Here's the scenario: There is a fire in a three-story apartment complex in its last phase of construction. The complex is a wood-frame structure and is probably about two-thirds complete with the roof on. This structure is well involved with immediate exposure problems on three of the four sides of the complex. The first-alarm companies laid in from the two closest hydrants and attempted a quick but brief interior attack to no avail. The chief ordered everybody out and said this is a defensive fire; deploy heavy streams. Because the closest hydrants are on the same loop, and because engines are already using these hydrants, every drop of water from this hydrant system or main is already being used. And because of this situation, companies are having a hard time deploying heavy streams.
The chief orders a 2,000-gallon-per-minute (gpm) quint with a 2,000-gpm water delivery capability from the platform into service with the intention of deploying an elevated stream to attempt a knockdown as quickly as possible. Because the chief has been through this scenario before, he is not surprised to see that not only is the platform incapable of 2,000 gpm, but it has a difficult time even producing 1,000 gpm. So what happens? It's simple. They don't have enough water from the hydrant system.
To avoid this kind of scenario, I want to talk about using 2,000-gpm quints and non quints with 2,000-gpm elevated water delivery capabilities to their fullest potential. Our goal is to deliver 2,000 gpm.
To fight fire, it's important to have the appropriate tools. So what tools are needed to flow 2,000 gpm through a 2,000-gpm elevated stream? Necessary tools include the following:
- The line feeding the inlet of the truck needs to be attack hose rated because of the required high inlet pressure (non quint).
- Hydrants capable of 2,000 gpm.
- The correct supply line evolution to deliver 2,000 gpm.
- A pump capable of delivering 2,000 gpm.
- The proper discharge to deliver 2,000 gpm.
- The appropriate appliance and nozzle to deliver 2,000 gpm.
Does a single fire hydrant have the capability to flow 2,000 gpm? To say a definite yes or no would not be an accurate answer. Obviously a hydrant system that is designed by code in a high-flow potential area would have the best chance of achieving this goal; however, that doesn't mean it necessarily will.
It is important to remember that the potential of the fire hydrant is not completely based on the static pressure. I am sure you have heard this statement: "Oh yeah, this hydrant is great; it's got an 80-psi pressure." In reality, what is being described is the system pressure feeding the hydrant, not flowing water, which is static. The true test of a hydrant is what it is capable of flowing under whatever system pressure it has. The system pressure when flowing is actually the residual pressure. So, if an 80-psi hydrant is opened up and, after flowing 1,000 gpm the residual pressure comes down to, oh, let's say 10 psi, this is not an indication of a hot hydrant. Yes, the initial pressure was high but, after flowing the 1,000 gpm, which is below most code requirements, the hydrant was done--out of water.
So we're back to our initial goal of 2,000 gpm. Should we bypass the hydrant I just described or use it and supplement it with more water? Let's say that we are going to use it. The next step would be to supplement this hydrant from another hydrant, whether it is the next one up from it or possibly another one that might be a little farther away but has more potential because it is coming from another main system.
The following flow tests were done on an eight-inch looped hydrant system using two hydrants similar to the above scenario.
- Static pressure: 70 psi.
- Total capacity of main supplying hydrants in excess of 3,500 gpm.
- Flow out of single 2Â½-inch hydrant outlet: 1,188 gpm.
- Flow out of single four-inch hydrant outlet: 2,016 gpm.
- Flow from 2Â½-inch and four-inch hydrant outlets from single hydrant simultaneously: 2,348 gpm.
- Flow from four-inch hydrant outlets from two hydrants simultaneously: 3,216 gpm.
The second part of the flow test was to set up supply line evolutions and do the flow tests again.
The four supply line evolution flow tests showed different scenarios for getting water from a hydrant system. The results were very interesting, and there were a few things that really stood out. Look at the difference in flows between the single lay using the 2Â½-inch port and the four-inch port. The four-inch port was only able to get 250 gpm more than the 2Â½-inch port.
Now how can that be when the hydrant flow tests revealed a 2,016 gpm to a 1,188 gpm comparison? The answer is simple: The five-inch hose, as large as it is, and the intake valve were the restricting factors. Even though the system started off with a 70-psi pressure before the water was flowing (static pressure), the actual pressure that was available to move the water was lowered down to 48 and 50 psi respectively. These flows were good, but they didn't allow the pumper to be used to its fullest capacity if needed.
Test four was the only test that was capable of delivering 2,000 gpm. Test three could have potential on a really hot hydrant, but I have found that as a general rule most hydrants cannot flow 2,000 gpm even with two supply lines connected to them.
Supply Line Evolution
Several supply line evolutions can be used to support a 2,000-gpm stream. What's important to remember is that the evolution design is based on several factors, including the potential of the hydrant system, the diameter of the hose, the length of the supply line itself, and setting up a proactive evolution.
By proactive I mean setting up for a worst case scenario with regard to the hydrant potential. This means placing a pumper on the second hydrant in relay every time. This will allow for the greatest potential of water delivery. On the other hand, if you roll the dice and set the evolution up without a pump on the second hydrant and it is not enough, you are looking at a minimum five-minute interruption to beef up the evolution with a second pumper.
