Obtaining a water supply on the fireground is one of those “gotta haves” for a successful outcome combating a fire. For the simple low-flow fireground operation, this task is fairly easy. When fire hydrants are available, a single line from the hydrant will usually do the trick.
What about the more complex large-flow fires that require large volumes of water to support master streams and big handlines to get the job done? This is where water supply operations can get quite difficult. There are a lot of things that can dictate how well a water supply operation works, including fire hydrant performance and availability, supply hose, available units, topography of the fireground, and management of water supply.
In this article, I’m going to discuss three types of supplemental water supply operations for large flow water delivery involving multiple units. A supplemental water supply is defined by the International Fire Service Training Association as a method of operation for bringing in additional water to a pumper that is already connected to a water supply and needs more water.
Relay Pumping
A relay pump operation is used when there is not enough pressure in the water supply to move the water through the supply hose to the pumping apparatus on the fireground. It involves placing a pumper at the water source to increase the pressure in the supply hose. A relay pump operation is the backbone of big water operations because the additional water needed to support the fireground operations will likely come from distant hydrants. The longer the supply line, the more the pressure loss because of the friction loss in the hose.
It has been an accepted practice to allow shorter large-diameter hose (LDH) supply lines to be supplied solely from hydrant pressure. Remember the old saying, “Laying an LDH supply line is like taking the hydrant to the fire or like laying an above-the-ground water main.” In other words, LDH laid from a hydrant, especially on the shorter lays, is going to bring in maximum flow. It is this type of thinking that can get us in trouble. LDH is great but can still have its restrictions. LDH must be used to its best capability in conjunction with everything else on the fireground to reap its benefits.
Looped Supply Line Operation
The first supplemental water supply operation is what I like to call a looped supply line operation. A looped supply line operation is a combination of supply line hose evolutions set up to work as one. Large flow operations almost always require multiple supply lines from various locations all working toward the goal of providing an overall water supply for the incident. These operations can be quite complex and taxing because the overall goal is to provide the required flow to multiple units without interruption. Notice I said goal, as it can be extremely hard to implement a water supply operation and accomplish it without issues.
The looped supply line operation is designed to deliver a supplemental water supply to as many pumpers as possible, based on the placement of the apparatus on the fire. Think of this as a fire hydrant water main system. A single supply line connected to a pumper is like a fire hydrant connected to a dead end main only getting water from one supply, the main that is feeding it. The hydrant that is connected in the looped grid system is actually receiving additional water from another point in the grid system itself, thus the term supplemental. If it works with underground water mains, it should work above ground with supply hose as well.
The operation that is a key factor in building a looped supply line operation is a pump operation called dual pumping. Dual pumping is a water sharing evolution designed to share water between pumpers. This has actually been done throughout the years by one pumper discharge pumping into another. This works and can usually move slightly more water than a dual pump operation.
So why don’t we just use this operation? When you discharge the pump through a hoseline, the water only goes in one direction, from discharge to intake. This can hinder a true looped operation. Dual pumping is an operation that connects two or more pumpers together through the unused intakes of the pumps involved to share the water. Yes, I said intake to intake. Because there is no actual discharge pumping in the dual-pump operation, the water can flow in either direction. The water will flow in the direction of the pumper that has the lowest residual pressure.
Let’s say a pumper lays in a five-inch supply line and goes to work. The supply line has the capability of moving 1,500 gpm and the pumper that laid the line is going to flow 500 gpm. After flowing 500 gpm, the intake gauge of the pumper reads 60 psi. The 60 psi is a residual pressure of the water supply left over after the 500 gpm is flowing. The 60 psi represents water under pressure from the hydrant that is available within the supply line and the intake side of the pump. Now let’s say this first-in pumper wants to share some of its water with another pumper. A line is connected from its unused intake to the intake of the pumper it is going to share water with. When the command is given to share the water, the first pumper opens the intake valve that is connected to the dual pump line and the water will start to move through the supply hose to the next pumper under the 60 psi residual pressure. You can really just think of this as being connected to a hydrant because the 60 psi residual pressure is actually coming from the hydrant. It’s before the impeller of the first pumper’s pump, therefore it does not have anything to do with the pumping capabilities of the first pumper. When the water is received by the second pumper, the pump operator simply opens up the intake valve and gets the shared water from the first pumper.
One of the unique things about this operation is that the pumper that is sharing the water with the next pumper can never be robbed of water it is discharging. Because of the pump’s design, all available water that comes into the initial pumper will always be available for that unit. Let’s go back to the initial part of this example. After the first pumper is flowing 500 gpm and sharing water through a dual pump operation to the next pumper, the first pumper has to increase its flow by another 500 gpm. The only thing the pump operator will have to do is open the proper discharge lines and throttle up to the proper pressure to flow that extra 500 gpm. The water will basically be taken back from the dual pump operation to the next pumper. Again, the initial pumper receiving water from the water supply will always have priority.
