By John Shafer
When firefighters think of the word “recipe,” most likely, an image of the firehouse chef whipping up some great food comes to mind, not their next fire. However, there is a grim recipe that has been in the making for some time that could lead to unnecessary injury and death if firefighters are not aware of the changes in the buildings to which they respond.
This article presents a brief overview of the ingredients of this recipe and how the building affects fires that occur inside. To understand how this recipe has evolved, we look to history.
Many things and events have changed the structures of today; however, probably the greatest catalyst was the energy crisis of the 1970s. Overnight, Americans became environmentally conscious of the amount of energy they used and looked for ways to reduce not only energy consumption but also ways to change the buildings to make them more energy efficient. Government initiatives and code requirements have taken many different paths, but in the end it was all about saving energy.
In addition to lowering energy bills, energy codes can reduce load growth and the need for new energy-generation capacity while limiting air pollution and greenhouse gas emissions. Recognizing these benefits, a majority of states have adopted some form of building energy codes for residential and commercial construction. Although this event was the most significant for creating the energy-efficient component of this recipe, there is much more in this deadly environment. This recipe of modern buildings can be broken into two major categories–the building itself and its design, method of construction, and the fuel packages inside.
The best way to describe the difference between modern buildings and their predecessors is that the modern structures are built with materials that have less mass and span greater distances. This allows for large, open floor plans that do not have compartmentation. The emphasis on energy efficiency then creates a super-insulated building envelope. On top of all these changes, there are also alternative power sources, such as solar and wind, that add new hazards for firefighters.
The variety of elements firefighters could encounter is too vast for one commentary. This article presents an overview of these topics to peak your interest so you will further investigate these changes. There is so much more to learn about building construction than the five types of construction covered in National Fire Protection Association 220, Standard Types of Building Construction.
Structural elements have evolved from large heavy timber columns and beams to low-mass engineered members made of sawdust and glue. Lightweight truss construction is nothing new to most firefighters and has been around for as long as I can remember. However, most firefighters focus only on the gusset plates and glued connections. The real danger is that engineered products no longer have mass compared to legacy elements and were designed to span the great distances with the least amount of material. The gusset plates fail early in the fire because the material is consumed so quickly. In recent Underwriters Laboratories studies, they examined loss mass engineered wood I-beams and found that they could fail in as little time as 3 minutes, 28 seconds compared to 11 minutes, 9 seconds that it took a solid wooden floor beam.1 If wooden I-joists were not enough, we now have I-stairs instead of those of crafted, solid wood. These I-stairs may have already failed on arrival or may fail as you try to ascend or descend. Since the failure time is shorter in modern construction, the initial arriving fire crews could be in grave danger of a structural collapse when entering the structure. Moreover, instead of losing just one support member, a catastrophic failure of the whole structural system could occur.
Open Floor Plan
Today’s larger home with open floor plans is the next deadly ingredient. This ingredient is a result of low-mass engineered products. Because these products are designed to span greater distances through geometry, they make possible one of the most common attributes of the modern structure, the open floor plan with high valuated ceilings. These changes have created a multitude of potential problems for firefighters who treat fires in modern structures as they did fires in the structures of yester years. These larger buildings affect fires in several ways: They allow a larger volume of products of combustion to be inside the structure. Larger volumes of smoke can present a greater chance of a significant rapid fire event when all three components of the fire triangle are in the right conditions. The larger amount of smoke makes uncoordinated ventilation less forgiving and prone to sudden flashover. Other common traps firefighters fall into with open concept floor plans and higher ceilings is that they go much deeper into the structure since it is usually all open. They then go under large volumes of rich overhead smoke and do not feel the radiant heat as in the past with eight-foot ceilings.
As mentioned before, the changes that started in the energy crisis of the 1970s have led to many of the practices that make the structure envelope air tight. Modern energy-efficient structures such as structural insulated panels (SIP) and insulated concrete forms (ICF) are two types of modern structures that present challenges when compared to the typical type V wood-frame structure.
Both of these types of panels are load bearing and not a normal point-to-point load transmission of structural hierarchy. SIPs are composite structural panels with an insulating core of rigid foam –usually polystyrene or polyurethane –and structural facings, most commonly of 7/16” thick oriented strand board (OSB). A SIP home can have up to 90 percent less air leakage and save 40 percent energy than traditional stick frame structures.2
ICF is a system of plastic foam formwork for reinforced concrete that stays in place as a permanent interior and exterior substrate for walls, floors, and roofs. The forms are interlocking modular units that are dry-stacked (without mortar) and filled with concrete. The forms lock together somewhat and serve to create a form for the structural walls or floors of a building. There are many other types of energy-efficient structural components. However, almost every home built in the past five to 10 years have been wrapped with house wraps that can be made of a variety of materials; they can work as water vapor and air barriers that make homes more air tight.
Windows play a major role in making buildings energy efficient. In the past, windows were usually the first thing to fail in a fire. We would arrive and fire was showing from the windows. However, today’s thermal pane windows can have three layers and sometimes may be the last part of the structure to fail, eventually making the fire ventilation controlled. The fire consumed the available air and the windows stayed intact, leading us to think that nothing is showing when in reality the structure is full of fuel-rich smoke that only needs air to flash over.
Increased insulation is by far the greatest factor in making structures airtight and energy efficient Insulation is nothing new and was in structures in the past; however, the major difference is that more insulation and foam plastics are used today. There is a major push to have less wood and more insulation in modern residential structures because several types of insulation can be used to increase the R value (how well building insulation materials can resist heat). Rigid foam is one way home builders can increase the R value of the home and not change methods of construction. Also, many new state and local codes are allowing more rigid foam to meet national energy initiatives, such as Environmental Protection Agency Energy Star requirements. This increase is great to the homeowner’s pocketbook all year round, but it has added a way more flammable fuel load to the building envelope than ever before, which can lead to shorter flashover times and buildings burning down faster.
Alternate renewable energy sources such as solar and wind present additional hazards, such as shock and slip trip that can be found in today’s modern energy-conscious environment. Most fire departments are not properly trained or prepared to deal with these hazards. Solar panels can create roof-access issues if your tactical plan calls for vertical ventilation. Preplanning these alternate energy sources is essential.
The biggest and most deadly ingredient in this fatal recipe comes from what is within the building. Household contents have evolved from natural products such as cotton and wood to synthetic materials. Synthetic materials such as polyurethane foam have replaced cotton as the padding in upholstered furniture. However, the added flammable fuel is not just in the upholstered furniture. Look around your home or the home of your next medical call. You will see everything from plastic electronics to the foam padding we walk on. They will add massive amounts of fuel-rich smoke to the building that will need only air to burn completely.
In view of these changes, it is paramount that the firefighter be a constant student of the built environment and the changes it is undergoing almost continuously.
John Shafer is a 22-year veteran of the fire service and a captain and the training officer for the Greencastle (IN) Fire Department. He instructs in building construction, fireground search, and command management. He is a technical panel member for Underwriters Laboratories UL, Chicago, for current fire service testing. He is also the Indiana Homeland Security District 7 fire training coordinator. He has served as an adviser to the Indiana Department of Homeland Security for the state’s development of its Fire Training System and assisted with the development of the District 7 Training Council and the District 7 Response Task Force. He manages the social networking site Green Building Construction for the Fire Service on Facebook. He is the owner/writer for Green Maltese LLC and co-owner of Fire Training Toolbox.com.