In “Highway Hydraulics: Main Street to Country Roads, Part 1” (August 2021), we explored the need for all departments, regardless of their primary water system, to understand the workings of alternative water supplies better known as a water shuttle.
Regardless of where a water shuttle takes place, how water makes it from a tender to the attack engine is determined by many factors. The most important is how much water is needed to bring the fire under control. Eventually the heat release rate of the fuel (Btu/min) will match Btus absorbed by the water flow being applied. If a 150-gallon-per-minute (gpm) stream is applied to a fire with an equivalent heat release of 500 gpm, eventually enough fuel will be consumed to bring the heat release to match the 150-gpm stream and go out.
The duty of the incident commander and water supply officer is to ensure water supply tactics provide sufficient water to overwhelm the fire. If the fire needs 500 gpm, then 750 gpm should be thrown at it. Two tactics can be used to get shuttled water to the attack engine: nursing and dump operations. The fire will determine which method to use. It is important to listen to what the fire is telling you. Running a 500-gpm shuttle for nursing operations because it is easier than setting tanks is not the proper decision when the fire tells you it needs 750 gpm.
Nursing is a basic way to supply water to an engine from a tender or another engine. This tactic is useful for fires requiring less than 500 gpm or as a transitional method while dump tank operations are being set. In the urban environment when the initial water supply apparatus will be engines without rapid offloading capacity, nursing will initially be the primary tactic. Nursing operations consist of a supply line stretched between a pump discharge on the nurse tender (or engine) and a pump intake on the attack engine. This is relay pumping with the hydrant replaced by the water tank on an apparatus.
If the engine is close to the tender, the drivers of the engine and tender work together to make the connections for nursing operations. Longer distances require additional assistance. Short distances allow 3-inch supply hose to be used instead of large-diameter hose (LDH), saving water to fill the hose and making it easier for a single person to handle.
It is not always possible to get the tender near the engine because of potentially blocking the tender in a driveway with other apparatus or blocking other apparatus from the scene. In the urban setting, nursing operations will likely be farther from the fire, as the area near the fire scene will be occupied by early arriving apparatus and collapse zones are a consideration. In these cases, an engine will lay into the fire scene with LDH or potentially dual 2½- or 3-inch lines from the offloading site.
The engine operator will be responsible for making the connection to the engine intake while the tender officer or driver will make the connection to the tender discharge. With a long lay of LDH, the tender operator must know how much is on the ground to estimate the amount of water needed to fill the hose. Long lays are not conducive to a simple nursing operation; when the tender is disconnected, a significant amount of water is lost unless a hose clamp or water thief is used to close down the line.
When nursing over a great distance, it is advantageous to use a supply engine, as tenders may not have the pump capacity to overcome friction and deliver the needed flow. Having a supply engine in place for nursing reduces the time needed to convert to dumping operations should supply tactics change.
Additional time is needed to connect and disconnect the supply hose from the tender compared to dump operations. This added time decreases the flow of the shuttle by increasing the time a tender must wait before leaving for the fireground. While this may only be a few seconds, over the course of the operation all the seconds add up. Additional personnel are needed at the nursing site to connect and disconnect hose while the driver prepares for the pumping operation.
If nursing is used as the supply tactic, tenders must have a pump capable of producing the flow needed to support fireground operations. Tenders can have pumps ranging from 500 to 1,500 gpm and above. Larger pumps are more capable of supplying an engine in nursing operations. Even with large pumps, large flows may not be produced because of the plumbing restriction between the tank and the pump. Apparatus with tanks larger than 500 gallons have a minimum flow requirement of 500 gpm from the tank to the pump.1 A majority of apparatus are designed to meet this minimum requirement with little or no additional margin. If plumbing is not specifically designed for large flows, the maximum flow available for the fireground will be approximately 500 gpm.
Putting this into perspective, for a residential structure, an uninterrupted water supply of 400 gpm must be established.2 Even if the tank-to-pump plumbing is an issue for large flow operations, tenders must have the capability to supply an attack engine in this scenario. This is one of the reasons 500 gpm is considered the decision point to go from a nursing to a dumping operation.
A tender will be able to provide the maximum flow contribution to the fire its first time at the fire scene. On subsequent trips, the available flow rate will decrease because of travel and fill times. For example, a 3,000-gallon tender supplying a 500-gpm fire flow will be on scene approximately six minutes before going to the fill site. The amount of handling time at the dump site is increased because the supply hose must be disconnected and then the driver returns to the cab and disengages the pump before leaving to the fill site. Compare this to the three to four minutes needed to offload water using dump operations. This time starts to add up on big >operations.
