The lowly tanker once was regarded as a necessary, but thoroughly unglamorous, workhorse of rural fire departments everywhere. It was parked behind the station, slowly dripping water, waiting to respond down some dusty road far from town. The tank usually was small, and the fill and dump fittings were undersized. The pump, if it had one, was better suited to fighting grassfires than structure fires. In many volunteer departments, the last person to arrive at the station got stuck with driving the tanker.

A lot has changed over the years. Today, more and more fire departments have learned new and better ways to use tankers, turning them into one of their more valuable and versatile apparatus.

Water on wheels

The most common use for tankers always has been to supply water in areas where there are no hydrants. That is still one of their primary functions, but the amount of water they can supply and the techniques used to do it have changed.

Most departments use tanker shuttles to move water from a nearby source to the fire site. This is still the most effective way to move water over distances of a mile or more, but it takes a lot of people and a lot of practice to maintain a steady flow. And to maximize the flow under the conditions established by the Insurance Services Office is even more difficult.

To meet the requirements for an ISO Class 8 or better Public Protection Classification using a tanker shuttle, a department must demonstrate that it can start pumping 250gpm within five minutes of the first engine's arrival. For a better classification, the department has 10 minutes from initial pumping to increase the flow rate and then maintain that flow rate for a period of time, usually two hours, without interruption. Any decrease or interruption in flow, or any unsafe act, will result in a termination of the ISO evaluation and an assignment of a Class 9 for the area. (See “Tanker Shuttle Quiz” on page 70 to test your knowledge of the ISO requirements for tanker shuttles.)

Some departments fail to meet the ISO requirements for tanker shuttles because they can't set up fast enough to start drafting from the drop tank within the allotted five minutes. This often is true when the number of personnel arriving on the first apparatus is limited. At the five-minute mark, they are forced to start pumping water from the tank on the engine, but they quickly run out.

One technique to handle this problem is to have a tanker respond with the first engine. Rather than have the tanker dump into the drop tank and go for a second load, the tanker can supply water directly to the engine — either with a pump on the tanker, or through a hard suction connection off the engine — and give more time for the department to set up the drafting operation. This technique only works when a sufficient number of other tankers arrive to fill the drop tank and sustain the desired flow rate before drafting starts. Once the pumper is drafting water from the drop tank, the first tanker can disconnect and join the shuttle.

Another reason departments often fail to get ISO credit for tanker shuttles is because they can't maintain the desired flow rate once pumping has started. Using larger tankers often can solve this problem. For example, many older tankers have 1,500-gallon tanks mounted on trucks with single rear axles. Even with large fill and dump connections and an experienced crew, this size tanker can shuttle only about 100gpm over a one-way distance of two miles using the ISO formula. To sustain a 500gpm flow rate, a department would need to run five of them.

If a department switched to a 2,000-gallon tanker with the same general specs and operating conditions, they could shuttle about 130gpm and would require only four tankers to sustain 500gpm. And if they uprated to a tanker with a 3,000-gallon tank on a truck with tandem rear axles, they could shuttle about 170gpm and would need only three of them to sustain 500gpm. Many departments have made these calculations for the operating conditions in their areas and have come to the conclusion that larger tankers can deliver more water per trip and can sustain the desired flow rate with fewer drivers and less traffic.

In areas where the nearest water source is too far away to shuttle water, departments can still use tankers as a water supply by taking advantage of the new ISO Class 8B. This classification recognizes departments that provide superior fire protection services and fire-alarm facilities but lack the water supply required for a Public Protection Classification of Class 8 or better.

To qualify, departments must meet certain requirements and achieve certain minimum ratings. They also must be able to start flowing 200gpm within five minutes of the arrival of the first engine and sustain that flow rate for 20 minutes. Using the ISO method for calculating tank capacity, a department could meet those requirements by bringing about 4,500 gallons of water to the fire site. Two tankers with 2,000-gallon tanks and an engine with a 500-gallon tank would do the job if the tankers fed the engine directly. More water would be required if the engine had to draft from a drop tank. ISO indicates they will be applying the Class 8B criteria as they survey communities over the next several years.

