Target on Training

Understanding and teaching the art of water hydraulics as pertains to fire fighting.

Volume 22, No. 6
November 2007
By Attila Hertelendy

Fire demands can have a significant impact on the size of a water distribution system, create additional localized stress on the water system, and may induce undesirable areas of low pressure. Sound engineering design practice dictates that the distribution system be capable of delivering all fire flows at the required minimum pressure. Computer network models provide an efficient and reliable approach for computing these flows and determining their impacts on system performance. Current fire flow models either require changes in the network structure and associated hydraulic equilibrium equations, or use a repetitive trial-and-error process. The result of using current models is inefficient performance at a greater cost.

This basically boils down to the fact that as technology becomes more and more sophisticated, firefighters tend to become rusty or perhaps incapable of calculating basic fire flow. Computers have their place, but I find it increasingly alarming that everything has become automated and when the pump operator relies solely on digital readouts, it is a most uncomfortable feeling to think that the person running your fire water is flying by the seat of his pants. It is easy to forget all the calculations we learned in fire school. I by no means have an aversion to technology but I feel it is important for everyone to remember how to do basic fire flow calculations.  How can you as the training officer provide refresher training without sending your entire fire brigade back to fire school to learn the basics?

In order to make this practicable I have outlined some basic steps you can take in your next training session. Below is enough for at least  three to four one hour sessions on basic field calculations. Modify the examples to reflect accurately your own facility. We are only reviewing here and trying to refresh basics. We’ll get to big water later.

Finding the proper engine pressure is most critical and valuable at the fire scene. Pump operators do not have the luxury of booting up their laptop computers or pulling out a calculator during an incident. Operators need to have some sort of pre-determined method to quickly deliver water to the hoselines with the proper pressure. This method is termed Fire Ground Calculations or Field Calculations. They aren’t designed to be exact but rather to be quick and close. Field Calculations require the operator to memorize certain constants such as nozzle pressures, appliance losses, and the friction loss in common hoselines. Below are Field Calculation constants that must be memorized.

Basic Formula for Engine Pressure (EP):

EP= Nozzle Pressure + Friction Loss(hose) + Back Pressure + Appliance Loss

EP = NP + FL + BP + APP

The components (NP, FL, BP, APP) of this formula will be explained below.

 Appliance Loss Figures (APP)

Appliance   Friction Loss Figure

Deluge (Turret or Deluge) 25 psi

Dry Standpipe connection  25 psi + BP

Wye or Siamese connection 5 psi

Appliance   Friction Loss Figure

Ladderpipe  80 psi

Sprinkler System (no fire) 100 psi + BP

Sprinkler System (with fire) 150 psi + BP

Nozzle Pressures (NP)

Appliance   Handlines  Master Streams

Barrel Tip (solid stream) 50 psi  80 psi

Fog Nozzle (fog or   80 psi  100 psi

straight stream)

These nozzle pressure figures are to be used for work problems where nozzle type, and not pressure, is given.

Back Pressure

The field calculation for back pressure is 5 psi per 10% of grade or 5 psi per story above the first floor.

 

Work Problems: Using Fire Ground Calculations, find the proper EP for the following:

a.) 200’ of 1½” handline with a fog tip nozzle flowing 100gpm

EP = NP + FL + BP + APP

EP = 80 + (35X2) + 0 + 0

EP = 80 + 70

EP = 150 psi

b.) 200’ of 1” hose flowing 30 gpm at 60 psi

EP = NP + FL+ BP + APP

EP = 60 + (30X2) + 0 + 0

EP = 60 + 60

EP = 120 psi

(FL figures must be multiplied by the number of 100’ of hose. When there are no figures for BP or APP use “0”).

c.) 400’ of 2 ½” handline with barrel tip nozzle flowing 250gpm on a hill 50’ above the fire truck

EP = NP + FL + BP + APP

EP = 50 + (15X4) + (5X5) + 0

EP = 50 + 60 + 25 + 0

EP = 135 psi

Siamesed Hoselines

When two or more hoselines are used to supply water to a desired point or appliance, calculations are simplified by calculating the friction loss in the average length of the siamesed hoselines. Each hoseline will deliver its equal share of water because the pressure applied by the fire pump will equalize in the hoselines. Discharge rate will be divided by the number of siamesed hoselines when determining gpm for each hoseline.

 The average length of the siamesed hoses is 600’

Total length / number of hoses

(600+600) + 2 + 600

The average flow of the hoses is 250 gpm

Total gpm / number of hoses

500 gpm / 2 = 250

Using fire ground calculations, we know that each 100’ length of 2½” hose flowing 250 gpm has a friction loss of 15 psi.

600 / 100 = 6

6 X 15 = 90 psi

Total friction loss in the siamesed hoses is 90 psi

Work problem: Using fire ground calculations, find the EP of the following evolution.

EP=NP+FL+BP+APP

First Step: Find NP

The NP for a master stream using a fog nozzle is 100, therefore NP = 100 psi

Second Step: Find FL

The average length of siamesed hoses is 400’

(400 + 350 + 450) / 3

1200 / 3 = 400

The average flow of the siamesed hoses is 200 gpm

600 gpm / 3 = 200

FL = 10 psi for every 100’ of 2½” hose flowing 200 gpm

FL = 10 X 4

FL =  40 psi

Third Step: Find BP

There is no BP for this problem, BP = 0

Fourth Step: Find APP

The appliance loss figure for a Deluge is 25 psi

APP = 25 psi

Step Five: Put all the figures into the formula

EP = NP + FL + BP + APP

EP = 100 + 40 + 0 + 25

EP = 165 psi

Wyed Hoselines

For wyed lines of equal diameter with nozzles of the same size, the friction loss for the average length of wyed lines will be considered. Find the average length and treat as one line. This means that the nozzle pressure of only one hose will be added to the NP portion of the EP formula. The hoseline supplying the wyed lines (before the wye) must provide the total amount of GPM to all the wyed lines. The total GPM will be used for all friction loss calculations behind (pump side) the wye. For all calculations in front of the wye (nozzle side of wye), use the discharge of only one hoseline.

You can look at any number of texts to get more information and most will have instructors’ notes that can help you to fine tune your lectures. For refresher training this is meant to be fluid (excuse the pun). This means that some in your audience will know this very well, and others will need to review right from the beginning. It is beneficial to assign problems for them to work out. It is always best to combine the didactic (in the classroom) with the field and show the brigade members how the calculations actually work in the field.

Comments? Questions? Is there an industrial fire training topic you would like to see covered in this column? Please send e-mails to ahertele@bellsouth.net. Attila Hertelendy is an instructor with the University of Nevada, Reno Fire Science Academy. He is also president and CEO of Great White Emergency Medical Solutions, Inc., a training and emergency response planning company.

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