Once the tender is out of water, the attack engine must operate from tank water until another tender arrives and is connected. During nursing, it is imperative that the attack engine operator fill the tank once a supply from the tender is established. The water supply officer must take into account that the water available for fire operations from the first tender is reduced by the volume needed to fill the tank on the attack engine.
Just like a relay, communication is key to the success of nursing operations. The operator of the engine being supplied must communicate to the tender operator to keep water flowing at the correct pressure. If the fire flows increase without the engine operator communicating this to the tender operator, there is a possibility the intake hose will collapse, restricting the flow and potentially damaging the pump, not to mention the loss of water to the attack crews.
1 An engine is set up to quickly deploy a jump siamese for rural hitch operations. (Photos by author unless otherwise noted.)
3 A supply engine and dump tanks are set up at the entrance of a parking lot.
The rural hitch is a progression of nursing that allows continuous flow of water to the attack engine. Instead of a tender directly connecting to the attack engine, the engine lays out a supply line to a clappered siamese. A jumbo siamese is used by most departments regularly employing this tactic to minimize friction and other system losses. This is not something most urban departments will carry on their rigs. A 2½-inch siamese can be used and adapted to LDH on the discharge side of the siamese. If using a 2½-inch siamese, only adapt the discharge to LDH, as additional contraction losses may negate any gains of using LDH over 2½- or 3-inch on the inlet legs. Lines are laid from the branches of the siamese to the positions where tenders will be parked. Leave enough distance between the ends of each leg line for tenders to pull in and out of position.
The line between the engine and the siamese is normally LDH while the branch lines can be LDH, 3-inch, or even 2½-inch. There are several advantages to using 2½- or 3-inch lines for the branches. Connecting and disconnecting from the tender is easier with smaller lines compared to LDH. Using smaller lines reduces the amount of water needed to fill these lines, limiting the amount lost when lines are disconnected.
Like everything, there is a give and take when using smaller lines to the siamese. There will be increased friction loss. This may have a significant impact if the tender has a small pump. The impact of smaller branch lines will be even more significant if there is a long run of LDH from the siamese to the attack engine. When there is significant distance between the siamese and the attack engine, it is good practice to place a supply engine near the siamese to take the burden of overcoming friction from the tenders. Significant distance is vague guidance, but it is meant to be, as it is different for every department. If all the tenders responding for water supply have 1,250-gpm pumps passing pump tests with flying colors, an engine may not be needed for an 800-foot lay of LDH to the attack engine. On the other hand, if tenders barely pass pump tests with 500-gpm pumps, then they may struggle to get water through 300 feet of supply line. Using LDH for the branch lines will help to reduce the friction loss in the system but may increase handling time or the number of personnel needed for the operation and result in losing more water when the lines are disconnected. It comes down to knowing your apparatus and the apparatus of your mutual-aid partners.
The rural hitch limits water and time loss when transitioning from one tender to another. While one water tender is pumping to the attack engine, the second tender connects to the other leg of the siamese. When the first tender reaches a quarter full, the second tender increases pump pressure to 5 to 10 psig less than the operating tender. The operator of the second tender should circulate water through the pump to prevent overheating of the pump while waiting to supply water to the scene. When the first tender is empty, the pressure from the second tender will overcome the pressure from the first tender opening the clapper in the siamese. Water then flows from the second tender to the attack engine. Once this happens, the operator of the second tender will stop recirculating and adjust discharge pressure based on the needs of the attack engine. The empty tender throttles down, closes its discharge, and disconnects from the siamese, allowing a full tender to take its place. This process repeats as needed with no interruption in supply to the attack engine. A single-clapper siamese is acceptable for this operation; however, a double-clapper siamese allows both legs to be disconnected without losing water in the main supply line should there be a time when no tender is available.
The rural hitch is highly effective when transitioning to dump tank operations. While tenders are supplying the attack engine, a supply engine can set up in a location, which still allows for the movement of the tenders in and out of the supply site. When the dump site is set up and loaded, the supply engine will connect to the empty leg of the siamese to take over supply duties. To achieve maximum flow from the supply engine, the line between the engine and siamese should be LDH. If smaller lines are used from the siamese, connecting both lines to discharges of the supply engine will maximize flow.
