he AMBUSH™ System is an air aspirating foam device designed to provide effective “system based” full-surface as well as rim seal fire suppression for external floating roof storage tanks.  It is another cutting edge innovation from Williams Fire & Hazard Control.

Effective full-surface fire protection may be delivered by an experienced response team deploying significant water and foam resources via large-volume manned portable fire monitors, which are staged some distance from a burning tank — offering “over the top” trajectory and safe attack distances. This projection of water/foam solution onto the surface of the tank from a ground position is referred to as a “Type 3 Application”.  Delivered from outside the tank, consideration must be given to “fallout” of a Type 3 application — that is the water/foam solution that does not land inside the tank due to wind or general stream erosion from the ground assault.

As a rim seal protection option, traditional fixed foam systems (foam chambers, or foam pourers) are referred to as providing a “Type 2 Application” — delivering a “cascading application” of water/foam solution from unmanned systems affixed to the tank itself.  This method of delivery usually deploys lower application volumes targeting the rim seal area. However, this method does not deliver adequate water/foam solution to extinguish a full-surface fire.


Mounted to the rim of a tank, the AMBUSH System delivers a Type 3 Application toward the center of the tank for full surface protection, while simultaneously delivering lateral Type 2 application streams along the tank wall for rim seal fire protection.  The benefit of a fixed system “Type 3 Application” is a potential increase in foam application density on the storage tank surface area.  The elevated position of the AMBUSH™ system at the tank rim minimizes wind erosion on Type 3 Application and at the same time delivers a more forceful seal area application — reducing application times and using less water and foam concentrate than a strict “Type 3 Application”.

The AMBUSH™ System is available in several different sizes to protect all sizes of tanks.  Each size functions similarly. The stream is broken into 4 components.  The Left/Right discharge streams are equal to each other and deliver foam left/right of the unit against the tank wall.  The upper stream discharges foam at a slight angle toward the center of the tank.  The fourth stream discharges foam back against the tank’s shell and protects the area just below the unit with a small stream.  As the multiple foam streams projecting toward the center of the tank converge, they extinguish the fire in the center of the tank then build back toward the tank’s shell.  At the same time, the left/right streams project foam around the circumference of the tank extinguishing any fire near the tank shell.  As the tank shell fire is extinguished, this coverage begins to grow toward the center of the tank to meet the foam blanket being established by the upper stream. Soon after, the entire tank will have a full foam blanket.

As a fixed system component, the AMBUSH™ provides a quicker response time and less man power than a portable large volume delivery approach.   Also, it requires less flow rate due to lower recommended application densities. Finally, use of the AMBUSH system requires less specialized training and exposes few personnel to a hazardous situation.

The Ambush System is designed to be installed above the roof joint and mounted above the highest level of the floating roof.  Foam solution is piped to the Ambush System from outside the hazard area.  For tanks less than 160 ft (48.8 m) in diameter, a single foam solution pipe will be required for each device to provide annular discharge against the tank shell.  This annular discharge restricts agitation of the burning surface and provides cooling of the tank wall.  For tanks greater than 160 ft (48.8 m) in diameter, an additional valved foam solution pipe will be required to supply a foam blanket to the exposed burning surface that cannot be reached with the annular discharge alone.

The Ambush System is manufactured using type 304 stainless steel and is available in six models. The Ambush Model 3305 contains a single air aspirating device through which expanded foam solution discharges through a left, right, and against the wall discharge points.  All other Ambush Models (4421, 5541, 6661, 6681, & 8811) include a separately piped inlet with an additional air aspirating device that discharges expanded foam solution towards to the center of the tank.  Water/foam solution inlets are flat faced and drilled to ANSI 150 lb standard provided with flange gaskets and hardware.  Air inlets are covered with 304 stainless steel screens.  All units are finished with durable red epoxy paint.

It is recommended a minimum of 100 PSI (6.9 Bar) inlet pressure be available to provide the optimum foam quality


Part Number Description
11730 Kit, 10″ backboard mount assembly for AMBUSH 3305, 10″ channel w/ fasteners
11738 Kit, 15″ backboard mount assembly for AMBUSH 4421, 5541, 6661, and 6681, 15″ channel w/ fasteners
11732 Kit, 18″ backboard mount assembly for AMBUSH 8881, 18″ channel w/ fasteners
11739 Kit,  inlet for AMBUSH 4421, 6″x6″x3″, valved Wye w/ gaskets and fasteners
11740 Kit,  inlet for AMBUSH 5541, 6661 and 6681, 6″x6″x4″, valved wye w/ gaskets and fasteners
11741 Kit,  inlet for AMBUSH 8881, 8″x8″x4″, valved wye w/ gaskets and fasteners