BY JAKE RIXNER
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Very few fire departments have the volume of large fires to become proficient at using aerial master streams. Far too often, you can open a trade journal and see the image of a ladder pipe or other aerial device such as a platform placed high above the fire, directing its stream onto a perfectly good roof (see photo 1). Adding insult to injury, a fog nozzle is often used when the reach and penetration of a solid stream are needed.
To understand the proper placement of aerial master streams, you need to understand basic fire behavior, the size and extent of the fire, building construction, the occupancy, fuel load, and the incident commander’s strategy for the fire. Know-ing how to use an aerial master stream as part of an offensive attack (see photo 2) as opposed to a defensive “surround and drown” job when the building is being written off is also important.
Knowledge of fire behavior can help the aerial operator understand and predict where the fire is going, which can enable him to make an educated guess where to position his aerial (see photo 3). The idea is to position ahead of the fire and protect unburned property. One concept some firefighters still do not understand well is pyrolysis. For solid fuels to burn, they must be raised to their ignition temperatures. As they approach their ignition temperatures, they begin to off-gas, or give off the actual vapors, which will burn. To achieve knockdown on these large fires, you must deliver copious amounts of water onto the burning solids to cool them and stop the off-gas process. This temperature reduction requires the water to reach the burning material in sufficient quantities to reduce the temperature of the solid material to below its ignition temperature. At large-area fires, thermal dynamics preclude the use of a fog stream for this task. While it is true that more surface area of the water is exposed with a fog stream, the tremendous thermal energy of large fires evaporates the fog stream before it reaches the burning material, and the fire continues to burn.
An important point that incident commanders must keep in mind is that the sky doesn’t burn (see photo 4)! When the fire finally vents from the roof, it’s actually a good thing, in most cases. The heat and smoke are no longer confined and trapped within the structure. Far too often, fire erupting through the roof is met with fire streams played into our naturally made ventilation opening. When this happens, it is much better to position your aerial streams at window openings on the lowest floor involved in fire and begin to extinguish the fire floor by floor as you work your way up.
The size and extent of the fire play important roles in how to position the aerial device. A large building fully involved on arrival requires a position outside of the collapse zone. The corners of such a building are ideal positions and allow for exposure protection on two sides of the fire. Remember, at a fully involved building fire, you cannot bring back destroyed property but you can keep the fire from extending to neighboring structures. While many refer to these jobs as “surround and drown,” keeping the exposure building wet should be the number one concern.
At some fires, you can use the elevated master stream on arrival to knock down the bulk of the fire while you position handlines to finish the job once you shut down the big guns. This past winter, my company was first in on a three-story, “U”-shaped apartment building with fire on all three floors in the bottom of the “U” (the “throat”). We took a position with the turntable in line with the courtyard. The operator extended the aerial horizontally into the courtyard and attacked the fire with the prepiped ladder nozzle through the many large window openings in the 1910-era apartment house. He started at the ground level and slowly raised the ladder and the stream as the fire darkened down. On reaching the roofline, he shut down the ladder pipe, and the eager ground troops attacked the remaining fire with handlines. This is a relatively safe practice with a platform or aerial ladder with a prepiped waterway; however, it is not recommended for a clamp-on portable ladder pipe. Note: Before operating outside master streams into an involved structure, the IC must be sure that all occupants and firefighting personnel are out of the structure.
THE ROLE CONSTRUCTION PLAYS
Construction, occupancy, and fuel load all play a large role in positioning for fire attack. Occupancy will often indicate the type and amount of fuel within the structure. Let’s look at each type of construction.
Type I Fire Resistive: protected steel or masonry such as reinforced concrete. The concern with these buildings is the occupancy or, more important, what’s inside the structure. The contents of the building are the only things that will present a fire problem. Collapse is of little concern unless there is an explosion.
Type II Noncombustible: building components made up of steel and concrete. The steel is often lightweight bar joists and unprotected. These buildings are in danger of collapse during heavy fire conditions, so keep this in mind during aerial positioning. This construction is often found in strip shopping centers and office buildings. Position aerials to cut off the spread of fire and to cool the steel to prevent collapse. Platform devices that can be positioned at sidewalk level are very effective at these buildings.
Type III Ordinary: structures built since the late 1800s consisting of masonry load bearing walls with wooden floor and roof systems. The main fire problem in ordinary construction is concealed spaces. Many early ones were built with 12-foot ceilings for natural light to enter and to keep the heat of the summer at bay. In many, the ceilings have been lowered, creating a void space through which fire can travel with amazing speed. Fully involved fires in these buildings require you to play the aerial stream against the ceiling to knock down the fire and puncture the wallboard, to get water into the concealed space to extinguish the fire.
Type IV Heavy Timber: also called mill construction, masonry walls with wooden floor and roof systems of large-dimension lumber. These buildings are most often churches today. Large fires in these buildings produce tremendous amounts of radiant heat. Exposure protection is critical at these fires, which can be of long duration (three to four hours is not uncommon). Aerial positioning must take into account the rapid spread and high heat produced by fires in this type of structure.
Type V Wood Frame: built of wood frame, older buildings are balloon frame, causing basement fires to travel unimpeded to the attic. As wood ages, it dries naturally. The aerial operator can be confronted with a fully involved wood frame structure at any time. Once again exposure protection and proper stream application will help quell the Type V fire in short order.
Occupancy is also important when considering placement at large fires. Buildings containing businesses such as paper recycling, rag storage, and other products—which absorb water—are dangerous during large fires. The building contents can absorb tons of water and add to the stress of a fire building. A two-inch tip on a ladder pipe flows 1,000 gpm; that’s equal to four tons per minute.
Another way to think of the stress the aerial stream is placing on the structure is to think of four tons a minute as one 1969 Cadillac being pumped into the building every minute. Pretty soon you understand that this building wasn’t meant to be a Cadillac warehouse.
Be very concerned if you don’t see much runoff from the heavy-duty streams. It is an indication that the building may be under stress and may collapse. Aerial streams will be operated during low-visibility conditions. The sound the stream makes when go-ing through a window opening is different from that of striking a wall.
During a fire, conditions will change, and the aerial operator may be temporarily blinded by smoke. He must be careful to play the stream into the building’s opening and not against the wall, where it can wash out mortar joints and cause the wall to collapse.
Consider fuel loads based on occupancy. A masonry supply house will present different challenges than a fuel oil dealer.
Remember, don’t put an aerial device any higher than necessary to knock down the fire or wet the exposed buildings. Deploy fog nozzles for exposure protection, not for fire attack where reach and penetration are needed. Use solid stream nozzles for big fires, and place them where they can affect the fire. The aerial device operator has the opportunity that few firefighters will ever have at large fires: He can place his apparatus in a tactical position where it can do the most good, in each situation.
Which of these two aerial streams appears to be more effective? (Photos by author.)
Jake Rixner is a 24-year veteran and a company officer with the Richmond (VA) Fire Department and a former member of the District of Columbia Fire Department. He is an adjunct instructor for the Commonwealth of Virginia and an active volunteer with Kentland 33 in Prince George’s County, Maryland. He has a degree in fire science and has presented at the Fire Department Instructors Conference.