Showing papers in "Fire Safety Science in 2014"

Experimental and survey studies on the effectiveness of dynamic signage systems

Abstract: Signage systems are widely used in the built environment to aid occupant wayfinding during both circulation and evacuation. Recent research conducted by the authors shows that only 38% of people ‘see’ conventional static emergency signage in presumed emergency situations in an unfamiliar built environment, even if the sign is located directly in front of them and their vision is unobstructed. However, most people who see the sign follow the sign. These results suggest that current emergency guidance signs are less effective as an aid to wayfinding than they potentially can be and that signs are likely to become more effective if their detectability can be improved while upholding the comprehensibility of the guidance information they provide. A novel dynamic signage design is proposed to address this issue. The effectiveness of the new sign is tested under almost identical experimental settings and conditions as in the previous experiments examining conventional, static signs. The results show that 77% of people ‘see’ the dynamic sign and 100% of them go on to follow the sign. In addition, a dynamic method to identify that an exit route is no longer viable is tested using an international survey to gauge understanding of the new signage concept. Survey results suggest that the purpose of the new sign can be clearly understood by over 90% of the sample.

Revisiting the Compartment Fire

Abstract: Understanding the relevant behaviour of fire in buildings is critical for the continued provision of fire safety solutions as infrastructure continually evolves. Traditionally, new and improved understanding has helped define more accurate classifications and correspondingly, better prescriptive solutions. Among all the different concepts emerging from research into fire behaviour, the "compartment fire" is probably the one that has most influenced the evolution of the built environment. Initially, compartmentalization was exploited as a means of reducing the rate of fire spread in buildings. Through the observations acquired in fires, it was concluded that reducing spread rates enabled safe egress and a more effective intervention by the fire service. Thus, different forms of compartmentalization permeated through most prescriptive codes. Once fire behaviour within a compartment was conceptualized on the basis of scientific principles, the "compartment fire" framework became a means to establish, under certain specific circumstances, temperatures and thermal loads imposed by a fire to a building. This resulted not only in improved codes but also in a scientifically based methodology for the assessment of structural performance. The last three decades have however seen an evolution of the built environment away from compartmentalization while the "compartment fire" framework has remained. It is therefore necessary to revisit the knowledge underpinning this seminal approach to initiate discussion of its continued relevance and applicability to an increasingly non-compartmentalised built environment. This paper, through a review of classic literature and the description of some recent experimentation, aims to inform and encourage such discussion.

Enabling the Investigation of Structure Vulnerabilities to Wind- Driven Firebrand Showers in Wildland-Urban Interface (WUI) Fires

Abstract: Wind-driven firebrand showers are a major cause of structural ignition in Wildland-Urban Interface (WUI) fires. Past firebrand investigations have not been able to quantify the vulnerabilities of structures to ignition from firebrand showers, as it is difficult to develop a measurement method to replicate wind-driven firebrand attack on structures that occur in actual WUI fires. To address this problem, research has been undertaken in an intricate area involving the quantification of structure vulnerabilities to wind-driven firebrand showers. This type of firebrand research has never been possible prior to the development of the NIST Firebrand Generator, also referred to as the NIST Dragon. Due the complexity of the WUI fire problem, great strides must be made to recruit the next generation of researchers to fire safety science from diverse backgrounds. This paper closes with a discussion of ongoing workshop activities intended to achieve this, as well as some challenges for future WUI fire research.

Fire Tests on Loaded Cross-laminated Timber Wall and Floor Elements

Abstract: Cross-laminated timber (CLT) panels are relatively new engineered wood products that can be used as load bearing walls, floors and roof elements in innovative and high quality modern timber structures. The fire behavior of cross-laminated timber panels requires careful evaluation to allow the expansion of CLT elements usage in buildings. A University of British Columbia study has been conducted at the Trees and Timber Institute CNR-IVALSA in San Michele all’Adige, Italy to experimentally evaluate the fire performance of Canadian CLT panels. In total, ten loaded fire tests were performed using standard fire curves (ULC/ASTM and ISO) to study the influence of different cross-section layups on the fire resistance of floor and wall elements and to investigate the influence of different anchors on the fire behavior of wall elements. This paper presents the main results of the experimental analyses and discusses in particular the charring rate, one of the main parameters in fire design.

