Compartment Fire Research Articles

Thermal Analysis Infrastructure in OpenSees for Fire and its Smart Application Interface Towards Natural Fire Modelling

Understanding the fire behaviour in buildings is fundamental and crucial to the practice of structural fire safety design. Traditionally, time-temperature curves associated with a burning rate developed from the “compartment fire framework” are most widely used by structural engineers and applied as a load to the structure. However, the adequacy of homogenous temperature distribution in fully developed fires was questioned by researchers after reviewing the existing fire test data, which suggested a localised burning nature of the fires in relatively large compartments. A groundbreaking travelling fire concept and travelling fire models were then proposed intending to provide an engineering description to this type of natural fire behaviour. The work in this paper was driven by such a trend and first summarises the modelling infrastructure in OpenSees to estimate the thermal response of structural members subjected to various scenario fires, followed by providing a smart application interface to capture the appropriate form of natural fire model through Python-OpenSees framework. The developed modelling infrastructure is validated against uniform and localised fire tests, which are also discussed regarding the smoke effect afterwards. Using the Python-OpenSees infrastructure, a real-scale localised fire test and the Malveira travelling fire test are modelled to demonstrate the modelling strategy. The work as preliminary attempts has shown the necessity of introducing additional variables when describing the natural fire impact, and this framework can be further improved in future by including more fire dynamics research and full-scale fire test input.

Structural Timber In Compartment Fires – The Timber Charring and Heat Storage Model

Abstract The influence of exposed timber surfaces on compartment fires has been well documented in various studies in recent decades. Yet available design concepts still typically neglect the influence of an additional fire load from linear structural timber elements such as beams and columns. As rules for large shares of exposed timber surfaces, e.g. by panels, are rare, authorities and fire safety engineers demand often mock-up compartment fire experiments to estimate the fire safety of a particular design. Such experiments, however, are costly, time consuming, and give limited insights into the potential fire scenarios and may fail to represent properly the fundamental effects arising from exposed structural timber elements in a fire. An approach to overcome these existing limitations is presented, which is able to estimate the contributions from structural timber to a fire from its fully developed- and decay phase until burnout. The model input is developed from an experimental campaign where the relevant effects of fire exposed structural timber could be isolated and measured. It was found that the energy stored in the char layer is a key characteristic for describing the fire dynamics of compartment fires with exposed structural timber. Consequently, the proposed approach describes a framework for the Timber Charring and Heat storage, the TiCHS-model. The validation of the model is shown in this paper by means of existing compartment experiments. A current limitation is the bond line integrity of the fire exposed components as the combustion characteristics of failed char pieces on the floor are currently unknown.

Effect of the Opening Area of Compartment on the Backdraft Time

When a fire occurs in a ventilation confined compartment, the fire gradually weakened and finally self-extinguishes due to the oxygen concentration in the compartment will decrease and eventually below the flammable limit. Meanwhile, a large amount of high-temperature combustible substance is generated in the compartment during this period by pyrolysis or evaporation of fuel. When the compartment ventilation is improved, such as the window is broken, fresh air flows into the compartment and mix with high-temperature combustible substances and lead to the fire occurs again. This special phenomenon during the development of a compartment fire is called backdraft. In addition, a large amount of high-temperature combustible substances is accumulated in the compartment before the backdraft occurs. Therefore, once a backdraft occurs, it always leads to a flashover, which means a fire has reached fully development stage and is out of control. Hence, a backdraft will lead to substantial finical loss and heavy casualties. To investigate the influence of compartment opening area on backdraft time, we conducted fire experiments of solid fuel in a reduced-scale compartment. The temperature and the gas concentration in the compartment were measured by thermocouples and gas analyzer, respectively. Results show that the backdraft time of solid fuel would become shorter as the opening area of the compartment increases. The results of this research could improve the understanding of the backdraft mechanism of solid fuel and provide a strategy to delay or even restrain the backdraft occurrence for firefighters.

