Fire Experiments Research Articles

Experimental study and modelling of real-scale vertical cable tray fires

Cables are one of the most important fire loads in nuclear power plants. It is therefore important to understand their fire behaviour and to predict their heat release rate curve. Electricité de France carried out a series of full-scale vertical cable tray fire experiments. Relevant measurement systems were used. The aim of this article is to give an overview of these experiments and their main results. Important aspects of the fire behaviour are discussed and compared with the literature. In addition, two models, namely the FLASH-CAT model and the ISO 18195 vertical cable tray model, are compared to the experiments and their ability to predict the heat release rate profile is discussed. The models are also compared with other real-scale experiments available in the literature. The ISO 18195 model shows good agreement with the different experiments for the heat release rate profile. The FLASH-CAT model obtains reasonable conservative results for the maximum heat release rate. However, the model significantly overestimates the growth rate in all the tests.

Distribution of probabilistic design fires for single residential items

When designing scenarios for fire safety in residential buildings, one should consider the natural variability of heat release rate of a single item that can possibly influence fire spread between multiple items. This study intends to represent experimentally measured design fire for single residential items using a combination of t-squared growth method and Ingason exponential decay method. The characterizations required three representative data from experiments including maximum heat release rate, time to reach the maximum heat release rate and total heat released. The methods have established good representations of the experimental design fires with more than 86% similarity. Distribution statistics are considered to characterize the design fires in a probabilistic manner which develop possible design fires from an average curve as well as within a minimum/maximum limit and a 5th/95th percentile limit. Comparisons denote that the probabilistic design fires are reliable to represent the possible heat release rate for single residential items.

Experimental study of the burning behavior and key parameters of gasoline pool fires with different ullage heights

Pool fires with different ullage heights are a common type of fire accident. A series of gasoline pool fire experiments with two sizes (D = 40 cm, 60 cm) and six ullage heights (h = 0, 0.2D, 0.4D, 0.6D, 0.8D, 1.0D) are conducted. The burning process, axial temperature profile, radiative heat feedback, and burning rate are measured and analyzed. The result shows that the fuel vapor layer and the down-reaching flame layer are distinguished based on the axial temperature profile for the steady burning stage. Meanwhile, the down-reaching flame length (Ldown) increases more profoundly for large tank diameters under the same ullage height. Subsequently, the dimensionless down-reaching flame length (Ldown* = Ldown/D) increases exponentially with the dimensionless ullage heights (h* = h/D). Finally, based on the classical burning rate model for the low ullage height and the heat transfer process from the flame to the fuel surface, a correlation with different ullage heights is established to calculate the burning rate, which is then validated against the experimental data in the paper and literature values. The results are of importance to understand the burning rate and the radiative heat feedback to the fuel surface for pool fires with different ullage heights.

A comparison of carbon monoxide yields and particle formation at various global equivalence ratios in vitiated and under-ventilated conditions

There have been previous studies comparing experimental methods for the purpose of capturing gaseous yields at a range of global equivalence ratios. However, no work has investigated the capability of the open controlled atmosphere cone calorimeter for collecting such data where its two modes of operation are directly compared. The aim of this study is to compare carbon monoxide yields collected using vitiated and under-ventilated modes of atmospheric control in order to identify the preferable method of replicating carbon monoxide yields reported from larger scale enclosure fire experiments. Cone irradiances of 30, 50 and 65 kW/m2 were applied to PMMA and plywood samples. Vitiated tests were conducted using a mixed air/diluent gas, with an inflow rate of either 100, 150 or 180 L/min, resulting in a reduced oxygen concentration of 17.5 vol. %. Under-ventilated tests were conducted using flow rates of 5, 10 and 20 L/min in an air atmosphere. Particle formations and emissions were also measured using a particle analyser and have been reported herein. Results indicate that the under-ventilated mode of equivalence ratio control offers a more promising method of capturing species yields with favourable comparisons to other bench scale methods.

