URBAN PUMP SERIES (EP 02) - Supply Hose & Maximizing Flow
Urban Pump Series
Part 1 - Getting Water
Episode 2 - Supply Hose & Maximizing Flow
Three, Four & Five Inch Hose
In my home department (DFD), we carry both 3" (400' flat loaded) and 5" hose (1,000'-1,200' flat loaded) for supply purposes. And although 5" is our primary supply hose, it's not uncommon to see 3" being utilized regularly in South Dallas. Further, if we include engine-to-engine or supply hose laid for ladder pipe operations, we'll see 3” hose plays a much larger role throughout the city than we might have initially thought.
A question that arises, or should arise for every member is, "when should we be using 3" vs. 5"?" And, for those of us here who work for a department that utilizes 4-inch as their primary supply hose, "How does this apply?"
Before we jump in, I have to put out this disclaimer (and I mean every bit of it)... Always follow your Standard Operating Procedures/Guidelines regardless of what you read here on The Roll Steady. This Urban Pump Series Episode is informational, not instructional. Although I will share some general rules of thumb (what I call "models"), you should never assume I am correct. Always measure what you see here against your MOP/SOP and use it as a conversation starter at your Fire Station.
Specs That Matter & Practical Rules of Thumb
Let's start by looking at general specs for 3", 4", and 5" hose...
First, I want to draw your attention to the third column and look at the dry weight of the 4" and 5" hose. One section or 100 feet of these two will be in the ballpark of 80-100 pounds of dead weight once it is lying on the ground. With this in mind, a simple model (or rule of thumb) that I work by consistently is that based on the dry weight of the 5” hose, the max I will hand jack (Dallas' term for manually pulling hose from the hose bed to the hydrant) is 1-2 sections (or 100'-200').
Let me add a bit more clarification here...
This model of only hand jacking one to two sections is also based on if I am left to pull 5" on my own or if I can utilize another member of my engine or from an ambulance crew that just arrived on scene. I only pull one section if I am just laying back to the plug. If I have that extra body to help, I can usually push this out to two sections, or 200'. Just realize that dragging 200 lbs of dead weight across the pavement is harder than it sounds. My previous Driver at Station 28, who had over 30 years of experience, was adamant that he would only consider one section. That might be advice worth considering too.
What about 3" hose? Do I have a model/rule of thumb for how much I'm willing to hand jack back to a plug with this diameter hose? Yes, but my reason isn't seen on the chart above and is something we will look at later in this episode.
But, while we're talking about a 3" hose, I do want to point out an interesting spec that should be considered when we utilize a 3" hose to supply another engine (as in a relay operation) or when using it for a long courtyard lay as we do here in Dallas with our Rapid Attack Pack (3" feeder to a gated wye that breaks into two 1 3/4-inch attack lines).
Notice that the static volume in a single section (50 feet) of 3” is roughly 20 gallons of water. Why does this matter? Well, it is important to know that...
200' (4 sections) = 15-16% of our tank water (500 gals)
250' (5 sections) = 20% of our tank water (500 gals)
Once you drop 200-250' of hose on the ground, it's important to realize that upwards of 20% of your tank water will be used just to fill your hose... without a drop hitting the fire. Just something you should consider and allow to influence your tactics.
Volume and Friction Loss Considerations
As I mentioned above, it is not uncommon to see a 3" supply hose being used to connect to a hydrant by our South Dallas Driver-Engineers. But I want to ensure we're all on the same page about WHY this happens and the thought process that these veteran Engineers are working from.
Below, you'll see that the friction loss PER 100' in a 3" hose is ~21psi when we are flowing 500 GPM. That means a single section is around 10psi/50' @500 GPM.
DOWNLOAD > Fire Hose Friction Loss.pdf
So, in theory, as long as you are within ~100' of the hydrant you are connecting to (and you could push this out to 125' using your short section as well), a single 3-in supply line is sufficient to deliver up to 500 GPM on the fire ground without having your engine outrun your water supply (which would be due to the friction loss in your supply hose).
