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NIOSH Publication No. 2009-114:Preventing Deaths and Injuries of Fire Fighters Working Above Fire-Damaged Floors |
February 2009![]() |
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SummaryFire 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 ExposureFire 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.
The engineered wood I-joist has a different cross-sectional profile than a standard solid sawn wood joist (see Figure 2) and in testing, burned more quickly. Typically, the thinner web was consumed first (see Figure 3). Time-to-failure testing has been conducted by several groups, most recently Underwriters Laboratories (UL) [2008]; [Straseske and Weber 1988; Weyerhaeuser 1986]. The UL tests show that unprotected lightweight engineered floor joist (I-joists) assemblies can fail in as little as 6 minutes, and that traditional unprotected residential floor construction assemblies failed in less than 19 minutes. Previous studies that used different test methods suggested even shorter times-to-failure. These study results indicate that any floor system can fail quickly, and that unprotected engineered wood I-joists may fail sooner. Results from experiments conducted by the National Institute for Standards and Technology (NIST) are expected in the spring of 2009, and will be available at www.fire.gov. The NIST experiments were conducted in ventilation limited conditions meant to represent an actual basement fire. Fire fighters who operate on fire-damaged floors of all types have fallen through the weakened floor and been trapped in the fire below [NIOSH 2005]. Similar hazards exist when fire fighters work under fire-damaged floor systems that collapse onto them. The following is a NIOSH case investigation involving an unprotected engineered wood floor system. The weakened floor was undetectable from above, although outside conditions indicated the possibility of a basement fire. Case StudyOn August 13, 2006, a 55-year-old male career engineer (the victim) died and his partner was injured after they fell through the floor at a residential structure fire. The house was built in 1999, and the first floor contained a heated flooring system consisting of a hot water piping system encased in lightweight concrete supported by engineered wood I-joists and trusses. The basement was unfinished and the bottom sides of the I-joists and floor trusses were exposed. An engine company was conducting a fast attack on a suspected basement fire, while a ladder company conducted horizontal ventilation. The victim and his partner were conducting a primary search on the ground floor. Smoke filled the ground floor and made visibility near zero, but little heat was detected as the victim and his partner conducted a left-hand search. They sounded the ceramic tile floor and took one crawling step forward on their knees when the floor collapsed. The partner fell on the other side of a basement door into a hallway and crawled out of a basement window. The victim fell into the room of fire origin and was recovered the next day. The floor collapsed about 11 minutes after the initial 911 dispatch [NIOSH 2006]. ControlsTo minimize risk when working above fire-damaged floors, NIOSH recommends that fire departments and fire fighters take the measures identified below. Many of these prevention measures are from the NIOSH Alert: Preventing Injuries and Deaths of Fire Fighters due to Truss System Failures [2005]. Lightweight truss systems and engineered wood floor joists have similar fire degradation risks.
In addition, NIOSH recommends the following:
AcknowledgmentsThe principal contributors to this publication were Tim Merinar and Jay Tarley, NIOSH, Fire Fighter Fatality Investigation and Prevention Program (FFFIPP) and Robert Koedam, formerly with NIOSH. ReferencesAPA [2005]. Wood I-joist floors, fire fighters and fire. APA—The Engineered Wood Association. Tacoma, WA. Form No. TT–015B. NIOSH [2005]. NIOSH alert: preventing injuries and deaths of fire fighters due to truss system failures. Cincinnati, OH: U.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, DHHS (NIOSH) Publication No. 2005–132. NIOSH [2006]. Career engineer dies after falling through floor while conducting a primary search at a residential structure fire—Wisconsin. Morgantown, WV: U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, Fatality Assessment and Control Evaluation (FACE) Report F2006–26. Straseske J, Weber C [1988]. Testing floor systems. Fire Command. June:47–48. Weyerhaeuser [1986]. Flame penetration ratings according to ASTM test method E119 utilizing a small scale furnace. Longview, WA: Weyerhaeuser Company Fire Technology Laboratory, Report No. 665. Underwriters Laboratories [2008]. Report on structural stability of engineered lumber in fire conditions. Northbrook, IL: Underwriters Laboratories, File No. NC9140. USFA [2008]. USFA Position Paper—Residential fire sprinklers. United States Fire Administration, U.S. Department of Homeland Security. March 28, 2008. http://www.usfa.dhs.gov/downloads/pdf/sprinkler_position_paper.pdf For More InformationThe NIOSH Alert: Preventing Injuries and Deaths of Fire Fighters due to Truss System Failures includes relevant information and prevention recommendations. Construction truss systems and engineered floor joists have similar collapse hazards associated with fire degradation. The NIOSH Alert is available at http://www.cdc.gov/niosh/docs/2005-132/ The American Forest and Paper Association (AF&PA) and the U.S. Fire Administration have developed the following Web site with information for the fire service about traditional and engineered wood products: http://www.woodaware.info/. A CD entitled Awareness Level Firefighter Training for Modern Wood Products developed in cooperation with the Illinois Fire Service Institute is available from fire@woodaware.info. Underwriters Laboratories, with funding from the Department of Homeland Security, has developed an on-line course for fire professionals, "Structural Stability of Engineered Lumber in Fire Conditions" available at http://www.uluniversity.us/ The National Institute of Standards and Technology (NIST), Building and Fire Research Laboratory maintains a Web site with links to publications on fire safety topics: http://www.fire.nist.gov/. To receive more information about occupational safety and health topics, contact NIOSH at Telephone: 1–800–CDC–INFO (1–800–232–4636) or visit the NIOSH Web site at www.cdc.gov/niosh For a monthly update on news at NIOSH, subscribe to NIOSH eNews by visiting www.cdc.gov/niosh/eNews. Mention of any company or product does not constitute endorsement by NIOSH. In addition, citations to Web sites external to NIOSH do not constitute NIOSH endorsement of the sponsoring organizations or their programs or products. Furthermore, NIOSH is not responsible for the content of these Web sites. This document is in the public domain and may be freely copied or reprinted. NIOSH encourages all readers of the Workplace Solutions to make them available to all interested employers and workers. As part of the Centers for Disease Control and Prevention, NIOSH is the Federal agency responsible for conducting research and making recommendations to prevent work-related illnesses and injuries. All Workplace Solutions are based on research studies that show how worker exposures to hazardous agents or activities can be significantly reduced. Preventing Deaths and Injuries of Fire Fighters Working Above Fire-Damaged FloorsDHHS (NIOSH) Publication No. 2009-114February 2009Safer • Healthier • People™ DEPARTMENT OF HEALTH AND HUMAN SERVICES
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