Spectral Aspects of Bench-Scale Flammability Testing: Application to Hardwood Pyrolysis

Abstract: The anaerobic pyrolysis of wood material used to palletize commodities is studied in a Fire Propagation Apparatus (FPA) for a range of heating conditions relevant to fires. The data collected, consisting of mass loss rate, cumulative mass loss, and surface temperature, are used to determine model-specific material properties using inverse modeling and optimization methodologies previously developed in our laboratory. However, in this study, considerable effort is placed on determining the radiation environment that characterizes the FPA tests as well as how the radiation interacts with the samples. This is done on the basis of the recognition that boundary conditions have a pronounced effect on the output of a given pyrolysis model and, thus, the optimization results. The spectral radiance from the FPA heaters as well as the absorptivity/emissivity of the material surface are measured herein. The spectral features of the surface indicate that markedly different effective emissivities and absorptivities can be exhibited by the material depending on the spectral distribution of incident radiation. These effects are included in the pyrolysis model used to extract model-specific material properties so that the optimization process can, in a sense, be decoupled from boundary conditions. Therefore, it is expected that the approach described in this study can ensure that the derived model-specific properties can be applied to practical scenarios that are characterized by radiation environments that differ from those in bench-scale test apparatuses such as the FPA.

Correlations for evaluation of flame spread over an inclined fuel surface

Abstract: The time-dependent flame spread process over thermally thick slabs of polymethyl methacrylate (PMMA) is investigated with particular emphasis on the burning behavior and geometry of the flame. 10 cm wide by 20 cm long samples are ignited and allowed to spread upwards at angles of orientation between pool and ceiling burning. Correlations between the flame length and the fuel mass-loss rate have revealed a delayed transition to turbulence for flames residing on the underside of fuel samples, and an earlier transition to turbulence for flames on the topside of these samples, compared to traditional vertical wall flames. As the fuel inclination increases, the relationship between the flame length and fuel mass-loss rate ranges between a recent theoretical prediction for a laminar wall plume dominated by diffusion and the traditional prediction for a turbulent wall plume dominated by convective mixing. The buoyancy-induced flow field, characterized by the flame tilt angle is shown to correspond to previously-found modifications of heat-flux profiles ahead of the flame front, which control flame spread, and the heat flux to the burning surface of the fuel, which controls fuel mass-loss rates. Other correlations between some of these parameters, such as the flame and pyrolysis lengths are also presented as a function of inclination.

Fire Testing a New Fluorine-free AFFF Based on a Novel Class of Environmentally Sound High Performance Siloxane Surfactants

Abstract: The most effective fire extinguishing agents for pool fires are Aqueous Film Forming Foams (AFFF). Today, all available AFFF contain polyfluorinated compounds (PFC), i.e. polyfluorinated tensides (PFT), to establish the aqueous film on the surface of a burning liquid. These fluorinated compounds are persistent, potentially bio-accumulative and toxic. Therefore it is essential to find environmentally sound substitutes for these problematic surfactants. Commercially available fluorine-free foams (FfreeF) lack the ability of aqueous film formation. Although FfreeF are performing well in many situations [1,2], there are numerous scenarios where an aqueous film forming component is mandatory for fast fire extinguishing, e.g. in case of burning liquids. To achieve a well performing AFFF, a new approach is to replace the film forming PFC/PFT by siloxane surfactants. Today, siloxane surfactants are typically used in plant protective agents, in textile surface treatment and as lubricants. As the properties of commercially available siloxane surfactants are not suitable for AFFF, new siloxane surfactants were designed, synthesized and tested for their suitability as film forming ingredients in AFFF formulations. The surface activity and foaming behaviour of model formulations have been determined. Finally, one experimentally fluorine-free AFFF formulation has been subjected to fire tests. In this context a new fire test for scarcely available chemicals is presented.

Gpyro3D: A Three Dimensional Generalized Pyrolysis Model

Abstract: All objects that burn in fires are three dimensional. However, almost all previous attempts to model the burning or pyrolysis of real materials has resorted to a one-dimensional description. This paper presents the mathematical formulation of Gpyro3D, a generalized three dimensional pyrolysis model that solves conservation equations for transport of heat, mass, and species in a chemically reacting porous medium, as well as its coupling to NIST’s Fire Dynamics Simulator (FDS) for simulating fire development. Gpyro3D facilitates pyrolysis modeling in complex geometries by masking grid cells on a regular Cartesian grid, similar to the way that geometry is specified in FDS. The model’s mathematical formulation is verified by comparing numerical simulations to analogous exact solutions. Next, it is shown that Gpyro3D qualitatively captures the major three dimensional features of long-duration (> 1 hour) oxidative pyrolysis of wet wood under radiative heating. Finally, fire development in a wood crib is simulated with the coupled Gpyro3D/FDS model. By observing condensed-phase temperature contours within burning elements of the wood crib, it is shown that strong three dimensional effects are present.

