Fire Prevention & Protection, Firefighting

Reading a Building: Construction Size-Up

Think about this question for a moment: What fire service task is responsible for the major portion of the annual loss of more than 100 firefighters? Other than heart problems and cancer, one of the leading causes of firefighter deaths and injuries in the United States is building collapse.

Without a doubt, safe, timely, and effective fireground operations are based on your knowledge of building construction and your ability to use that knowledge. Challenge yourself to visually and mentally undress a building, looking past the exterior and evaluating the interior of the structure. As an example, is there a difference between truss construction of the 1930s and 2004? You bet! The differences are a lack of fireground time and potential early structural collapse with 2004 truss construction. So take the opportunity to size up the building you are about to commit to, as every building tells a story.

Our size-up will consist of seven items as follows:

  • Construction
  • Age
  • Method
  • Style
  • Roof
  • Access and Egress
  • Name and Utilities

For size-up purposes, construction is defined as either conventional or lightweight.

Conventional construction (2X6-inch or larger) derives its strength from the size of its members, and generally employs independent members. For example, in a typical residence, the ceiling joists are not an integral part of the roof rafters. The advantages of conventional construction as compared to lightweight construction are enhanced fireground time, partitioning of fire, and potential partial collapse. Partial collapse can often be observed when fire is in a conventionally constructed attic area and the roof rafters and roofing material collapse on top of ceiling joists without causing a total collapse onto personnel below. This condition can allow personnel to escape the structure in a timely manner. A quick item of note: if personnel are suddenly caught in a collapse, safe areas to consider are doorways and hallways. Partitioning of fire has the ability to limit the extension of fire. As an example, assume a two-story residence uses 2X6-inch joists between the first and second floor, and the joists run in an east/west direction. If fire extends from the first floor to the aforementioned joists, the fire will easily extend east to west and have difficulty extending in a North to South direction.

Lightweight construction (typically 2X4-inch members for wood trusses, and smaller for all metal trusses) derive its strength from geometry (multiple members in tension and compression), and employ connectors (gang-nail plates) as opposed to nails. The disadvantages to this type of construction are reduced fireground time and enhanced extension of fire. Gang-nail plate trusses allow fire to extend in north/south and east/west directions simultaneously. Fireground personnel can expect a total collapse of all portions of trusses that are exposed to fire.

The next installment of Reading a Building will review more size-up items.