Some departments don't take a lot of time when they specify a tanker. They chose a chassis, select a tank size and add a few options. Check, check and check -- they're done. That's too bad because there are several other important details that should be considered when speccing a tanker to make it more versatile and efficient and safer to operate.

Applications

A water tanker -- or water tender, as they are called in the West -- can be used for several applications depending on the department's specific needs.

The most common application is a mobile water supply for pumpers. The tanker usually sets up a portable drafting tank at the fire scene, dumps its water into the tank, then drives to the nearest water source where it is reloaded for another trip to the fire. This technique, called a tanker shuttle, can be put into operation quickly and can deliver a steady supply of water over a distance of a mile or more. In this application, the tanker usually does not have a pump or preconnected hoselines, thus restricting its use to water transport only.

A more popular application is an attack tanker that can shuttle water for pumpers or can attack the fire directly using a pump and preconnected hoselines. Some larger attack tankers are also equipped with foam, remote-controlled monitors, and a limited amount of firefighting equipment. In this application, the tanker is more versatile and can be used in different roles depending on the situation.

Another popular application is a pumper/tanker that combines a large pump and tank with a full compliment of hose, ladders and firefighting equipment. Pumper/tankers are often used as the first-response vehicle in rural areas where it may take a long time to establish a sustained water supply from a tanker shuttle or other source.

Tank Shapes and Capacities

Tanks can be classified into three basic cross-section shapes -- round, elliptical and rectangular. Each shape has its own advantages and disadvantages.

Tanks with round cross-sections have good inherent side-to-side damping to reduce the forces caused by water surging in the tank. They are also inherently strong and can resist internal pressures and vacuums. A disadvantage of round tanks: For a given tank capacity and overall length, they have the highest center of gravity.

Elliptical or semi-elliptical tanks have a lower center of gravity than round tanks and offer a moderate amount of inherent damping. They are the most common shape used for tankers.

Rectangular tanks have the lowest center of gravity and provide a flat upper surface that can be used for hosebeds and equipment storage. One disadvantage is that the shape offers no inherent side-to-side damping.

In terms of capacity, many departments have found that tankers with single rear axles and 1,500-gallon to 2,000-gallon tanks are ideal. These mid-sized tankers are lightweight, easy to maneuver and can be used to deliver sustained flowrates of approximately 140gpm to 170gpm over a distance of one mile each way. With two or three of these tankers shuttling water, fire departments can often provide a sustained flowrate of 250gpm or more to meet the ISO Class 8 water supply requirement for areas without hydrants.

Loading and Unloading

When a tanker is used to shuttle water to the fire scene, the speed of loading and unloading determines how efficiently the tanker can operate.

To maximize the speed of loading, consider specifying quick-disconnect Storz or Cam-lock fittings rather than more cumbersome threaded fittings. Inlet ports to the tank should be direct and oversize -- multiple 2-1/2-inch ports are good; a single 4-inch to 5-inch port is better. Having a dedicated supply pumper at the water source allows loading rates of 1,000gpm or more. Using a vacuum tanker eliminates the need for a supply pumper and can also achieve loading rates of 1,000gpm or more.

To maximize the speed of unloading, consider using 10-inch square or larger dump valves to achieve unloading rates of 1,000gpm or more. Three dump valves -- one on each side, and one at the rear -- give the flexibility to unload into tanks on either side without having to maneuver the tanker into position. Three valves can also improve unloading rates by dumping into more than one tank at a time if the unloading site layout permits. Vacuum tankers can reverse the vacuum pump to pressurize the tank and speed up unloading.

Safety

With tankers, the height of the vehicle's center of gravity and the ability of the vehicle to maneuver around busy loading and unloading sites are two major safety concerns.

To lower the center of gravity, consider specifying a tank with an elliptical or rectangular cross-section. Using low-profile 22.5 tires instead of standard-profile 24.5 tires can lower the center of gravity of the entire vehicle by about 2 inches. An optional lowered rear suspension can shave another 2 inches off the height.

Specifying one or more dump valves on each side of the vehicle may reduce the hazards involved with maneuvering around the unloading site. With this arrangement, the driver pulls straight forward alongside the dump tank, unloads the water and drives forward to leave-- no backing, no maneuvering. Specifying powered valve actuators and chute extenders will keep the driver in the cab and eliminate the need for someone on the ground to operate the valves and chutes manually.

A note of caution: All the safety specs in the world won't prevent accidents if drivers aren't properly trained. Departments need to make sure drivers understand that tankers are more prone to tipover accidents than other apparatus and therefore require special driving techniques. Drivers also need to understand the hazards of maneuvering tankers around crowded loading and unloading sites. Requiring drivers to restrict their speed, to be cautious on high-crowned roads and curves, to always wear seat belts (passengers, too) and to always use ground guides when backing up will go a long way toward preventing tragic, and often fatal, tanker accidents.

NFPA Standard

Design and performance requirements for tankers are contained in the NFPA 1901, Automotive Fire Apparatus ( 2003). They include specifications for materials, construction, plumbing and other details. These are minimum requirements, and departments should specify tankers that meet their specific needs.