Numerical Simulation of Sprinkler Suppression of Rack Storage Fires

Abstract: Fire suppression tests with ceiling sprinkler protection in a rack storage fuel configuration are simulated using a Computational Fluid Dynamics tool. The fuel is arranged in a double-row, six pallet-load wide and three-tier high (2×6×3) rack storage array. Each pallet load consists of three nested double-wall corrugated cardboard boxes surrounding a metal liner. Two types of ceiling sprinklers are used in this study: a pendent quick response sprinkler designated as K14, and an upright standard response sprinkler designated as K11.2. The tests are simulated using FireFOAM, which couples necessary sub-models for fire growth, sprinkler response, and fire suppression. Numerical results are compared with experiments for both free burn tests under a 20-MW calorimeter and sprinkler suppression tests under a 7.6 m high ceiling. For the free burn case, the model results show good quantitative agreement of heat release rates in all three phases, from ignition to fire growth and steady burning. For the suppression cases, the model reproduces the suppression effectiveness of the two sprinkler protection designs: K14 sprinklers suppress the fire rapidly with only one sprinkler activation, while with K11.2 sprinklers, both in the tests and simulation, the fire spreads to the pallets on the end of the fuel array with multiple sprinkler activations. The modeled sprinkler activation times are within the estimated experimental uncertainty following three repeat tests. Quantitative results characterizing sprinkler suppression performance obtained from the simulations, such as the actual delivered density (ADD) and water evaporation rate, are also reported.

Fire development in different scales of train carriages

Abstract: A fire development analysis of three series of train carriage fire tests in different scales was carried out. These train carriage fire tests included 1:10 model scale tests, 1:3 model scale tests and 1:1 full scale tunnel tests. The heat release rate (HRR) correlations between different scales of carriage fire tests were carefully investigated. The mechanism of fire development is very similar in different scales of tests involving fully developed fires. After the critical fire spread, the fire travelled along the carriage at an approximately constant speed. The maximum heat release rate obtained for a fully developed fire is dependent on the ventilation conditions and also the type and configuration of the fuels, and a simple equation has been proposed to estimate the maximum heat release rate. A global correction factor of the maximum heat release rate is presented and examined.

Novel Testing to Study the Performance of Intumescent Coatings under Non-Standard Heating Regimes

Abstract: Intumescent coatings (also called reactive coatings) are widely used to protect structural steel from fire. These thin coatings swell on heating to form a highly insulating char, protecting steel members and preventing them from reaching critical temperatures that could cause them to fail. As is the case for most structural materials and assemblies, intumescent coatings for use in buildings are typically developed and certified solely according to the standard cellulosic fire resistance test by exposure within a fire testing furnace. Reliance on furnace testing is expensive, non-representative of realistic fire conditions, and insufficiently versatile to gather detailed performance information on the response of reactive coatings under the full range of design fires which might be considered during a rational, performance-based design assessment. This paper presents a novel testing methodology for studying the performance of reactive coatings when subjected to non-standard heating regimes. The new approach is calibrated and validated using furnace test data, and is shown to offer considerable advantages over furnace testing in terms of reliability, repeatability, versatility, speed and cost. An investigation is then presented to study the effective variable thermal conductivity of a commercially available reactive coating when subjected to various timehistories of heat flux. It is shown that the heating rate and dry film thickness of the coating do not drastically affect the development of effective thermal conductivity with substrate temperature, leading to a proposal for a simplified method for specifying coating requirements and/or performing heat transfer design calculations when designing to non-standard heating regimes.

A Model for Oxidative Pyrolysis of Corrugated Cardboard

Abstract: Pyrolysis of a double-wall corrugated cardboard was studied in anaerobic and oxygen containing atmospheres using thermogravimetric analysis and a newly developed Controlled Atmosphere Pyrolysis Apparatus (CAPA). Oxygen was shown to affect kinetics and thermodynamics of the cardboard degradation. A previously developed cardboard pyrolysis model, which was partially based on cone calorimetry tests, was demonstrated to reproduce anaerobic gasification experiments conducted in CAPA. This model was extended to include oxidation reactions and transport of oxygen inside the cardboard matrix. The extended model was validated against the mass loss rate data collected in CAPA at 10.5 vol.% of oxygen under incident radiant heat fluxes of 20, 40, and 60 kW m -2 .

