No abstract

Close inspection of accidental fires in large, open-plan compartments reveals that they do not burn simultaneously throughout the whole enclosure. Instead, these fires tend to move across floor plates as flames spread, burning over a limited area at any one time. These fires have been labelled "travelling fires". Current structural fire design methods do not account for these types of fires. Despite these observations, fire scenarios most commonly used for the structural design of modern buildings are based on traditional methods that assume uniform burning and homogenous temperature conditions throughout a compartment, regardless of its size. This paper is Part I of a two part article and is a literature review of travelling fire research.A brief background to the traditional methods that assume uniform fires is given along with critiques of that assumption, such as the heterogeneity of compartment temperatures and the observation of travelling fires in both accidental events and controlled tests. The research in travelling fires is reviewed, highlighting the pioneering work in the field to date. The main challenge in developing tools for incorporating travelling fires into design is the lack of large scale test data. Nonetheless, significant progress in the field has been made and a robust methodology using travelling fires to characterise the thermal environment for structural analysis has been developed. The research in quantifying the structural response to travelling fires is also reviewed.

An international study of fire modelling was conducted prior to the Dalmarnock Fire Test One in order to assess the state-of-the-art of fire simulations using a round-robin approach. This test forms part of the Dalmarnock Fire Tests, a series of experiments conducted in 2006 in a high-rise building. The philosophy behind the tests was to provide measurements in a realistic fire scenario involving multiple fuel packages and non-trivial fire growth, and with an instrumentation density suitable for comparison with computational fluid dynamics models. Each of the seven round-robin teams independently simulated the test scenario a priori using a common detailed description of the compartment geometry, fuel packages, ignition source and ventilation conditions. The aim of the exercise was to forecast the fire development as accurately as possible and compare the results. The aim was not to provide an engineering analysis with conservative assumptions or safety factors. Comparison of the modelling results shows a large scatter and considerable disparity among the predictions, and between predictions and experimental measurements. The scatter of the simulations is much larger than the error and variability expected in the experiments. The study emphasises on the inherent difficulty of modelling fire dynamics in complex fire scenarios like Dalmarnock, and shows that the accuracy to predict fire growth (i.e. evolution of the heat released rate) is, in general, poor.

a b s t r a c tWhen building fires occur in large, open compartments they rarely burn uniformly across an entire floor plate of a structure. Instead, they tend to travel, igniting fuel in their path and burning it out as they move to the next fuel package. Current structural fire design methods do not account for these types of fires. This paper applies a novel methodology for defining a family of possible heating regimes to a framed concrete structure using the concept of travelling fires. A finite-element model of a generic concrete structure is used to study the impact of the family of fires; both relative to one another and in comparison to the conventional codified temperature-time curves. It is found that travelling fires have a significant impact on the performance of the structure and that the current design approaches cannot be assumed to be conservative. Further, it is found that a travelling fire of approximately 25% of the floor plate in size is the most severe in terms of structural response. It is concluded that the new approach is simple to implement, provides more realistic fire scenarios, and is more conservative than current design methods.

Traditional methods for quantifying and modelling compartment fires for structural engineering analysis assume spatially homogeneous temperature conditions. The accuracy and range of validity of this assumption is examined here using the previously conducted fire tests of Cardington (1999) and Dalmarnock (2006). Statistical analyses of the test measurements provide insights into the temperature field in the compartments. The temperature distributions are statistically examined in terms of dispersion from the spatial compartment average. The results clearly show that uniform temperature conditions are not present and variation from the compartment average exists. Peak local temperatures range from 23% to 75% higher than the compartment average, with a mean peak increase of 38%. Local minimum temperatures range from 29% to 99% below the spatial average, with a mean local minimum temperature of 49%. The experimental data are then applied to typical structural elements as a case study to examine the potential impact of the gas temperature dispersion above the compartment average on the element heating. Compared to calculations using the compartment average, this analysis results in increased element temperature rises of up to 25% and reductions of the time to attain a pre-defined critical temperature of up to 31% for the 80 th percentile temperature increase. The results show that the homogeneous temperature assumption does not hold well in post-flashover compartment fires. Instead, a rational statistical approach to fire behaviour could be used in fire safety and structural engineering applications.Kirby et al. [15] ran a test series burning wood cribs in a long enclosure with approximate dimensions of 22.9 m long x 5.6 m wide x 2.8 m high. All of the tests were ignited at the rear, except one in which all wood cribs were ignited simultaneously. The results of all tests show that the fire moved relatively quickly from the ignition location to the front of the compartment, where the vent was located. After the fuel in the front of the compartment burned out, the fire progressively travelled back into the compartment and ultimately consumed all the fuel and self-extinguished at the rear. Temperature results of Test 1 from this test series are shown below in Figure 1 at the rear, middle and front of the compartment. structural elements are adversely affected by temperature gradients gives motivation to revisit the homogeneous temperature assumption and further explore its ramifications.While the full implications of the temperature heterogeneity of post-flashover fires are not explored here, it is apparent that post-flashover fires do not reach uniform conditions. The presented results highlight the need to increase the spatial resolution of measurements in fire experiments to capture the full variation within the compartment. Spatially resolved data can lead to a rational statistical approach to fire behaviour when applied to fire safety and structural engineering applications.