Since Engineered Wood Products (EWPs) have entered the building industry as structural elements, several fire safety concerns have arisen, especially for high-rise structures.The combustible nature of timber suggests that the current knowledge on compartment fire dynamics might not apply to compartments with timber boundaries, due to the increased fuel load and its redistribution across the compartment.In order to fill this knowledge gap, 24 medium-scale timber compartments have been executed to characterise the fire dynamics when timber members are present.This experimental campaign provides data about the gas-phase temperatures, the flow fields at the opening, the burning behaviour of timber and its contribution to the total heat release rate. This data is then compared to current tools that predict the fire development in conventional compartments.This comparison dismantles the limitations of the current framework, and the subsequent analysis proposes several changes to include the effect of burning timber elements. It is concluded that gas flow velocities increase with the amount of more timber present in the compartment. Therefore the fire transitions to a new regime where the gases do not have enough time to mix and react inside the compartment, the temperatures decrease and the horizontal velocities at the opening increase.
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.
This paper provides understanding of the fire performance of exposed cross-laminated-timber (CLT) in large enclosures. An office-type configuration has been represented by a 3.75 by 7.6 by 2.4 m high enclosure constructed of non-combustible blockwork walls, with a large opening on one long face. Three experiments are described in which propane-fuelled burners created a line fire that impinged on different ceiling types. The first experiment had a non-combustible ceiling lining in which the burners were set to provide flames that extended approximately halfway along the underside of the ceiling. Two further experiments used exposed 160 mm thick (40-20-40-20-40 mm) loaded CLT panels with a standard polyurethane adhesive between lamella in one experiment and a modified polyurethane adhesive in the other. Measurements included radiative heat flux to the ceiling and the floor, temperatures within the depth of the CLT and the mass loss of the panels. Results show the initial peak rate of heat release with the exposed CLT was up to three times greater when compared with the non-combustible lining. As char formed, this stabilised at approximately one and a half times that of the non-combustible lining. Premature char fall-off (due to bond-line failure) was observed close to the burners in the CLT using standard polyurethane adhesive. However, both exposed CLT ceiling experiments underwent auto-extinction of flaming combustion once the burners were switched off.
The modern building industry is continually seeking materials and products that are less pollutant, stronger, more aesthetically appealing and easier to construct with. As a response to these drivers, Engineered Wood Products (EWP) have entered the construction market as an evolution of very wellknown conventional products such as plywood. However, contrary to plywood, EWP consist of much thicker layers and contemporary glues. New manufacturing technologies enable the use of EWP on an entirely different scale. Today, wooden high-rise buildings, bridges, and other macro-structures can effectively be designed. Despite the multiple benefits of timber construction, new fire safety hazards have sparked with the arrival of EWP. These hazards correspond to increased fuel load density and the potential for structural collapse since timber structures are combustible. These changes challenge the fire safety strategy for timber buildings. The purpose of any fire safety strategy is to ensure a safe evacuation and operation of a building during and after a fire event. Most fire strategies rely on compartmentalisation (physical boundaries that restrict fire spread to other parts of the building) and on a robust structure that maintains its integrity after all the fuel has burned out. Compartment fire dynamics and external flaming are key to understanding how compartmentalisation can be achieved in timber buildings. To ensure compartmentalisation and structural integrity, it is fundamental that the timber walls and floors stop burning, i.e. self-extinguish. Charring materials such as timber have the ability to self-extinguish without external intervention under certain circumstances. This research aims at investigating the effect of exposed timber on the compartment fire dynamics and the external flaming with respect to the current fire dynamics' theory for buildings with noncombustible structures. This thesis also aims to study the mechanisms that lead to self-extinguishment of timber in compartments with a geometry representative of residential construction. For this purpose, three experimental campaigns using Cross Laminated Timber (CLT) were conducted. The first consisted of medium-scale compartment fires with varying configurations of exposed CLT with a kerosene pool fire as the fire source. The use of kerosene as the fuel facilitated the characterisation of the fire dynamics. The second consisted of medium-scale compartment fires with two exposed CLT walls and different densities of wood cribs as the fire source. The use of wood cribs as the fuel allowed for a progressive and long decay phase to be achieved. The third consisted of a large-scale demonstration test to enable a scaling analysis and validation of the results from the medium-scale tests.
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