BY DAVID RHODES
A mammoth residential building was under construction next door to our fire station, and we all noticed that the contractor was using red lumber in some of the framing. The contractor told me that this was lumber that had been treated with a fire retardant. After acquiring a sample of the product, we put the flame to it—and he was right! It would char, but it would not sustain combustion. Soon, we were seeing this material being used all over our area in large, multistory residential buildings that normally would have used steel. This sparked my curiosity, and so I investigated further.
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With the rising price of steel, many builders are turning to fire retardant treated (FRT) lumber instead of fire-rated noncombustible assemblies incorporating steel or concrete (photos 1 and 2). FRT lumber is a new generation of construction material for use in weather-protected conditions. Some of the past treatment methods have created a very corrosive wood and problems with hygroscopicity (the capacity of the lumber to react to the moisture content of the air by absorbing or releasing water vapor). Of decisive significance for water vapor absorption or release is the product’s water content. This was a problem in extremely humid climates. This new generation of chemicals and process claim to have reduced these effects dramatically to a point where the FRT lumber is no more corrosive than normal wood. This significant improvement ensures that the treatment remains intact and does not leach out. Long-term exposure to weather will diminish the effectiveness, however, so the FRT lumber is used for interior and exterior unexposed components.
 (1) A building under construction using typical concrete and metal materials. (Photos by author.)
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 (2) This is a similar-size building and occupancy using fire retardant treated lumber. |
FRT lumber has an Underwriters Laboratories classification for surface burning (flame spread) but does not have a fire resistance rating in hours. Hourly ratings are assigned to door, wall, and roof or deck assemblies. The lumber can be used as a component in these applications, whereas untreated lumber is not allowed. With the use of FRT on roof trusses, a one-hour rating can now be achieved with only one layer of 5⁄8-inch Type C gypsum applied directly on the bottom chord of the truss. The UL classification standard Treatment Testing states: “Provide D-Blaze FRT wood treatment which has been tested by Underwriters Laboratories, Inc. (UL) of Northbrook, IL, and has been designated UL classification FRS, which signifies a flame spread and smoke developed rating of 25 or less. When tested for 30 minutes, there shall be no evidence of significant progressive combustion. Each piece of treated material shall bear a UL classification stamp and meet or exceed requirements for Class 1 or Class A flame spread ratings.”
THE PROCESS
The fire retardant treatment process is completed in wood treating facilities that have been treating lumber with preservatives for decades. To apply the fire retardant, the lumber is placed in a chamber and pressurized with the fire retardant chemical. Once this process is completed, the dimensional lumber is then kiln-dried to a moisture content of 19 percent and the plywood to 15 percent. The material safety data sheet for the product identifies the chemical as phospho-ammonium-boron complex. The chemical treatment is clear, and therefore product and process stamps are applied to identify the FRT lumber (photo 3). Great Southern Wood Company uses D-Blaze® to create its proprietary brand Flamefreeze.® This red or orange wood is easy to identify on the construction site (photo 4). There are other brands, with their own proprietary product lines and marketing, and the treatment is usually colorless.
 (3) A fire retardant stamp on plywood sheathing or subflooring. |
 (4) A fire retardant stamp and proprietary red or orange dye on exterior load-bearing walls. |
The manufacturer recommended use included the following building components: roof trusses, roof decks and sheathing, beams and purlins, floor trusses, subflooring, joists, interior nonload-bearing walls, exterior load-bearing walls, studs, architectural mill work and trim, blocking and furring, and paneling (photos 5 and 6).
 (5) A FRT subfloor was required four feet inside the fire retardant wood exterior in this building (the interior of the building in photo 2). |
The wood loses some strength once it has undergone the treating process. This requires a conversion chart that is available from the manufacturer. Other than that, the wood is typically used in a normal fashion. The wood can be cut to length, drilled, or diagonally cut without having to apply any additional coating in the field. The wood cannot be ripped or milled, however. Builders must research local codes before using this product for certain applications.
IMPACT ON FIREFIGHTING OPERATIONS
Although the code allows for the use of FRT lumber in place of noncombustible materials, do not be lulled into a false sense of security. These mammoth wooden mid-rises have the laminated wooden I-beam floor systems attached to FRT lumber. Even with the requirement of a sprinkler system, these buildings are unprotected in unused attics under NFPA 13R, Standard for the Installation of Sprinkler Systems in Residential Occupancies Up To and Including Four Stories in Height (buildings five stories and up would need to be provided with complete protection throughout, including attics, under NFPA 13, Standard for the Installation of Sprinkler Systems). We all know that if the roof burns off, the building usually comes down. The floor system was required to be protected only by the drywall ceiling on the bottom and by the fire treated plywood decking on the top. This decking was required to be FRT only four feet inside from the exterior wall. This configuration will allow for the horizontal spread of fire in the void spaces and poke-through holes in the flooring system.
The FRT lumber does what it is supposed to do. The problem we face as firefighters is not with the lumber treating or process. The problem resides in the codes and what is required or exempt for fire treating. These lumberyards in the sky pose a high risk to firefighters operating in them under fire conditions. As you can clearly see in photo 6, the laminated oriented strand board I-beam floor truss was not required to be fire retardant treated. Do not let the massive size of the building fool you into thinking that the fire will behave like a 10- or 20-year-old building of the same size. Note that the use of wood as load-bearing membersfire retardant treated or notis limited to five or six stories under most modern building codes for residential buildings.
It is imperative to constantly look for and research new construction materials and methods to keep our crews safe on the fireground. It is easy to mistake the loft-style exterior of the building for ordinary or fire resistive construction. Preplanning and dialog with the contractors during construction are essential for our continued education.
DAVID RHODES is a battalion chief and a 23-year veteran with the Atlanta (GA) Fire Department. He is a chief elder for the Georgia Smoke Diver program, a member of the FDIC executive advisory board, the H.O.T. logistics coordinator for FDIC, and a member of the Fire Engineering editorial advisory board. He is an adjunct instructor for the Georgia Fire Academy. He is the incident commander for the Georgia Emergency Management’s Metro Atlanta All-Hazards Incident Management Team and a task force leader for the Georgia search and rescue team. He codeveloped the “Marketing the Mission” video (Fire Engineering, 2000).