Effect of ratio between incoming cool air and outgoing hot gases on behaviour of compartment fire

Many factors have an influence on the development of compartment fire notably on its heat release rate as well as on its capability to propagate and become a flashover situation. The main element which rapidly conveys fire from a compartment to another is hot smoke flowing out through openings of the compartment source of fire. The present work aims to experiment the impact of the variation of heat release rate of the source on the behavior of fire. So, five fire tests with different heat release rates were thus carried out in a reduced scale room. Temperature of burned gases inside the room, were measured during tests by sensors connected to a data acquisition system. Results revealed that temperature of burned gases as well as its content in CO, evolves differently according to two ranges of the incoming air/outgoing gases ratio. The first range of which the ratio is lower than 2, corresponds to the case where both parameters decrease rapidly. The second range of which the ratio is higher than 2, corresponds to the case where both parameters decrease moderately. The transition from the first to the second range, points out the passing from the ventilation-controlled fire to the fuel-controlled fire. A relation expressing the variation of the mass-flow rate of outgoing burned gases according to the heat release rate of the fire source has been given.

Survey on Existing High-Rise Building Fire Safety Assessment Based on Fire Compartment and Fire Protection System Maintenance

Advanced fire safety standards and laws are being applied to new high-rise buildings, but existing high-rise buildings are maintained and managed based on previous fire safety standards, which makes them weak to fire hazard response. This study was conducted to evaluate the survey results for the maintenance status of fire compartments and principal firefighting facilities of 157 buildings using the performance evaluation table for fire safety of existing high-rise buildings. This paper presents actual problems in the maintenance of fire compartments and firefighting facilities of existing high-rise buildings. In addition, it provides reference materials that can be used to establish policies for supplementing the fire safety performance the buildings in the future.

A numerical study of backdraft phenomena under normal and reduced gravity

Backdrafts are violent events that occur when oxygen is suddenly introduced to an oxygen-depleted compartment fire and are primarily driven by the presence of gravity currents. However, with human travel potentially expected beyond the confines of earth gravity, it is not clear how the magnitude of the gravity constant can contribute to the intensity of these events. This issue can be relevant when dealing with fires on space stations or on future bases on the Moon and Mars. In this study, we carry out backdraft simulations in a compartment under different reduced gravity conditions using the NIST Fire Dynamics Simulator (FDS) code. A combustion compartment, initially containing under-ventilated heated methane, is opened to the surroundings using a vertical opening slot. Through the bottom of the opening flows a gravity current of oxygen. When the current reaches the far wall of the combustion compartment, the mixture is ignited, and a violent backdraft event occurs. Measures of heat release, fire development, and pressure rise suggest that the effects of backdraft are highly nonlinear based on the gravity constant. Even small values of the gravity constant (as low as 0.01g) can trigger relatively strong backdrafts.

A systematic process for developing fire scenarios in risk assessment for nuclear power plants

In nuclear power plant fire probabilistic risk assessment (FPRA), numerous single-event fire scenarios are analyzed for risk quantification. The analysis results, however, are often subject to the allocation of project resource such as personnel, time and budget, and most importantly, the judgement of analysts. Through repetitive detailed simulation and quantification, the risk of a fire compartment can be modulated in accordance to the expectations of analysts, leading to the misleading risk significance of a fire compartment and weakened credibility of its risk ranking. In view of the unintentional bias in the conventional FPRA, this study aims at providing an objective, dependable risk ranking that reflects areas of high fire risks, and thereby the personnel in the plant can act accordingly. Here, a computational systematic procedure was constructed to consistently simulate the development of all fire scenarios. Through batch-processing, fire scenarios are disintegrated into parts for analysis and quantification. Importantly, details of a fire scenario are kept to the extent that an in-depth research on fire scenario quantification can be proceeded further in the future.

Thermo‐mechanical behaviour of cross‐laminated timber slabs under standard and natural fires

SummaryThe results presented in this paper are part of a multi‐partner collaborative project named ‘The Épernon Fire Tests Programme’, the purpose of which is to analyse the different behaviours of combustible and non‐combustible loaded structures when they are tested under standard and ‘natural’ fires. The project has several objectives, such as quantification of the energy participation of combustible materials in fire tests, the influence of combustible surfaces and ventilation factors on the dynamics of compartment fires, and the thermo‐mechanical behaviour of concrete and timber elements under natural fires. This paper focuses on the thermo‐mechanical behaviour of cross‐laminated timber (CLT) slabs under standard and natural fires. The objective is to provide new experimental data on the behaviour of unprotected CLT slabs exposed to fire. In addition, we present a detailed analysis of the thermo‐mechanical behaviour of the slabs, particularly aimed at better understanding the mechanical failures of some of the slabs during and after fire exposure.

