Fire Protection
While no building is completely fireproof, construction materials and systems can make a building fire safe. Fire-resistive construction allows time to discover a fire, suppress it before it spreads and evacuate if necessary. In many cases, ordinary wood-frame construction with plywood or OSB sheathing provides ample fire safety and is perfectly acceptable. When unusual circumstances require additional protection, the designer’s options include protected construction, heavy timber construction and fire retardant treated construction.
Properly designing a building for fire safety means properly executing all applicable building code regulations. This means dividing a building into fire-resistant compartments, which, combined with an efficient protection system, allows fires to be localized and suppressed easily. To prevent fire from spreading from one compartment to the next, codes require finished assemblies to be able to withstand full fire exposure without major damage while acting as barriers to heat transfer.
Standard fire tests measure the fire endurance performance of a variety of structural assemblies and boundary conditions that make up compartments. In North America, ASTM Standard E119 sets forth the conditions of the test and the interpretation of the results. Test results are measured in terms of the assembly’s ability to withstand a severe fire for a period of time. Performance times are measured in hours: one-hour rated, two-hour rated, etc. The codes reference these hourly requirements for various building construction types and occupancies.
The major source documents for dimension lumber fire-endurance assemblies are the American Forest & Paper Association’s ASD/LRFD Manual for Engineered Wood Construction, Chapter M16 ( 3.38MB PDF), the American Forest & Paper Association’s DCA 3 – Fire Rated Wood Floor and Wall Assemblies, the Fire Resistance Design Manual published by the Gypsum Association, and the Fire Resistance Directory published by the Underwriters Laboratories, Inc. (UL). The major source document for metal plate connected truss fire-endurance assemblies is the Metal Plate Connected Wood Truss Handbook, section 17 Fire Performance of Trusses and section 18 Sound Transmission and Fire Resistance Rated Truss Assemblies, found at www.woodtruss.com.
There are numerous fire-endurance assemblies detailed in these source documents. These assemblies include different options, such as the direct application of gypsum or gypsum used in combination with resilient channels, insulation or suspended ceilings. They range in performance from 45 minutes to two hours, providing flexibility for any project need.
Also important is the fact that wood outperforms non-combustible materials in direct comparison fire tests. As illustrated in the graph below, a 2x4 timber tie maintained more of its original strength under higher temperatures and for a longer period than did aluminum alloy or mild steel. This is because of wood’s unique charring properties, which actually protect it from fire. Although in some ways counter-intuitive, wood can be an excellent performer under fire conditions. Another test comparing the performance of a glulam beam to a steel beam conducted at the Southwest Research Institute demonstrated the fire performance superiority of the glulam beam when both members were directly exposed in an ASTM E119 fire test.
Also of note is the relatively new requirement that finger jointed products use heat resistant adhesives where fire ratings are mandated under the International Building Code. Finger jointed products are considered interchangeable with solid-sawn dimension lumber of the same size, grade and species. Products joined with heat resistant adhesives include the designation “HRA” in the grademark.
Click here for information on flame spread.
Sources
APA – The Engineered Wood Association and the Southern Pine Council
More information
General Fire
- ANSI/AF&PA NDS-2005 – National Design Specification® (NDS®) for Wood Construction, Chapter 16 – Fire Design of Wood Members – American Wood Council/American Forest & Paper Association standard, 268 pages
- ASD/LRFD Manual for Engineered Wood Construction, Chapter M16 – Fire Design – American Wood Council/American Forest & Paper Association, 174 pages ( 3.38MB PDF)
- Designing for Fire Protection - WoodWorks, 4 pages ( 1.94MB PDF)
- Fire-Rated Systems – APA – The Engineered Wood Association, 24 pages
- Fire Safety: A Wood Frame Building Performance Fact Sheet – Joint publication of FP Innovations – Forintek Division and the Canadian Mortgage and Housing Corporation, 4 pages ( 235KB PDF)
- Fire Safety Defined – Canadian Wood Council, 25 pages
- Performance of Ayhesives Used in Finger Jointed Lumber in Fire-Resistance-Rated Wall Assemblies – Canadian Wood Council in cooperation with FP Innovations – Forintek Division and the US Forest Products Laboratory
- T4 Fire and Sound Resistance of Walls – Tables excerpted from the National Building Code of Canada, provided by the Canadian Wood Council, 6 pages. For the full National Building Code of Canada 1995 with footnotes, click here. ( 2.21MB PDF)
- Technical Topics: Wood I-Joist Floors, Firefighters and Fire – APA – The Engineered Wood Association, 2 pages
- Wood-frame Construction: Fire Resistance and Sound Transmission – Joint publication of FP Innovations – Forintek Division, Société d’habitation du Québec and the Canada Mortgage and Housing Corporation, 12 pages ( 1.55MB PDF)
Code Acceptance
|
