrant is better than trying to connect LDH to just one of the 2 1/2" ports.

Reality #6

It seems reasonable...two ports would flow more than one, right? But this set-up actually creates higher friction-loss. Flow tests show that a single LDH line connected directly to one of the 2 1/2" hydrant ports will flow about the same as trying to use both ports.

Myth #7

You must fully open a nozzle when it's in use.

Reality #7

The bale on a nozzle is just like the accelerator pedal in your car. If the stream is too hard to handle, gate the nozzle down to halfway...you'll still get a workable stream. Don't judge a stream by how it looks...judge it by how it works.

That's it! Don't trust your safety and effectiveness to myths and outdated tradition. Use your training drills to see what really happens. Seeing is believing!