Development of realistic design fire time-temperature curves for the testing of cold-formed steel wall systems

Fire resistance rating of light gauge steel frame (LSF) wall systems is obtained from fire tests based on the standard fire time-temperature curve. However, fire severity has increased in modern buildings due to higher fuel loads as a result of modern furniture and light weight constructions that make use of thermoplastics materials, synthetic foams and fabrics. Some of these materials are high in calorific values and increase both the spread of fire growth and heat release rate, thus increasing the fire severity beyond that of the standard fire curve. Further, the standard fire curve does not include a decay phase that is present in natural fires. Despite the increasing usage of LSF walls, their behavior in real building fires is not fully understood. This paper presents the details of a research study aimed at developing realistic design fire curves for use in the fire tests of LSF walls. It includes a review of the characteristics of building fires, previously developed fire time-temperature curves, computer models and available parametric equations. The paper highlights that real building fire time-temperature curves depend on the fuel load representing the combustible building contents, ventilation openings and thermal properties of wall lining materials, and provides suitable values of many required parameters including fuel loads in residential buildings. Finally, realistic design fire time-temperature curves simulating the fire conditions in modern residential buildings are proposed for the testing of LSF walls.     

A Parametric Study on the Time-to-Failure of Wood Framed Walls in Fire

A model has been developed for predicting the time-to-failure of gypsum board clad wood framed walls exposed to fire. This model was developed for designing wood framed walls in accordance with new performance-based building fire codes being introduced around the world. The model has been used to undertake a parametric study of the effects of a wide range of variables on the time-to-failure due to structural collapse. The study found that the most dominant variables in building construction in descending order of importance are depth and breadth of stud sections, fire temperature, thickness of gypsum board, elastic modulus of wood in compression, enthalpy of gypsum board (that is the product density and specific heat) and vertical load. Variations in the thermal properties of wood do not dominate the influences affecting the time-to-failure. The study supports the component additive method for estimating the fire resistance of walls.     

Fire development in a 1/3 train carriage mock-up

To study what parameters that control the initial fire spread and the development to local flashover in a metro carriage, a total of six fire tests were conducted in a mock-up of a metro carriage that is about 1/3 of a full wagon length. They were carried out under a large scale calorimeter in a laboratory environment. The focus was on the initial fire development in a corner scenario using different types of ignition source that may lead to a fully developed fire. The ignition sources used were either a wood crib placed on a corner seat or one litre of petrol poured on the corner seat and the neighbouring floor together with a backpack. The amount of luggage and wood cribs in the neighbourhood of the ignition source was continuously increased in order to identify the limits for flashover in the test-setup. The tests showed that the combustible boards on parts of the walls had a significant effect on the fire spread. In the cases where the initial fire did not exceed a range of 400–600 kW no flashover was observed. If the initial fire grew up to 700–900 kW a flashover was observed. The maximum heat release rate during a short flashover period for this test set-up was about 3.5 MW. The time to reach flashover was highly dependent on the ignition type: wood cribs or backpack and petrol. A full developed carriage fire was achieved as a result of intense radiation from the flames and ceiling smoke layer. This was mostly dependent on the amount of fire load nearby the ignition source and how strong the vertical flame spread on the high pressure laminate boards mounted to walls and ceiling above the ignition source was, leading to a ceiling flame. In such cases, the seats alone did not contain sufficient fuel for the fire to spread within the train, and additional fuel (luggage) is required near the seats. For fully developed carriage fires, the fire starting on the seat in the corner spread to the opposite seat on the same side of the aisle, then horizontally spread to seats on the other side of the aisle, and finally a longitudinal flame spread along the carriage was observed. When and where the fire stopped or whether it reached a fully developed stage was mostly dependent on the amount of fire load nearby the ignition source and how strong the vertical flame spread on the high pressure laminate boards mounted to walls and ceiling above the ignition source was.     