Overview of problems and solutions in fire protection engineering of wind turbines

Abstract: The wind energy industry is one of today’s leading industries in the renewable energy sector, providing an affordable and sustainable energy solution. However, the wind industry faces a number of challenges, one of which is fire and that can cast a shadow on its green credentials. The three elements of the fire triangle, fuel (oil and polymers), oxygen (wind) and ignition (electric, mechanical and lighting) are represent and confined to the small and closed compartment of the turbine nacelle. Moreover, once ignition occurs in a turbine, the chances of externally fighting the fire are very slim due to the height of the nacelle and the often remote location of the wind farm. Instances of reports about fires in wind farms are increasing, yet the true extent of the impact of fires on the energy industry on a global scale is impossible to assess. Sources of information are incomplete, biased, or contain non-publically available data. The poor statistical records of wind turbine fires are a main cause of concern and hinder any research effort in this field. This paper aims to summarise the current state of knowledge in this area by presenting a review of the few sources which are available, in order to quantify and understand the fire problem in wind energy. We have found that fire is the second leading cause of catastrophic accidents in wind turbines (after blade failure) and accounts for 10 to 30% of the reported turbine accidents of any year since 1980’s. In 90% of the cases, the fire leads to a total loss of the wind turbine, or at least a downtime that results in the accumulation of economic losses. The main causes of fire ignition in wind turbines are (in decreasing order of importance): lighting strike, electrical malfunction, mechanical malfunction, and maintenance. Due to the many flammable materials used in a wind turbine (eg. fiberglass reinforced polymers, foam insulation, cables) and the large oil storage used for lubrication of mechanical components, the fuel load in a turbine nacelle is commonly very large. The paper finishes with an overview of the passive and active protection options and the economics (costs, revenue and insurance) of wind turbines to put in context the value of a loss turbine compared to the cost and options of fire protection. We hope that this paper will encourage the scientific community to pursue a proper understanding of the problem and its scale, allowing the development of the most appropriate fire protection engineering solutions.

Fire Toxicity Assessment: Comparison of Asphyxiant Yields from Laboratory and Large Scale Flaming Fires

Abstract: In a fire, normally non-hazardous thermoplastic materials can produce lethal concentrations of toxic effluents in the smoke. The toxic product yields of the asphyxiants carbon monoxide (CO) and hydrogen cyanide (HCN) from developed fires are typically 10 times greater than those generated in small-scale laboratory fire test apparatuses. Since most fire deaths, and most fire injuries, result from inhalation of toxic effluents, accurate replication is important for both fire hazard assessment and forensic fire investigation. The stoichiometric equivalence ratio allows the ventilation condition of flaming fires to be compared across different scales. The yields of CO and HCN from five laboratory-scale methods have been compared to large-scale data under the range of flaming fire conditions. Toxic product yield data from the smoke density chamber (SDC) (ISO 5659-2), the controlled atmosphere cone calorimeter (CACC) (based on ISO 5660), the fire propagation apparatus (FPA) (ASTM E 2058), the French railway test (NFX) (NF X 70100), and the steady state tube furnace (SSTF) (ISO/DIS 19700) are compared to published large-scale enclosure fire data (from a standard ISO 9705 room) for two polymers, polypropylene (PP) and polyamide 6.6 (PA 6.6). The results from the SSTF and FPA show the best agreement with those from the full and ⅓ scale ISO room for both materials under a range of fire conditions. The CACC and SDC show reasonable agreement for well-ventilated burning, but fail to replicate the more hazardous under-ventilated fire conditions. The NFX generates data intermediate between the well-ventilated and under-ventilated fire conditions.

