Many have been instructed to fight a fire by pulling a certain line, taking it to the seat of the fire and applying water. In certain books you will read that a 1 1/2-inch line will put out 1,200 square feet of fire when properly applied. That may be true for a class B spill on the tarmac, but we deal in cubic feet of fire.
Some people will contend that the time span for trusses to fail (collapse) when exposed to flame impingement ranges from three to 10 minutes. That may also be true, but to me a more important fact is that you can no longer determine from the outside of a building how it was constructed because more builders are constructing a structure to mimic another type.
The following article provides basic cues to help you identify the type of construction you are facing. It will also give some strategic and tactical considerations.
The facets of buildings and their construction should always be the topic for drills for all, from the new firefighter to the most experienced chief, because every day the building industry is striving to build them cheaper and quicker.
Ordinary Construction
In many parts of the country there are stretches of buildings with parapet walls (unsupported masonry above the roof line), intricate cornices and elaborate masonry work with arches on the exterior walls, and these buildings are joined together to form rows.
Inhabitants of cities and towns 100 years ago grew tired of rebuilding their communities every time there was a fire. The old-style wood-frame row buildings contributed to the conflagrations, and people wanted an alternative. The builders gave them a structure with a row configuration. The structures had multiple wythe vertical masonry walls with horizontal wooden members (serving as floor joists) embedded in the masonry. The front and rear walls are non-bearing.
The buildings usually are 12 to 20 feet wide and can be up to 100 feet long. The structures can be three or more floors, although I have seen buildings like these 10 stories tall and 150 feet wide. The wood floors are embedded into the vertical masonry at the side walls only; the intermediate connections are often found to be cast iron columns. The elaborate front facades were the outlets for the creativity of the builders, who created intricate patterns of masonry using brick or stone, often using arches over windows and doors. The cornices (horizontal projections at the roof line) were made of metal, masonry or wood.
The roofs of these buildings are usually flat and most contain skylights and penthouses for roof access. The framing for the roofs runs front to back to provide the pitch needed for rain control. The cockloft (the area between the ceiling of the top floor and the underside of the roof) is framed similar to the floor assemblies. The common use for these structures calls for a firewall to extend up through the roofline. Builders used mansard framing or some other trick to create a more aesthetically pleasing roofline. Many end units of the row have turrets or domes, or both. It is similar to the wooden framing of townhouses today.
By design a fire can occur in one of these buildings and be severe, but the fire will be contained within the building of origin by the masonry walls that form impervious barriers. However, if there is a common roof, all of the buildings in the row are in jeopardy, but this is more of an anomaly than a standard. These buildings can contain mercantile, residential or industrial tenants or a combination of any of these known as a "taxpayer." A taxpayer has a commercial venture on the first floor and renters, or "taxpayers," on the upper floors.
A fire in one of these buildings is usually not complicated. Get a line or lines to the seat of the fire, vertically ventilate, horizontal ventilation is accomplished by clearing the glass front and back, check above and you're done - unless there is no outside basement entrance or if the fire gets into the cockloft.
The District of Columbia Fire Depart-ment lost an officer in one of these buildings in 1997. The fire occurred in a taxpayer in the early morning. The first floor housed a grocery store with apartments on the upper two stories. The owner of the building met the units and reported that no one was on the upper floors. The first-arriving engine companies made an aggressive entry with 11/2-inch handlines. The conditions on the first floor, as reported later during the investigation, were that the floor was too hot to kneel on, cans were exploding and bottles were popping and tongues of fire were intermittently occurring at the ceiling, all of this in heavy black smoke. The units attempted to leave the building when the floor failed and an officer went into the basement. For the next 14 minutes, command was unaware that he was missing. The remaining officer failed to notify command, even though members of the officer's company reported that the officer had not come out.
After command became aware of the situation, a rescue was attempted, but access to the basement couldn't be found. Remember, a builder does not have the luxury in these buildings to put a 40-square-foot opening, required for stairwells, in more than one spot. The upper apartments were the key. The wooden stairs to the upper floors will be the ceiling for the interior access to the basement below, but this knowledge was not employed on that day. The officer was found in the basement under this area. He had drowned.
