The master stream is an extremely effective weapon in the arsenal of firefighting equipment. Its large-caliber stream has saved many firefighters and prevented the destruction of millions of dollars in property.

When improperly used, however, the master stream can result in the death or injury of firefighters and the destruction of property. Firefighters must be trained to position apparatus correctly, control the supply of water to the apparatus, and properly direct the master stream. Three or four tons of water speeding through a nozzle at 100 feet per second is a tremendously destructive force. When improperly directed, master streams have collapsed ceilings, overloaded floors, knocked over brick walls and chimneys, lifted roofs off buildings, and exploded large roof sections of slate shingles into the air.


A fire department master stream is a ground-based or aerial device with a fog or straight stream capable of delivering more than 300 gpm. Because hand-held nozzles attached directly to hoselines are too difficult to control and direct at this rate of delivery, mechanical, electrical, or hydraulicassists are required. Fog streams with a delivery rate of more than 300 gpm and solid-stream nozzles of 1 ½ inches or more in diameter are considered master-stream nozzles.

Ground-based master streams include deck guns mounted permanently on top of apparatus and portable deluge nozzles that can be operated from the top of an apparatus or removed from the apparatus and positioned closer to a fire. Aerial-mounted master streams are ladder pipes affixed to ladder rungs, snorkels, or aerial platform nozzles.

The following changes in design and use over the past 25 years have increased the effectiveness of masterstream equipment:

  • The hose diameter supplying water to master streams has increased.
  • Radio communications and mutual-aid agreements have improved, enabling fireground commanders to quickly put into operation large numbers of master streams.
  • Most important, the master stream no longer is restricted to the ground; it has been elevated 50 to 100 feet above street level. At serious fires 25 years ago, firefighters operated more deck guns than aerial master streams; today they use more of the latter.

While these changes have increased the effectiveness of master streams, they also have increased their destructive capability. The pressure of a master stream is greatest in the area where the water leaves the nozzle. When the nozzle of a highpressure aerial master stream is maneuvered close to parapets, chimney tops, coping stones, cornices, or roof dormers, it can blast sections of these structures aw ay from the building and cause partial collapse. Firefighters working near a burning building in which an aerial stream is operating can be struck by building fragments knocked loose by the powerful stream.

Water from master streams also can become trapped inside a watertight, sealed floor area and quickly build to dangerous proportions—sometimes as high as windowsill level. At one firewater accumulated from master streams was seen spilling over windowsills and running down the front of a fire building seconds before all interior floors suddenly collapsed, burying firefighters operating below the fire floor.

The January 17, 1991 fire in Paterson, New Jersey requiring general alarm plus heavy mutual-aid response.

(Photo by Bill Tompkins.)

When there is no danger of collapse, master streams can be used aggressively and effectively with a close approach through an open window. Here, firefighters in Passaic, New Jersey train aerial streams, ground monitor streams, and handline streams into the commercial first-floor occupancy of a mixedoccupancy structure.

(Photo by Ron Jeffers.)

Firefighters today often must operate master streams without the supervision of a company officer. An inexperienced firefighter who has used only small, hand-held streams in the past may not be aware of the hazard potential of a large-caliber nozzle.


All firefighters should understand and consider the following when controlling and directing master streams: Weight of water. Firefighters directing a master stream must constantly remind themselves that the nozzle is pouring two to four tons of water a minute into the building. When a fire is extinguished in one window, the stream should be moved to another window and never be directed at smoke. Firefighters should notify the commanding chief when visible fire darkens down and suggest that the stream be shut down or repositioned.

Dangers of the upper portion of a building. The upper portions of old structures, such as chimney tops, parapets, and cornices, may be structurally unsound and present a collapse danger even before a fire occurs. More exposed to the elements than other parts of the building, the upper portion deteriorates more rapidly, and its maintenance is expensive and often neglected. When a deck gun or an aerial stream sweeps the upper portion of a burning structure at close range, it can knock over a section of chimney, collapse a side or rear of a parapet, or dislodge loosened coping stone.

Water accumulation. With a greater overall view of the fire scene, firefighters operating elevated streams high above street level usually are the first to detect hazards such as water buildup on a floor or roof. They immediately should notify the incident commander of any water accumulation.

Roofs surrounded by a parapet on the four sides of the building especially are prone to water buildup. If drains are clogged and several ground-level master streams are operating, a roof area may fill up with water quickly and collapse on firefighters inside the building. The hollow area inside a marquee or canopy attached to a building is another place water accumulates. The weight of the water collecting inside the void of a marquee whose drains are clogged can cause the marquee to collapse and bring down the front facade wall to which it is fastened.

Stone or brick veneer wall collapse. When a master stream on a burning masonry building is redirected from window to window, it strikes the brick wall between openings at close range. If the cement bonding between the finished stone or brick veneer and the back wall to which it is attached has lost its adhesive qualities over the years, the impact of the stream can cause large sections of the stone or brick veneer to collapse into the street below. A master stream continuously directed at a brick or wood-shingle wall at close range can blast away the wall and throw fragments of it into the air.

A crew member from Los Angeles County Fire Department's Engine 8 operates a deck gun into movie sets at the Universal Studios fire on November 6, 1990.

(Photo by Alan Simmons.)

Sounds of a master stream. When smoke reduces visibility in the street to zero, firefighters must rely on the sounds the master stream makes while striking objects to determine the stream’s effectiveness. A master stream striking a brick wall hidden in smoke, for example, creates a splattering sound; when striking the side wall of a wood building, it makes a drumming sound; and when entering a window, it makes only a distant rumbling sound.