Cues to Transition to Dump Operation
The topic of nursing vs. dropping dump tanks can trigger as passionate a discussion in some areas as smooth bore vs. combination does throughout the fire service. One side will say dump tanks must always be set for alternative water supply; the other side always sets up nursing operations with no consideration for dump tanks. In truth, nursing and dump tanks are tactics and, as such, the decision to use one or the other or both in sequence should be driven by operational considerations. Water needs, available staffing, equipment, and training must all be evaluated in determining water supply tactics for each incident. This is one reason a water supply officer must be appointed early in any operation.
The initial tactic used for water supply will often be nursing. This allows getting additional water to the attack engine quickly with minimal resources. When is the right time to switch to dump operations? In the urban setting, nursing will be the mainstay of shuttling water until resources arrive to expand to a dump operation. This makes the decision of the urban water supply officer a bit easier. Once resources arrive to set up a dump site, then a decision must be made as to how long to continue nursing operations.
Here are a few considerations when determining if it might be time to set the dump tanks. Remember, these are guidelines, not hard-and-fast rules:
- If the fire is not under control with a second tender, dump tanks should be set because higher flows are needed to quell the flames.
- When the required fire flow is more than 500 gpm, expanding to a dump operation is the most efficient way to achieve the needed flow.
- When the aerial goes up, the tanks go down. Nursing cannot support the flow required for aerial operation for any length of time. If the water system fails and an alternative operation is required during operations including an aerial, the best option is to feed the aerial with two rural hitch operations.
- The first tender or two may be the only ones available for an extended time; using dump tanks will optimize the flow from the limited resources available.
- Once tenders are making their second trip to the fireground, it is time for tanks. Tenders provide the highest flows from nursing on initial arrival to the fire; all other trips have lower flows because of extended time at the fireground, travel time, and fill time.
While many want clear-cut rules to always use tanks or always nurse, the only way to have an efficient water supply operation is to be trained and knowledgeable on the benefits, trade-offs, and complementary nature of the two tactics.
Dump tank operations generate higher flow rates than nursing operations since tenders spend less time at the fire scene offloading and maneuvering. The restriction from the tank to pump plumbing is eliminated with water drafted by the supply engine through the main intake. Setting up dump tank operations requires planning prior to placing the first tank because once the initial tank is set, it is not moving. For better or worse, the rest of the water supply operation will build on the first tank.
The location of the dump site is important for many reasons. It must allow room to set up multiple tanks, allow operating space for the supply engine, and provide for smooth movement of tenders while not cutting off the fire scene. In the urban setting, there are several considerations rural water supply officers do not normally face before setting the tanks. Most rural scenes do not present collapse zone issues. Dump tanks need to be out of the collapse zone to not jeopardize the water supply should a collapse occur.
4 Dump tanks are set in the entrance to an industrial complex. Notice how they sit back from the road, forcing tenders to maneuver to dump.
5 An inlet valve with a primer.
7 Comparison of a 2,000-gallon single-lane and standard dump tank.
Dump tank location cannot impede placement and operation of aerial apparatus. At one fire, dump tanks were set close to the building, forcing the tower to set up away from the building. This limited the reach the tower had over the roof of the building, meaning we could not hit the fire.
The size of the dump tanks will determine how much area is required for the dump site. These dimensions can greatly limit the ability to set up on many roads, especially if there are deep ditches or parked cars limiting the width of the street.
Another option is pulling the supply engine in a driveway and setting tanks in a yard or at the end of the drive. The recent introduction of single-lane dump tanks provides more options on dump tank setup. These tanks are designed to have a width similar to a standard traffic lane while maintaining the needed volume capacity. For example, a 2,100-gallon tank is only eight feet wide by 14 feet long. These tanks can be set up on the road while keeping a lane of traffic open. When one tank is set, it is best practice to set at least a second tank to provide more capacity, allow two tenders to offload at once, and provide redundancy should the primary be damaged during the operation. Being able to avoid dumping into the primary tank prevents aeration of the water near the strainer, potentially causing a loss of draft.
Though operating a water shuttle in an urban environment has challenges, there are some potential advantages over the rural setting. Dump sites take a large amount of real estate. Intersections provide added area needed for dump tanks and the supply engine while giving an open lane of traffic for the flow of tenders. In the city, intersections are numerous; setting a dump site in an intersection is the equivalent of having a hydrant on the corner of the block. In the rural setting, it can be miles between intersections, necessitating dump sites to be established in a lane of the road or the drive of a neighboring property, potentially hampering the flow of tenders and requiring a substantial amount of LDH to get water to the fire scene. Take care not to block access to the fire scene, especially in the rural setting, where there may be only one route of access. The street layout in urban environments often provides multiple routes to access the scene, allowing for greater flexibility in dump site placement.
