A Review and Analysis of the Thermal Exposure in Large Compartment Fire Experiments

Developments in the understanding of fire behaviour for large open-plan spaces typical of tall buildings have been greatly outpaced by the rate at which these buildings are being constructed and their characteristics changed. Numerous high-profile fire-induced failures have highlighted the inadequacy of existing tools and standards for fire engineering when applied to highly-optimised modern tall buildings. With the continued increase in height and complexity of tall buildings, the risk to the occupants from fire-induced structural collapse increases, thus understanding the performance of complex structural systems under fire exposure is imperative. Therefore, an accurate representation of the design fire for open-plan compartments is required for the purposes of design. This will allow for knowledge-driven, quantifiable factors of safety to be used in the design of highly optimised modern tall buildings. In this paper, we review the state-of-the-art experimental research on large openplan compartment fires from the past three decades. We have assimilated results collected from 37 large-scale compartment fire experiments of the open-plan type conducted from 1993 to 2019, covering a range of compartment and fuel characteristics. Spatial and temporal distributions of the heat fluxes imposed on compartment ceilings are estimated from the data. The complexity of the compartment fire dynamics is highlighted by the large differences in the data collected, which currently complicates the development of engineering tools based on physical models. Despite the large variability, this analysis shows that the orders of magnitude of the thermal exposure are defined by the ratio of flame spread and burnout front velocities (VS / VBO), which enables the grouping of open-plan compartment fires into three distinct modes of fire spread. Each mode is found to exhibit a characteristic order of magnitude and temporal distribution of thermal exposure. The results show that the magnitude of the thermal exposure for each mode are not consistent with existing performance-based design models, nevertheless, our analysis offers a new pathway for defining thermal exposure from realistic fire scenarios in large open-plan compartments

A Thin Skin Calorimeter (TSC) for quantifying irradiation during large-scale fire testing

This paper details a novel method for quantifying irradiation (incident radiant heat flux) at the exposed surface of solid elements during large-scale fire testing. Within the scope of the work presented herein, a type of Thin Skin Calorimeter (TSC) was developed intending for a practical, low cost device enabling the cost-effective mass production required for characterising the thermal boundary conditions during multiple large-scale fire tests. The technical description of the TSC design and a formulation of the proposed calibration technique are presented. This methodology allows for the quantification of irradiation by means of an a posteriori analysis based on a temperature measurement from the TSC, a temperature measurement of the gas-phase in the vicinity of the TSC and a correction factor defined during a pre-test calibration process. The proposed calibration methodology is designed to account for uncertainties inherent to the simplicity of the irradiation measurement technique, therefore not requiring precise information regarding material thermal and optical properties. This methodology is designed and presented so as to enable adaption of the technique to meet the specific requirements of other experimental setups. This is conveyed by means of an example detailing the design and calibration of a device designed for a series of large-scale experiments as part of the ‘Real Fires for the Safe Design of Tall Buildings’ project

Characterisation of Dalmarnock Fire Test One

Journal paperThe Dalmarnock Tests comprise a set of fire experiments conducted in a real high-rise building in July 2006. The two main tests took place in identical flats, Test One allowing the fire to develop freely to post-flashover conditions while Test Two incorporated sensor-informed ventilation management. The test compartments were furnished with regular living room/office items and fully instrumented with high sensor densities. The furniture and objects acting as fuel were arranged to provide conditions that favour repeatability. A full description of the set up of the tests, including fire monitoring sensors, is provided. Focus is on the larger Test One fire for which the major events are reported together with a thorough characterisation of the fire using sensor information. The main aim of the experiments was to collect a comprehensive set of data from a realistic fire scenario that had a resolution compatible with the output of field models. The characterisation of Test One provides a platform with potential for analytical and computational fire model validation

Ventilation effects on the thermal characteristics of fire spread modes in open-plan compartment fires

Our understanding of fire behaviour and heating conditions for load-bearing structural elements was developed from an immense body of research in small under-ventilated compartment fires. Within the context of contemporary architecture, large open-plan compartments are commonplace, yet understanding of the first principles that define fire behaviour in such enclosures remains limited. Past experiments have revealed that fires in open-plan compartments exhibit three distinct fire spread modes: a fully-developed fire, a growing fire, and a travelling fire. This paper studies the thermal characteristics arising from these fire spread modes and the effects of the ventilation imposed. An experimental analysis of the energy distribution and spatial heating is conducted on a series of large-scale compartment fire tests, with the fire spread mode and ventilation conditions systematically varied. Each fire spread mode is shown to induce significant and characteristic spatial heat distributions. Moreover, the analysis of the ventilation modes shows equivalent thermal loads imposed on the structure in cases where the opening areas are large, and plume flows are dominant despite lower gas temperatures and irradiation. Thus, fires in open-plan compartments pose unique and possibly more severe thermal loading to structural systems, a characteristic not captured by current design fire methodologies

Forensic analysis of fire induced structural failure

Fire investigation has generally focused on the identification of the cause and origin of a fire. Thus methodologies developed for this purpose are mainly based on the dynamics of fire growth and the investigation of its effect on the different objects within the structure affected by the fire. It is unusual to come across a fire investigation emphasizing structural damage as a means to obtain information for fire reconstruction. A series of dramatic fire events such as the Windsor Tower (Spain) and the World Trade Centre (USA) collapses have emphasized the need to introduce a structural analysis alongside the evaluation of the fire timeline. Only the combined analysis is capable of providing a complete reconstruction of such an event and therefore a solid determination of causality. This paper presents a methodology to establish the sequence of events leading to a fire-related structural failure, by means of modern structural and fire analysis tools. This analysis will be compared with classic cause and origin techniques emphasizing the importance of a comprehensive study. Specific structural features and fire conditions that lead to unique forms of failure will be discussed establishing the complexity of linking fire, structural characteristics and failure mode. A series of examples will be used to illustrate different forms of failure and the fires that originate them

An experimental study of full-scale open floor enclosure fires

A full-scale experimental series is undertaken to generate a comprehensive data set to study and characterise fires in large open-plan spaces, typical of contemporary infrastructure and Tall Buildings in particular. Developments in the understanding of enclosure fire dynamics for large spaces is intended to complement the knowledge of relatively smaller, low ventilation spaces developed from the extensive body of research that underpins the original compartment fire framework. A total of twelve experiments are conducted, ten using box gas burners and two using a bed of wood cribs. Both the fire development and ventilation characteristics are varied systematically to enable the careful examination of the effect of each on the fire dynamics within the compartment. For this set of tests, sensor instrumentation is, as far as practicable, provided at a resolution to enable benchmarking of field models. These tests form part of the Real Fires for the Safe Design of Tall Buildings Project. The current paper, the first in a series of publications, provides a thorough description of the full-scale experimental compartment, the various sensing techniques deployed within it, and the range of combined fire and ventilation conditions for each of the twelve tests performed. Characteristic results from the first experiment that forms part of the ‘Edinburgh Tall Building Fire Tests’ (ETFT) test series are presented