Tisova Fire Test – Fire behaviours and lessons learnt

One of the largest unknowns in structural fire engineering design is the fire itself, particularly in large internal environments, where real fires have been observed to travel around the floor plate. Several methodologies have been proposed to characterise these fires, most of which rely on the separation of the fire exposure into two so-called fields - near and far – allowing simplifying assumptions to be made. These models are now being used in the structural fire design. However, there is a paucity of validation data for these models with only a few tests reported in the literature. The Tisova Fire Test was conducted on the ground floor of a 4-storey concrete frame building, with concrete and composite deck floors. The fire compartment had a total area of ca. 230 m2, a height of 4.21–4.28 m, and a uniform fuel bed across the floor at 40 kg/m2. This paper presents temperatures, spread rate and the observed behaviour of the travelling fire, comparing the current design guidance with the low temperatures observed in the experiment. The paper also examines the experimental issues and the planning of these experiments with a view to helping others plan for and execute large scale fire tests in the future.

Experimental investigation of burning behavior of a running vehicle

In recent years, automobile fire accidents have occurred frequently. To effectively understand the characteristics of car fire accidents, the burning behaviors of a running sedan vehicle and the fire spread characteristics were studied in this study. The spread progress of automobile fire was recorded by cameras installed in the front, side and inside of the car. The surface temperature and interior temperature of the car were measured by the infrared thermal imager and thermocouples. The engine compartment burned quickly after the fire, and smoke entered the car through the air-conditioning vents. The cab reached flashover after 10 min, and the temperature was over 1000 °C. The plastic materials of the car engine compartment were dripping in flames and the car tires were ignited by flaming droplet after 5 min. The experiment shows that in the case of engine compartment fire, personnel escape and firefighting should be performed within 6 min.

Effect of ignition heat source on design fire curve of polyethylene foam in a compartment fire

This study analyzed a design fire curve in accordance with of an ignition heat source in a compartment. For this purpose, a structure with a 1:3 reduced scale of the ISO 9705 room corner tester was fabricated using fireboard, and the time variant heat release rate was calculated according to the volume of a polyethylene foam combustible. To predict the design fire curve, the exponential equation proposed in a previous study was compared with the heat release rate measured in a fire experiment. The retard index, which is the main factor used to predicting the time required to reach the maximum heat release rate, decreased proportion to the ignition heat source. This relationship was presented in an empirical equation. Especially, the retard index decreased according to the size of the ignition heat source regardless of the volume of the polyethylene foam combustible. By establishing experimental data considering the type and change in the volume of combustibles, the findings of this study can be used to create improved design fire curve prediction models.

FDS simulations and modelling efforts of travelling fires in a large elongated compartment

SummaryThe present paper investigates a travelling fire scenario in an elongated structure (Length 18 m × width 6 m × height 3 m) with a controlled fire source of six trays filled with diesel (width 4 m × length 0.5 m). The fire spread is controlled manually by initiating fires consecutively in the pools. Fire dynamics simulator (FDS) is used to a‐priori investigate variations in geometry, material data and fire load, whereas simulations using the final design and measured heat release rates (HRR) were performed after the test. The input to the model beside fire source and geometry are thermal material data. The FDS simulations were used to determine the appropriate size of the downstands (2 m from the ceiling in the final design) on the side to create a sufficiently one‐dimensional fire spread. The post‐test simulations indicate that although there are a lot of variations not included in the model similar results were obtained as in the test.

Study on Selection of Optimal Installation Positions of Fire Dampers to Secure Fire Safety Performance

Building regulations in recent times require that fire dampers be automatically closed when detecting smoke or flame in the event of a fire. However, they may be vulnerable to fire themselves because they contain combustibles, such as motors. Therefore, the optimal installation locations of fire dampers for securing fire safety performance were selected through performance verifications in this study. Thus, it was found that fire dampers installed in contact with the fire compartment wall surfaces would be advantageous for securing the required fire safety performance.