Studying the Synergetic Effect of Point-Extraction and Longitudinal Ventilation on the Maximum Smoke Temperature and Back-Layering Length in Tunnel Fires

This study investigates the impact of combining longitudinal and point-extraction ventilated systems on temperature distribution and back-layering length in tunnel fires. Numerical simulations are conducted using a fire dynamic simulator (FDS), and reduced-scale tunnel fire experiments with a scale of 1/10 are introduced to provide supplementary data. Results indicate that the longitudinal velocity is more critical than other factors in reducing the highest temperature and casualties. Lowering the temperature below the tunnel ceiling is not caused by increasing the ceiling extraction velocity. Additionally, the study reveals that the fire source-ceiling distance and their relative positions play a crucial role in temperature distribution and plug-holing phenomenon in the tunnel. By using the Taguchi method, it is determined that a fire at a height of 0.125 m has a maximum ceiling temperature of 1.8, 1.3, and 1.1 times when the fire source happens on the floor with longitudinal velocities of 0.133, 0.265, and 0.53 m/s, respectively. The extraction point has diverse effects provided that the longitudinal ventilation velocity is set by critical velocity. The study’s objective is to provide tunnel engineering managers with a correlation to predict the highest temperature, which is a vital parameter for emergency evacuation. In conclusion, this study highlights the importance of considering longitudinal and point-extraction ventilated systems and their relative speeds in reducing the severity of tunnel fires.

Impact of forest fire on the mercury stable isotope composition in litter and soil in the Amazon

Mercury (Hg) emissions from forest fires, especially tropical forests such as the Amazonian forest, were shown to contribute significantly to the atmospheric mercury budget, but new methods are still necessary to improve the traceability and to reduce the great uncertainties related to this emission source. Recent studies have shown that the combustion process can result in Hg stable isotope fractionation that allows tracking coal combustion Hg emissions, as influenced by different factors such as combustion temperature. The main goal of the present study was, therefore, to investigate for the first time the potential of Hg stable isotopes to trace forest fire Hg emissions and pathways. More specifically, small-scale and a large scale prescribed forest fire experiments were conducted in the Brazilian Amazonian forest to study the impact of fire severity on Hg isotopic composition of litter, soil, and ash samples and associated Hg isotope fractionation pathways. In the small-scale experiment, no difference was found in the mercury isotopic composition of the samples collected before and after burning. In contrast, the larger-scale experiment resulted in significant mass dependent fractionation (MDF δ202Hg) in soils and ash suggesting that higher combustion temperature influence Hg isotopic fractionation with the emission of lighter Hg isotopes to the atmosphere and enrichment with heavier Hg in ashes. As for coal combustion, mass independent fractionation was not observed. To our knowledge, these results are the first to highlight the potential of forest fires to cause Hg isotopic fractionation, depending on the fire severity. The results also allowed to establish an isotopic fingerprint for tropical forest fire Hg emissions that corresponds to a mixture of litter and soil Hg isotopic composition (resulting atmospheric δ202Hg, Δ200Hg and Δ199Hg were −1.79 ± 0.24‰, −0.05 ± 0.04‰ and −0.45 ± 0.12‰, respectively).

Fire intensity regulates the short-term postfire response of the microbiome in Arctic tundra soil

Arctic tundra fires have been increasing in extent, frequency and intensity and are likely impacting both soil nitrogen (N) and phosphorus (P) cycling and, thus, permafrost ecosystem functioning. However, little is known on the underlying microbial mechanisms, and different fire intensities were neglected so far. To better understand immediate influences of different fire intensities on the soil microbiome involved in nutrient cycling in permafrost-affected soil, we deployed experimental fires with low and high intensity on an Arctic tundra soil on Disko Island, Greenland. Soil sampling took place three days postfire and included an unburned control. Using quantitative real-time PCR, copy numbers of 16S and ITS as well as of 17 genes coding for functional microbial groups catalyzing major steps of N and P turnover were assessed.We show that fires change the abundance of microbial groups already after three days with fire intensity as key mediating factor. Specifically, low-intensity fire significantly enhanced the abundance of chiA mineralizers and ammonia-oxidizing archaea, while other groups were not affected. On the contrary, high-intensity fire decreased the abundance of chiA mineralizers and of microbes that fix dinitrogen, indicating a dampening effect on N cycling. Only high-intensity fires enhanced ammonium concentrations (by an order of magnitude). This can be explained by burned plant material and the absence of plant uptake, together with impaired further N processing. Fire with high intensity also decreased nirK-type denitrifiers. In contrast, after fire with low intensity there was a trend for a decreased nosZ : (nirK+nirS) ratio, indicating – together with increased nitrate concentrations – an enhanced potential for nitric oxide and nitrous oxide emissions. Concerning P transformation, only gcd was affected in the short term which is important for P solubilization.Changes in gene numbers consistently showed the same contrasting pattern of elevated abundance with low fire intensity and decreased abundance with high fire intensity. Differentiating fire intensities is therefore crucial for further, longer-term studies of fire-induced changes in N and P transformations and potential nutrient-climate feedbacks of permafrost-affected soils.