An Investigation into the Circumstances Surrounding Elderly Dwelling Fire Fatalities and the Barriers to Implementing Fire Safety Strategies among this Group

Abstract: Examination of real-fire data has indicated that, globally, the elderly, particularly elderly males are those most at risk of becoming a dwelling fire fatality. This paper presents an analysis of the circumstances surrounding elderly dwelling fire fatalities gleaned from coronial reports. The analysis indicated that many elderly fatalities were involved in ignition and had existing health conditions that played a role in the fire. The most common fire scenario (which started in home furnishing located in the living room by carelessly discarded smokers’ materials) accounted for a quarter of elderly fatalities. The risk factors associated with elderly fatalities were similar to other adult fatalities. However, there were some statistically significant differences. The elderly were less likely to have alcohol play a role in their death, more likely to be involved in fires where their clothing was the seat of the fire, have physical illness play a role, and have burn injuries as their primary cause of death. The fire risk to elderly householders was frequently identified by members of the community; however, many felt it was inappropriate to intervene to negate the risk although there were some examples of fatalities that occurred even where fire safety measures had subsequently been adopted. The most concerning result from this study is the minimal attention given to how elderly householders, especially those with poor mobility, would escape in the event of a fire.

A Validation Data-Set and Suggested Validation Protocol for Ship Evacuation Models

Abstract: An evacuation model validation data-set collected as part of the EU FP7 project SAFEGUARD is presented. The data was collected from a cruise ship operated by Royal Caribbean International (CS). The trial was a semi-unannounced assembly trial conducted at sea and involved some 2500 passengers. The trial took place at an unspecified time however, passengers were aware that on their voyage an assembly exercise would take place. The validation data-set consists of passenger; response times, starting locations, end locations and arrival times in the assembly stations. The validation data were collected using a novel data acquisition system consisting of ship-mounted beacons, each emitting unique Infra-Red (IR) signals and IR data logging tags worn by each passenger. The results from blind simulations using maritimeEXODUS for the assembly trial are presented and compared with the measured data. Three objective measures are proposed to assess the goodness of fit between the predicted model data and the measured data.

Effects of oxygen availability on the combustion behaviour of materials in a controlled atmosphere cone calorimeter

Abstract: The reaction-to-fire of materials is commonly studied with bench scale experiments conducted under controlled test conditions. Two bench-scale instruments commonly used for this purpose are the cone calorimeter and the fire propagation apparatus. Research performed with these test apparatuses on the burning behaviour of polymeric materials has demonstrated the significant effect on the results of test variables such as pressure, irradiance, flow velocity, etc. In spite of the fairly large number of studies, little is known concerning the effect of oxygen vitiation and reduced ventilation on the burning behaviour of polymeric materials. Recent work in a controlled oxygen environment raises the question of interpretation and accuracy of the results. This paper reports the results of a study to evaluate the effect of oxygen vitiation and reduced ventilation on the burning behaviour of materials in a controlled atmosphere cone calorimeter. The study was performed on a typical thermoplastic material, i.e., a black poly(methyl)methacrylate. The dependence of the results on the experimental fire conditions is presented and discussed. The experiments show that the inlet airflow rate is a major factor to consider when studying the burning behaviour of polymeric materials in an enclosure. It strongly affects the available amount of oxygen that can react and may lead to a misinterpretation of the results when the effects of oxygen are studied.

A new Experimental Rig for Oil Burning on Water – Results for Crude and Pure Oils

Abstract: A new experimental apparatus, the Crude Oil Flammability Apparatus (COFA), has been developed to study in-situ burning of crude and pure oils spilled on water in a controlled laboratory environment with large water-to-oil ratios. The parameters and phenomena studied for an asphaltic crude oil (Grane) and two pure oils (n-Octane and dodecane) with different initial oil layer thicknesses include burning efficiency, burning rate, regression rate, flame height and boilover. Pyrex glass cylinders (157 and 260 mm ID) placed on top of a steel foot in a water basin (1m x 1m x 0.5m) enabled free circulation of the water, which, along with the large water-to-oil ratios (up to 10,000) ensured that the oil burning barely increased the temperature of the surrounding water environment, which created more realistic offshore conditions than seen in many other laboratory studies. The burning efficiency was found to be nearly 100% for n-Octane and of dodecane, whereas the crude oil burning efficiency ranged between 35% and 65%. The main reason for this variation proved to be the onset of an extremely violent boilover, which occurs for oils with relatively high boiling temperatures when the water sub layer is superheated. When the initial crude oil layer thickness exceeded 20 mm the oil became solid and no boilover occurred. The heat-loss to the water sub-layer also had an effect on the burning efficiency and the regression rate was found to reach a constant value after increasing continuously as the oil was heated. Similar results were found regarding the flame height which reached a steady flame height. The pure fuels, n-Octane and dodecane, produced a much higher steady flame height than the crude oil, however they did not reach boilover, though dodecane showed boilover tendencies. Theoretical predictions with existing correlations and input data specific for the current oils generally compared well with the experimental data for both the time to boilover and the regression rates. As such, the COFA is envisioned to produce high-fidelity results in the future and thereby contribute to the further development of in-situ burning as an alternative response technique for oil spills on water.