Even though these buildings are referred to as "ordinary," don't be misled. In 1996, the Philadelphia Fire Department responded to a fire in such a building. Firefighters encountered fire on all three floors. They made multiple rescues and the job went well. After knockdown, units were overhauling when the building collapsed in 13 seconds. Nine firefighters rode the upper floors into the basement. Thankfully, all of the firefighters were rescued, but what had happened? At one time, there was another building beside this one, but it had been demolished. Whenever you find a break in the row or an end unit shows evidence that it had a partner at one time, be wary, as without the shared lateral support these buildings can and will fail.
A fire in the cockloft can be challenging. It requires aggressive interior operations to open the area and enough lines to quell the fire within. These buildings can be successfully handled, but you need to recognize them early and respect them at all times.
Non-Combustible
Responding units roll up to a strip mall with heavy smoke showing (thick and viscous, giving the impression of pushing out). The mall has a masonry facade with a metal mansard parapet. The first-in engine company takes a line and goes searching for the fire. The first-in truck company begins a search for victims. Without warning, the roof collapses and everyone wonders what happened.
The National Fire Academy defines non-combustible construction as "construction where the main structural components will not burn but are unprotected and susceptible to early collapse under fire conditions." Non-combustible is a misnomer when it comes to our job. It gives the impression that the structure is impervious to the effects of fire and nothing can be further from the truth. The structural components are usually some form of masonry-brick, concrete masonry units (CMUs) or concrete. The roof members are usually lightweight steel bar joists or a combination of bar joists and steel beams. The roofing material can be rolled membrane or built up tar and rock. The roof is usually a corrugated steel deck.
In steelmaking, products called fluxes are added to iron ores to remove impurities. Different fluxes are added, depending on whether the contaminant is a base or an acid. Steelmaking requires high heat, in excess of 1,500 degrees Fahrenheit. Many steel products used today are the result of alloys or the combining of chemicals to give the steel properties that help it resist corrosion or to give it more strength, especially tensile strength. The tensile strength is the steel's ability to support itself and the load on it without deflecting. Nothing can be added to the steel to make it resist the effects of heat because that would interfere with the process. So, steel products come from the manufacturing process for use with an inherent flaw against fire.
The building industry responded to the need for certain processes or uses for a building where the users did not want to lose a building if a fire of a smaller magnitude occurred. The insurance companies reacted to the use of masonry and steel by allowing the process to go forward with acceptable rates for their clients. The use of steel let even greater spans be bridged, thus permitting structures to be wider than was done previously when the use of wood for floors and roofs was practiced. It also was thought that by using steel in combination with masonry the contents were oblivious to the effects of fire for a protracted time.
The earliest fires proved this theory fallible. Buildings with steel collapsed when attacked by direct flame impingement. Sprinklers were added, but they could not stop the effect of heat on steel. Although it is true that steel won't burn, the important fact is that it will and does FAIL. Steel will start to expand or move at temperatures of 1,100F to 1,300F. This causes the connectors between the columns and beams to let go and the steel component to fail, or it pushes the masonry support walls out and the entire assembly fails and falls quickly to earth. Steel will begin to melt under temperatures as low as 2,000F. This will cause catastrophic conditions for firefighters operating under or near the failure.
So what must we do when operating at these buildings to be safe and effective? First, don't be misled by the appearances. Although you are looking at masonry and may see steel, don't take for granted that they will protect you. If you enter a building like this with heavy fire, then it is as important to get water above you on the roof members from the inside as it is to get water at the seat of the fire. The effects of the heat will make your position untenable without warning.
Determine why you must be inside the structure from the beginning. If there isn't the possibility that victims will be inside the building, then as few personnel as are needed go in to perform reconnaissance and these firefighters should be experienced and cautious.