This is the foundation for these South Dallas Engineers using 3" at specific fires. The majority of these houses are between 800-1,250 square feet and require two 1 3/4" hand lines at most to extinguish the fire - this is where I've heard some old heads call this, "A two crosslay fire."
Here are the details:
A single crosslay's target flow = 150-160 GPM
Two crosslay = 300-320 GPM
100' of 3-in flowing 500 GPM = 21 psi of friction loss
With a yellow or blue top hydrant (in Dallas) you should see around 70-90psi (static) on your intake gauge, leaving you enough residual once your first and second lines are deployed.
If this is a little confusing, I'll give you a real-world example...
A few years ago, I arrived at a working box with a single-family house and a detached garage with heavy fire showing in the back. We were the third-up engine. As we pulled up, I noticed they hadn't secured a permanent supply yet, so my Driver went to work helping the first due Engineer hand jack to the blue top on the corner while we stretched a line to cover the primary exposure. The fire was easy work, and after a quick overhaul, we started to break down and reload our hose... This is when I noticed that the two drivers had laid 100' of 3-in as our supply line. My interest peaked... "Hey Coop, talk me through your choice on laying the 3-in." Now, driving the first up the engine was a veteran FRO, who is probably more competent than most Battalion Chiefs I know. That's not a knock on our Chiefs, but a testimony to the fact that this guy really knows his stuff. "Simple." He said. "This was only ever going to be a two-crosslay fire... tops three if you really needed another exposure line.” The house was roughly a 1,200 sq ft single-family dwelling with a detached garage. His argument was, even if the whole house was carrying the mail, we could put it out with two, well-supplied hand lines. So here is the model I've built into my own mind - If this is a "two crosslay fire," meaning I don't expect to utilize more than 500 GPM, I'm good utilizing a single 3" (up to 100') supply line between the hydrant and my engine. Now... keep in mind... this works because we have a killer hydrant system in Dallas. This is not a blanketed, across-the-board model that will work for every city in America.
Another option for utilizing 3", and is common in Battalion 1C, is to run two Engines in series utilizing a 3" with the supply engine pumping up to 100' of 3" to the attack engine (which again, we'll discuss in another episode in the future).
Something else that can be considered is dual 3" supply lines. You'll see in the chart below that this dramatically reduces your friction loss and increases your working limits.
There are a lot of other rabbit holes we could wander down as we look at 3", 4", and 5" supply hose. These are just some practical ways I've taken the theory and my experience(s) and built models to assist in my decision-making skills once the bell hits. I encourage you to consider these numbers and your existing MOP/SOP. Maybe this will give light on WHY that specific MOP/SOP is in place already. Also, consider these in light of what you see the more experienced members in your department doing, but you might not have understood the reasoning until now.
Maximizing Flow At A Working Fire
Understanding Our Limits
"Eventually you'll run out of engine,
or you'll run out of water"
Running Out of Engine:
Every Engine has a "working limit" and can only turn so many RPM, which translates into 1) volume and 2) velocity of water (measured in psi) from our pumps.
As you can see in the images below, these two apparatuses have a maximum governed speed of 2250 RPM and 2130 RPM. So, these engines' maximum or working limit will be 2250/2130 RPM. Eventually, you'll run out of the engine (RPM) on the fire ground. Fortunately, my experience has been that this is very rare in our urban environment, and what we see more often is Engineers running out of water long before they run out of RPM.
Running Out of Water:
Our water supply system (public water system, hydrants, etc.) has a limit to the volume (measured in GPM) they can also supply us with. You can only pull so much water out of the ground and through your pump before she says, "No more!"
Something I've seen time and time again though is a Driver selling themselves and their hydrant short, thinking that they are out of water because that compound gauge is at 10-20psi and that engine is practically walking away it's shaking so much.
Let's jump back to last month’s episode and remind ourselves of a few things when maximizing our flow from a single hydrant. Then I'll share three practical ways to get the most and ensure you're really out of the water before you tell that Battalion Chief that you can't add a fourth handline to cover an exposure on the bravo side.