Modelling carbon monoxide transport and hazard from smouldering for building fire safety design analysis

Smouldering produces massive toxic smoke and carbon monoxide (CO) that is responsible for the majority of fire deaths, but current building fire safety design rarely considers smouldering hazards. This work investigates the transport and hazards of CO from smouldering fire for the building performance-based design practice. The numerical model is firstly validated by reproducing two flat-scale fire experiments, revealing the characteristic surface temperature and CO yield of smouldering sources. The smouldering fire scenario is then designed in an atrium to review the evolution of CO concentration and its associated Available Safe Egress Time (ASET). Results show that a smouldering fire of the same burning rate as a flaming fire not only can provide a similar ASET, but also present a greater threat to occupants and rescue teams by forming a cold layer of lethal CO on the ground. Hence, the smouldering fire scenarios and their CO hazards should be considered in the performance-based design of building fire safety. Simulations also reveal that the smouldering fire can be more dangerous as the atrium height decreases, and ceiling ventilation is particularly effective in extracting CO emissions from smouldering fires.

Experimental Study of the Charring of I-Joists and Recession of Combustible Insulation in Light Timber Frame Assemblies with Comparison to Eurocode 5

Design models are commonly used in fire safety design of light timber frame assemblies. Parameters for use in the models are available for rectangular members with mineral wool, wood fibre or cellulose insulation and for assemblies with I-joists and mineral wool. For assemblies where I-joists and combustible insulations are combined, design parameters are missing. Five fire experiments with two I-joist types and four combustible insulation products have been conducted. The aim was to study charring of I-joist flanges and recession rates of combustible insulations and in addition, to compare their behaviour to the new and existing models of Eurocode 5. Charring rates for the flanges were 0.40–0.76 mm/min and 0.54–1.72 mm/min for the protected and post-protected phase, respectively. Rates decreased with increasing flange size. Charring rates for flanges of solid wood and LVL were comparable. The results show that lateral charring of I-joist flanges can be significant in the protected phase. The tested insulation products showed a lower recession rate than values reported for glass wool insulation, with a more pronounced difference for wood fibre and cellulose insulations. The low recession rates compared to previously reported generic values can possibly be explained by better product-specific properties, negligible shrinking and slightly different test set-up. The insulation stayed well in place after gypsum board fall-off and best-practice for keeping the insulation in place is given. The results, completed with future loaded full-scale tests, can give basis for further development of design models for assemblies with I-joists and combustible insulations.

Optimizing fire extinguishing effects of pneumatic sandblasting fire extinguishers based on experiments and CFD-DEM coupling simulations

This study focuses on addressing specific issues and research gaps related to pneumatic sandblasting effects for forest fire prevention and control. The primary objective is to determine the sensitivity of geometric parameters and recommend optimal design parameters for the extinguisher. The investigation employs a combination of Computational Fluid Dynamics-Discrete Element Methods (CFD-DEM) coupling simulations and experiments. The simulation and experimental results suggest flat outlets have the farthest sandblasting distance. Further experimentation shows that the outlet with different diameters show different sandblasting distances and accumulation effects, and the increased air duct length leads to decreased average airflow velocity at the outlet. In addition, the blade number of impellers was also studied for a longer sandblasting distance. Finally, the study found that the optimal parameters (79 cm air duct with the flat outlet of 8 cm diameter, 20-blade impeller), resulted in longer fire extinguishing length in fire extinguishing experiments compared to the original extinguisher. The findings provide valuable insights for improving the effectiveness of fire extinguishers and enhancing forest fire management strategies. The research outcomes have the potential to make a substantial impact in mitigating the devastating effects of forest fires and safeguarding natural resources and human lives.