Parking lots are more prevalent in the urban setting than in rural areas and provide plenty of solid area to set up a dump site. However, not all parking lots are created equal. Lots with several entrances and exits allow the dump site to be in the middle with tenders able to come in the entrance, dump, and leave through a separate exit—a safer and more efficient one-way traffic flow. If the entrance and exit are the same, the tanks should be set in the drive and the supply engine in the lot. This allows the tenders to drive past the tanks and dump with little additional maneuvering. While it may be possible to set up in the middle of the lot with a combined entry and exit, tenders will be forced to perform additional maneuvering and potentially wait for another tender to enter or leave.
Not all fires and water system failures will happen at 3:00 a.m. with empty parking lots. Most of the time there will be parked cars. In the time needed for dump site resources to arrive, it is possible to use police resources to help clear the lot. If there still is not enough room, take an entrance or exit to set up.
Engine availability and configuration impact how and where the dump site is set up. If available, it is best to use a dedicated supply engine. The response time of the supply engine will determine how long it will take for the dump site to be operational. This is when a rural hitch is advantageous until the supply engine is set up. Advantages of a supply engine include redundancy if the attack engine has a mechanical failure, the tank of the supply engine increases the emergency water reserve, the dump site can be located remote from the fire scene to allow the best flow of tenders, and each operator can focus on a specific task—attack or supply.
It is possible to draft with the attack engine when no other engine is available in a timely fashion. The dump site can potentially be set up quicker without waiting for a supply engine. Another reason for drafting with the attack engine is having only one or two tenders immediately available and dump tanks must be set quickly to allow the tenders to offload and refill to maintain flow.
To draft with the attack engine, it must be equipped with a valve on the intakes to allow the use of tank water for initial attack while the dump tanks are set. If there is no valve on the intake, the initial attack cannot take place until the tanks are set and filled and draft is established. An intake valve also allows the use of tank water should the dump tanks run dry. Having separate primer lines to the upstream side of the intake valve allows the suction line to be primed to the valve, providing a smoother transition from tank to draft once the valve is opened.
Drafting with the attack engine presents the possibility of the interior crew losing water if draft is lost. This requires the operator to be at the pump panel at all times to quickly reprime the pump or switch to tank water. Drafting with the attack engine puts extra responsibility on the pump operator, who must now manage the attack lines, maintain a draft, and manage water supply. This should not be an issue for a seasoned pump operator but may be a lot to ask of a junior member.
It is possible to start an operation with the attack engine drafting and switch to a supply engine once it arrives. To do this, the dump tanks should be set up in front or behind the attack engine. When the supply engine arrives, it pulls to the dump tank, leaving room to set a second tank if one is not already in place. If a second tank is not set up, it should be placed between the first tank and the supply engine. The supply engine will set up to draft from the second tank. Supply line is run from the supply engine to the unused intake on the attack engine. With water in the second tank, the supply engine pulls a draft and charges the supply line. The intake on the attack engine from the supply engine is opened and the valve to the suction line is closed. The attack engine is now being supplied by a second engine without disrupting the water flow to the scene.
If the fire is down a long drive, water tenders will need to negotiate the drive to offload if the attack engine is drafting from the dump tanks. This will reduce the available flow rate because of the increased maneuvering time. It is likely only one apparatus will be able to fit down the drive, which will prevent another apparatus going to the dump site until the other has cleared the drive. Using a supply engine allows the dump site to be set up at the end of the drive, allowing a free flow of tenders on the main road to increase shuttle flow rates.
In many instances, the equipment needed to set up a dump site is carried on tenders. As the tenders arrive, the equipment should be removed and placed at the dump site. This includes dump tanks, tarps, low-level strainers, jet siphons, suction hose, and spare hose. Having this equipment on a tender as opposed to an engine reduces the amount of equipment a department needs to purchase. When this equipment is needed, so is the tender, making it logical to have the majority of the water supply equipment on the tender.
Dump tanks. Dump tanks come in different designs, shapes, and capacities. Framed dump tanks are the most common design used by municipal fire departments. These tanks are square or rectangular with a liner suspended in a ridged aluminum or steel frame. The tanks are designed to fold flat for storage.
Self-supporting tanks are more common in the wildland setting. This style of tank does not have a frame but is self-supported by its round shape and a flotation collar. The collar floats on the water as the tank is filled, maintaining an opening. These tanks can be folded for storage in a compartment but are heavy. Self-supporting tanks do not generally work well for dump operations because of the distance from the side of the tank to the opening.