Performance-based firefighting in dense historic settlements: An exploration of a firefighting approach combining value and risk assessment with numerical simulation

In view of the fire problems left in dense historical settlements in China, such as fire hazards that are prone to fires, difficulties in fighting fires, and the incomplete applicability of current fire codes due to the high historical value of buildings, this paper proposes a scientific and systematic performance-based fire protection method that gives priority to value preservation. This method is applied to dense historical settlements, and the effectiveness of this method is verified by evaluating the results of fire protection planning and renovation through multiple rounds of computer numerical simulation. The results show that in a connected cluster of buildings, one of the fire retrofitting requirements in the horizontal or vertical direction needs to be met between two adjacent buildings to ensure that the fire does not spread, and the retrofitting direction has to be selected based on the value and risk assessment results. When dense historical clusters are renovated for fire prevention planning, the optimal renovation path to meet fire safety can be effectively selected based on the method proposed in this paper.     

Numerical modelling of load bearing light gauge steel frame wall systems exposed to realistic design fires

Fire safety has become an important part in structural design due to the ever increasing loss of properties and lives during fires. Conventionally the fire rating of load bearing wall systems made of Light gauge Steel Frames (LSF) is determined using fire tests based on the standard time–temperature curve in ISO834 (ISO 834-1, 1999 [1]). However, modern commercial and residential buildings make use of thermoplastic materials, which mean considerably high fuel loads. Hence a detailed fire research study into the fire performance of LSF walls was undertaken using realistic design fire curves developed based on Eurocode parametric (ENV 1991-1-2, 2002 [2]) and Barnett's BFD (Barnett, 2002 [3]) curves using both full scale fire tests and numerical studies. It included LSF walls without cavity insulation, and the recently developed externally insulated composite panel system. This paper presents the details of finite element models developed to simulate the full scale fire tests of LSF wall panels under realistic design fires. Finite element models of LSF walls exposed to realistic design fires were developed, and analysed under both transient and steady state fire conditions using the measured stud time–temperature curves. Transient state analyses were performed to simulate fire test conditions while steady state analyses were performed to obtain the load ratio versus time and failure temperature curves of LSF walls. Details of the developed finite element models and the results including the axial deformation and lateral deflection versus time curves, and the stud failure modes and times are presented in this paper. Comparison with fire test results demonstrate the ability of developed finite element models to predict the performance and fire resistance ratings of LSF walls under realistic design fires.     

Variation of heat release rate with forced longitudinal ventilation for vehicle fires in tunnels

Many tunnels are equipped with longitudinal ventilation systems to control smoke in the event of a fire. However, the influence of such ventilation on fire development and fire spread has rarely been considered. This paper presents the results of a study using a Bayesian methodology to estimate the effect of forced longitudinal ventilation on heat release rate (HRR) for fires in tunnels. The behaviour of car and heavy goods vehicle (HGV) fires with a range of forced ventilation velocities is investigated. Results are presented and the implications are discussed. It has been found that forced ventilation has a great enhancing effect on the HRR of HGV fires, but has little effect on the HRR of car fires.     

The effect of flow and geometry on concurrent flame spread

Flame spread is an important parameter used in the evaluation of hazards for fire safety applications. The problem of understanding and modeling flame spread has been approached before, however new developments continue to challenge our current view of the subject, necessitating future research efforts in the field. In this review, the problem of flame spread will be revisited, with a particular emphasis on the effect of flow and geometry on concurrent flame spread over solid fuels. The majority of this research is based on that of the senior author, who has worked on wind-driven flame spread, inclined fire spread, flame spread through discrete fuels and the particular problem of wildland fires, where all of the above scenarios play an important role. Recent developments in these areas have improved our understanding of flame-spread processes and will be reviewed, and areas for future research will be highlighted.     