The worst scenario is when you can't find the fire right away. It is very important to maintain accountability, knowing where your people are operating and who is in the building, and the safety position must be manned at this time with a rapid intervention team (RIT) standing by. Units in the building must report changing conditions to command, which must keep track of how long the incident has lasted. If crews have to come out to change self-contained breathing apparatus (SCBA) without finding the fire, it is usually time to regroup and think outside streams.
You can have safe operations at these buildings, but you must never underestimate the extent of the problem. You must never overestimate your resources at the scene. You must have accountability at all times. You must have safety resources manned and standing by. And, finally, don't risk firefighters by failing to pull out when it appears doubtful.
Wood Frame/Balloon
Many residents of early towns and cities lived in homes like those depicted in western movies. The buildings were constructed of wood and in row-type configurations. Wooden facades disguised the fronts and the wooden sidewalks lined the street. A fire in one of these buildings often led to a fire in the entire town.
Around the middle of the 19th century, the homebuyer was given an opportunity to live just outside of the towns and cities. This suburban setting gave the homebuyer a sense of security because the home was detached and it also gave the owner an estate feeling, as the home would be built on a small to midsize lot.
This type of house was built much in the same manner as barns. Exterior walls were built on the ground and raised into position. There are no horizontal fire stops. The roof was added and tied the four walls together. Mostly the roof was constructed as a hip-roof style (as you look at it, you see upside down Vs on each side). Dormers were added to increase the headroom in the attic.
Floor assemblies were built next and they actually are in shear load as the floor joists were nailed into the sides of the vertical studs. If the client had money and the builder was reputable, a ledger board might have been inset into the studs and the floor joists then laid on top of this assembly. Interior partitions were built last, on top of the completed floor assemblies that were nominal-sized planks laid diagonally extending to the interior edges of the vertical exterior studs. Windows, doors and stairways were framed much in the same way as they are today.
The roof and exterior wall coverings are interesting. The type of covering was dependent only on the pocketbook of the owner, the available materials and the skill of the builder. You will find this type of building with stone, masonry, stucco, wood or a combination of these materials as the veneer. Roofs are covered with terra cotta tile, slate or shingles.
This style of construction for detached dwellings continued until the end of World War II, when the demand for housing by the returning veterans made it impossible for the lumber suppliers to keep up. Also, the need for craftsmen caused a severe strain on the available workforce. The main demise of this type of home, however, resulted from the need for vertical studs 25 to 30 feet long and straight. It is also these studs that cause the fire service the most problems.
If you have buildings like this in your community, then most likely they are of balloon-frame construction. You are faced with vertical channels, the exterior stud chases that are open from the basement to the roof. This is what does you in if you don't identify it quickly or if you underestimate the speed at which a fire will communicate within this type of structure. Responders must key in on this point or they are in for a long battle. Worse, firefighters can be killed in these structures easily because of flashovers and collapses.
The worst scenario is a basement fire. In a building like this the fire is moving throughout the building solely dependent on the heat of itself - and it doesn't call time out if you are not ready.
Don't try to make a stand on the floor above while units attack the floor below. The fire has already passed you and will be moving fast. Don't fight this fire from the interior with only one or two lines and only one or two companies. You must get to the upper floors as soon as possible with enough lines and personnel to open up the exterior walls and get water into those chases.
To protect these crews you must also have enough personnel to provide a line to protect the stairwells and enough ladders and personnel to ladder the entire exterior of the building so that firefighters can get out if they need to.
Trusses: How & Why They Fail
Trusses are found in many types of structures in use today. No longer can we assume that trusses are only being used in tract housing subdivisions. You can find trusses in multistory multiple-occupancies, offices, warehouses, taxpayers and residences, including high-dollar as well as low-income houses.
Trusses have been in use for about 100 years. Some early forms of trussing can be found in heavy timber construction where cast iron tie rods were used to connect the members. As mentioned earlier, after World War II the need for housing outstripped the lumber industry's ability to supply the wood required. Also, the conventionally framed building required craftsmen to construct it.
