By Vincent Dunn
Do you really know the dangers of wood-frame building collapse? In 1998, two Fire Department of New York officers died when the second floor of a three-story wood-frame building collapsed, throwing them into the fire on the first floor. In a two year period in the 1980s, a chief and an officer were killed and an officer and nine firefighters were seriously injured in four separate collapses of braced frame wooden buildings.
Of the three types of wood frame building collapses, the inward/outward collapse is the most dangerous. It gives no warning and can result in the simultaneous collapse of two or more sides of the structure. Of the five types of building construction– fire resistive noncombustible, ordinary, heavy timber, and wood frame–only the triple decker, wood, braced-frame burning building suffers multiple-side wall collapse in which three or four sides collapse at once.
Three contributing causes of “triple decker” wood frame building collapse are (1) fire destruction of bearing walls, (2) failure of mortise and tenon joint, and (3) the overload of an exterior wooden wall. Burning wooden buildings of three or more stories collapse more frequently than burning one- or two-story wood buildings. Wooden buildings on a corner plot or standing alone are more susceptible to collapse when exposed to fire than wood buildings in the center of a row of similar buildings.
To understand how a burning wood-frame residence building “triple decker” collapses and how to extinguish a fire within a wood-frame building, a firefighter must know how a wood-frame building is constructed. The four most widely used methods of wood-frame, “triple decker” construction over the past 200 years are braced frame, balloon frame, platform frame, and lightweight wood truss construction.
Deputy Chief Dunn (Ret., Fire Department of New York) is the author of a number of textbooks, including the new Strategy of Firefighting (Fire Engineering, 2007), Collapse of Burning Buildings (Fire Engineering, 1988), Safety and Survival on the Fireground (Fire Engineering, 1992), and Command and Control of Fires and Emergencies (Fire Engineering, 1999).