URBAN PUMP SERIES (EP 01) - Urban Water Supply

Urban Pump Series
Part 1 - Getting Water
Episode 1 - Urban Water Supply

"Rated Capacity"

Before we begin discussing urban water supply systems, we need to establish what our Engines/Pumpers can produce for us on the fire ground. Regardless of how much water our hydrants can produce, every engine will have a limit on the amount of water it can spit out on the discharge side of its pump.

The key phrase we need to know/understand here is "Rated Capacity."

Every engine will have a placard like this somewhere on its panel:

This Waterous, dual-stage pump has a rated capacity of 1,500 GPM at 150 psi on the discharge panel.

Two key things you need to know about this information:

Per NFPA 1901, this standard must be met while drafting through 20' hard suction and 10' height.

In an urban environment (this is the URBAN Pump Series, after all), we don't normally draft but rather utilize a pressurized water supply system (via hydrants). Because of this, our "rated capacity" will be much higher than what the engine says its output will be. For example, the engine I currently ride in Dallas has a rated capacity of 1,500 GPM @ 150psi. However, I have successfully delivered over 2,500 GPM on multiple occasions because I was connected to the city’s water supply system.
- **Update - Recently, on Engine 30, one of our new Pierce engines, we pushed ~3,000 GPM with around 20psi still on our intake gauge! We'll cover more of this in a future episode where we talk about maximizing water from a single hydrant.
Keep this next one in mind for future episodes on when we should be switching from Pressure to Volume on a dual-stage pump...

The "books" will teach you that we transition from Pressure to Volume mode "when the discharge volume exceeds one-half of our rated capacity." But remember, when tied into a pressurized hydrant, our rated capacity will be much higher than what that little placard says.

For my brothers and sisters here in Dallas, I usually teach that the "break over" point for switching between Pressure and Volume is often around 1,000 - 1,200 GPM. So, practically... if you know you're going to be flowing to a ladder pipe, go ahead and make the transition. If you are setting up to relay pump at a large fire, make that transition. Anytime you're anticipating a target flow of less than 1,000 GPM, you're best to leave the engine in pressure (with a few exceptions).

Key Takeaway - Water supply in an urban city is determined by:

Your engine's pumping capacity, and
Available water supply.

Remember that when we hook into a hydrant and read 60, 70...100 psi of pressure on our intake gauge, our rated capacity will be much higher than what the manufacturer says... because we're not drafting from 10' and through 20' of suction hose.

Your City Standard

We just made the point that the amount of water you can deliver on the fire ground will be based on your engine's pumping capacity and available water supply.

Now, when it comes to our available water supply, every city looks a little different. The key is knowing what your city has implemented and how they adhere to or deviate from the NFPA standards on supply systems and how they are marked.

The Start of The Supply Chain

NFPA 291 - Recommended Practice for Fire Flow Testing and Marking of Hydrants, outlines the recommended guidelines for hydrant coloring and the minimum GPM each color-top should provide:

Class C - Red - > 500 GPM
Class B - Orange - 500 - 999 GPM
Class A - Green - 1,000-1,499 GPM
Class AA - Light Blue - 1,500 GPM or greater

Some Cities Deviate...

Such is the case here in Dallas. After talking with Luis E. Bodington, a Senior Engineer with the city of Dallas Water Utilities Department, it became clear that Dallas has opted to utilize a completely different color system that indicates something very different from the NFPA recommendations.

In Dallas, we utilize what we call RABY..

Red
Aluminum (or Silver)
Blue
Yellow

But what do these colors indicate? GPM? Not necessarily. Rather, the Water Department says that the hydrant's color will indicate the SIZE (diameter) of the pipe supplying the hydrant. Although they deviate from the NFPA standard on how to mark hydrants, the Water Department has partially adopted NFPA’s recommendations on minimum flow. I say “partially” because they improve on the recommended GPMs supplied for Class B hydrants.

Red = 4” supply pipe with < 500 GPM
Aluminum (or silver) = 6" supply pipe with > 1,000 GPM
Blue = 8” supply pipe with > 1,000 GPM
Yellow = 12 or greater supply pipe with > 1,500 GPM
** Note that the Water Department says we should get 1000 GPM from a blue top hydrant.

Again, the key is knowing your city’s water supply system. How have they adopted the NFPA standard or deviated? This plays a role when you pull up at a burner and anticipate multiple ladder pipes flowing throughout the incident. I'm looking for the closest "yellow top" in this instance. I certainly don't want to hook up to a "silver top" if I'm anticipating target flows of more than 2000 GPM.

Key Factors on Flow

Remember, the amount of water you can deliver on the fire ground will be based on two main factors:

Your engine's pumping capacity, and
Your available water supply.

Now, when discussing your available water supply, beyond the color of your hydrant (ie. what volume or GPM you are expecting from that hydrant), three key factors will affect your expected available water supply:

Peak Hours
For us here in Dallas and many other municipalities across the country, the time of day can impact your water supply. When we tie into a "yellow top" and expect 1500 GPM, we must recognize that this standard was set with peak consumption hours in mind. Our volume will likely increase when we are outside those peak hours. Peak hours are early morning and late evening when consumer demand for water (showers, cooking, etc) is highest.
Number of Discharges
For many cities, our expected volume from a single hydrant is based on us utilizing all of the discharges on that hydrant (usually 3).

For example, I recently had a large mulch yard fire where we anticipated target flows of more than 2,000 GPM and thus started with two five-inch supply lines off a single yellow top hydrant. To achieve the dual 5" supply lines, we used the primary 5" connection (which has 4.5" threads) and one of the 2.5" discharges with a 2.5" to 5" adapter to supply our first engine in the relay series.
Supply Hose Utilized
Most cities use 5" LDH along with 3" as their primary two options for supplying an engine/pumper.

Which supply hose you choose will dramatically affect your available water supply due to friction loss. A 3" hose has significantly more friction loss than 5" LDH. Next month our entire episode will be dedicated to what you can expect from each of these and when each is necessary and/or appropriate on the fire ground.

CONCLUSION

Water supply on the fire ground is based on two things:

Your engine’s pumping capacity
Your available water supply

And three factors that will affect your available water supply are:

Peak hours of operation
Number of discharges utilized
The supply hose utilized

Until next episode…

Hold fast & raise the bar,

DISCLAIMER: Dallas Fire-Rescue does not endorse or necessarily promote these videos. The information herein is my best understanding of the material covered and the subsequent views expressed are my own and not necessarily those DFR. These videos are strictly for educational purposes only. It is critical that you follow your department's MOP/SOP, and talk with your Station Officer (and crew) before implementing anything you see here on The Roll Steady.