Highway Hydraulics: Main Street to Country Roads, Part 3: Routing and Fill Sites

Ed Collet discusses the benefits of a smoothly operating fill site.
Whether you are using nursing or dumping operations in the urban or rural environment, a smoothly operating fill site is critical for developing an effective water shuttle.

A fill site can use a pressurized hydrant, lake, pond, river, stream, or any accessible source with an adequate store of water. Regardless of the water source, the target flow rate for filling tenders is 1,000 gallons per minute (gpm). While this is the goal, it is important to observe the tank manufacturer limits on fill pressure and flow rates. For poly tanks, the limit is generally a maximum pressure of 100 pounds per square inch gauge (psig) and a maximum rate of 1,000 gpm.

Highway Hydraulics: Main Street to Country Roads, Part 1
Highway Hydraulics: Main Street to Country Roads, Part 2: The Fire Scene

Water Supplies

The most important attribute of a fill site is a substantial and accessible water supply. Without a water source able to support fireground operations, a fill site is of little value. A static source must be capable of satisfying the National Fire Protection Association (NFPA) 1142 (2016) continuous flow recommendation of 250 gpm for two hours.1 This requires the source to have at least a capacity of 30,000 gallons. NFPA 1710 (2019) sets a minimum rate for water supply for a residential structure fire at 400 gpm.2 Using this flow for two hours, the source must have 48,000 gallons. These are minimum standard methods of evaluating a water source. Every jurisdiction must evaluate the water supply needs for its target hazards and identify water sources to meet those needs.

 Multiple portable pumps used to access water from a stream. (Photos by author.)

 An open relay fed by portable pumps.

 A million-gallon frack water tank with connections for fire department drafting.

A hydrant on a municipal water system is a great source for a fill site as long as the hydrant is capable of 1,000 gpm flow and the water system has the volume to support the shuttle. In most cases, an engine should be placed on the hydrant to ensure tender fill rates of 1,000 gpm. Depending on the design of the hydrant, it is good practice to connect to the hydrant steamer connection and one or both of the auxiliary discharges to maximize the flow from the hydrant. Some hydrants are capable of producing flows well over 1,000 gpm with adequate pressure to fill tenders; in this case, the engine would restrict the flow rate. Knowing the capability of the water system is key in determining if an engine is needed on the hydrant.

Since continuous flow is not needed at the fill site, it is possible to use a hydrant with less than 1,000 gpm flow to achieve tender fill rates of 1,000 gpm. A dump tank is positioned at the hydrant and the hydrant fills the dump tank, creating an open relay. The fill engine then drafts from the dump tank to fill tenders. A key element to making an open relay fill site work is having enough time to fill the dump tank before the first tender arrives. Optimally, the dump tank and engine tank volume will be greater than the capacity of the largest tender in the shuttle. While the engine is filling, the hydrant will still be supplying the dump tank so water is always going into the tank. As an added buffer, a second dump tank can be set as time allows.

Static sources for fill sites include lakes, ponds, rivers, streams, cisterns, wells, and above-ground tanks. An engine can draft directly from a static source using a dry hydrant or floating strainer. Dry hydrants are a system of piping and a strainer installed in a static water source to reduce drafting setup effort. The engine simply connects a suction hose between the dry hydrant and the pump inlet. While dry hydrants are commonplace in the rural environment, they are a rarity in an urban setting. Urban departments with static sources should consider installing dry hydrants as a backup to the municipal water >system.

Normally the pump operator will use tank water to backflush the dry hydrant system until bubbles are seen at the water’s surface. The operator then opens a discharge and increases the throttle to start flowing water with minimal use of the primer. Depending on the distance and diameter of the piping, backflushing may take a significant amount of tank water. Take care not to deplete the tank water while flushing. Backflushing provides the potentially false sense the inlet strainer is clear as bubbles can be seen in the water when only a part of the strainer is clear. Once a portion of the strainer is clear, water will take the path of least resistance and flow out of the clearing, potentially leaving the rest of the strainer plugged. Departments using dry hydrants for a water source must have a comprehensive maintenance and testing program in place.

 Connecting a tender with a dual 2½-inch fill.

 A fill station for LDH (connected) and dual 2½-inch.

