By Randy Frassetto
Published Wednesday, February 1, 2012
| From the February 2012 Issue of FireRescue
Sometime early in a firefighter’s career—usually as part of fire school—building construction is touted to be one of the most important things firefighters should be aware of in their new trade. They learn how to date a building, predict collapse tendencies and patterns, determine fire severity from smoke factors and, as this article addresses, how to best ventilate the structure.
Buildings are broken down into five categories (Types 1–5), ranging from the stoutest of construction to that which will most likely fail rapidly when under fire conditions. Each building type has specific characteristics that ladder companies must be familiar with so that they are able to ventilate the building in the safest and most efficient way possible.
A building is best identified during preplanning, but there are distinct features that will help firefighters identify the building type as they pull up on scene. There are also several diagnostic techniques that ladder companies can use when they’re up close and personal with a building.
Note: In addition to how the building type affects fire behavior and ventilation, fire code requirements drive many building features that affect ladder company tactics. Specifically, many municipalities follow Universal Building Code and NFPA 101 as it relates to building code provisions.
Let’s now address what ladder crews should know about each building type.
Type 1: Fire-Resistive
Type 1 structures are high-rises, and they’re the stoutest of all construction types when exposed to fire. High-rises are usually defined as buildings more than 75 feet tall, with some agencies making amendments for buildings that are 35–55 feet tall.
Type 1 structures are constructed of concrete and protected steel (steel coated with a fire-resistant material, most often a concrete mixture), and are designed to hold fire for an extended amount of time in order to keep the fire at bay in the room and/or floor of origin.
As far as the typical ventilation operation of getting on the roof and cutting a hole, that’s not really an option when dealing with Type 1 construction. Even horizontal ventilation becomes challenging, as the windows are thick, tempered glass and may not be an efficient way to ventilate the structure.
Ladder companies must be aggressive in securing the stairwells for both firefighters and victims evacuating the structure. If the structure meets building code, it will be equipped with self-pressurizing stairwells and have HVAC systems that will aid in air movement. If necessary, the ladder company may need to mechanically pressurize the stairwells using a series of fans strategically placed at the base of the stairwell and every 10–12 floors depending on the effectiveness of the fans. The fire protection and fire-related systems in these buildings are overwhelming, so crews should make it a priority to locate a maintenance worker and keep them close throughout the incident.
Type 1 structures are easy to identify on height alone. It’s important for firefighters to know their city’s building codes, as this may affect which features are found inside the structures. Ladder crews should frequent Type 1 buildings in their area and be familiar with the systems that they may encounter (elevators, HVAC, fire pumps, etc). Finally, they must not forget to maintain good working relationships with the maintenance workers at these buildings.
Type 2: Non-Combustible
Type 2 construction is typically found in new buildings and remodels of commercial structures. The walls and roofs are constructed of non-combustible materials. Specifically, walls are usually reinforced masonry or tilt slab, while roofs have metal structural members and decking. The top of these roofs are often covered with lightweight concrete, foam, an insulated membrane or a combination of these materials. Because most of these buildings are newer builds, they’re usually up to code and include fire suppression systems. And because metal roofs may fail with heat—not just from direct fire—expect early collapse, especially in some of the bigger buildings that have a substantial fire load.
Firefighters should suspect Type 2 construction in newer commercial structures (both big box buildings and strip malls). A good habit to practice: sounding the walls to determine whether they’re made of a combustible material.
When on the roof, ladder crews should cut an inspection hole to identify the decking material. Once a metal roof has been confirmed, the rooftop crew should consider opening skylights or resorting to natural ventilation in the form of large roll-up doors that are often found in the rear of the big-box structures. Common ventilation tools (chainsaws and circular saws) may simply not be efficient enough for cutting large holes on the roof to support ventilation for interior crews, as a circular saw will often cut through only small areas of metal and “gum up” with insulation, or the blade will wear out quickly.
Type 3: Ordinary
Type 3 buildings can be of either new or old construction, and they have non-combustible walls and a wood roof. Older construction buildings may consist of unreinforced masonry and have a conventionally framed roof, while newer buildings will have lightweight roof systems supported by reinforced masonry or tilt slab. The most common types of roof systems in a commercial setting of Type 3 construction include parallel cord truss and panelized roof systems.
To identify if a building is of an older style, firefighters should look for clues, such as collar ties, king’s rows and arched lintels. If operating on one of these buildings, firefighters should be suspect of conventionally framed materials that may be weathered, built-up roofs or roof-on-top-of-roof systems. If it is determined that the roof is tenable, a ladder company should be able to effectively use chainsaws to ventilate the building and make the appropriate cuts based on the type of roof system.
If approaching a building with no signs of unreinforced masonry, firefighters should sound the walls to determine wall type before going to the roof. Once on top, they should be able to identify the roof system and make an aggressive ventilation operation using saws.
Newer construction uses truss systems in both panelized and parallel cord truss roof types that are known to fail rapidly and unexpectedly with direct fire impingement. As such, ladder companies should sacrifice some property for time and make vent holes over smoke, not fire.
Whether conventional or lightweight, vertical ventilation on Type 3 construction is feasible and can be very effective. But safety is paramount; crews should always remain on ledger walls or structural members. Sounding and diagnostic cuts are effective ways to not only ensure the location of the structural members but also to allow the ventilation crew to monitor the roof conditions and act accordingly.
Type 4: Heavy Timber
Type 4 construction is found in older buildings and utilizes large dimensional lumber for structural members and interior elements. These buildings hold up well under fire conditions, but it’s critical that firefighters not feel a false sense of security, as these buildings are often poorly maintained, or have termites and/or weathering issues that can contribute to an earlier-than-expected collapse.
Firefighters can identify these buildings by the large lumber used for walls and the long distance of roof spans. These buildings were most commonly built before 1960, when bolts and metal plates were used as connectors.
Vertical ventilation may be achieved on these buildings, but sawyers may encounter thicker-than-expected decking that may make for a longer completion of a ventilation hole.
Type 5: Wood-Framed
Type 5 construction is found in many modern homes. The walls and roofs are made of combustible materials—most commonly wood. If the walls are wood-framed, the roof usually is as well. Rooftops are ceramic tile or asphalt shingles placed over lightweight trusses and OSB. Both UL and NIST studies have found that lightweight construction will fail within minutes of direct fire impingement.
Firefighters should sound the walls prior to going to the rooftop. Whether operating on tile or asphalt rooftops, alternatives to rooftop ventilation should be considered if there is heavy attic involvement. If fire is isolated to a room, flashover (not collapse) is the main concern, and aggressive ventilation is beneficial. Because the roofs are made of wood, ventilation can occur through the asphalt shingles, but tiles should be removed first if encountered. Positive-pressure attack is another tool that may prove beneficial for Type 5 construction.
Building construction types are truly the building blocks of how we operate on the fireground. By breaking structures into the five different building types, we can see the similarities and differences among them, and which factors influence how we ventilate different structures.
Also, one of the biggest hurdles to combat on the fireground is communication. If your ladder company can’t operate on the roof, the reason why should be immediately communicated to the rest of the fireground. The ability to ventilate (or not ventilate) a structure often drives the outcome of the fire attack. If ladder companies are unable to operate on top of the fire building due to collapse potential or inability to ventilate, then the incident commander will need to determine if interior crews should be operating inside the building at all.
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