What's it Going to Take?

The Underwriters Laboratory (UL) is involved in further evaluating the performance of the lightweight wood trusses under the fire conditions.

On December 4, 2006, the International Association of Fire Chiefs (IAFC) issued a "Member Alert" notifying their membership about the hazards associated with the lightweight construction in residential occupancies. In that Member Alert titled "Caution Urged with Composite Floors" it was stated:

"There have been several cases of firefighters falling through floors made of composite structural components and an even greater number of near-miss situations. This type of construction is being investigated as a contributing factor in a line-of-duty death...These components and systems are most often found in situations where applicable codes do not require any rated fire resistance between floor levels. They have much less inherent fire resistance than conventional wood joist floor systems and conventional wood decking. Remember - many codes do not require any fire resistance in residential floors! In the several cases of firefighters falling through floors, those floors had been exposed to fire from below for relatively short periods."

Then, on October 1, 2007, in a report that was indicative of a strong systematic effort by the fire service to take a more scientific and in-depth look at this structural failure, IAFC in an article titled "Underwriters Laboratories Receive DHS Grant" indicated:

"Earlier research by the National Engineered Lightweight Construction Fire Research Project indicated that unprotected lightweight wood truss assemblies can fail within 6 to 13 minutes of exposure to fire....Lightweight wooden trusses, made with engineered lumber, are commonly found in 65 percent of new residential and commercial developments, according to the Wood Truss Council of America. Allowing for faster, more cost-effective construction, recent anecdotal evidence has indicated that lightweight wood trusses may become unstable and collapse more quickly in fire situations than traditional trusses."

The concern about the poor performance of the engineered lightweight wood construction under the fire conditions is nothing new. We have known about it for more than a couple of decades. Obviously, the very first name that comes to mind when talking about this subject is the legendary Francis Brannigan, and his famous Building Construction for the Fire Service book. There are many great reports, but just a handful of them are mentioned here.

Back in 1992, United States Fire Administration (USFA) did a report, titled "Wood Truss Roof Collapse Claims Two Firefighters (December 26, 1992)"; National Institute for Occupational Safety and Health (NIOSH) did a report on April 2005 titled "Preventing Injuries and Deaths of Firefighters due to Truss System Failures"; National Institute of Standards and Technology (NIST) did a report on January 2007 titled "A Study of Metal Truss Plate Connectors When Exposed to Fire".

These reports basically indicate that the problem with these engineered lightweight wood structural members is that they are adversely affected by the fire much sooner than the denser building materials. And that typically, the metal truss connector plates (gusset plate - gang nail that penetrates the wood about a quarter of an inch) is the primary location of the structural failures in these wood trusses.

What contributing role does failure of these engineered lightweight wood structural members have on the national fire fatalities? Fact of the matter is that in the majority of the civilian fire fatality cases, the lethal products of the combustion (smoke and heat) are the main cause of death in the victims, and not the structural failures. Either the occupants were alerted and they evacuated the house safely; or in the most unfortunate cases, they fell victim to the smoke, and died of asphyxiation at the earlier stage of the fire. So, who are the real victims of such structural failures? Our own firefighters.

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