Construction Concerns: Char as Fire Protection
By Gregory Havel
For more than a century, it has been proposed that a layer of char on the surface of heavy timbers acts as insulation and will slow or prevent further burning of the wood. This proposal was questioned by Francis Brannigan in 1971 and 1982 in the earliest editions of his (and its other authors) book Building Construction for the Fire Service. Yet buildings of wood construction, whether of heavy timber, wood frame, or lightweight wood structural components continue to burn and are destroyed by fire. If there were merits to this proposal, spectacular photos and videos of these fires would not appear as often as they do on televised news broadcasts or on the Internet.
This proposal is again being used by the people who today promote the use of “mass timber” in construction, which includes glulams, “cross laminated timber [CLT],” “nail laminated timber,” and other variations.
The U.S edition of the Cross Laminated Timber Handbook is free to download at https://www.thinkwood.com/products-and-systems/clt-handbook. It is distributed by the American Wood Council, the Wood Products Council, and other organizations and government agencies. It restates this proposal in Chapter 8, “Fire Performance of Cross Laminated Timber Assemblies.” However, it states in the later sections of Chapter 8 that in the full-scale fire compartment tests in a test building of CLT construction, the walls, and ceilings of the test rooms were protected with gypsum drywall board.
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