Fire influences ant diversity by modifying vegetation structure in an Australian tropical savanna.

Fire is a dominant ecological force shaping many faunal communities globally. Fire affects fauna either directly, such as by killing individuals, or indirectly, such as by modifying vegetation structure. Vegetation structure itself also modulates fire frequency and intensity. As such, faunal responses to fire need to be seen through the lens of variable fire activity and vegetation structure. Here, we incorporate information on fire activity and vegetation structure to enhance an understanding of the response of ants to long-term (17-year) experimental fire treatments in an extremely fire-prone tropical savanna in northern Australia. A previous analysis revealed limited divergence in ant communities after five years of experimental fire treatment. Hence, we first investigated the extent to which ant communities diverged over a subsequent 12 years of treatment. We then assessed the relative contribution of fire treatment, cumulative fire intensity (fire activity) and woody cover to responses of ant species frequency of occurrence, richness and composition. We found that, even after 17 years, fire treatments explained little variation in any ant response variable. In contrast, woody cover was a strong predictor for all of them, while fire activity was a moderate predictor for abundance and richness. Ant species occurrence and richness increased in open habitats receiving higher levels of fire activity, compared with plots with higher vegetation cover experiencing low (or no) fire activity. Moreover, species composition differed between plots with high and low vegetation cover. Our findings provide experimental support to the principle that the effects of fire on fauna are primarily indirect, via its effect on vegetation structure. Furthermore, our results show that a 'uniform' fire regime does not have uniform impacts on the ant fauna, because of variability imposed by interactions between vegetation structure and fire activity. This helps explain why there is often a weak relationship between pyrodiversity and biodiversity, and it lessens the need for active management of pyrodiversity to maintain biodiversity. This article is protected by copyright. All rights reserved.

Characteristics of the spatial and temporal evolution of the environmental parameters for belt fire in underground coal mine roadway

The high temperature and toxic gases produced by burning belt in mine are a serious threat to the miners’ safety. A full-scale fire experiment was conducted in an exercise roadway, as a basis for which a physical model was established. The spatial and temporal evolution of the environmental parameters was obtained in the U-shaped working face, and the effect of wind speed on the fire parameters was studied. It was found that the smoke concentration and temperature from large to small are the downwind side of the transport roadway, working face and return airway. The structure of smoke layer near the working face is disorganized, which is related to the local turning structure of the roadway. The smoke reverse occurs later than the spread of smoke downstream of the fire area. The thickness and maximum temperature of counterflow layer decreases linearly with the increase of ventilation speed. Increasing the critical ventilation speed can control the smoke reserve and increase the risk downstream of the fire area. The harmfulness of wind speed to smoke reserve and spread in single roadway and complex network is then discussed. In addition, the influencing factors of fire evolution in confined space are put forward.

Bushfire performance of native Australian wood species

This paper describes fire safety experiments on Australian native timber samples with a special focus on their use in bushfire-prone areas. Nine species were assessed through testing in a cone calorimeter, thermogravimetric analysis and differential scanning calorimetry (DSC). The effects of density, moisture content and chemical extractives content were evaluated. Marked differences in ignition times were found, possibly due to variations in density across species, as well as the chemical extractives content. Analysis of the heat flow through DSC indicated that the type of extractives can influence the fire safety performance and that this aspect of wood properties merits further study. One additional species was identified as a suitable candidate for bushfire-resisting species in the Australian bushfire context.