Destruction of aerial platforms and ladders. A master stream operated from an aerial platform or aerial ladder is most effective when placed close to the building’s window. This position gives the stream deep penetration and a wide horizontal range inside the floor area. A master stream positioned near the window opening quickly can extinguish a large, burning floor area. This close-up approach also increases the stream’s demolition power. Interior partition walls and ceilings can be knocked down, exposing concealed fire.

The close-approach aerial stream should not be used if there is a danger of structural collapse, and no part of the aerial stream nozzle should be positioned where it could be struck by a falling wall, caught beneath a falling fire escape, or snagged inside an open window or a falling ornamental cornice. Sudden building failures during fires have pulled down the bucket of an aerial platform and catapulted it back into the air, torn the bucket from the boom of the apparatus, and tipped the entire aerial and truck over on its side below the falling building.

Renovated buildings. Brick buildings undergoing renovation have all interior partitions removed and only the four brick walls and wooden floors in place. An aerial master stream is particularly effective when there are no interior partition walls to obstruct the stream’s reach, as the stream can penetrate the entire depth of the burning floor. When a fire occurs in a renovated building that does not have great floor depth from the front to the rear wall, however, the powerful master stream directed through a front window can travel through the burning floor area and strike the inside of the rear wall w ith sufficient impact to cause it to collapse into the rear yard. Firefighters operating a hoseline in the rear yard can be buried under the resulting tons of falling brick.

Collapse zone for aerial streams. Some incident commanders use an unusual firefighting strategy when operating at major fires. When the wall of a building is in danger of collapse, they order all firefighters working at ground level to withdraw from the perimeter of the building and to establish a collapse danger zone; then they order firefighters manning aerial master streams to begin operations, with the elevated streams positioned close to the perimeter of the building and within the collapse danger zone.

Chiefs establishing a collapse zone for firefighters operating in the street should take similar safety precautions for firefighters operating aerial master streams. Such precautions are imperative: An increasing number of building collapses in recent years have killed or seriously injured firefighters operating aerial master streams. The collapse zone for an aerial stream varies slightly from that for ground level because of the height of the nozzle above ground level. The tip of the aerial ladder or platform bucket should be kept away from a weakened wall for a distance equal to the height of the wall above.

Photo by Bill Tompkins.

Flanking afire building. If there is a danger of a wall collapsing outward with explosive force and being driven beyond a normal collapse zone, firefighters should operate master streams from a flanking position. If a portable deluge nozzle or an aerial platform is placed in front of an adjoining building at one side of a weakened wall of the fire building, the stream range into a window or doorway of the burning building will be at an angle and may be limited, but the firefighter operating the stream would be in a safe position should the weakened wall fall outward beyond the collapse zone. Aerial streams directed from above the roof of a burning building also will be less effective, but firefighters will be safely above the collapse zone of a weakened wall.

If there is no danger of wall collapse and aerial master streams are needed because of the size of the fire, firefighters may operate the aerial nozzle close to the flaming windows of the building for effective penetration.

Ceiling collapse. Firefighters often use master streams when fire spreads through concealed spaces above suspended ceilings in shopping centers and rows of stores. These streams are most effective when directed from below the ceiling. If part of the suspended ceiling has fallen or burned away, revealing the concealed space above, the area can be swept with a master stream. In other instances, the force of a high-pressure stream directed from below can break through a ceiling and expose flame above. Ibis method can be effectively utilized when firefighters operate master streams near the front of a store or supermarket, because they have previously removed a large display window to vent the fire.

When an interior partition or the absence of large windows precludes this strategy, firefighters must operate aerial master streams from above, through a burning roof, when the fire is beyond control by an inside hoseline attack.

When either of these strategies is used, water from master streams may become trapped in pools above a watertight suspended ceiling or absorbed into soundor heat-insulating material in or above the suspended ceiling. If the water weight becomes excessive, a large section of the ceiling can collapse suddenly. This is one reason it is unsafe to direct outside master streams into burning buildings while firefighters are inside the structure. Even after they have shut down and reentered a building with a suspended ceiling, firefighters should examine the space above the ceiling tor water accumulation or absorption.


Chief officers have a personal responsibility to safeguard firefighters when master streams are in operation. Even though company officers or firefighters direct and control the master stream, the incident commander orders the equipment into operation, and he constantly must monitor and evaluate its effectiveness. He also must confirm that all firefighters have withdrawn to a safe position before allowing the use of a large-caliber outside stream. It is not enough simply to order all companies to withdraw—the chief must wait for the officer directing operations inside the building to confirm the safe withdrawal of all personnel. Over the years, firefighters retreating from fire buildings have been burned and scalded by the steam created by outside master streams being directed into the building: They had not been given sufficient time to leave.

The safe transition from interior to exterior attack of a structural fire requires three elements: effective communication between interior and exterior sector commanders; an interior sector commander who has effective command and control over the firefighters; and an exterior sector commander who understands the never-changing priorities of fireground strategy, which are the protection of lives (including firefighters’), the containment of fire, and the protection of property.

When master streams are put into operation for extinguishment, the force of the high-pressure streams and the weight of the water poured into the building weaken the structure. The IC must prepare for eventual collapse of the building; he must withdraw the firefighters operating inside the building and also order those working around the perimeter of the building to move beyond the collapse zone.

The IC also should order master streams shut down as soon as they have accomplished their task. Before any firefighter is ordered to reenter the burned-out, smoldering, watersoaked structure to overhaul, an experienced officer, a safety officer, or the IC should survey the interior conditions. If the structure is deemed unsafe, no firefighter should be allowed to reenter. Instead, department members should establish a watch line.*

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