Structural behaviour during a vertically travelling fire

This study considers a multi-storey composite frame subject to a fire which travels vertically between three floors. Previous work has analysed the behaviour of this structure when subject to simultaneous fires on three floors. It highlighted the importance of the cooling regime adopted and the relative axial stiffness of the steel beams to the overall behaviour of the structure. This paper extends that work by investigating the more realistic case of a vertically travelling fire. Various inter-floor time delays are considered as well as two floor beam sizes. It is found that the inter-floor time delay affects the global behaviour substantially. The behaviour is also in part dependent on the stiffness of the floor beams. Axial forces caused by thermal expansion in individual floors may induce cyclic loading on the column which is not normally considered in structural fire design but may be important in determining structural behaviour. Identifying a worst-case rate of vertical fire spread is not possible due to the range of structural responses, so it is recommended that designers consider several rates of spread and ensure structural integrity for each.     

Determination of Separation Distances Inside Large Buildings

In this study, an analytical framework is developed to determine the hazards posed by an uncontrolled fire burning indoors. This scenario, unlike unconfined outdoor fires, has received little attention in the literature and associated engineering methods for risk evaluation are unavailable. The present analyses are limited to overventilated fires burning in large non-combustible buildings. Hazards are evaluated on the basis of thermal radiation and firebrand transport. Thermal radiation is assessed using a solid flame radiation model; transport of firebrands is evaluated taking into consideration the convective ceiling layer established by the fire plume. Given the considerably different geometry of the scenario of interest herein, as compared to unconfined fires, efforts are placed in developing a rigorous physical and mathematical approach so as to make the developed methodology sufficiently general. The model derived is validated against limited heat flux data obtained for free-burn fires (up to 50 MW) involving Class 2 commodity rack storage arrays. In addition, general trends are investigated using a hypothetical sample scenario. Results show that thermal radiation is the main phenomenon driving the hazards encountered in indoor fires; firebrand transport, due to ceiling confinement, presents a much lesser hazard.     

A study of non-flashover and flashover fires in a full-scale multi-room building

Realistic fire environments in a prototype multi-room apartment in a multi-storey building are studied. The fires are designed as non-flashover and flashover types, using standard polyurethane mattresses as fuel. A comprehensive set of experimental data is presented. The measured results include flame spread velocity, mass release rate, gas temperature, radiation heat flux and gas analysis. A computational fluid dynamics (CFD) model, called a CESARE-CFD fire model, has been used to simulate these polyurethane slab fires. The CFD model is described by three-dimensional transport equations for mass, momentum and enthalpy. The turbulence flow was modelled using the k−ϵ model. A soot formation model and a flame spread model were incorporated into the CFD model. The flame spread velocity and the mass release rate of the polyurethane slab fires were predicted in this study. It was found that the CFD model provided reasonable predictions of the magnitude and trends for the experiments both in the non-flashover and flashover fire cases.     

Modelling of two-dimensional flame spread across a sloping fuel bed

A significant contributing factor to wildland fire development is the slope effect which causes the fire spread rate to increase considerably as compared to horizontal spread. This leads to difficulties in determining the development of the fires hence in coordinating forest fighting efforts. In the present study, a two-dimensional non-stationary model for a fire spreading across a sloping fuel bed made up of Pinus pinaster litter is described. Based on a series of hypotheses, we first defined a medium equivalent to the pine needle litter for which we provided a thermal balance. By coupling this balance to a diffusion flame model we obtained the fire spread model numerically solved by means of the SIMPLEC procedure. The fire spread rates given by the simulations were then compared to experimental results generated by small-scale laboratory fires for a range of slope values. Predicted flow field structure, and temperature field are also discussed.     

The influence of longitudinal ventilation systems on fires in tunnels

Many tunnels are equipped with longitudinal ventilation systems to control smoke in the event of a fire. However, the influence of such ventilation on fire development and fire spread has rarely been considered. This paper presents the results of a study investigating the influence of forced longitudinal ventilation on car fires, pool fires and heavy goods vehicle fires in tunnels. A Bayesian probabilistic approach is used to refine estimates, made by a panel of experts, with data from experimental fire tests in tunnels. Results are presented and the implications are discussed. The influence of longitudinal ventilation on heavy goods vehicle fires is predicted to be much larger than the experts’ estimates, causing a fire to grow ten times larger than if natural ventilation was used. The effect of ventilation on a pool fire in a tunnel depends on the size of the pool; the heat release rate of small pool fires may be reduced by forced ventilation, whereas it may be enlarged for large pool fires. The size of a car fire is not expected to be greatly affected by forced ventilation at low ventilation velocities.     

