New Types of Construction Require Rapid Opening Up, Larger Streams
Whether buildings are being constructed better today is debatable. The fact that today’s structures are being built to collapse on fire fighters and speed the spread of hidden fire is not debatable.
Time is one of the most valuable factors we have going for us on the fireground and the architects are taking that away from us. In more and more buildings, it is vital to the safety of fire fighters that the first line provide a large enough rate of water application to darken down the fire. In such buildings, there isn’t time to consider bringing in additional lines or to think of water damage. Unless the fire is quickly darkened down, collapse—partial or total—will occur.
In other modern buildings, aesthetic features that delight the hearts of architects foster the rapid spread of hidden fire. While you are making progress in subduing flame, the concealed fire may be destroying the building around you. Unless you open up immediately at the slightest suspicion of hidden fire, you will lose the building.
Light wood trusses
Because of its increasing use, you might say that the 2 X 4 wood truss is here to stay—at least until there is a fire in the building. Today, 2 X 4s are more likely 1 1/2 X 3 1/2 inches, which means that there is not as much wood to burn as there used to be before the loadcarrying capacity of a 2 X 4 fails. Unfortunately, the failure of one member of a truss leads to the rapid failure of the entire truss.
These 2 X 4 trusses contrast with the older wood trusses whose least dimension is 4 inches. When trusses are made of at least 4 X 4 or 4 X 6 timbers, there is considerably more wood that can, burn—and that translates into time— before failure of the truss occurs.
Furthermore, the larger wood truss members are held together with bolts, which add to truss stability. The modern 2 X 4 truss members are connected by escutcheon plates. These thin, steel plates are stamped to create a number of short prongs which enter the wood truss members when the plate is hammered into place. It is a matter of conjecture whether the plates could collect and transmit enough heat to the prongs so that the wood around the prongs is charred enough to end the friction that holds them into the wood, causing failure of the truss before the wood burns to the point of failure.
However, we do know that under severe fire conditions, 2 X 4 wood trusses fail rapidly. There is little time to open up and get a hose stream of adequate volume into the area to knock down fire before collapse occurs.
Flat wood trusses
These light wood trusses made their appearance not too long ago as triangular trusses under roofs of condominiums or town houses. Most recently, 2 X 4 trusses have been given another configuration. They are being constructed flat to replace floor beams and rafters under flat roofs. As floor beams, these trusses can span greater distances than can be spanned with available lengths of solid wood beams, and they do it economically.
They also do this at the expense of an increased hazard of faster fire spread and speedier collapse. In a fire, the economy of the flat wooden truss can be a myth, but architects, like most people, don’t see the possibility of a fire occurring.
These flat wood trusses are being used not only in wood frame buildings, but also in buildings with masonry walls. When they are installed to sustain floors, the only chance you have to learn of their presence is during construction of the building. Afterward, these trusses are concealed by floors and ceilings.
The result is that there is what amounts to a cockloft, or concealed open space, under every floor. Just as in true cocklofts under roofs, fire can spread rapidly from one end of the area to the other. There are no solid wood beams to slow down fire spread by making the flames work their way from one channel between beams to the next. Adding speed to the fire development is the fact that the lumber is in small dimensions so that it burns more readily than do 2 X 8 and 2 X 10 wood beams.
Whether there are fire stops in this type of construction depends on the applicable fire code and how well it is enforced. In some areas, there may be no fire code and the fire stops may be the end walls of a condominium. In any event, once fire gets into the area between the ceiling and floor above, you have to pull a large area of ceiling immediately without worrying about doing excessive structural damage because it’s your last chance to knock down fire feeding on the flat wood trusses before the fire does a tremendous amount of structural damage. Furthermore, the size stream you use should be adequate for a fast knockdown.
Triangular wood trusses
When triangular 2 X 4 wood trusses are used, they usually support a roof with a low pitch—3 to 5 inches—and create a cockloft that is too shallow to work in but high enough to nurture the development of a large volume of fire in a brief time. The plywood roof deck is frequently only half an inch thick and in some cases only 3/8 inch.