 A water thief configured for two dual 2½-inch fill stations and one LDH station.

The alternative is to use a floating strainer connected to several lengths of suction hose. This system does not have the drawback of unknown system conditions. Since most engines only carry two sections of suction hose, multiple engines are needed to supply longer distances between the engine and source. With the introduction of air primers to the fire service, it is possible to prime greater distances than the 20 feet provided by the suction carried on the engine without fear of burning up a traditional primer motor.

Portable pumps can be used to access static water supplies beyond the reach of an engine’s drafting capabilities. Most portable pumps will not have the ability to fill tenders at 1,000 gpm alone, but several working together may achieve this flow. It is possible to meet this fill rate using several portable pumps feeding into an open relay. This is the same setup used for underperforming hydrants. Initially only one portable pump may be available to start the operation, but additional pumps should be set in place as resources become available. Adding pumps to the open relay can be done in one of two ways: running a dedicated supply line between each pump and the tank or using a siamese to bring several supply lines into a single large-diameter hose (LDH) line supplying the tank. High-volume portable pumps operate at relatively low pressure; the increased pressure loss from combining two streams in a siamese will decrease the flow rates of the pump. For the best flow rate, individual supply lines should be run from the pumps to the portable tank.

Portable eductors can be used to access distant water sources. This system works by using a jet of water to drop the pressure in the eductor to draw water into the supply line. The eductor must be supplied by water from the engine’s tank until water from the source reaches the pump intake; then a portion of the water will be returned to the eductor. The eductor pressure may be higher than the allowable tender fill pressures. This requires the operator to gate the lines used to fill the tenders, keeping pressure less than 100 psig while maintaining the needed pressure to generate flow at the eductor.

Another solution is using an open relay and a second engine. The engine running the eductor operates at the required discharge pressure and discharges at that pressure into a portable tank. The second engine then drafts from the portable tank to fill the tenders. This solution requires more resources and space to set up, making it less practical.

Site Setup

The fill site should be as close as possible to the fire scene and must be large enough to accommodate two positions for filling tenders and a fill engine. Traffic flow at the fill site must be smooth and allow tenders to maneuver when empty. Ideally, the tenders will be pointed in the direction of the fire scene once they are filled. This may necessitate setting up the filling area tenders distant from the water source.

A majority of tenders are designed with 2½-inch or LDH fill connections. Depending on the configuration of the tenders in the shuttle, the fill site will need both hose types or adapters. Tenders with 2½-inch fill connections should be filled using two 2½- or 3-inch lines. When the tenders have a mix of LDH and 2½-inch connections, one station at the fill site is dedicated to LDH connections and the other for dual 2½-inch filling. While the goal is for tenders to fill at the dedicated station, this will not always be possible; each station must have adapters for the other style in case the designated station is occupied when a second tender using a particular connection style arrives. Using a water thief is an easy way to configure a fill station to accept tenders configured for LDH or double 2½-inch connections.

Make sure there is enough space between the two fill stations to allow tenders to enter and exit without excessive maneuvering. It is a good practice to mark the front of the fill station with traffic cones.

Fill lines can come directly from the fill engine or from a water thief connected to the engine through LDH. Connecting fill lines directly to the engine discharges is done when the water supply and fill area are in close proximity. Grouping pairs of fill lines on the same side of the engine helps to reduce operator confusion. Make every effort not to use the discharges on the pump panel to increase operator safety. Use different color hose for each fill station as another way to minimize confusion. The operator should mark the gauges with a grease pen to indicate the lines supplying each fill station to reduce the potential of accidentally charging lines that are not connected.

Using LDH to supply a manifold for tender filling can be logistically beneficial when the water source is not located where tender traffic flow is optimal. This allows the fill engine to be hundreds of feet from the fill stations without having to pull multiple lines. It minimizes the friction loss between the engine and tenders while placing fill control at the location of the fill station. Another advantage to the water thief is moving wear and tear from the valves on the engine to the water thief, which is easier and less costly to repair.