Effect of Particle Size on Pyrolysis Kinetics of Forest Fuels in Nitrogen

Abstract: Pyrolysis of forest combustibles is an elementary process in the ignition and spread of forest fires, and particle size is an important parameter which affects the pyrolysis kinetics. In this work, samples of pine needle (PN), pine branch (PBr) and pine bark (PB) were subject to thermogravimetric experiments, in order to examine the effect of particle size on pyrolysis characteristics. For all the samples, one peak and two shoulders are observed in all of the mass loss curves, at different positions for different levels of particle size. The observation of the mass loss curves and the analysis of peak temperatures by Kissinger method indicated that the major mass loss steps in different heating rates have consistent pyrolysis kinetics. For all the samples, the particle size has no obvious effect on the temperatures of the major peaks. Basically, the peak mass loss rate increases with increasing particle size for smaller particles, however the increased temperature gradient inside the sample may have a remarkable suppression on the mass loss rate when the particle size exceeds a certain level. The mass loss rates for the two shoulders show complex variations for different samples and particle sizes, which reflects the difference in chemical components. A kinetic model which includes three pseudo components was used to simulate the pyrolysis for different dimensions, and the obtained kinetic parameters were compared and discussed in details. By industrial analysis the products of ashes for different particle sizes were compared, and especially it was implied that to some extent the activation energy and ash content involve negative correlation.

Fire performance evaluation of different resins for potential application in fire resistant structural marine composites

Abstract: This work explores the possibility of reducing the flammability of unsaturated polyester (UP) resin, commonly used in marine composites, by co-blending with less combustible and char-forming resins such as phenol-formaldehyde, melamine-formaldehyde and furans. The compatibility and curing properties of UP, other resins and their blends in 50:50 wt-% ratios have been have been studied by differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA) techniques. Based on the successful establishment of curing conditions, plaques of resins have been cast and cured. Thermal stability has been studied by thermogravimetry (TGA), whereas the fire performance evaluation was carried out by limiting oxygen index (LOI) and cone calorimtery at 50kW/m 2 heat flux. According to a fire risk assessment based on cone calorimetric data, the resole phenolic resins and their blends with UP achieved the highest fire safety rating.

Experimental Study on Thermal Breakage of Four-Point Fixed Glass Façade

Abstract: As the weakest part of building facades, glass panels can easily break in fires and change the compartment fire dynamics by creating new openings for air to enter. A series of full scale tests were conducted to investigate the thermal breakage and fallout of four-point fixed glass facades, in which glass panes of 1200 × 1200 × 6 (mm 3 ) were placed at 35, 45, 50 and 70 (cm) away from n-heptane pool fires on a 500 × 500 (mm 2 ) square pan. Both float and toughened glasses were investigated. The glass surface temperature, gas temperature at the centre of the exposed side and heat release rate were measured and analyzed. The cracking patterns and glass fallout processes were recorded by digital camera. It is found that all the cracks initiated from the fixed point and their intersections formed islands to cause glass pieces fallout when the exposed side reached around 200-300 °C for the float glasses tested. The fallout fractions suggest that once the first crack is initiated, the point-supported glass panes are much more easily to fallout than edge covered glasses. The toughened glass panes were found to be softened by the fire and bent, but they did not crack even when the fire directly impinged on them.

Fire Whirl due to Interaction between Line Fire and Cross Wind

Abstract: During the wildland fire of Brazil in 2010 (http://www.dailymail.co.uk/sciencetech/article-1306088/Braziltornado-Whirling-column-flames-sweeps-burning-fields.html), a special fire whirl occurred over a narrow but long fire front and moved due to the wind effect. This paper presents an elementary study on such a moving fire whirl by conducting line fire experiments with cross wind. Experimental analysis indicates that a line fire near the ground, a reasonable attack angle between the line fire and the cross wind, and wind speed within a critical range are the three essential conditions for the formation of fire whirl in a line fire. By examining the advection and bending of vorticity, it is also deduced that the concentrated vortex of fire whirl results from the coupling of the line fire plume and the horizontal vortex line near the ground surface. By assuming the solid-body rotation of fire whirl flame, a possible mechanism of moving fire whirl is proposed, which states that the flame moving is mainly controlled by the drag force, lift force and ground friction. Accurate experimental measurements are needed to testify or verify this mechanism in the future work.

