Five full-scale fire experiments were conducted to observe the performance of a two-level apartment-style structure constructed of mass timber. Each level consisted of a one bedroom apartment, an L-shaped corridor, and a stairwell connecting the two levels. One of the primary variables considered in this test series was the amount and location of exposed mass timber. The amount of mass timber surface area protected by gypsum wallboard ranged from 100% to no protection. For each experiment, the fuel load was identical and the fire was initiated in a base cabinet in the kitchen. In the first three experiments, the fire reached flashover conditions, and subsequently underwent a cooling phase as the fuel load from combustible contents was consumed. The first three experiments were carried out for a duration of up to 4 h. In the fourth experiment, automatic fire sprinklers were installed. Sprinklers suppressed the fire automatically. In the fifth experiment, the activation of the automatic fire sprinklers was delayed by approximately 20 minutes beyond the sprinkler activation time in the fourth experiment to simulate responding fire service charging a failed sprinkler water system. A variety of instrumentation was used during the experiments, including thermocouples, bidirectional probes, optical density meters, heat flux transducers, directional flame thermometers, gas analyzers, a fire products collector, and residential smoke alarms. In addition, the experiments were documented with digital still photography, video cameras, and a thermal imaging camera. The experiments were conducted in the large burn room of the Bureau of Alcohol, Tobacco, Firearms and Explosives Fire Research Laboratory located in Beltsville, Maryland, USA. This report provides details on how each experiment was set up, how the experiments were conducted, and the instrumentation used to collect the data. A brief summary of the test results is also included. Detailed results and full data for each test are included in separate appendices.
A large-scale fire test was conducted on a compartment constructed from cross laminated timber (CLT). The internal faces of the compartment were lined with non-combustible board, with the exception of one wall and the ceiling where the CLT was exposed directly to the fire inside the compartment. Extinction of the fire occurred without intervention. During the fire test, measurements were made of incident radiant heat flux, gas phase temperature, and in-depth temperature in the CLT. In addition, gas flow velocities and gas phase temperatures at the opening were measured, as well as incident heat fluxes at the facade due to flames and the plume leaving the opening. The fuel load was chosen to be sufficient to attain flashover, to achieve steadystate burning conditions of the exposed CLT, but to minimize the probability of uncertain behaviors induced by the specific characteristics of the CLT. Ventilation conditions were chosen to approximate maximum temperatures within a compartment. Wood cribs were used as fuel and, following decay of the cribs, selfextinction of the exposed CLT rapidly occurred. In parallel with the large-scale test, a small scale study focusing on CLT self-extinction was conducted. This study was used: to establish the range of incident heat fluxes for which self-extinction of the CLT can occur; the duration of exposure after which steady-state burning occurred; and the duration of exposure at which debonding of the CLT could occur. The large-scale test is described, and the results from both the small and large-scale tests are compared. It is found that selfextinction occurred in the large-scale compartment within the range of critical heat fluxes obtained from the small scale tests.
An experimental study of the influence of an exposed combustible ceiling on compartment fire dynamics has been performed. The fire dynamics in compartments with combustible cross-laminated timber ceilings vs non-combustible reinforced concrete ceilings in otherwise identical compartments with three different ventilation factors were investigated. The experimental results are compared against predictions from two theoretical models for compartment fire dynamics: (a) the parametric fire model given in EN 1991-1-2, and (b) a model developed at Technische Universität Braunschweig, which are the parametric fire models currently used in Germany. It is confirmed that the introduction of a combustible timber ceiling leads to higher temperatures within the enclosure, both under fuel-controlled and ventilation-controlled scenarios. It is also demonstrated that the theoretical models considered in this article require refinement in order to adequately represent all relevant scenarios when combustible ceilings are present. A refinement of the German model, by adding the fuel from the combustible ceiling to the occupancy fuel load, was shown to not adequately capture the response for the ventilation-controlled fires.