Wall and Corner Effects on Fire Plumes as a Function of Offset Distance

A series of compartment fire experiments is described in which a square natural gas burner was positioned in a corner or against a wall and gradually moved towards the room center to assess the relative effects on the plume and compartment temperatures. The experiments were conducted to validate computational fluid dynamics simulations that were performed to provide guidance for probabilistic risk assessments in nuclear power plants. The measurements consist of one dimensional vertical thermocouple arrays to measure the hot gas layer temperature and height, and a three dimensional thermocouple array to measure the temperature of the fire plume as the burner is moved away from the corner or wall. As a result of the modeling and experiments, recommendations have been made that quantify wall and corner effects as a function of offset distance.

Characterising the exposure of Australian firefighters to polycyclic aromatic hydrocarbons generated in simulated compartment fires

Firefighters are exposed to a wide variety of chemicals including polycyclic aromatic hydrocarbons (PAHs) while attending fire scenes. The objective of this study was to understand the exposure of firefighters to PAHs when attending simulated compartment fires that consisted of either a diesel pan or particleboard fire. Firefighters remained in the compartment fires for 15min while using standard gear including self contained breathing apparatus (SCBA). Firefighters were able to remove firefighting clothing and shower within 10min of leaving the burn. Air samples were collected from inside the compartment during the fire. Twenty-six (26) firefighters participated in the study providing urine and skin wipe samples collected from the wrist and neck before and after either one of the burn types. The concentrations of PAHs were measured in skin wipes and air samples, while concentrations of monohydroxy metabolites of PAHs (OH-PAHs) were measured in urine. The concentrations of all PAHs were significantly higher (p<0.05) in the smoke layer of particleboard fires than in diesel pan fires. Correspondingly, the level of PAHs deposited on the wrists and necks of participants attending the particleboard fires was higher than those attending diesel pan fires. Urine samples from participants who attended diesel pan fires showed no significant difference (p>0.05) in the concentration of all OH-PAHs between pre-burn and post-burn. Samples from participants who attended particleboard fires, showed no significant difference (p>0.05) between 1-hydroxypyrene (1-OH-PYR) concentrations in urine pre- and post-burn. However, median concentrations of hydroxynaphthalenes (OH-NAPs), hydroxyfluorenes (OH-FLUs) and hydroxyphenanthrenes (OH-PHEs) increased significantly from 5.2, 0.44 and 0.88μgg-1 creatinine pre-burn to 12, 1.4 and 1.2μgg-1 creatinine post-burn, respectively. This suggests that in compartment burns with high concentrations of PAHs in the smoke layer, such as those created by the particleboard fires, exposure to PAHs can be observed though urinary OH-PAH metabolites. Overall, concentrations of urinary OH-PAHs were relatively low considering the potential exposure in these burns. This suggests protective equipment in combination with rapid removal of firefighting ensembles and showering are relatively effective in controlling exposure.

Post-fire behaviour of continuous reinforced concrete slabs under different fire conditions

An experimental investigation of the performance of reinforced concrete continuous slabs is presented in this paper, following the exposure of the slabs to different compartment fires. The influence that several factors, including compartment fire scenarios, reinforcement ratio, and bar arrangement, have on the deflections, strains, crack patterns, and failure modes is analysed. Results that compared to the uniform fire case, localized or extended punching shear failure modes are more likely to occur in the fire-damaged slabs subjected to the traveling fire due to more cracks. The residual structural stiffness and ultimate loads are enhanced with the increasing reinforcing ratio, but the brittle punching failure readily appeared. Finally, the deflection failure criterion (l/50) and the ACI 318-08 punching shear theory are helpful in predicting the residual ultimate loads of the fire-damaged slabs subjected to any fire scenario.

