Working Above Fire-Damaged Floors

NIOSH Publication No. 2009-114:
Preventing Deaths and Injuries of Fire Fighters Working Above Fire-Damaged Floors
February 2009 http://www.cdc.gov/niosh/docs/wp-solutions/2009-114/default.html

Summary
Fire fighters are at risk of falling through fire-damaged floors. Fire burning underneath floors can significantly degrade the floor system with little indication to fire fighters working above. Floors can fail within minutes of fire exposure, and new construction technology such as engineered wood floor joists may fail sooner than traditional construction methods. NIOSH recommends that fire fighters use extreme caution when entering any structure that may have fire burning beneath the floor.
Description of Exposure
Fire fighters are at risk of falling through fire-damaged floors. Floors may fail within minutes of flame contact. Carpet, ceramic tile, lightweight concrete, and similar floor coverings may increase the danger to firefighters because of the added weight being supported by the floor system and the insulation these materials provide that may cause the floor to not feel warm, despite the fire underneath.
All wood-based construction materials are subject to failure when exposed to fire. Experimental studies and NIOSH investigations suggest that engineered wood floor systems may fail sooner than traditional sawn lumber floors. The difference in times to failure appears to be a matter of minutes, and fire fighters will seldom know how long a fire has been burning when they arrive on scene. Consequently, fire fighters must use extreme caution when operating on any flooring system potentially exposed to fire.
Engineered wood I-joists represent a rising technology in the building sector; they offer several advantages over traditional construction methods. Engineered wood I-joists are typically prefabricated using sawn or structural composite lumber for the top and bottom flanges (usually 1 ½ to 3 ½ inches wide) and plywood or oriented strand board (OSB) sheathing for the vertical web (3/8 to 7/16 inches thick) (see Figure 1). Engineered wood I-joists are lighter, stiffer, and will not warp, twist, or shrink like traditional framing materials.
Engineered wood I-joists also reduce total construction time and labor costs by their ease of installation.
Engineered wood I-joists have grown in use since the early 1990s and by 2005 were estimated to be used in more than half of all wood-frame construction [APA 2005]. Changes in the building construction industry driven by technological advancements and societal needs suggest that the use of engineered wood products will continue to grow.