A full-scale compartment fire test was performed to assess gypsum plasterboards and wood based panels as cladding materials for the fire protection of light and massive timber elements. The test compartment was constructed using both the Timber Frame and the Cross Laminated Timber techniques; a wood crib was used to achieve realistic fire conditions. Temperature measurements and optical inspection evidence suggested that gypsum plasterboards offered adequate fire protection since they did not fail and no charring was observed in the timber elements. A free standing wall inside the test compartment, protected by wood-based panels, partially collapsed. Measured values of characteristic failure times, such as time to failure of fire protection cladding and time to onset of charring, were compared to relevant Eurocode correlations, achieving good levels of agreement. The obtained set of measurements, describing the time evolution of a large variety of physical parameters, such as gas and wall layer temperatures, can be used for validation of relevant advanced fire simulation tools.
Project contact is Kuma Sumathipala at the American Wood Council
Summary
The United States has a vast supply of forest biomass, which provides an abundant resource suitable for the manufacturing of mass timber products. Recent research has shown that these mass timber products can be safely implemented in tall buildings. In 2018 and 2019, this research led to changes allowing the construction of 18 story buildings with mass timber structures in the 2021 International Building Code (IBC). Although this development has created opportunities, it does not respond to recent architectural trends, as the new regulations do not allow for visible mass timber in buildings exceeding 12 stories in height and only allow for limited areas of visible Cross Laminated Timber (CLT) surface in buildings from 9 to 12 stories in height.
The strict limitation on the area of visible mass timber in 2021 IBC was based partially on fire performance of CLT manufactured to an earlier edition (2012) of ANSI/APA PRG 320. New adhesive qualification requirements in the 2018 standard have significantly improved the fire performance of CLT. This improved fire performance represents an opportunity to justify increases to code-prescribed limits on exposed mass timber areas which would respond to current, and likely future, architectural aesthetic demands, allowing for an expansion of the market for tall mass timber buildings.
In order to justify these increases in allowable exposed mass timber areas, compartment fire tests will be designed and performed to demonstrate that the fire performance of increased exposed mass timber surfaces are consistent with the (newly-recognized) International Building Code safety criterion. In addition, fire safe solutions for the intersections between exposed mass timber members and restoration of fire-damaged exposed mass timber are needed to be developed and tested. Test results and other findings will be used to develop and justify new requirements for U.S. model building codes, thereby enabling more innovative utilization of renewable U.S. forest resources in construction.
Recent architectural trends include the design and construction of increasingly tall buildings with structural components comprised of engineered wood referred to by names including; cross laminated timber (CLT), laminated veneer lumber (LVL), or glued laminated timber (Glulam). These buildings are cited for their advantages in sustainability resulting from the use of wood as a renewable construction material. Previous research has shown that timber elements contribute to the fuel load in buildings and can increase the initial fire growth rate – potentially overwhelming fire protection system and creating more severe conditions for occupants, emergency responders, and nearby properties.
The overarching goal of this project Fire Safety Challenges of Tall Wood Buildings Phase 2 is to quantify the contribution of CLT building elements (wall and/or floor-ceiling assemblies) in compartment fires and provide data to allow comparison of the performance of CLT systems against other building systems commonly used in tall buildings.
Recent architectural trends include the design and construction of increasingly tall buildings with structural components comprised of engineered wood referred to by names including; cross laminated timber (CLT), laminated veneer lumber (LVL), or glued laminated timber (Glulam). These buildings are cited for their advantages in sustainability resulting from the use of wood as a renewable construction material. Previous research has shown that timber elements contribute to the fuel load in buildings and can increase the initial fire growth rate – potentially overwhelming fire protection system and creating more severe conditions for occupants, emergency responders, and nearby properties.
The overarching goal of this project Fire Safety Challenges of Tall Wood Buildings Phase 2 (involving five tasks) is to quantify the contribution of CLT building elements (wall and/or floor-ceiling assemblies) in compartment fires and provide data to allow comparison of the performance of CLT systems against other building systems commonly used in tall buildings.
There is a current trend towards mid- and high-rise mass timber buildings. With this trend, there is a research need to develop a comparison between mass timber compartment fires and non-combustible compartment fires. In an effort to address the knowledge gaps in the fire performance of cross-laminated timber compartments, a full-scale fire test series was developed. The fire test series included five tests with varying levels of exposed cross-laminated timber on a two story cross-laminated timber structure. Here we present a detailed summary of the fire test series, instrumentation plan, and an overview of the results.
