This paper presents a review of the pyrolysis, ignition, and combustion processes associated with wood, for application in tall timber construction. The burning behaviour of wood is complex. However the processes behind pyrolysis, ignition, combustion, and extinction are generally well understood, with good agreement in the fire science literature over a wide range of experimental conditions for key parameters such as critical heat flux for ignition (12 kW/m 2 ± 2 kW/m 2) and heat of combustion (17.5 MJ/kg ± 2.5 MJ/kg). These parameters are key for evaluating the risks posed by using timber as a construction material. Conversely, extinction conditions are less well defined and understood, with critical mass loss rates for extinction varying from 2.5 g/m 2 s to 5 g/m 2 s. A detailed meta-analysis of the fire resistance literature has shown that the rate of burning as characterised by charring rate averaged over the full test duration is observed to vary with material properties, in particular density and moisture content which induce a maximum 18% variability over the ranges expected in design. System properties are also shown to be important, with stochastic phenomena such as delamination and encapsulation failure resulting in changes to the charring rate that cannot be easily predicted. Finally, the fire exposure as defined by incident heat flux has by far the largest effect on charring rates over typical heat fluxes experienced in compartment fires. Current fire design guidance for engineered timber products is largely prescriptive, relying on fixed ''charring rates'' and ''zero-strength layers'' for structural analyses, and typically prescribing gypsum encapsulation to prevent or delay the involvement of timber in a fire. However, it is clear that the large body of scientific knowledge that exists can be used to explicitly address the fire safety issues that the use of timber introduces. However the application of this science in real buildings is identified as a key knowledge gap which if explored, will enable improved efficiencies and innovations in design.

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In recent years, large-scale structural fire testing has experienced something of a renaissance. After about a century with the standard fire resistance test being the predominant means to characterize the response of structural elements in fires, both research and regulatory communities are confronting the many inherent problems associated with using simplified single element tests, on isolated structural members subjected to unrealistic temperature-time curves, to demonstrate adequate structural performance in fires. As a consequence, a shift in testing philosophy to large-scale non-standard fire testing, using real rather than standard fires, is growing in momentum. A number of custom made, non-standard testing facilities have recently been constructed or are nearing completion. Non-standard fire tests performed around the world during the past three decades have identified numerous shortcomings in our understanding of real building behavior during real fires; in most cases these shortcomings could not have been observed through standard furnace tests. Supported by a grant from the Fire Protection Research Foundation, this paper presents a review of relevant non-standard structural fire engineering research done at the large-scale around the world during the past few decades. It identifies gaps and research needs based both on the conclusions of previous researchers and also on the authors' own assessment of the information presented. A review of similar research needs assessments carried out or presented during the past ten years is included. The overarching objective is to highlight gaps in knowledge and to help steer future research in structural fire engineering, particularly experimental research at the large-scale.

The need for hierarchies of acceptance criteria for probabilistic risk assessments in fire engineering. Fire Technology.

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