Wildland fire spot ignition by sparks and firebrands

Wildland and Wildland Urban Interface (WUI) fires are an important problem in many areas of the world and may have major consequences in terms of safety, air quality, and damage to buildings, infrastructure, and the ecosystem. It is expected that with climate changes the wildland fire and WUI fire problem will only intensify. The spot fire ignition of a wildland fire by hot (solid, molten or burning) metal fragments/sparks and firebrands (flaming or glowing embers) is an important fire ignition pathway by which wildfires, WUI fires, and fires in industrial settings are started and may propagate. There are numerous cases reported of wildfires started by hot metal particles from clashing power-lines, or generated by machines, grinding and welding. Once the wildfire or structural fire has been ignited and grows, it can spread rapidly through ember spotting, where pieces of burning material (e.g. branches, bark, building materials, etc.) are lofted by the plume of the fire and then transported forward by the wind landing where they can start spot fires downwind. The spot fire problem can be separated in several individual processes: the generation of the particles (metal or firebrand) and their thermochemical state; their flight by plume lofting and wind drag and the particle thermo-chemical change during the flight; the onset of ignition (smoldering or flaming) of the fuel after the particle lands on the fuel; and finally, the sustained ignition and burning of the combustible material. Here an attempt has been made to summarize the state of the art of the wildfire spotting problem by describing the distinct individual processes involved in the problem and by discussing their know-how status. Emphasis is given to those areas that the author is more familiar with, due to his work on the subject. By characterizing these distinct individual processes, it is possible to attain the required information to develop predictive, physics-base wildfire spotting models. Such spotting models, together with topographical maps and wind models, could be added to existing flame spread models to improve the predictive capabilities of landscape-scale wildland fire spread models. These enhanced wildland fire spread models would provide land managers and government agencies with better tools to prescribe preventive measures and fuels treatments before a fire, and allocate suppression resources and issue evacuation orders during a fire.     

Effectiveness of vertical barriers in preventing lateral flame spread over exposed EPS insulation wall

Insulation panels made of organic, combustible materials are frequently used in the exterior thermal insulation systems (ETIS) for buildings. Such combustible insulation panels have been involved in several catastrophic building fires in recent years in China. One potential strategy to mitigate this fire hazard is to limit fire spread over the ETIS. The present work evaluates the effectiveness of vertical fire barriers in inhibiting fire spread over exposed insulation walls made of expanded polystyrene (EPS) panels. Reduced-scale experiments were carried out indoors using EPS panels with or without two vertical barriers made of non-combustible mineral wool, the fire started at the bottom center of the middle panel. The interval and width of the barriers were varied systematically, while the temperature distribution on the wall, the radiation heat flux from the fire, and the infra-red (IR) images were recorded. To demonstrate the validity of the concept, an outdoor, full-scale experiment was carried out using a 7-floor building. Our reduced-scale experiments showed that the installation of two vertical fire barriers successfully stopped the lateral flame spread, decreasing the peak temperatures of the two side panels by about 300 °C for all barrier configurations tested. When barrier width was fixed at 5 cm, an increase of the barrier interval from 30 to 90 cm led to increases in the peak temperatures, radiation heat flux, and the maximum rate of upward flame spread. By contrast, when barrier interval was fixed at 90 cm, an increase of the barrier width from 2 to 5 cm had little influence on the combustion dynamics of the middle panel but the peak temperature on the side panels dropped, consistent with the smaller heat transferred with wider fire barriers. In the regions of the side panels next to the barriers, pyrolysis and deformation could be observed with barrier widths of 2 and 3 cm, but not 5 cm. Finally, our outdoor, full-scale experiment demonstrated that a 30 cm wide vertical barrier made of air-filled cement successfully stopped the lateral flame spread over exposed EPS wall. The study highlights the effectiveness of vertical fire barriers in preventing the lateral flame spread over the exposed EPS insulation wall and provides another option for enhancing the fire safety of the combustible insulation systems.     