There are a couple things that need to be monitored by both pump operators during a dual pump operation. Once the initial pumper shares the remaining water supply, it will lose some residual pressure because the residual pressure is being used to move the water to the next pumper. So the pump operator on the initial pumper might have to apply more throttle to increase the pressure to its required pressure. If the pump is equipped with an electronic governor, it will automatically adjust the rotations per minute to the new residual pressure. Again, the initial pumper is not losing any water, only residual pressure. If the initial pumper needs to take back some water, the pump operator should communicate with the pumper that is receiving the extra water that he will be taking water back, which will in turn drop the intake pressure of the receiving pumper. The pump operator on the second pumper should try to maintain the engine pressure that was required for its flow and may have to throttle up because of a drop in intake pressure. Illustration 1 shows a basic dual-pump operation.
Summary of Dual Pump Operations
- Dual pumping moves water from one pumper to another with supply hose connected intake to intake.
- The water is moved by the residual pressure of the first pump.
- Dual pumping works well for low-flow operations such as handlines when the water source to the initial pumper comes directly from a hydrant with hydrant pressure only.
- If a dual-pump operation is going to be used to share big water, the water source to the initial pump needs to be boosted from the hydrant with a relay pump operation.
- The distance of a dual-pump operation is based on the flow requirements and the available residual pressure.
- Open the intake valves slowly until the line is charged to avoid cavitation.
- Since dual pumping shares residual pressure, pump operators need to monitor the pump discharge pressures in case there is a drop in residual pressure.
Most firefighters have never heard of dual pumping before so before integrating it into a looped supply line multicompany operation, go out and train with it to get comfortable with its operations and see what it can do for your department.
Illustration 2 shows the beginning of a multicompany large-flow operation. It can involve multiple pumpers connected to their initial water sources. This is basically the first-alarm assignment. These units are in the big water mode so they are really starting to tax the main that is connected to the three hydrants. Grabbing the closest hydrants by first-in companies is a realistic scenario, and there is the possibility of some, if not all, hydrants being on the same main. Now is when these first-in units start running low on water. Just running low on water in itself isn’t the risk as long as the engines aren’t trying to deliver more water than their current discharge evolutions. However, often, especially with the first-alarm assignment, the units are usually in a good spot to deploy multiple streams. With this being the case, this first alarm assignment will need more water.
Illustration 3 shows supplemental pumping by use of the looped supply line operation, which involves relay pump operations and looping or connecting the receiving pumpers together to share a common water supply. Remember, these units already have water coming into them from their initial supply lines; they just need to freshen up their water supplies. In some cases, they won’t need that much more water while in others they may need to double their current flow. As mentioned earlier, when units are connected in a dual-pump operation, the water will automatically flow in the direction of the pump that has the lowest residual pressure.
I’m a big fan of preparing for worst-case scenarios. With regard to this operation, it’s best if the pumpers are equipped with at least three large intakes, the two steamers coming off the pump and either a front or rear suction. There are manufacturers that make valves that can be connected to the main steamer that allows two supply lines to be connected. Illustration 3 shows two dual pump operations using pumpers with two intakes and pumpers with three intakes. Both will work; however, the pumper with three intakes allows for more options.
Manifold Operations
The second method for supplementing a water supply at a large-flow operation is to use LDH manifolds in conjunction with a relay pump operation. Remember, in a supplemental operation, we are giving additional water to units that already have their own supply lines but are running low on water and need more. There are two types of LDH manifolds available. One has an LDH inlet and outlet as well as multiple 2½-inch outlets. This style is designed more for handline operations supported by a large-diameter hoseline. In our situation, where we are attempting to move large volumes of water only, the 2½-inch discharge ports on the manifold will be very restricting and therefore should not be used for this type of operation.
The other manifold that I recommend has an LDH inlet and two LDH outlets. The body of these manifolds is large, has unrestricted waterways, and very efficiently moves big water. These manifolds work best in conjunction with a relay pump operation. The manifold should be placed on the fireground close to the units that it will be supplying and can be fed by a single LDH relay line.
Although this is an efficient operation, it’s important to remember that the water is discharged through the entire hose evolution and will only flow the water in one direction. Therefore, it cannot be used in a looped system.
Pumper Supplying Multiple Large-Diameter Supply Lines
The third method for supplying a supplemental water supply to units on the fireground is by simply pumping multiple LDH discharge lines to the individual units. This can be done either from the hydrant or at the end of a relay on the fireground. Most units only have one large-diameter discharge; however, the 2½-inch discharge adapted to an LDH can move 1,000 gpm fairly efficiently.
Unit Support
There are several ways to support units with an adequate water supply on the fireground, including the three evolutions discussed here. The key to a successful operation is to be proactive with the water supply and develop an evolution that works best for your agency based primarily on safety and efficiency.
