Building construction

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 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,orthe blade will wear out quickly.

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 panelised 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 panelised 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 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 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.