The snap tank is popular in some parts of the world because of its compact size for storage. Like a framed tank, it has a rigid frame and liner, but the frame is stored as individual pieces and the liner is not attached to the frame. The drawback to this tank is that it requires assembly of the frame and the installation of the liner.
9 A floating strainer with a bottom pan used in a dump tank.
10 A portable pump is driving a jet siphon.
Bigger is not always better when it comes to dump tanks. Large tanks may be difficult for one or two members to set up because of size and weight. A bigger footprint may restrict where it can be set up and will leave more water when the limit of the low-level strainer is reached. A standard square dump tank can range in size from 12 × 12 feet for 2,000-gallon tanks to 14.5 × 14.5 feet for 3,000-gallon tanks.3
Obstructions or ditches provide challenges when setting up tanks that are wider than the road. Single-lane tanks are 8 feet wide and up to 14 feet long depending on the desired capacity. Some single-lane tanks have an extended hexagon shape to provide increased capacity while minimizing storage length. The points of the hexagon provide an area of refuge for firefighters working at the dump site to be out of the flow of traffic. No matter what size or style of tank a department has, it is important to train to be able to deploy it and understand how the size can impact dump site configuration.
Strainers. Low-level strainers have a significant impact on drafting operations from a portable tank. There are three major considerations when evaluating low-level strainers: flow rate, the depth a vortex is formed, and the lowest level draft that can be maintained. Designs of low-level strainers have changed over the years to increase flow rates. Some old designs struggle to produce 750 gpm, while newer designs easily achieve more than 1,500 gpm. When older strainers were designed, the majority of fire pumps were rated at 750 to 1,000 gpm. Today, with 1,250 gpm being the minimum pump size used by most departments, a legacy low-level strainer can greatly restrict flow. When spending upward of $500,000 on a new state-of-the-art engine, does it make sense to save hundreds of dollars by using an existing piece of equipment that will restrict the performance of the new engine to the level of the one it replaced?
Total flow is not the only consideration when evaluating a low-level strainer. The purpose of this strainer is to draft as much water as possible out of a dump tank. As the water level drops, a vortex forms above the strainer, drawing air into the suction line. Depending on the design of the strainer, this vortex can form with up to 18 inches of water still in the tank, drawing enough air into the system to make it challenging to maintain prime.
There are countermeasures to the vortex. You can put a beach ball or some other floating object in the tank so it will be drawn to the vortex and seal it. Whatever the object is, it must be substantial enough to remain on the surface and not succumb to the power of the vortex. Even though it is possible to diminish the impact of the vortex, selecting a strainer with a small vortex at the lowest water level will improve overall performance.
Floating strainers can be used in dump tanks. Ideally, the floating strainer will have a pan or support legs to keep it from pulling to the bottom of the tank. Without a means to keep the strainer off the bottom, the operator must pay close attention to the water depth. Departments planning on using a floating strainer must practice to determine the water level where it pulls to the floor of the tank.
In a pinch, you can use a barrel strainer, which is designed to be vertically submerged with 2 feet of water on all sides. When placed in a dump tank, the strainer lies horizontally on the bottom with a goal of drawing water as low as possible. In this application, a vortex is generated, even with a considerable amount of water in the tank.
One trick to decrease the effect of a vortex is to put the barrel strainer in a 5-gallon bucket. This prevents it from drawing the bottom of the tank into the holes and helps to break up the vortex. While it is not ideal, we firefighters know it is necessary to use what is available to adapt, overcome, and get water to the fire.
Transfer devices. When using multiple dump tanks, a means is needed to transfer water into the primary tank. A jet siphon is commonly used to accomplish this task. It works by injecting a stream of water into a section of suction hose, creating low pressure in the suction hose. Atmospheric pressure then pushes water from one tank to another. The faster the jet, the lower the pressure and the higher the transfer flow. Traditional jet siphons cannot draw water lower than the top of the suction hose, limiting the amount of water transferred. New designs of low-level strainers incorporate a jet siphon, allowing water to be drawn to a lower level.
It can take between 100 and 300 gpm to drive a jet siphon. This is pump capacity unavailable to provide flow to fireground operations. For large incidents with multiple dump tanks, another way to drive the jet siphons is needed to maximize flow available for the fire attack. Often, a dump site is not configured to allow a second engine to conveniently set up at the secondary tanks to draft and drive the jet siphons. Whenever a second engine can access a secondary tank without impeding the shuttle flow, use it to drive the jet siphons and free the pump capacity of the supply engine. When you cannot use an engine, consider using a grass truck or portable pump for the jet siphons.