On the attack

In addition to using tankers to shuttle water, some departments use them to attack fires directly. For example, adding a 750gpm or larger pump to a tanker gives a department an apparatus that can initiate a high-volume attack with preconnected portable monitors or a deck gun as soon as it rolls onto the scene. In many cases, this blitz attack can knock down the fire in less than a minute, while other engine companies lay a line from a hydrant or establish a water supply from other sources. This technique can be used in both city and rural situations and is especially valuable when the first-arriving apparatus is staffed with a minimum crew. It requires that departments establish a sustained water supply within the first five minutes, however, if they want ISO credit.

Other departments have taken this concept one step further by using engine/tankers that carry a full complement of ground ladders, supply hose and other equipment. This can give the department ISO credit for an engine company while also allowing a rapid, high-volume attack. A few rural departments have even specified pumper/tankers or engine/tankers equipped with aerial devices to allow the use of elevated master streams on fires in large structures, such as fruit packing plants, warehouses and others.

The latest use for tankers is to provide mobile water supplies for brush rigs and engine companies during wildland fires. Large wildland fires can be chaotic events, with apparatus constantly on the move as the fire front shifts. Water sources are often not readily accessible. One solution has been to assign tankers to support small groups of pumpers by refilling their tanks, then driving to the nearest water source and returning. One department uses a tanker to support several 4×4 attack rigs engaged in pump-and-roll operations on open rangeland fires. Another department assigns a tanker as part of a task force of four structure pumpers protecting homes in a wildland-urban interface zone. In both cases, using a tanker provides a mobile water supply that can keep up with shifting fire situations.

Tankers also are used to support helicopter water-drop operations by shuttling water from remote fill sites to more open areas where high-wall portable dip tanks are located. The tankers dump their water into a series of intermediate holding tanks, and the ground crew pumps the water into the large dip tanks as needed.

Shapes and sizes

In most cases, the overall shape and size of a tanker depends on how it is used. Engineers refer to this as the “form follows function” rule of design.

Rectangular tanks have flat sides and tops to allow the maximum space for compartments, drop tank storage racks and hose beds. The rectangular cross-section results in a low profile and a low center of gravity but provides no inherent damping. Adequate internal baffling must be included to prevent dangerous side-to-side surges of water.

Semi-elliptical tanks have room for small hose trays along the sides of the tank, but compartments usually have to be located below the tank. This shape has a higher profile and a higher center of gravity than a rectangular tank, but provides better inherent damping, although it still requires internal baffles. A variation of this shape, with flattened sides and top, provides a compromise between a semi-elliptical and a rectangular tank with more room for compartments, but with less inherent damping.

Round tanks are used on vacuum tankers to provide the strength necessary to resist external air pressure on the tank. They have room for small hose trays along the sides of the tank, but compartments are usually mounted low. This shape has good inherent damping but results in a high profile and a high center of gravity. Manufacturers usually compensate for this by using a longer but smaller-diameter tank.

In terms of capacity, rectangular tanks give the highest capacity with the lowest center of gravity. Tankers with 2,000- to 2,500-gallon tanks usually have rectangular tanks, especially if the department wants maximum compartment space or wants to use the top of the tank for a hose bed. Tanks of this size can be mounted on relatively short chassis with single rear axles for excellent maneuverability and ease of operation.

Tankers with 3,000- to 4,000-gallon tanks usually have semi-elliptical tanks to provide additional damping for the larger volume of water. Tanks of this size are mounted on longer chassis with tandem rear axles to support the additional weight. These tankers take more room to maneuver and require more experienced drivers, but they can deliver more water to sustain higher flow rates in situations where maneuverability is not an issue.

Fill and dump

In tanker shuttles, the most critical parts of the entire cycle are the fill and dump operations. That's where departments make the most mistakes and lose the most time. It's also where most accidents happen because ground personnel have to work close to the vehicle to make and break hose connections or open and close the dump valve.

Practice and strict adherence to safety guidelines are two key ingredients to successful fill and dump operations. Good specs help, too.