It's safe to say that most municipal departments have gotten away from at least 2Â½-inch supply lines. Just for the heck of it, let's see what it would take to move 2,000 gpm using 2Â½-inch hose and two hydrants with statistics similar to the hydrant flow tests we discussed. Because 2,000-gpm pumpers are not too common and 1,500-gpm pumpers are, the supply line illustrations we are going to discuss will all have 1,500-gpm pumps and will be supplying a quint.
As you can see, using 2Â½-inch hose is doable. In fact, besides having multiple lines laid to accomplish this feat, the engine pressures are very respectable. Notice that the multiple lines coming into the intake seem to center in at one point. This illustration uses the six-inch intake on the pump with a trimese manifold 2Â½-inch appliance connected to it to allow up to three lines to be used. Also notice that the lines that the engines used to hook to the hydrant are thicker, indicating that they were large-diameter hose (LDH) soft suctions.
Next, we'll take a look at the same operation with the same goal of moving 2,000 gpm, but this time we are going to use four-inch and five-inch supply hose with a maximum operating pressure of 185 psi for the supply lines. Note that the evolution for each size hose is the same.
What a difference! First, we've eliminated the relay operation between the truck company pump and the first hydrant. Second, we've eliminated a total of five lines because of the lower friction loss in the four-inch and five-inch hose. Notice that the use of two hydrants has not changed, the reason being that one hydrant, even with multiple lines connected to it, will usually not be able to produce 2,000 gpm.
The five-inch operation was able to mirror the four-inch operation. Even though there is a possibility of two hydrants delivering 2,000 gpm total with the five inch without a relay, because we are being proactive we are placing a pumper on the second hydrant to get maximum flow. If the relay is able to produce more than 2,000 gpm, then there is no harm. On the other hand, if the relay wasn't set up and our 2,000 gpm goal could not be met, it would take a lot of time and effort to play catch up.
There are also elevated platforms that are capable of 2,000-gpm flows that do not have pumps. Let's take a look at what it would take to supply these trucks using the same hydrant system that was used for the quints. The discharge line from the pumper supplying the truck company is LDH attack hose with a maximum operating pressure of 275 psi.
As mentioned before, all pumps used in the supply line evolution illustrations were rated at 1,500 gpm. Some of you might be wondering how that is possible when the flow was 2,000 gpm for the pumper supplying the quint as well as the quint itself. A pump's rated capacity is based on a net engine pressure. Net engine pressure is the pressure created totally from the power plant of the fire apparatus operating the pump. Because of the way pumps are designed, as a pressure rises above 150 psi net engine pressure, the capacity starts to drop.
So how is it possible to get more than the rated capacity of a pump? When a pressurized water source is introduced into a pump, such as it would be from either a hydrant system or from another pump in relay, the intake pressure adds to the net engine pressure. With this being said, the incoming pressurized water source reduces the amount of overall work that the power plant of the apparatus needs to do to create the net pressure.
The Proper Discharge
The most appropriate discharge to use to deliver 2,000 gpm is the large-diameter discharge. Bigger is better, but with that being said, a four-inch discharge with either a 3Â½-inch or four-inch valve would be the ultimate setup. A three-inch discharge could work, but it would depend on its design. There would be more friction loss in a three-inch discharge; however, it could be doable. If all you have on your pumper is 2Â½-inch discharges, then I would recommend using two LDH lines to the quint because a single 2Â½-inch discharge can only efficiently deliver around 1,000 gpm. If a 2Â½-inch discharge is to be used, make sure it's the one coming off the side of the unit. Rear 2Â½-inch discharges have way too much plumbing and therefore cannot deliver even 1,000 gpm.
The Required Master Stream Appliance and Nozzle
To flow 2,000 gpm from a master stream appliance, it has to be rated to do so. The standard master stream appliance, whether it's on an engine company or a truck company, is usually rated at 1,250 gpm and, because of manufacturers' recommendations, cannot be used to deliver more than that. The good news is, if you have a 2,000-gpm waterway on a quint, it'll more than likely have a 2,000-gpm appliance.
The most common 2,000-gpm master stream nozzles are the automatic and the smooth bore. The automatic nozzle is designed to flow usually from around 100 and 150 gpm to 2,000 gpm. Nothing changes on the nozzle. It does it all by itself, hence the name automatic. There are two different sizes of smooth bores that can be used to flow 2,000 gpm. The first one is the 2Â½-inch-diameter tip. The nozzle pressure needed for the 2,000-gpm flow is right around 118 psi. The other smooth bore is a 2Â¾-inch with a required nozzle pressure of 80 psi.
It's very important to follow all the ladder operation guidelines for the specific unit that you are using. Most platforms have a wide range of uses with regard to their elevation and angle at 1,250 gpm. However, the 2,000-gpm flow ranges will be more restrictive because of the higher nozzle reaction being produced. Every ladder truck will have a range capability chart at the pedestal, so make sure you follow what it says.
Having the proper equipment to deliver the required stream is only half the battle. A complete understanding of everything involved with a pump operation is a must to use the equipment to its fullest capacity.