Microscopic Character and Movement Consistency of Pedestrian Group: An Experimental Study in Campus

Abstract: The research of human crowd dynamic is significant for the building designers and emergency guiders. However, current researches mainly focus on the interactions among isolated individuals, the influence of social interactions among pedestrian is needed to take into consideration in the pedestrian dynamic study. In this manuscript we carried out observed experiments of the movement of pedestrian group and used optical flow algorithm to extract pedestrian’s trajectory from the video. Then the movement characteristics of the group members were analyzed and discussed, which include the angle, the distance, the velocity, the group alignment, step frequency and the offset angle of group member. It indicates group members have adaptive ability to maintain the group structure and the velocity fluctuation of the group is small. It is found that the velocity and step frequency of group member are smaller than that of individuals under the same scenario. Movement consistency of the group members is also verified. These experimental results will be a support for modeling pedestrian group.

Convection Ignition of Live Forest Fuels

Abstract: Wildland fires are an extremely costly and deadly problem. Crown fires, where live foliage ignites and burns, are particularly unpredictable – in part because live fuel ignition and combustion is poorly understood. Many wildland fire models assume radiation is the controlling heat transfer mechanism. However, there is a growing indication that radiation is insufficient to ignite the small, thin fuel particles that carry a wildland fire and that convective heating and flame bathing is a critical component. Unfortunately, ignition by convection heating of any fuel is poorly understood. Ignition of live forest fuels by any means is also completely unknown due to complicated moisture content and fuel chemistry considerations. To gain some insight into the wildland fire problem, an apparatus was built using two 6.5 kW electrical heaters to heat gas (air, nitrogen, etc.) over a range of temperatures from ambient up to 1200°C. The flow rate of these “airtorches” is adjustable. This apparatus was used to convectively ignite a range of both live and dead forest fuels. Fuels from all over the United States where used including Southern California, Utah, Florida, and Montana. To examine ignition threshold conditions and to have distinguishable differences in ignition times, air temperatures of 500°C and 600°C were used. The airflow rate varied slightly from 1.3 m/s to 1.4 m/s due to the density difference. Because live forest fuels contain large amounts of water, the evolution of both water and carbon dioxide was measured with time using a differential gas analyzer. Flaming ignition was seen for all dead fuels at 500°C, but the live fuels mostly showed glowing ignition. At 600°C, all fuels showed flaming ignition within 1-26 sec. Interestingly, all live fuels were still actively releasing water at ignition, implying there are steep temperature gradients within these physically thin fuels (i.e. not thermally thin). Simple heat transfer analysis in conjunction with the water evolution information was used to help explain the differences in ignition times due to fuel geometry.

Study on Fires Following the 2011 Great East-Japan Earthquake based on the Questionnaire Survey to Fire Departments in Affected Areas

Abstract: The 2011 Great East-Japan Earthquake of March 11, 2011, caused large-scale fire damage across a wide area, with the type and extent of fire damage exceeding that caused by the 1995 Kobe Earthquake. A particularly distinctive characteristic was the many fires caused either directly or indirectly by the tsunami. The mechanism of occurrence and development of tsunami-induced fires differs significantly from typical earthquake-induced fires. Given these two very different types of initiation scenarios, fires following the Great East-Japan Earthquake were analyzed based on factors such as regional distribution, causes of ignition, pattern of fire development and spread, and size of fire. Data for these analyses were collected from questionnaire surveys of fire departments located in the affected areas. In addition, data are presented on the relationship between seismic intensity and the incidence of earthquake-induced fires. A significant finding from the analysis is that, given the impacts to infrastructure and extent of damage, tsunami-induced fires are likely to spread beyond the control of fire brigades. Therefore, the prevention and mitigation of tsunami-induced fires in the future earthquakes is of great significance.