The moral is that you had better live the good life because such a roof deck on light wood trusses isn’t going to hold up long once it is subjected to a heavy volume of fire. There is a lot of lumber to burn in the cockloft and that lumber is going to burn rapidly to the point of failure. Then roof collapse occurs.
Unless the roof is opened up immediately, fire that enters the cockloft is going to spread throughout this area and drop down to spaces throughout the floor below, such as apartment rooms in a condominium or stores in a mercantile building. However, this is where light wood truss construction foils your desired strategy. Such roofs are burning rapidly to failure throughout this nation and time is against you.
Consider roof condition
The first-in officer has to consider the evident volume of fire and the roof construction, and then he has to ask himself, “Is there time to send men to the roof to ventilate, or is the roof already unsafe?” The brief time it takes fire under these roofs to approach collapse starts before you receive the alarm and roof integrity may have ended before the arrival of the first company.
It’s a matter of experienced judgment, but when a sizable volume of fire exists under these lightly constructed roofs, it is already too late to send men to the roof. In such cases, the good news is that the fire will soon vent itself.
In even some of the most expensive condominiums and multiple occupancy mercantile buildings with light wood trusses in the cockloft, there are either no fire walls or the fire walls have openings around conduits which allow fire to pass through them. Sometimes what starts out as a fire wall gets discouraged and stops at the bottom cords of the trusses, so there is still a wide open space for fire to run the length of the cockloft. In other cases, a purported fire wall terminates under the wood roof deck, which allows flames consuming the roof deck to pass to the other side of the wall. A true fire wall, by definition, must pass through a combustible roof deck and terminate in a parapet.
Because of the fast-burning cockloft construction, standard operating procedures for this type of construction should call for an initial line of at least 250 gpm into a burning cockloft from below (after pulling ceiling) to get the stream penetration and heat absorption you may need. If the fire is not that extensive, the nozzleman shuts down that much sooner.
If the fire has not entered the cockloft upon arrival of the first company, the officer should recognize when that possibility is imminent and make his initial attack with a line that has a water application rate large enough to assure immediate knockdown of the fire. He must keep that fire out of the cockloft. That means the first stream may have to have 250-gpm capability when a 100gpm stream would be a reasonable choice in a better constructed building. In some cases, the fire condition might call for a master stream as the first stream.
Architects have designed these buildings to burn and collapse, so water damage has to be secondary to darkening down the fire before you have more fire than you want to see. The idea is to keep fire fighters from being killed and to prevent a total loss. To minimize water damage under these conditions, all you have to do is to train your nozzlemen to shut down the moment they have darkened down the fire.
Modern mansard roofs
Mansard roofs were quite common in the Victorian age. They offer some problems when we have fires in these old buildings, but that doesn’t satisfy today’s architects. Instead of using the solid lumber of yesterday, you find 2 X 4 wood trusses supporting mansard roofs of fast food stands and multiple occupancy mercantile buildings. There is a vast amount of light lumber to burn under these roofs.
While discussing modern mansard roofs with one of my classes in building construction one time, 1 showed some slides of a McDonald’s stand under construction and warned that if a serious fire ever developed in this structure, they should expect early roof collapse. About a year later, one of the fire fighter students informed me that the roof of that stand did exactly that.
Sometimes to pretty up an old building, sometimes to lend an aesthetic touch to a new building, phony mansard roofs—or eyebrows—are constructed. They are veritable lumberyards forming a collar around the uppermost portion of the building. The shingled exterior of these vertical roof adjuncts are framed out from the building with—you guessed it——2 X 4s in great quantity.
Concealed spaces for fire
You will find these phony mansard effects on shopping malls, condominiums, office buildings—you name it, they’re there. They’re there to foster fire spread—undetected if you are not aware of the hazard. Sealed off at the bottom, usually with plywood, these eyebrows form a concealed space in which fire can propagate from one end of a building to another.
Once an interior fire gets into the roof area and extends into one of these eyebrows, it is off and running. You didn’t build this concealed space monstrosity, so you should have no compunction about ripping it apart to get to the fire. At the slightest suspicion of fire, you should open up a phony mansard roof because otherwise the building may suffer excessive fire damage.