Technology stepped in. Engineers calculated the loads delivered to the framing members and in turn designed patterns involving geometry and physics to build a wooden or steel member that would support the same load with smaller component parts. The outcome was that larger open areas could be created in a structure, as not as many internal framing supports were required and craftsmen were not needed to put the pieces together.
The use of trusses has burgeoned since then. It would be a safe bet for a firefighter to consider that any residential and most commercial buildings constructed in the last 50 years contain trussed components.
One of the first disasters involving trusses and firefighters occurred during a fire at an auto dealership in Hackensack, NJ, but this has continued through the last 20 years - in Memphis, TN (a church), Chesapeake, VA (an auto parts supplier), and outside Fort Worth, TX (another church). But even with this well-documented history and many hours of training on the subject, firefighters continue to operate in, under and around trusses, seemingly oblivious to the dangers.
Let's look at the truss itself. Wooden trusses are usually constructed of three major components: the upper member or top chord, the lower member or bottom chord, and the intermediate members or web. The size of the members is usually 2X4 or 2X6, depending on the total span to be bridged or the load anticipated to be placed on them. The components are joined together not by nails, but by lightweight metal gussets stamped to create small projecting points that penetrate the wood only about a quarter-inch.
The height of the web members is dictated by the span that is bridged and by the spacing of the trusses. When the span is established, the truss manufacturer sets up a jig to receive the wooden members needed to fabricate the truss assembly.
At the center of each truss is a gusset. The total length of the truss is factored and each side of that length is constructed from the center out to the ends. This is usually done in 10- to 12-foot increments with gussets joining each connection. This is the Achilles heel for trusses, in my opinion. At the exact point of the most load stress is the existence of the one part of the truss that will fail first. Recall that steel fails at 1,100F to 1,500F, but it won't take that much heat to cause the gusset to lose its ability to hold the wood members together when it loses its tensile strength.
The steel bar joist is constructed under the basic principles of its wooden counterpart, with a top chord, bottom chord and web members. The sizes are calculated using the same formula methods. The biggest difference is the raw materials used in the construction and that the members are welded to form the connecting joints. This type of truss is subjected to a different flaw in that when exposed to heat and or flame it will begin to expand and finally will lose its tensile strength and give up its ability to carry weight or support itself. It's the movement of this truss that usually causes it to lose its contact with the building and thereby fail before the failure of the steel itself.
Trusses are excellent in their ability to support weight when placed under the conditions of compression, but terrible when placed in tension. The time when a truss is most vulnerable to failure is when it's going up or coming down. If you have watched trusses being installed, you would see how unsteady they are before they are tied in and "racked in" by installing a floor or roof covering on them.
If you have an incident where you suspect the construction is trussed or better yet you have catalogued the building from its beginnings and know it to be trussed, then you have to take extremely measured actions. First, if the fire is suspected to be attacking the floors or roof, you can't be on or under this condition. You need to ventilate from the ends of the gable roof or non-bearing walls or, if the roof is another configuration (hip, for example), the venting needs to be accomplished without getting onto the roof. If you must be inside to conduct search and rescue, you can stay close to the bearing walls.
The key to any operation involving trusses is to respect them and understand that they will fail, it's just a question of when and where you are in relation to the failure. It's not risk vs. gain, but live firefighters vs. gain. Take time to process this information- it could save a life.
Michael L. Smith, a Firehouse® contributing editor, is deputy chief, director of safety in the District of Columbia Fire Department. He has spent 28 years in the department, mostly with truck companies. Smith's education includes degrees in fire science, construction management and labor law, and holds a journeyman carpenter certificate. He completed the public managers course at George Washington University and is a Certified Municipal Manager (CMM). He also has completed the Executive Fire Officer (EFO) program at the National Fire Academy, where he is an adjunct instructor. Smith teaches building construction and advanced strategy and tactics at the University of the District of Columbia. In addition, for over 25 years he has worked as a carpenter, foreman or superintendent on projects ranging from residential housing to high-rise office buildings and including commercial retrofits and historical restorations.
