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American Wood Council

Key Mass Timber Fire Tests Completed


The two-story structure was used for five fire
tests before being repurposed by Yale University
architecture students who will use salvaged CLT
panels to design and construct temporary housing.
The third test, shown above three hours after
ignition, exposed two interior CLT walls to a
severe contents fire. Following burn-out of the
contents, the char layer which formed on the
exposed CLT prevented further burning.

A significant milestone was achieved in the understanding of mass timber fire behavior this past summer in a quiet suburban community just outside of Washington, D.C.

A team of fire experts from the U.S. Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) working alongside scientists from the U.S. Forest Products Laboratory put identically furnished, multistory, one-bedroom apartments constructed of exposed, partially exposed, and unexposed (protected) five-ply cross-laminated timber (CLT) through a series of rigorously monitored fire tests.

The purpose of the tests is to provide data that will help inform any recommendations the ICC Ad Hoc Committee on Tall Wood Buildings (TWB) will propose for the 2021 International Building Code. Notable among the considerations: Should wood structures rise above six stories without special alternative means and methods approval?

This installment of Code Counts takes a closer look at the fire tests, what was observed, and where to go for more information.

Why a Fire Test?

With the growing popularity of mass timber construction here and abroad, interest to better understand mass timber characteristics in real world situations is coming from many quarters, including owners, developers, architects, and engineers. So much so, the ICC is investigating the use of mass timber in building applications that may go beyond current code. Ideally, the efforts of the TWB Ad Hoc committee will result in prescriptive criteria for mass timber construction in the next edition of the code, so that design professionals and code officials will be working from a common set of well-vetted building code requirements.

One person who is helping lead that conversation is Sean DeCrane, chair of the TWB Fire Work Group and Industry Relations Manager for Building and Life Safety Technologies at Underwriters Laboratories.

"The test structure and format was based on input from our workgroup," DeCrane reports. "We had a couple goals. One, to understand the contribution of CLT to the fire fuel load. And second, to measure the conditions a responding fire crew would encounter in the hallway if an apartment constructed in CLT was involved in a fire."

What Did the Fire Tests Examine?

A series of five tests were conducted. Each test was designed to replicate real world conditions across five scenarios. Identical, furnished, one bedroom apartments were constructed in a multistory building. The door between the living and sleeping areas was left open in both apartments. Test scenarios were as follows:

100 Percent Gypsum Wall Board Coverage. The mass timber structure was fully sheathed in a double layer of gypsum wall board in a large furnishings and contents fire. The test was terminated after three hours without significant wood charring.

Partially Exposed CLT Ceiling. Thirty percent of the CLT ceiling surface areas in the living room and bedroom was left exposed. The test was terminated after four hours. The exposed CLT stopped burning after char formation on the exposed CLT ceiling surface areas.

Parallel CLT Walls Exposed. One in the living room and one in the bedroom. Once the apartment furnishings and contents were consumed, the mass timber structure stopped burning after char formation.

Active Sprinkler Protection with No Gypsum Wall Board Coverage. Two sprinkler tests examined the effects of 100 percent exposed mass timber in the living room and bedroom. Test 4 demonstrated the effect of a single sprinkler (it easily contained the fire). In Test 5 the fire was allowed to freely burn for 23 minutes before the sprinkler was activated. The fire was quickly controlled.

Test Matrix
Test Matrix


How You Should Understand the Fire Tests?

"I think the tests are very important," DeCrane says. "It's the first time we've seen these structures tested at full-scale. This lets us observe the fire behavior and pattern of a typical apartment in Los Angeles, Chicago, or New York City. This is the fuel load you might see on the street. These are good solid tests that we can really start to base our Workgroup discussion on."

Jason Smart agrees with that assessment. Smart is the manager of engineering technology for the American Wood Council, an organization that helped underwrite the costs of the tests, along with the Forest Products Laboratory. Smart was also active in helping formulate test design.

"I think the general feeling was that performance exceeded expectations," Smart says in referring to the outcome of the tests. "In our view, the outcome was very much in line with predicted results, based on modeling that was done prior to the tests. There were no major surprises."

What are the Fire Test Findings and Who Interprets Them?

Smart says test result data and the interpretation of the findings w​ill be released sometime after the public meeting of the ICC Ad Hoc Committee - Tall Wood Buildings, recently held in suburban Chicago. Experts from the Forest Products Laboratory are reviewing the data and will provide the analysis and interpretation.

What Will the TWB Ad Hoc Committee Recommend?

The goal expressed by Steve DiGiovanni, chair of the TWB is for the committee to reach consensus on the draft recommendations and make them available for public review during the 4th quarter of 2017. "We have enough information now to advance a discussion." DeCrane says the next step beyond that arrives in January 2018 when the submission of code changes for the 2018 Group A Cycle (IBC) takes place.

Where to Go for More Information

"You don't have to read 21,000 pages of information," DeCrane advises. "But building and fire code officials do have a responsibility to understand the facts before they vote. Familiarize yourself with the issues. Know what the experts are saying."

A good place to start is AWC.org/tallwood, which serves as a de facto clearinghouse for the latest information. The ICC also maintains a site for review of the latest Work Group and Committee details.

For information on available training, latest information or questions related to the Mass Timber Tall Wood project, contact John Catlett, MCP, Code Development Manager for AWC at jcatlett@awc.org or at 202.463.2708.


The views and opinions expressed in this article are those of AWC and do not necessarily reflect those of the International Code Council, or Hanley Wood.


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