NFPA Journal®, May/June 2008

One of the first, and most important, decisions the first-arriving company officer faces at an incident scene is whether to initiate an offensive or defensive fire attack. Later-arriving officers will affirm or change the operational strategy as they assume command.

Most structure fires occur in dwellings, where firefighters rarely need more than one or two standard pre-connected lines to attack a fire. When first-arriving units encounter an early-stage fire confined to a small area, a quick attack on the fire’s main body from an interior position may succeed in containing it. When units confront an advanced fire in a large, undivided area, however, larger fire streams are needed to meet rate-of-flow requirements. When it is safe to conduct an offensive attack on a larger fire, larger-diameter handheld hose streams are normally deployed. On rare occasions, master streams are brought inside a building as part of an offensive attack.

When the incident commander decides on a defensive strategy, master streams are the water application tools of choice. During defensive operations, lots of water is needed to “darken down” the fire and cover exposures. Master streams provide more water from a greater distance and require fewer personnel to operate. Handheld lines may be of value during a defensive attack at a small structure fire or protecting small exposures, but the master stream is generally the better choice in a defensive mode.

Most departments have groundbased, apparatus-mounted, and aerial master stream appliances. Each has a place in defensive operations. Ground-based master streams can be placed in locations where it is impossible to position a fire apparatus. Further, ground-based master streams cause less congestion in the fire area and can be left unattended after they are in position. However, the ground-based master stream generally requires more personnel and time to place in service than apparatus-mounted master streams.

When the fire is on an upper floor, ground- and apparatus-based master streams will have limited penetration due to the angle of deflection. But aerial master streams can reach upper floors, provided the fire is not significantly beyond the aerial device’s reach. When using an aerial stream, the apparatus must be placed within its effective range.

An aerial stream can be used to apply water directly on the burning fuel through the roof of some buildings, but this has a major drawback: It can reverse vertical venting.

In offensive attacks, venting the roof over the fire channels the fire and releases heat and smoke, allowing firefighters to more effectively apply water directly on the fire. Placing a master stream into a vent opening during an offensive operation reverses vertical ventilation and can drive fire into unburned areas. Further, it can prove to be very dangerous for firefighters in the building. There are times when the roof opening is large enough that applying water from above will not reverse the venting process, but this strategy should be employed only during a defensive operation.

Master streams are a seldom-used tool in our arsenal. It is important that firefighters train to set them up and that officers understand the advantages and disadvantages of each type of appliance.