Fire performance of combustible insulation in masonry cavity walls

The risk of fire spread in buildings, from one room/compartment to another, through cavity walls filled with a range of combustible insulating materials has been investigated.Tests have been carried out on small-scale or storey-high walls having two masonry facings, insulated with typical examples of loose fill, board or in situ foamed plastics products. A small localized penetration of both facings simulating for example an ineffectively sealed air brick was built into the lower part of the experimental wall and two ‘eave’ conditions were investigated viz with the perimeter either sealed or partially open. A small crib was positioned adjacent to the cavity penetration and the subsequent extent of spread of fire and smoke was noted visually; temperature measurements within the cavity were recorded together with heat flux measurements in the combustion zone.The experiments showed the dependence of the extent of fire spread on the air supply to the combustion zone; in this type of wall with the upper perimeter sealed, the risk of flame or smoke spread from one area to another is negligible. With the upper edge partially unsealed, no flame and only negligible smoke spread was noted with in situ foamed insulations. With granular fill, retained in position within the cavity, some smoke percolated upwards but the risk of eventual spread of fire through the eave opening was restricted to three products, which have subsequently been withdrawn from the market. Thermoplastic bead flowed through the hole into the fire area contributing to the fuel load but when installed with an adhesive the bead was effectively maintained in position and performed like the in situ foamed products. It was found with one specific test condition that slow flame spread could be sustained through a continuous cavity adjacent to expanded polystyrene insulating boards provided the eave perimeter of the cavity was unsealed. Whilst such flame spread is unlikely to affect directly any inhabited areas of the building, sealing of cavities insulated with combustible boards is considered to be essential to prevent smoke spread, possible roof fires and destruction of the insulant.     

Instrumentation of wildland fire: Characterisation of a fire spreading through a Mediterranean shrub

Although considerable progress has been made recently in the modelling of the spreading of a forest fire, there remains a lack of reliable field measurements of thermodynamic quantities. We propose in this paper a method and a set of measuring structures built in order to improve the knowledge of the fundamental physical mechanisms that control the propagation of wildland fires. These experimental devices are designed to determine: the fire front shape, its rate of spread, the amount of energy impinging ahead of it, the vertical distribution of the temperature within the fire plume as well as the wind velocity and direction. The methodology proposed was applied to a fire spreading across the Corsican scrub on a test site. The recorded data allowed us to reconstruct the fire behaviour and provide its main properties. Wind and vegetation effects on fire behaviour were particularly addressed.     

An approach to modeling wall fire spread in a room

An attempt is made to develop a framework for modeling wall fire spread in a room. The zone methodology for treating developing room fires is used, and its characteristic layer equations are discussed. A review is made of studies on the rate of burning and spread on vertical surfaces. Both of these phenomena are shown to depend on the incident radiative heat flux and the local oxygen concentration. Functional expressions are suggested, and a strategy is presented for incorporating these component analyses into a wall flame spread model. The goal of this model would be to assess the risk of rapid fire growth (flashover) relative to wall property data found through fundamental principles and through emperical fire test methods.     

室外变压器火灾燃烧特性全尺度实验研究

开展35 kV室外变压器全尺度火灾实验研究,探究变电站火灾燃烧特性。同时考虑4处火灾,在变压器不同位置设置火源,分析火焰传播情况、温度变化曲线,为变电站消防建设和应急救援提供理论支撑。研究表明：变压器火灾具有隐蔽、立体、多尺度的燃烧特征。多个尺度不一的立体火源在燃烧过程中存在多个火焰的相互碰触、合并行为;在充分燃烧阶段,变压器上部火焰存在火焰震荡、分离等不稳定现象。火焰形态在下方主要为贴壁火焰,在上方主要为扩散燃烧形成的连续火焰和间歇火焰;温度分布在垂直方向呈现逐渐降低的规律,在水平方向呈现中间温度高,两侧温度低的规律。