Niosh Report -- Fire Safety Case #1

NIOSH Report -- Fire Safety

Case #1 - Explain the primary hazards presented by bow-string trussed roofs that are involved in a fire.

The void space created by a bow-string truss can allow smoke, heat, and fire conditions to go undetected causing a false sense of security for firefighters operating beneath it (Fornell, 1995). Because more surface area is exposed to flames than with standard construction, collapse can take place in a much shorter time frame (Dunn, 2006). In Case #1, a captain became a victim due to just such a scenario. He became trapped after fire conditions changed dramatically on the roof, leading to a collapse and ultimately the blocking of the main escape and rescue entries.

Communications and updates between interior and exterior personnel must be continual when dealing with any type of truss construction. At many incidents involving trusses, reports from crews inside the building indicate that they have little or no signs of smoke when heavy smoke may be visible from the roof on the exterior (Dunn, 2006). Any fire where truss construction is suspected must have ceilings opened quickly to expose the truss area for inspection. If trusses are found, it is highly recommended that crews be withdrawn and defensive measures be utilized (Fornell, 1995). There is no way of knowing exactly how long the fire in the truss space may have been burning and what damage may already be done. It is important to note however, that firefighters must exercise caution when opening up ceilings in truss construction to eliminate back draft or flashover potential once air is fed into the void space.

Case #2 - Explain how firefighters can recognize and prevent firefighter injuries and deaths from parapet walls.

Understanding building construction is critical. During operations, firefighters must take special note of factors that may signal the potential collapse of a parapet wall. These may include bulging or cracked masonry walls, a wavy or curved appearance to a normally straight surface, unlevel top parapet ledge, failed connections, or separations between parapet wall and side wall, and parapet wall and flat roof (Dunn, 2006). A potential failure can also be visualized by noticing facade signs, HVAC units, or overhangs that are racked, out of shape, or compromised. This could very well be a signal of worse things to come.

While on an emergency scene with a potential for collapse, firefighters can prevent injuries and casualties by setting up clear collapse zones for all structures and parapet walls that may be faulty or weak (Fornell, 1995). A parapet wall has little, if any, lateral stability and will present a high potential for collapse (Malanga, 1996). These structures can be easily identified because of the signs or awnings that may be attached. It is safe to assume that the parapet wall has not been engineered to take the weight and forces being applied by additional dead and live loads as a result of a fire (Dunn, 2006).

To properly establish a collapse zone, multiply the height of the building times 1 1/2 to account for falling and scattered debris (Fornell, 1995). Another critical element in preventing parapet-related firefighter deaths is preplanning. Size-up needs to start even before the run goes out. Crews should identify occupancies that present additional risk to life, safety, and property in our response area, and establish plans for that specific target hazard. It is also advised that crews should identify the age of structure, its integrity, the type of roof and interior structures and supports, building materials, and building class to make proper assessments for next steps (Dunn, 2006).

Case #3 - Explain the hazards that lightweight wooden trusses with gusset plate connectors present to firefighters working inside a structure fire.