To improve fill times if the tanker is filled from a supply pumper or pressurized hydrant, use multiple 2H-inch ports or a single 4- or 5-inch port with quick-disconnect Storz or Cam-Lock fittings. If the tanker uses an on-board pump to draft from a static water source, use lightweight suction hose and 4-inch or larger pump-to-tank connections. Vacuum tankers can self load at flow rates up to 1,000gpm.

To improve dump times, use 10-inch or larger square dump valves with self-extending chutes and controls located in the cab. Having dump valves on the sides, as well as the rear, allows the driver to pull up alongside a drop tank and dump to either side without backing into position — good for efficiency, great for safety. Vacuum tankers can reverse the vacuum pump to pressurize the tank and greatly speed offloading.

Dump tanks also are critical. Rigid-frame rectangular dump tanks can be set up on a single lane of narrow roadways to let tankers pull alongside and dump. Self-supporting tanks with flotation collars are compact, lightweight and can be set up by a single person. Some tanks incorporate rigid corner supports with lightweight liners to combine the advantages of rigid frame and self-supporting designs.

Next time you specify a tanker, think about the tank size and shape, chassis, fill and dump ports, pump, hose bed, controls, plumbing, monitors, area lights, and a host of other points. With a little thought, you can turn your lowly tanker into a much more valuable and versatile apparatus.

Tanker Shuttle Quiz

The Fire Suppression Rating Schedule used by the Insurance Services Office recognizes several alternative water supplies that fire departments may use instead of, or in addition to, pressurized hydrants. These include dry hydrants, suction points, large-diameter hose relays and hauled water using tanker shuttles.

For tanker shuttles, ISO determines the water supply rating based on a time-line analysis of apparatus arrival times, travel times, tank capacities, fill rates, discharge rates, wait times for tankers to fill or discharge their water supply, available water supply at the fill site, fire flow at the fire site and several other factors. Certain conditions and restrictions apply. Based on this analysis, ISO determines the total water supply flow rate that the department is able to sustain for a period of time, usually two hours.

Here is a short true-false quiz to test your knowledge of ISO tanker shuttles:

1. Tanker shuttles can be used as an alternative water supply to obtain an ISO Class 8 or better Public Protection Classification for structures located more than five road miles from the nearest responding fire station.

   False

   The ISO rating schedule does not apply to structures located more than five road miles from the nearest responding station, even if a department is able to shuttle water to the site. These structures are generally assigned a Class 10, the lowest possible public protection classification, although there may be exceptions on a case-by-case basis. The key word is “road” miles, not straight-line miles.

2. Tanker travel times are based on an average speed of 35mph when responding to the fire site or operating in a shuttle.

   True

   ISO calculates all travel times with a formula that is based on a 35mph average speed. It includes a factor for acceleration and deceleration. Departments will not be given credit for shorter travel times by attempting to demonstrate that they can travel at higher speeds. ISO will use lower speeds and assign longer travel times, however, if an apparatus is underpowered.

3. Tankers shuttling water get credit for the full capacities of their tanks.

   False

   ISO subtracts 10% of each tanker's capacity to account for spillage and incomplete filling and draining. For example, a 2,000-gallon tanker is given credit for delivering only 1,800 gallons per trip. Consult your ISO office to determine the correction used for vacuum tankers.

4. Tankers responding on a second alarm can leave their stations as soon as the first apparatus arrives at the fire.

   False

   ISO assigns a three-minute delay to tankers responding from stations with paid (on-duty) tanker drivers to allow time for the personnel on the first-arriving apparatus to evaluate the situation and call for the second alarm. Stations with volunteer drivers are assigned a 6-minute delay to allow additional time for the drivers to arrive at the stations. Add travel times to the fire site from each station to determine when these units can join the shuttle.

5. Tanker shuttles can be used to supplement the water supply for structures located within 1,000 feet of a hydrant.

   True

   Although the water supply for structures within 1,000 feet of a hydrant is usually supplied by the hydrant, ISO will allow departments to supplement it with any alternative water supplies, including tanker shuttles. Departments must document this method as their standard operating procedure and be able to demonstrate that they can perform it.

For more on alternative water supplies, go to www.isomitigation.com and click on “ISO's Public Protection Classification Program,” and then “Alternative Water Supplies.”

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