When supplying the manifold or water thief through LDH, the maximum flow will be limited based on the pump discharge plumbing. It may be necessary to supply the LDH from several discharges using a siamese or triamese to bring them together for the LDH. There are cases where the flow from extremely good hydrants is limited because of the engine’s plumbing. In cases like this, connecting a section of LDH from the hydrant to a manifold will provide better flow rates. This is one reason fill sites must be planned, to know if a hydrant needs an engine or not for the fill site to be effective and efficient.


Whether filling tenders in an urban or a rural setting, the methods for efficient operations are the same. Two fill stations are established, allowing two tenders to be connected at once even though only one tender is filled at a time. Filling two tenders at once reduces the fill rate for each tender and produces a lower overall flow rate to the fireground. Even if two tenders can simultaneously fill at 1,000 gpm, they would arrive at the dump site at the same time, potentially causing tenders to wait at the dump site. Staggering the arrival and departure of tenders improves the flow and efficiency of operation at both the dump and fill sites.

When a tender is full, only the fill site manager can tell a tender driver to leave. Tender operators must be trained to take direction from the fill site manager only or other designated ground guide. The fill site manager must have a clear view of the operations and know when tenders are full and disconnected. Without this level of control, there is a real possibility tenders could leave while still connected to the manifold, causing injury to personnel and equipment damage.

Stationary tenders do not add to the fireground flow. The knee-jerk reaction of most fill site managers is to call for a second fill site when tenders start to wait in line to be filled. While this realization is important, pulling the trigger on the second fill site needs serious thought. If the additional fill site adds more travel time than the wait time at the first fill site, the additional fill site can reduce the overall flow of the shuttle. A tender just arriving to the fill site as the second spot is taken and a 3,000-gallon tender just starting to fill will have to wait in line for four minutes—three minutes to fill and a minute for maneuvering and connecting lines. The additional fill site cannot add more than four minutes to round-trip travel time than the first site to improve water flow at the fireground. This example is for one tender waiting to fill. The more tenders waiting in line to fill, the more travel time to a second fill site can be increased and still improve the flow rate.

Integrating Vacuum Tenders

The key benefit of vacuum tenders is their ability to establish their own fill site from a static water source with minimal staffing. Often, well-trained operators can set up a fill site for a vacuum tender on their own. If possible, vacuum tenders should find a separate fill site to maximize this benefit. If the closest fill site is from a hydrant or there are no practical static sources for the vacuum tender to use, it can be integrated into a fill site in two ways. The easiest is to treat it as a conventional tender. Most vacuum tenders have adapters to go from the 6-inch cam-lock intake to a 2½-inch threaded connection. When loading a vacuum tender as a conventional tender, it is important to remember to open the vent. The other option requires more equipment and space but once set up allows the vacuum tender to fill independently of the conventional tenders. A dump tank is placed at the far end of the fill site and filled by the engine between filling conventional tenders. The vacuum tender can then go to the dump tank and fill itself as if it were at a static source.


Once a tender is empty, simply telling the driver to go to the fill site is inefficient and has the potential to drastically lower the shuttle flow rate or set the stage for roadway mishaps. Shuttle routes must be planned, since often the shortest route is not the quickest or safest. While it may not be possible to plan for every route to every possible fire, you can plan general routes to areas based on a designated fill site. A primary and at least one alternate route from the primary and secondary fill site should be planned in case of construction, weather, or heavy traffic.

In the urban environment, planning routes is normally not considered, since using a water shuttle is an emergent event. Even though a shuttle may never be used, it is a good idea to identify several water sources as fill sites and determine routes to known high hazards. If a nearby river or lake is to be used for water supply, what is the best way to get into downtown in the middle of the night and during morning or evening rush hours? Having a couple of planned shuttle routes will save valuable time when establishing an alternative water supply.

Speed is not how shuttle flow is increased. In fact, it has the potential to take the shuttle flow to zero when a tender becomes involved in an accident and blocks the shuttle route, along with taking resources to deal with the accident. It is amazing how an apparatus constituting a small percentage of the nation’s fire fleet is involved in a disproportionate number of accidents involving injury and death. This is such an issue that the U.S. Fire Administration produced the publication Safe Operation of Fire Tankers. This should be required reading for drivers and officers of departments with tenders. Shuttle flow calculations are based on an average speed of 35 miles per hour (mph).1 A 3,000-gallon tender in a 5-mile loop route could increase its flow rate from 190 gpm to 220 gpm by increasing its speed from 35 to 45 mph. Increasing from 45 mph to 55 mph, the flow could be increased to 244 gpm. These potential gains are made by assuming some very real risk. You can produce larger and safer flow increases by adding additional tenders, reducing travel distances, or adding fill sites. There is absolutely no reason for firefighters or the public to be injured or killed in a tender accident. Slow down, drive with due regard, respect the apparatus, and call more tenders early in the incident to increase flow.

