Basic Forest Fire Suppression Course - Online Lessons


4.3 Back Tank Pump

The back tank pump consists of a water container, a hand pump for applying water and carrying straps.

The containers are constructed of either rigid or collapsible materials. Rigid containers may be galvanized metal, stainless steel or polyethylene. Collapsible containers are constructed of rubber or neoprene nylon fabric. Container capacity is approximately 18 - 20 litres and weighs approximately 20 kg, when full. All containers must be equipped with a corrosion resistant screen in the filler opening, an appropriate filler cap and a device for connecting the discharge hose to the container.

Water Application

Water application with a back tank pump achieves two results:

1) Reduces heat

2) Increases moisture content of unburned fuels which increases their resistance to ignition

Water can be applied in a spray or a solid stream. A spray pattern can be achieved by pressing the flat spray spring on the pump or by simply applying thumb pressure over the nozzle during the compression stroke. Thumb pressure requires considerably less effort than pressing the flat spray spring. A spray produces a fan shaped shower of water.

A solid stream is an unrestricted flow during the compression stroke. The pattern produced by a solid stream is a long, narrow band of water.

A spray pattern is important in obtaining maximum results from the limited amount of water being applied. Water applied in a spray will absorb heat more rapidly than water applied in a solid stream. The amount of surface area of water exposed to the fire's heat by a spray pattern is many times the surface area of water exposed by a solid stream pattern. Water should be applied in a spray pattern whenever possible.

Water applied in a spray pattern should be at right angles to the fire edge. Water applied at right angles will cover a larger area of the fire perimeter. A solid stream should be applied parallel to the fire edge. All water applied with a back tank pump should be directed at the base of the flames.

When surface fuels are light and flame heights are low, the crew members should apply water in a spray pattern at right angles to the fire edge. When the surface fuels are heavier and heat from flames prevents crew members from working close to the flame front, water should be applied in a solid stream pattern, parallel to the fire edge. Once heat has been reduced by a solid stream pattern, crew members should apply water in a spray pattern at right angles to the fire edge. The type of pattern and size of water droplets can be varied by the amount of pressure applied with the thumb.

To apply water beyond 3 meters, a solid stream must be used to maintain any accuracy (water directed at fire in stubs or snags). Accuracy is achieved by keeping the hand on the piston handle stationary while pumping with the other hand at the base of the cylinder. The nozzle stream is directed with the hand on the piston handle. Back tank pumps can be used to extinguish either smudges or hot spots during mop up operations. Exposing deep burning embers, with grubbing tools or shovels, for water application, can increase effectiveness.

A back tank pump full of water is difficult to handle, therefore proper lifting techniques must be used to avoid back injuries. Two recommended procedures are:

1) Use a second crew member to assist you.

2) Place the pump unit on a platform, such as a vehicle tailgate, to get the correct height so you are able to slide your arms through the carrying straps.

The container may be filled by:

1) Dipping the container directly into a water source

2) Filling the container using a pail or hard hat

3) Filling from a tanker, barrel or patrolling hose

Ensure that no debris is allowed to enter the container. Debris could block the flow of water.


Ensure that the container is clean, free of leaks, has a filler cap, screen and gasket and carrying straps in good condition.

Ensure the pump operates freely with all parts functioning properly.

Containers and pumps should be thoroughly drained and stored in a dry area with good air circulation. Caps should be loosened to ensure full drying and to prevent rusting as well as fractured metal inside the pump because of ice build up during winter storage in an unheated building.