External fire spread from timber lined compartments

Mass timber or engineered timber products have become increasingly high profile in the past decade. They are advocated by the construction industry as structural elements, or elements of the building envelope that perform well in terms of sustainability, energy efficiency, and aesthetics. Nevertheless, these novel materials, since they are comprised of timber and adhesives, contribute in a fire scenario. The contribution of timber has been addressed so far by the use of plasterboard, in order to protect the timber; however, architects and stakeholders push towards more timber surfaces to be exposed. At present day, research has developed an understanding about the way timber behaves during a fire from a structural perspective, how it affects the compartment fire dynamics, and what are the critical values in order to achieve auto-extinction. The external fire spread aspect has not been addressed in the community to the same extent; this project aimed to understand the hazards of external fire spread from timber-lined compartments. A series of experimental programmes was undertaken. Experiments were performed to record a “traditional” (i.e., non-combustible internal linings) compartment behaviour, as a baseline; following that, differences on the external fire spread, presented by the internal timber linings, could be quantified. The first experimental campaign established a clear difference in external fire dynamics. Heat fluxes on a façade above the opening were 20-30% (for one exposed timber lining) and up to 60% (for two exposed timber linings) higher than a compartment with non-combustible linings; heat fluxes opposite are dependent on distance from the opening; near-field values are approximately equal; far-field plumes from timber compartments recorded higher values compared to the inert ones. Heat release and mass loss rates were 20-30% and 35-40% higher, respectively, when timber surfaces were exposed. External fire spread from timber lined compartments xiv After the preliminary experiments, a following experimental series attempted to isolate the contribution of timber from that of the fuel source. At the first stage, a baseline was created using exclusively non-combustible insulation as linings. A novel experimental system was used; the fuel source was a propane burner (thus excluding a heat feedback aspect); an external thermocouple tree was used to measure plume temperatures; calorimetry was performed in total and at the compartment opening; calibrated cameras were used. The gas phase temperatures of the external plume and the overall shape of the plume were quantified. With respect to classic plume theory correlations, the compartment presented a comparable behaviour; this baseline was later used to compare results with exposed timber linings. The final experimental campaign revealed differences in plume behaviour from the baseline. Exposed timber ceilings, depending on the amount of exposed surface, affected the plume trajectory, and deviated from the baseline; exposed back wall, regardless of the amount of exposed surface, performed more similarly to the inert compartment baseline. With exposed ceilings heat fluxes on the façade were higher; on the other hand, the exposed wall led to higher heat fluxes opposite the compartment. Momentum and buoyancy increased as more timber was exposed. The Lee et al. model, which was modified by Gorska, was expanded for datasets of both under- and well-ventilated compartments with the full thesis’ dataset. Understanding the hazards of timber-lined compartments will allow architects and engineers to deliver safer, more sustainable, and aesthetically pleasing buildings to the public.