Sometimes buildings with eyebrows have brick veneer exterior walls, but the brick may extend only up to the bottom of the mansard roof effect. What you have is a wood frame building inside the brick veneer, so don’t let the veneer lull you into security.
Modular steel buildings
There is an increasingly popular type of construction that is regarded by the uninitiated as “noncombustible” or “fireproof because it consists of modular steel units for the frame, siding and roof deck. Buildings of this type are being erected in many urban and rural areas for a variety of occupancies, ranging from offices to machine shops and warehouses. I have seen several such buildings used for the storage of plywood, millwork and boards in lumberyards—a little like arranging kindling and logs in a fireplace.
The interesting thing about these “fireproof’ buildings is that although the steel construction will not burn, the contents will, and the building may very shortly collapse.
If you have a large volume of fire on arrival, you had better put the largest stream you can into such a building right away because that is your one and only chance to get control of the fire and save the building. The stream has to have a rate of flow that is large enough to immediately reduce the intensity of the heat.
Master streams needed
A large volume of fire means that structural steel collapse is an imminent threat. Therefore, you can’t put men inside while the possibility of a fatal collapse exists, and the only way you can put water where it will do some good is by using heavy streams—hopefully a deluge gun operated from its mount on the apparatus or quickly set up on the ground. If your first-in engine company does not have this capability, then that company should operate at least a 250 to 300-gpm hand line.
Before such “fireproof’ steel buildings are erected, there are two things that can be done to improve the integrity of these structures under fire conditions. First, in the absence of a code requirement, the fire chief can convince the owner of the value of installing a sprinkler system during the construction of his building. Secondly, if this approach is unsuccessful, the chief can urge that at least plastic skylights should be installed in the roof. Domed skylights are available for built-up roofs on steel decks, and if the building has a simple corrugated steel roof, modular corrugated plastic sheets can be installed in the roof.
The advantage of a sprinkler system is obvious. The plastic in skylight or sheet form will at least provide ventilation by melting at relatively low temperatures right over the fire. A roof that is too treacherous to ventilate mechanically because of the volume of fire below might be vented by the melting of the plastic skylights before the first engine company arrives.
Steel with wood fuel
We are all familiar with the hazards of unprotected steel in ordinary construction buildings that fails when the contents burn and generate sufficient heat. These older buildings have masonry walls and usually have wood beams with wood floors on the steel girders. Newer buildings have steel beams with concrete floors poured on steel decking.
Now architects are giving us combination steel and wood frame buildings so that if the contents fire is not hot enough to collapse the steel, the building’s wood framing will supply the additional fire heat needed to ensure steel failure. Instead of the steel framing being supported by masonry walls and columns, the steel girders are supported by small diameter circular columns. Exterior walls are made of 2 X 4 lumber—just as in a strictly wood frame building. The roof is supported by 2 X 4 flat wood trusses to obtain longer spans and limit the number of columns needed inside the building, and the interior walls may also be made of 2 X 4s.
The result is that the unprotected steel is nested in kindling that will speed its failure and the collapse of a portion of the building when a serious fire occurs.
Steel is concealed
It is important to realize that all this steel framing will be covered when the building, usually for stores or offices, is completed, and your only opportunity to know of its existence is by observation during the construction stage. This knowledge should impel that first-in officer to use a large enough initial attack stream to darken down the fire before the steel is endangered and to consider the possibility of collapse before he takes his company into the building.
Steeples, masonry or wood, have always been a hazard at church fires, and now modern construction is expanding the problem. Some of the newer church steeples have a steel frame covered with wood siding that will help provide the fuel to collapse the steel.
For many years, steel girders have been used in both new and remodeled wood frame buildings to span openings in walls where wood beams would be inadequate because of the width of the opening or the weight of upper floors— or both. Although they are a small part of the wood frame building, they present the same hazards in the area where they are used that were discussed in the previous paragraphs.
About the only thing you can be certain of as new construction met hods and materials are adopted is that the problems for the fire service will not diminish. It is up to the fire service to take a tough stance and use the techniques that will save lives and buildings.
If buildings are going to continue to be built the way they are now, then larger streams and rapid opening up of concealed spaces must be the answer of the fire service.