Another advantage to using a second pump for jet siphons is an increase in net transfer rate. When the supply engine is used for the jet siphon, the water used to drive the jet siphon comes from the primary dump tank and is dumped back into the primary tank along with water from the secondary tank. If the total flow from the jet siphon between the two tanks is 800 gpm and 200 gpm is needed to drive the jet siphon, only 600 gpm is being transferred from the secondary tank to the primary tank. When a second pump is used to drive the jet siphon, it can draft from the secondary tank, adding the flow to drive the jet siphon to the total transferred volume.
Jet siphons are useful as a recirculating device. When water demand at the fire scene is reduced, the supply engine operator needs to recirculate water back to the dump tank to help maintain draft and cool the pump. With low flow to the jet siphon, little water is transferred from the secondary tank, allowing recirculation without overfilling the primary tank. When the supply engine is not used to run the jet siphons, a dedicated recirculating line is needed.
The suction hose used with a jet siphon must be secured to the frame of the dump tank as close to the end as possible to prevent the hose from snapping upright and creating a fountain when the jet siphon is charged. A bungee cord, hose strap, or even a piece of webbing will satisfy this need, but the best tool for the job is a ratchet strap.
Fill spouts. If tenders without quick dumps or engines are used in a shuttle, water will be pumped into the dump tank using the apparatus’ fire pump. To minimize traffic backups at the dump site, station these apparatus away from the main flow of rapid dumping tenders. Use a fill spout to prevent the hose from kinking and to secure it to the tank. If a spout is not available, improvise one using the remote base for a deck gun, an elbow, and a ratchet strap or other means to secure it to the tank.
Determining the best place to set up the dump site is critical, as once the tanks are in place, they are not easy to move. The dump site must have room to position the supply engine and dump tanks on solid ground. It is imperative that the dump site configuration provides tenders with a smooth flow of traffic, preferably a one-way flow with no backing required. This is a primary consideration, as additional maneuvering reduces the available flow of the shuttle and increases the risk of accidents. Remember in the urban setting to consider collapse zones and aerial placement.
When setting the initial dump tank, consider a second and even a third tank. The second tank provides greater volume on the ground, redundancy should one tank be damaged during the operation, and the ability to dump from two tenders at once. As flows increase, more tanks will be needed to provide adequate volume on the ground to keep pace with demand. The water supply officer must keep this in mind when establishing the dump site. If the fire grows and there is no way to set more tanks, flow will be limited no matter how many tenders are in the shuttle. Then the only option will be to establish a second dump site, increasing the complexity of the shuttle and water management.
11 A transfer line is secured to a dump tank.
12 Commercial fill spouts. (Photo by Sebastian Galleguillos.)
13 A deck gun base used as a fill elbow. Note the kink in the hose. Using an elbow from a pump panel will help reduce this.
14The rear intake of a mid-mount pump.
15 A homemade drafting elbow.
16 A rear-mounted pump set up for drafting. (Photo by Sebastian Galleguillos.)
17 Two dump tanks using a side intake.
18 Two additional dump tanks transferring directly to the primary tank.
When forced to set up the dump site in the roadway, it is better to place the tanks in the front or rear of the supply engine. This minimizes the amount of available lane width used and maximizes the available road for tender traffic. When setting the tanks, it is a good practice to have the tank past the side of the engine on the pump panel side to give the operator a view of the water level in the tank. While a dump site manager ensures tanks are kept full, this position may not be filled early in the operation. When there is no water supply officer, the pump operator must monitor the water levels in the dump tanks and keep the primary full. Even when there is a water supply officer, being able to see the water levels allows the pump operator to proactively manage the level of secondary and tertiary tanks.
Front suctions are convenient for setting up tanks in line with the engine but often provide as little as 50 percent pump capacity. Well-designed systems may have the ability to reach 75 percent capacity, but it is extremely rare for the front intake to provide full rated pump capacity. The other drawback to front suctions is that the arch over the axle has the potential to trap air, which requires a properly designed priming system to prevent air pockets in the plumbing.
Rear intakes provide the same setup benefits as the front suction but have improved performance because of better plumbing routes. While providing more flow than front suctions, rear suctions normally do not allow full pump capacity to be achieved.
How is it possible to get full pump capacity while using an in-line setup? One way is by specifying an engine with both front and rear intakes. This setup provides pump capacity when both ends of the engine are used at the same time but increases the cost of an engine. Using drafting elbows allows tanks to be placed at the front or rear of the engine while using the main pump inlets.
