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When operating in an offensive mode, a buildup of water within a building requires that immediate action be taken to alleviate these conditions. The remedy may be as simple as moving fire debris that is restricting runoff. Realize that at the same time that this additional weight is being introduced into the fire building, the structure is being weakened by the fire.
Water not coming out of a building as fast as it is going in. Defensive attacks are handled by master streams from the exterior. These devices deliver large quantities of water to control the fire. This effort places tons of water per minute into the fire building. The incident commander must monitor the amount of water going into a building in relation to the amount of runoff coming from the building. If water is being retained within the structure, then the building must support more weight. A point will be reached when the weight of the firefighting efforts place such a strain on the building that collapse will occur.
Water runoff from between bricks. The water being used to attack a fire can present a problem if the water runoff washes out mortar joints. The water flowing through the wall indicates a weak point in the wall. If this is allowed to continue, additional mortar joints will be destroyed along with the supporting strength of the wall.
Bales of absorbent material in a building. Another way that water is retained in a building is through absorption. The building will absorb some water. A danger exists if the building contains stock or material that can absorb large quantities of water. This is especially true with bales of absorbent material. Through absorption of water their weight can drastically increase placing extremely high loads on supporting members.
Another serious problem with absorbent bales is that they can expand and push out load bearing walls or supporting columns. Bales piled one upon another when expanding can shift. These piles become unstable and if they fall create a tremendous impact load to the floor of the building. They have seriously injured and killed firefighters in the past.
Large machinery or heavy contents in a building. The building contents or live load can impact upon the building's stability. Large machinery or heavy stock must be considered. Industrial buildings can contain many materials that will place tremendous loads on a building.
Excessive or unusual roof loads. Roof loads must be monitored during a building fire. Excessive or unusual roof loads can cause early roof failure. Large roof air conditioning units, water tanks, billboards and signs can place a heavy dead load on a building. It should be determined if their support is dependent upon the roof or entirely on the bearing walls.
Trucks and other vehicles that have outlived their useful life are sometimes painted and placed on the roof of a building for advertising purposes. This practice can prove dangerous to firefighters fighting a fire below.
Live Loads, Dead Loads, Eccentric Loads & Impact Loads
A concern that firefighters should be aware of is how different loads affect a building. The live load can constantly change. This includes furniture, clothing and food in a dwelling; the stock or merchandise in a business establishment. Firefighting can introduce many live loads into and upon a building.
Dead load is the weight of the building components themselves. It includes the masonry, lumber, light fixtures, piping, molding, windows, etc. When added together, these items contribute to the overall total weight or dead load.
An eccentric load acts like a downward thrust on a wall. A wall sign places a downward weight on the wall it is attached to. To compensate for the eccentric load, this weight must be offset. The weight can be shifted to interior structural members through cables or additional supports.
A marquee consists of beams cantilevered through the front wall. It may receive additional support by wires or rods attached to the front wall. Like the wall sign, the marquee places an eccentric load on the wall. Should fire attack and weaken the connection points supporting an eccentric load, collapse can occur.
The impact load can be a critical factor in a building's stability during firefighting operations. An impact load is a weight forced upon a building. It can occur by a main ladder being dropped upon a cornice or roof, a firefighter chopping with an axe to open a roof or floor, or a firefighter jumping onto a roof surface from an adjoining roof or ladder.