Our rated volume capacity from a hydrant is based on three factors here in Dallas:
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) are 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 at least 1,500-2,000 feet of distance between the hydrant and the attack engine. Thus we started with two 5” supply lines off a single yellow top hydrant. To achieve the dual 5" supply lines, we used the primary 5" connection (which has 4" 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.
Three Ways To Maximize Flow
1. Multiple Connections From A Hydrant
As I said earlier, I think a good number of times, we sell ourselves short on maximizing our volume from a single hydrant by only connecting a single 5" supply line.
It's been my experience (and the key word here is "experience"), that even with a 70psi hydrant (static on my intake), I max out around 1250-1500 GPM. And this is with only 100' of supply line on the ground. Now, I have hit 2,000 GPM in training evolutions with a 100psi plug, but IMO those are rare and shouldn't be our expectation.
But are we really running out of water? Or, are our pumps simply outperforming our hydrants? Most often, it's the latter that is true. Thus, a simple way to maximize our volume is to add additional supply lines from the same hydrant to our engine.
SIDE NOTE - This is a huge soapbox issue for me here in Dallas. Every time we cut a plug... every...freaking... time... we should be attaching the in-line hydrant valve that is in our plug kit. It takes an extra 15 seconds to connect and opens up a world of tactical options that we didn't have before. Personally, I teach that this should be our first connection, and water flowing through it is the cue to our Driver to start laying into the fire. No radio necessary, no hand signals... just confirmation that the in-line valve is on and we have a working hydrant. OK, off my soap box.
Now, everyone asks, "Well, how much more water can I get from adding an extra 3"... or 5" supply line?"
I wish there were a simple answer, but there are just too many variables (distance, pressure, supply hose used, etc), making it virtually impossible to provide a concrete answer to this question. There are formulas that people have developed (percentage method) that can give you a rough number, but to be honest... in my opinion, they aren't remotely practical on the fire ground. About the only concrete thing I can tell you is that you'll never maximize your volume unless you utilize every discharge on that hydrant.
With this in mind, I will share some of my experience (again, the key word is experience) with you as it relates to the gains I've seen by adding both 3" and 5" on top of my initial 5" supply line.
If the distance between my engine and the hydrant is less than 100'..
Adding an additional 3" has afforded me an additional ~500 GPM
Adding an additional 5" has afforded me an additional ~1,000 GPM
An example of this was in a recent training evolution where we were pumping to Truck 27, running our 2" SB Deck Gun, and our RAM XD portable monitor. You'll see in the image above we had dual 5" supply lines coming off the hydrant, along with a single 3" as well. When it was all up and running, we had this hydrant ripping close to 3,000 GPM with a bit of room to go on our intake gauge. It was really impressive to see.
Truck 27 - Flow meter was reading = 1,500+ GPM
2" SB Deck Gun with 80psi to the tip = ~1,000 GPM
Blitz Fire Monitor with 100psi to the nozzle = ~500 GPM
Now, all of this was in a controlled environment, with a 90psi yellow top hydrant and in close proximity to the plug. Optimal, optimal, optimal! Issues trying to duplicate this will quickly surface when you are 500' from the hydrant and start with a static pressure of 60psi from the blue top you're tied into. Never be fooled into thinking this will always play itself out on the fire ground every time. It's great to see in a training evolution, but recognize how quickly this could fall apart as well.
The key thing to understand is that if we need to maximize our flow, we should consider running multiple lines from the hydrant. Plain and simple.
2. Pumping In Series
The second way we can maximize flow off a single hydrant is by pumping in series (stacking multiple engines in line, hooked up discharge-to-intake). Now, I won't go into the HOW here (that is saved for a future episode), but we must know that the WHY behind pumping in series is directly related to overcoming friction loss, and moving water as fast as possible through the pump to maximize flow.
When we are talking about pumping in series to overcome distance, most refer to it as Relay Pumping. The idea here is that we utilize our engine to boost pressure down the line to overcome the friction loss associated with our volume and/or distance needs.