Drafting elbows provide minimal restrictions to pump capacity while being an economical means to draft from the front and rear of the engine. Another option is to bend a section of suction hose around to get to the front or rear of the engine. This requires an extra section of suction hose and is difficult to maintain the bend.
Another option to allow in-line setup is the use of front- or rear-mounted pumps, although this breaks the “traditional” mold of fire engines in North America. At one time, many rural departments specified front-mounted pumps for this very reason, to put dump tanks in front of the engine and to allow the engine to pull up to other static water sources. Rear-mounted pumps are widely used in many other countries and allow for easy in-line setup. Both options allow the operator to be next to the pump and tanks, which is not possible in an in-line setup with a mid-mount pump. While it breaks with tradition, a front- or rear-mounted pump for a rural supply apparatus can help improve the efficiency of the water supply operation.
Setting tanks on the side of the engine allows for direct use of the side intake of mid-mounted pumps but requires a significantly wide setup area. Intersections, parking lots, multilane roads, and driveways wide enough to park the engine crosswise are needed for this setup. Tanks will likely be in a lane of traffic or even with the curb to provide easy access to tenders. A tank is placed on each side of the inlet centerline with enough gap to walk between the tanks. This allows the strainer and suction to be quickly transferred to the secondary tank should the primary become damaged. Remember to leave enough space between the tanks and the engine to access compartments. For engines with swinging compartment doors, open the compartment doors when setting the tank to ensure enough clearance.
As discussed earlier, it is a best practice to have more than one dump tank in place to provide additional volume on the ground and act as a safety backup. No matter how many tanks are used at the dump site, they should all funnel into the primary tank used for drafting. The number and configuration of the tanks will dictate how the transfer is done and the amount of equipment needed. When there are only two tanks, it is pretty simple: a section of suction hose and a jet siphon. If three tanks are used with the primary tank in the middle, the concept is mirrored to the third tank.
It gets a little complicated with three tanks having the primary tank at the end. An early configuration would have the third tank dump into the second tank and the second tank into the primary. As time progressed, a more efficient option was developed. Creating a bridge across the second tank with a roof ladder allows two sections of suction hose to transfer water directly into the primary tank.
Another rarely used option available for a two-tank configuration is connecting the drains to make one large tank. The best way to do this is by setting both tanks at the same time and making the connection. If two tanks are not available, it is possible to place a board over the open drain to prevent draining the primary tank. This is not a perfect seal, and some water will be lost until the second tank is connected. If there is any incline to the ground, make sure the primary tank is at the lowest level so other tanks can drain into it.
Using multiple intakes with a separate dump tank for each can be very efficient. This method takes additional equipment and vigilance on the part of the operator. If one tank goes empty, the intake must be closed so prime is not lost. Once water is resupplied to an empty tank, the intake must be opened and reprimed. If tanks can be kept full, this is an efficient way to use multiple tanks at the dump site; otherwise, it is an added burden on the operator.
Dump tank operations can obtain higher flow rates than nursing operations but require additional time, equipment, and personnel to set up. When dump tanks are used, it is imperative a water supply officer be in place to manage the flow of tenders, the water available for fireground operations, and communication with command. Traffic control at the dump site is critical to prevent injury and equipment damage.
Once a tender enters the dump site, all movement is at the direction of the dump site supervisor. Tender operators must be trained to follow direction from a guide and to not move otherwise. If properly laid out, tenders can simply pull alongside a dump tank and dump.
Sometimes the layout will require tenders to back to the dump tanks. When backing is required, one person is stationed at each tank to back the tenders. Even with people at each tank to guide tenders into position, there is still only one person assigned the responsibility for overall traffic management at the dump site. No tender moves without direction from this person.
The water supply officer is responsible for determining when to shut down each tender. Getting every last gallon out of the tender is not an efficient way to operate a shuttle, as the height of the water in the tank decreases the dump rate of a conventional tender because of the reduction in static head. There is a point where the flow rate drops enough to lower the overall flow rate of the shuttle. At this point, it is more efficient to stop dumping, send the tender to the fill site, and pull the next tender into the position.
If there is no impending arrival of another tender, it is acceptable to hold a tender to drain the maximum amount of water. However, if a full tender is close by, it is best to send a tender to the fill site without fully draining it.
Every water tender loses efficiency at different rates, depending on design. It is important for departments to calibrate tenders to establish the actual point of diminishing returns for their apparatus. It is possible to calibrate a tender so the flow rate at any given time during offloading is known. This level of calibration allows the tender to stop once the offload rate drops significantly below the fire flow. Some departments drill a hole in the dump chute at the level of diminishing returns. When water stops coming out of the hole, the water supply officer can stop the tender and send it to the fill site.