 A supply engine with an LDH manifold preconnected.

 LDH fed by two 2½-inch discharges.

 A vacuum tender being filled as a conventional tender.

Ideally, the route should be a loop. While this type of route may be longer than a back-and-forth route, it prevents tenders from having to pass each other on narrow country roads or city streets and eliminates maneuvering. When adding fill sites, it is important to make sure the additional routes mesh with the original route so all tenders are moving in the same direction approaching the dump site.

There are situations when the back-and-forth route is the best or only option. This routing works best if tenders can avoid passing through the dump site on the return trip to the fill site. Having to pass through the dump site empty requires full tenders to wait for the empty tender to drive through before offloading. At the fill site, tenders should maneuver to the direction of return travel while empty. There are two fill sites in my district where the intended routes are primarily back-and-forth, which are in parking lots with two entrances. This allows the tenders to enter the fill site at one entrance, fill, exit using a second entrance, and use the same route to the fire. When using this type of routing, tender drivers must make sure not to go over bridges and culverts at the same time as other tenders. While the bridge may be safe for a single tender, the weight of two may cause a failure. It is best to wait a few seconds to let the other pass as opposed to damaging the bridge and forcing command to find a different route and taking two tenders out of the shuttle.

Most routes will not be fully looped or fully back-and-forth but a hybrid of the two. The best example of this is a subdivision or large apartment complex where the route to and from the main entrance is back-and-forth, with the route from the subdivision entrance to the fire being a loop. In these cases, the back-and-forth portion is usually a road with wide lanes, allowing tenders to pass without issue. The loop portion is in the narrow side streets or roads, making it difficult for tenders to pass each other.

When setting a route, consider hazards and limitations as well as the types of tenders used in the shuttle. When larger tenders are used, routes should include roads with minimal curves. Bridges and culverts may have weight limits, preventing larger tenders from crossing. Even if weight limits are seasonal, plan routes as though the limit is in effect year-round. This will avoid confusion as to when to use the summer route or the winter route. Weight limits may dictate only small tenders be dispatched for certain areas. Working with the local highway engineering office is a great benefit in identifying limitations in shuttle routing.

In cold climates, it is critical to have a good working relationship with the city, county, and state road departments. When snow starts to fall and roads get icy, one of the first calls a water supply officer needs to make is to the road department for salt or sand. The shuttle route along with the dump and fill sites must be treated to improve safety.

Even routes you plan in advance may require modification because of weather, construction, or newly presented route hazards. As the shuttle evolves and routes are established, consider asking for law enforcement support to help with traffic on the shuttle route to improve the flow and safety of the route.

Wrapping it Up

Calling resources that have never worked together for a water shuttle is running the water supply operations on hope and prayers. Urban areas with pressurized water systems can easily fall into the trap of thinking, “We will never need a shuttle here.” This is all well and good until the water plant goes down or a major water main break occurs and then you hope to find a way to get water to the fire.

Training is critical to rapidly establish an alternative water supply when the hydrants stop flowing. At minimum, conduct once a year a multicompany drill using several engines to nurse an attack engine. This at least gets companies familiar with nursing and fill site operations. The best training involves calling neighbors with tenders to participate. This lets them get familiar with maneuvering their tenders in an urban environment and lets the host department learn from neighbors who run water shuttle operations on a regular basis. Everyone learns and benefits from such training, especially the community being protected whether or not there is water coming out of the hydrants.


1. National Fire Protection Association. (2016). Standard 1142, Standard on Water Supplies for Suburban and Rural Fire Fighting, Edition 2017. Quincy, Ma.

2. National Fire Protection Association. (2019). Standard 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.

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.

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