It's here that I want to share a simple model that I've developed that comes into play when we are laying large amounts of 5" supply hose (greater than 500') and are anticipating target flows in excess of 1000 GPM (such as the use of a ladder pipe).
Let's say you have a large warehouse fire and the closest hydrant is 800' from your engine. If you were to have forward laid 800' of 5" supply, you should anticipate roughly 120psi of friction loss @ 1500 GPM. Now, there isn't a hydrant that I am aware of in the city of Dallas that will give you enough pressure to overcome that friction loss and still supply one of our ladder pipes with 1200-1500 GPM. It just won't happen... trust me, I've seen this play out on the fire ground.
So what is a solution? For me, if I find myself in a situation where I need large volumes of water (1000+ GPM), and I am going to be laying in more than 400' of 5" supply line. I will immediately call for the second due engine, (or third and even an additional engine) to "pump on the hydrant" to overcome the anticipated friction loss that is created by both my volume needs and distance. What this looks like practically is we lay in but do no connect to the hydrant. When the next engine pulls up, they will connect to both their intake (to the hydrant) and discharge (to our engine). Then, both Engineers will work together to keep us in the fight with adequate water. It would be important to add here that the 2 1/2" in-line should be attached to the hydrant and considered an option should we need more water on the attack side.
For those utilizing 4" supply hose, here is the same chart...
As we said previously, we can also pump in series as a way to move water through our pumps at greater velocity and in turn, greater volume. This is exactly what Battalion 1C is doing when they run in series via 3" supply lines (engine-to-engine), dumping their tank and then pumping the rest of the fire in series with either a 3" or 5" connected to the hydrant (to the supply engine).
This can be a bit complex, but if we think about it in terms of drafting vs. connecting to a hydrant, it makes complete sense. You'll recall from last month that our engines rated capacity is set by the manufacturer while drafting at 10' with 20' of hard suction. But the second we move that same engine to a pressurized hydrant, you're rated capacity increases dramatically. This increase is not because your engine somehow is able to make more water. Rather, by increasing the speed (or velocity) of water into your pump, you are getting closer to the max that your pump can produce.
3. Hydrant Assist Valves (HAV)
Another way to maximize flow from a single hydrant is to utilize a Hydrant Assist Valve, or HAV. This is very similar to pumping in series, as discussed above; however, it's done through a dedicated 4-way valve.
We don't use these in Dallas, but after talking with Mike Bishop, who works for Beverly Fire Department (MA), these can be a great option for maximizing volume.
The 4-way valve connects directly to the hydrant. Next, you connect your primary supply line to the front of the HAV and forward lay towards the structure. A second apparatus then arrives at the plug and connects one supply line to their intake side and another to their discharge. This becomes your supply engine and allows you to "pump the hydrant," increasing the pressure that the hydrant is feeding your attack engine. A one-way clapper valve prevents the supply engine from actually pressurizing the hydrant, aiming the velocity downstream toward the attack engine.
CONCLUSION
When it comes to delivering big water on the fire ground, we eventually will run out of engine, or we'll run out of water. Fortunately, those limits have substantial margin in the urban environment and often are throttled by our competency, not our actual supply.
We've laid out three ways you can ensure you're getting as close the maximum volume you have at your disposal...
Multiple Connections
Pumping in Series
HAV
We also encourage you to discuss these with the Senior Engineers and members at your station. There is a wealth of knowledge beyond what we're offering here that these guys/girls have that you can tap into and learn from.
Until next episode...
Hold fast & raise the bar,
RESOURCES:
- https://www.firehouse.com/operations-training/hoselines-water-appliances/article/12373752/water-supply-for-fireground-operations-hydrants-ldh-water-main-firefighter-training
- http://www.elkhartbrass.com/files/aa/downloads/performance/Fire%20Hose%20Friction%20Loss.pdf
- https://www.fireengineering.com/leadership/from-leather-to-cotton-to-synthetic-how-fire-hose-evolved-in-300-years/#gref
- https://www.fireapparatusmagazine.com/equipment/comparing-four-and-five-inch-large-diameter-hose/
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.
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