When setting up and operating a dump site, it is important to take into consideration the apparatus in the shuttle. For the most part, tenders will be able to dump from either side or the back. There are several tenders requiring special considerations when configuring a dump site for smooth traffic flow.
19 Connected tank drains. (Photo by Cristian Guzman.)
20 Tenders side dumping into a dump site maintaining a flow of traffic.
21 When tenders can only offload to the rear, time is wasted at the dump site because of the additional backing and maneuvering required.
22 The remote fill line going to the engine offloading area.
23 A large-capacity tender driving along the dump tanks, filling each one.
24 A vacuum tender dumping under pressure.
Engines. Engines can be used for a water shuttle and will be the initial water tenders when a shuttle is instituted as a backup water supply in an urban environment. It is best to have an area away from the dump tanks for engines to stage and pump water into the dump tanks. This area should be out of the way of the flow of tenders with the capability of dumping into the tanks. This requires multiple 2½- or 3-inch lines to be run from the engine to the fill spouts on the dump tank. While it is possible to find an LDH fill spout, it places a great deal of load on the dump tank in a single spot compared to several smaller spouts distributed around the tank. Using all apparatus capable of transporting water is critical in the early stages of a shuttle until enough specifically designed tenders arrive. Never discount using an engine to shuttle water; just make the proper accommodations at the dump site.
Large-capacity tenders. Having a tender carrying 8,000 gallons seems like something every incident commander would love to see. In reality, if the dump site is not configured to integrate large-capacity tenders, they may decrease the efficiency of the shuttle. A large-capacity tender has the ability to fill multiple dump tanks in one trip. It takes time to offload this much water: Using the 1,000-gpm standard, an 8,000-gallon tender will take 7.2 minutes to dump compared to 2.7 minutes for a 3,000-gallon tender. This time difference will cause tenders to back up behind the large-capacity tender, reducing the flow of the shuttle.
Several options exist to efficiently integrate large-capacity tenders into a shuttle. If they are equipped with a pump, treat large-capacity tenders like an engine and place them in a separate staging area to pump water to the dump tanks. Large-capacity tenders without a pump can be placed at the end of a secondary dump tank to fill the tank as needed. An engine can pump the water from a large-capacity tender and send it to the dump site through supply lines. Any option requires a great deal of extra room, depending on the size of the tender.
A separate dump site can be set up exclusively for large-capacity tenders. A second supply engine is needed for this, along with an area to set up the site within a reasonable distance of the fire scene. Integrating large-capacity tenders into a shuttle requires planning and training to maximize the added volume available.
Vacuum tenders. Vacuum tenders can seamlessly integrate into any dump site operation. Use caution if the vacuum tender is the first to fill a dump tank. Many operators will pressurize the tank before opening the dump valve to fill a dump tank. If the dump tank is empty, the velocity from a pressurized dump chute can move the dump tank, potentially injuring personnel and damaging equipment. Vacuum tenders must start to fill a dump tank with the vent open so it acts as a conventional tender. Once the dump tank is weighted down, the tank can be pressurized to increase and maintain dump rate.
Getting the setup right at the fire scene is critical for getting water from the tenders to the fire, regardless of the tactics employed. The operation can be complex and difficult if not impossible to change once set up, so take a couple of extra minutes to plan the best layout for an expandable offloading operation. This is not wasted time but a key investment in a successful shuttle operation.
1. National Fire Protection Association (2015) 1901, Standard for Automotive Fire Apparatus. Edition 2016. Quincy, Ma.
2. National Fire Protection Association (2019) 1710, Standard for the Organization and Deployment of Fire Suppression Operations, Emergency Medical Operations, and Special Operations to the Public by Career Fire Departments. Edition 2020. Quincy, Ma.
3. Fol-da-tank. (n.d.). Fol-da-tank. Retrieved October 8, 2019, from fol-da-tank.com/page/portable%20collapsible%20tank.aspx.
Ed Collet has been in the fire service for 19 years and is a firefighter/AEMT on the Jackson Township and Canal Fulton Fire Departments in Stark County, Ohio. He is the lead instructor for the Bowling Green State Fire School Pump Operation and Water Supply class. He is a co-chair of the Ohio Fire Chiefs Association Water Supply Technical Advisory Committee, which helps to develop and spread best practices for alternative water supply throughout the state. He has a bachelor’s degree in mechanical engineering from the University of Akron and a master’s degree in engineering management from Ohio University.