Balloon frame: This structure incorporates wall studs that run continually from the foundation all the way up to the eaves line, with no inherent fire stopping between floors.
Platform frame: This type is constructed using a framing system which all studs terminate at onestory in height and the floors provide some sort of fire-stopping.
Type V Inherent Hazards - As these structures are all wood, there is no consideration made to the lower floors to help support the additional load of the upper floors. Two-by-four studs may in fact be holding up an entire upper floor, with no built-in compensation supports to consider. Secondly, many of these structures have a veneer wall, made of decorative masonry materials, to accent the front side of the building (see Photo 5).
These walls are attached to the wood wall, placing an eccentric load on the wall that it is not designed to handle. Lightweight construction components, such as trusses, truss joist I-beams (TJIs) and Oriented Strand Board (OSB) can be found in all types of construction, but are much more prevalent in Type V buildings. Furthermore, buildings are being built with larger square footage, but are being constructed with half of the materials that were used in the past, creating a structure that will collapse much faster than earlier construction methods.
After responding to the collapse, identifying the type of collapse that occurred will be vital. Knowing the type of collapse will help identify the type of voids created, that may provide some safe havens for victims to be trapped in. It will also help identify the shoring that will have to be incorporated prior to the rescuers making entry into the debris pile. It will also allow the incident commander to evaluate the scene to determine the safest areas for operations, staging, and logistical needs of the incident.
Lean-to Floor Collapse: This collapse occurs when the roof or floor supports fail on one side of the structure, and the opposite side of the floor is still connected to the wall. It results in a void space that is close to the remaining wall (see Photo 6).
V-shape Floor Collapse: This collapse occurs when lower walls or floor joists fail, due to heavy loads located in the center of the floor. It results in two voids, one near each exterior wall (see Photo 7).
Pancake Floor Collapse: Destruction of the load bearing walls will cause the floor supports to fail, dropping the floors and the roof on top of each other. Voids will be created between the floors, where there is debris allowing for spacing between floors (see Photo 8).
Cantilever Floor Collapse: This collapse occurs when one or more walls have failed, and the other end of the floor is still attached to the other bearing wall. Voids will be sporadic throughout the debris. This is the most dangerous type of collapse to operate in, and adequate shoring must be in place before operations can commence (see Photo 9).
A-frame (Tent) Floor Collapse: This collapse occurs when the flooring separates from the exterior bearing walls, but still is supported by one or more interior walls or partitions. Voids are created near the center of the structure.
90-degree (Full Wall) Collapse: In this collapse, the entire wall falls out as one unit, falling outward the full height of the wall. Masonry walls collapse more commonly in this fashion, but Type V structures with veneer walls can fall victim to this collapse as well.
Inward-Outward Wall Collapse: This collapse occurs when the wall literally breaks in two, with the bottom section of the wall falling outward, and the top floors falling inward. Braced frame buildings are known to fail in this fashion. This type of collapse occurs more commonly in wood frame buildings, many times without warning.
Curtian Fall Wall Collapse: These collapses occur when a masonry wall falls almost straight downward, resulting in a large rubble pile close to the original structure. This is often associated with brick veneer walls.
Lean Over Collapse: Common in type V structures, this collapse occurs when the building shifts at the upper floor area, which results in the structure leaning onto adjacent buildings or totally collapsing sideways.