What’s This “Big Stream” Stuff
DEPARTMENTS
Volunteers Corner
Many fire departments attack fires with booster lines for speed and ease while others prefer 1 1/8 to 2-inch preconnected hand lines. However, for several years many fire departments have attacked fires with BIG STREAMS initally, whether from hand-held nozzles, portable monitors, turrets mounted on pumpers, and nozzles on aerial devices or special apparatus.
Generally, a big stream is 400 gpm or larger. In initial attack procedures these streams are used for a quick knockdown of a large, fast-moving fire. A major error is the reluctance to go to these “big guns” early. A short application of water at a high volume will control many fires with a minimum number of gallons. But far often fireground officers use the large delivery in a defensive mood after the building is beyond saving. A lengthy water delivery from smaller streams can actually require greater quantities of water for extinguishment than a short burst at a high delivery rate.
There are some precautions to consider before beginning a big stream attack. If an interior attack has been started and is making satisfactory progress, a big stream must not be directed into the structure. That would drive out the interior fire fighters. A large stream can be used in coordination with the interior attack for an efficient operation such as stopping a vertically spreading fire, but must not be directed against the interior attack. The wrong positioning of a large-caliber stream can push fire, heat and gases throughout a building. Often aerial streams are directed down into a roof opening. This upsets the ventilation flow and can have a negative effect rather than speed fire control.
A basis for this type of attack is to estimate the amount of water necessary and begin with a delivery that meets this need. A good method of estimating needed delivery is to take the cubic feet of area involved (or potentially involved) and divide it by 100 to give the gallons per minute. This may have to be increased if there is a high fire loading. Remember that whether the flow is going to be delivered by hand lines or a mechanical device, the gpm required will be the same. As long as the size and fire loading are constant, the flow will have to be developed no matter how delivered. The big difference is in the maneuverability of the hand line when personnel are available.
Many fire departments are extremely concerned with water supply and believe they cannot initiate the type of attack required. In fact when there is large volume of fire, water can often be conserved by a quick knockdown with a large stream, and final extinguishment and mop up with smaller lines. The following application rates and times illustrate how a tank size of 1000 gallons can be used.
A tremendous volume of fire can be controlled with this quantity of water when applied to absorb maximum heat. Of greater importance is the assistance that can be gained for rescue purposes. Entry will be faster, escape routes can be protected, and even those in need of rescue can be covered with protective streams.
At this point it is interesting to tie the formula given for water required to the delivery rates. Using the 1000 gallons at 500 gpm for one minute and 125 gpm for four minutes, a fire department could control an area of 50,000 cubic feet during the first minute and 12,500 cubic feet the remaining four. An area of 12,500 cubic feet would be approximately 25 X 50 X 10 feet. It should be obvious why a large delivery in gpm even for very short times like 20 or 30 seconds can bring almost immediate control in smaller areas.
The secret is to use the big delivery and shut off the nozzle as soon as the fire darkens. This saves water and avoids upsetting the thermal balance. A smaller line can then be used in overhaul and extinguishment of any remaining spot fires.
In order to discharge water at these high rates during an initial attack using tank water, the piping from the tank to the pump must be adequate. Discharge piping to mounted turrets, aer.ial devices or rear outlets must also be of adequate size and have a minimum of bends. The flow rates desired should be included in apparatus specifications and tested before acceptance.
The delivery of the large initial attack can be with constant-gallonage or automatic fog nozzles, especially where the fire has not vented itself through the roof and the stream can be used for a close-in attack via a window or door. For a vented fire a solid stream may be needed for reach and for penetration through the convection currents to begin cooling. Remotely controlled nozzles can be effective on elevated streams.
Maneuverability is essential in the application of the large stream to get full value of its fire killing potential. Mounted devices often lack maneuverability and then positioning becomes critical. The stream must be able to hit as much fire as possible. Preferably the stream should be rapidly moved from window to window or room to room. The nozzle cannot be stationary and achieve maximum heat absorption of the water. Direct discharge high toward the ceiling through any available openings. Elevated streams can often be placed in windows for a direct attack on the fire with a rapidly cooling fog pattern.
Several departments, realizing the mobility limitations of master stream devices, developed hand-held nozzles to make large stream attacks. The Memphis “Mankiller” was one of these early large delivery nozzles. Suburban departments like Glendale, Md., and rural departments like Muddbrook, Conn., also went to “blitz” attack lines. A lightweight device that can either be carried or used as a portable monitor was constructed by the Louisville, Ky., Fire Department. Although the hand-held master stream has the advantage of being movable to enhance fire control, it has the disadvantage of requiring considerable personnel to do this.
Wherever the potential for a fastspreading fire exists due to construction, interior finish, fire load or large open area, the capability to deliver a big stream attack is necessary. Since this attack often will only be necessary for a short time, rural departments as well as those that operate in areas protected by hydrants must strive to meet this challenge. When the need arises, we must be ready to deliver the knockout punch.