A comparison of an explicit and an implicit transient strain formulation for concrete in fire

Abstract: This paper reviews the phenomena of concrete behavior which is captured in the material data of the Eurocode and reviews additional phenomena which may be included to improve results in certain cases. As a case study, a series of tests which were conducted by Anderberg and Thelandersson in the 1970’s in Sweden on concrete samples are studied using first of all the temperature dependent material model which is used in the Eurocodes. The impact of load induced thermal strain is discussed through comparison of the implicit model which is used in the Eurocode and a simple explicit model based on the test results.

Real-time Stochastic Evacuation Models for Decision Support in Actual Emergencies

Abstract: This paper introduces and proposes the use of evacuation models for decision support during actual emergencies. Two examples are presented: EvacTrain 2.0 and EvacTunnel. The proposed models are essentially stochastic, quick and easy to use and can generate and process results of several simulations within a few seconds. The main output parameter is the percentile (0.90, 0.95 or 0.99 th) of total evacuation times. They also provide other statistical characteristics and additional outputs. Both models have been compared with other validated evacuation models. Results suggest that the proposed models provide consistent and reliable results. The general findings described in this paper suggest that it is possible to develop efficient evacuation models for supporting emergency decisions in real-time.

Flaming Ignition Behavior of Hot Steel and Aluminum Spheres Landing in Cellulose Fuel Beds

Abstract: The ignition of combustible material by hot metal particles is an important fire ignition pathway that remains relatively unstudied. In this work, the flaming ignition behavior of powdered cellulose fuel beds by hot steel and aluminum spheres of various diameters and initial temperatures was studied. Understanding ignition in this scenario could offer insight into the mechanisms by which metal particles initiate wildland fires and fires in industrial settings. Earlier work on this topic has shown that ignition propensity has a relationship with the temperature and diameter of the sphere. However, little is known about the physical processes governing this relationship. This work provides further information regarding the conditions required for ignition, and useful observations for the development of a theoretical framework for predicting ignition propensity of combustible fuel beds. For the conditions tested, powdered cellulose ignition appears to exhibit limiting behavior in two regimes: for larger spheres, temperatures below 600 C did not ignite the cellulose and spheres with diameters below 2.38 mm for steel or 2.03 mm for aluminum and temperatures up to 1100 C did not ignite the cellulose either. We also observed that in the range of sphere diameters from 4-8 mm, aluminum spheres of a given diameter are more likely to cause ignition than their steel counterparts. This seems to be due to the fact that the aluminum spheres are molten at temperatures greater than 657.2 C; melting contributes to a spheres bulk energy through the latent heat of melting and allows for sphere deformation and splatter during impact. Furthermore, qualitative analysis of high speed schlieren videos shows differences in pyrolysis and ignition behavior and suggests that, different controlling processes may be at work for spheres of different sizes and for molten versus solid spheres.

Effective stress method to be used in beam finite elements to take local instabilities into account

Abstract: In the fire situation, Bernoulli beam finite elements are the workhorse used in numerical calculation model for simulating the behaviour of the structure. Such finite elements treat all sections as class 1 (stocky) sections whatever the slenderness of the plates that make the section, allowing the development of a full plastic stress distribution in the section which leads to complete plastic redistribution along the members in the structure. This type of element is thus not adapted for modeling structures that contain slender sections of class 2, 3 or 4. This document presents a new approach to take into account local instabilities in slender sections using beam finite elements. The new approach is based on an effective constitutive law of steel. The effective law is not symmetrical with respect to tension and compression because, in tension, the stress-strain relationship is not modified whereas, in compression, the stress-strain relationship is modified.

Enclosure and Facade Fires: Physics and Applications

Abstract: Facade fires being a disastrous hazard for high rise building, as several historical and recent incidents have shown, have attracted the interests of numerous fire scientists, engineers and regulators. This work has as an objective to present issues in this area that are challenging and need further attention. It focuses on characterizing the flame height and heat fluxes from facade flames produced from under-ventilated enclosure fires on a facade that is not flammable. Such an investigation is an important consideration for practical applications as well as a prerequisite for examining fire spread on flammable facades and for designing a test for modern facade assemblies. The mass pyrolysis rates and burning of real fuels are discussed in under ventilated enclosures, rectangular or corridor like, for various openings presenting the current state and some critical issues. Facade flames are analyzed from experiments using gaseous burners to have control on the fuel supply rate by introducing physical length scales for the opening geometries to model flame heights and heat fluxes. An important parameter for the facade flames is the excess heat release rate of the fuel burning outside the enclosure. Finally, applications for facade flames with sidewalls and facade flames from two openings are presented.