Numerical analysis to determine fire suppression time for multiple water mist nozzles in a large fire test compartment

In this study, a numerical sensitivity analysis was performed to determine the fire suppression time for a large number of water mist nozzles in a large fire compartment. Fire simulations were performed using FDS (Fire dynamics simulator) 6.5.2 under the same condition as the test scenario 5 of the International Maritime Organization (IMO) 1165 test protocol. The sensitivities of input parameters including cell size, extinguishing coefficient (EC), droplets per second (DPS), and peak heat release rate (HRR) of fuel were investigated in terms of the normalized HRR and temperature distribution in the compartment. A new method of determining the fire suppression time using FDS simulation was developed, based on the concept of the cut-off time by cut-off value (COV) of the heat release rate per unit volume (HRRPUV) and the cooling time by the HRR cooling time criteria value (CTCV). In addition, a method was developed to determine the average EC value for the simulation input, using the cooling time and cut-off time.

A comparative study of statistical methods for critical parameters at tempered glass fallout in an enclosure fire

Tempered glass is substituting float glass and extensively employed in glass façades and some structural members. However, previous studies primarily focus on float glazing, little is known about the statistical characteristics of tempered glazing fallout in a compartment fire. In particular, the correlation between critical parameters and fallout time of tempered glass is still unknown. Based on the previous experimental data in open literature of 11 tempered glass panels in a compartment model, a comparative analysis was performed to optimize the statistical methods of the breakage behaviour for tempered glazing. The parameters from the previous Wang et al.’s research, such as tempered glass fallout time, the temperature at the center of tempered glass surface, the temperature at the edge of tempered glass surface, the temperature difference between fire exposed and frame covered areas, and total heat flux at tempered glass fallout, were analyzed by 7 different statistical functions, including the Normal, Lognormal, 2-parameter Weibull, 3-parameter Weibull, Exponential, Gamma and Logistic distributions. The results suggested that the most appropriate distributions for tempered glass fallout time, the temperature at the center of tempered glass surface, the temperature at the edge of tempered glass surface, the temperature difference between fire exposed and frame covered areas, and total heat flux at tempered glass fallout are respectively Lognormal, 3-parameter Weibull, 2-parameter Weibull, 3-parameter Weibull, and 3-parameter Weibull distributions. Overall, the 3-parameter Weibull distribution is more suitable for the statistical analysis of fallout behavior of tempered glazing in fires. For critical parameters of tempered glass fallout, the 50th percentile is close to the most probable percentile. To avoid the fallout of 6 mm thick tempered glazing, the temperature difference between fire exposed and frame covered areas as well as heat flux should be controlled under 319 °C and 38.5 kW/m2. From the correlation analysis between fallout time and each critical parameter, it was established that the surface temperature may give more reliable prediction than total heat flux for tempered glass fallout.

Experimental Study on the Effect of a Metal Storage Cask and Openings on Flame Temperature in a Compartment Fire

Experimental Study on the Effect of a Metal Storage Cask and Openings on Flame Temperature in a Compartment Fire

High-temperature material degradation of Q345 cold-formed steel during full-range compartment fires

High-temperature material properties are the most important input parameters for the study of the fire resistance of steel structures. Meanwhile, the structural failure of steel structures might occur during compartment fires. This paper presents steady-state experiments on Q345 cold-formed steel (CFS) during the rising and falling temperature periods. The results show that whether in the rising or falling temperature periods, the material properties of Q345 CFS decrease as the load testing temperature increases. Meanwhile, the difference between the test results of the rising and falling temperature periods can not be ignored. Under the same load testing temperatures, the differences in the elastic modulus reduction factors of Q345 CFS between the rising and falling temperature periods are within −0.16 to 0.057; meanwhile, the differences in the yield strength reduction factors between the rising and falling temperature periods are within −0.009 to 0.142. For the fire resistance design, if the material properties during the rising temperature period are used to replace those during the falling temperature period, the calculation results of the fire-induced deformation for Q345 CFS members may be conservative, but the corresponding high temperature bearing capacity will be over-predicted. In addition, the differences in the reduction factors of material properties for Q345 CFS caused by the maximum temperature are significantly lower than those for G550 CFS. Finally, a maximum temperature influence coefficient is introduced and unified expressions are put forward, which can be appropriately used to predict the material properties and stress-strain curves of Q345 CFS during full-range compartment fires.