Experimental Study on the Effect of Sub-Flash Point Fuel Temperature on the Spread Characteristics of Spill Fire

The spill fires caused by liquid fuel leaks greatly threaten the safety of fuel transportation and storage. In this work, the effect of fuel temperature on the spread characteristics of flowing flames was investigated through n-butanol spilling fire experiments. The spill fire spread can be divided into three stages at different temperatures and leakage rates (I) full spread, (II) gradually extinguished spread, and (III) unable to spread. The oscillation of the flame is related to the fuel thickness and the discharge rate. As the discharge rate or temperature increases, the spread mode changes from pulsation to uniform. With an increase in temperature, the surface flow of the flame is reduced, leading to a decrease in both the preheating time and pulsation amplitude. However, the rate of liquid surface detachment from the flame increases with increasing temperature. The view factor of flame spread can be calculated by the solid flame model, and the flame influences the heat radiation spread state with stable phases or peaks. The research findings presented in this paper hold significant implications for the development of fire safety regulations pertaining to fuel leakage fires.

Experimental field study on smoke characteristics and CO concentration of high-altitude tunnel fires induced using gasoline and diesel

High-altitude environments exhibit reduced atmospheric pressure, low oxygen density, and low air temperature conditions, which considerably affect tunnel fire characteristics. In this study, small-scale tunnel fire field experiments were performed at high altitudes to investigate the heat release rate (HRR), smoke temperature, and CO concentration of gasoline and diesel pool fires. The results revealed that with the increase in altitude, the HRR declined but the combustion duration increased. Furthermore, the maximum ceiling temperature decreased with the increase in altitude. The longitudinal ceiling temperature declined slowly in the high-altitude tunnel. By contrast, the smoke temperature spread rapidly among the cross-section in the high-altitude tunnel. The ceiling CO concentration behaviors for gasoline and diesel pool fires were categorized into four and three stages, respectively. Furthermore, the steady ceiling CO concentration and the maximum ceiling CO concentration decreased slightly with the increase in the altitude for gasoline pool fires, whereas the differences were greater for diesel pool fires. However, the steady ceiling CO concentration per unit mass burning rate increased linearly with the altitude for both fuels. The results revealed that the steady CO concentration at the height of 110 mm in the cross-section was nearly identical for various altitudes in the case of gasoline pool fires. However, for diesel pool fires, the CO concentration was higher at higher altitudes.

Deep-learning-based data loss reconstruction for spatiotemporal temperature in piloti structures: Enhancing applicability with limited datasets

A time-temperature curve, representing the fire characteristics of structures, can be obtained by real fire experiments. However, these experiments are inherently susceptible to data loss, which can compromise the accuracy of results. To address this challenge, this study proposed the framework utilizing a long-short-term memory (LSTM) with Bayesian optimization to reconstruct temperature histories by learning the spatiotemporal correlation of the data. The proposed framework is first validated using simulated datasets from computational fluid dynamics analyses. The field applicability of the model is further demonstrated through real fire test results, affirming its reliability in practical scenarios. The study also introduces a novel data processing technique to mitigate overfitting issues in LSTM applications with limited data, enhancing the robustness and reliability of temperature history reconstruction. Overall, the results highlight the potential of deep learning in accurately and practically reconstructing temperature histories in fire experiments.

Experimental study on burning behavior of small-scale n-heptane pool fire with brash ice

In-situ burning is an effective method for oil spill cleanup in ice-covered areas. Although brash ice is commonly contained in the oil spill, nearly no work has been conducted to explore the influence of brash ice on pool fire burning. Aiming at characterizing the influence of the brash ice content on pool fire, a series of small-scale pool fire experiments were conducted using burners with different sizes (5, 7.5, and 10 cm). The results show that the brash ice significantly affects the ignitability and burning behavior of pool fires. When the brash ice content exceeds the critical value, the pool fire with brash ice is non-ignitable. And during the brash ice melting process, the flame height and mass loss rate decrease with the brash ice content increasing. Based on the theoretical and heat transfer analysis, it was found that the heat transfer between the fuel and ice would decrease the mass loss rate. Furthermore, the dimensionless mass loss rate could be correlated with the dimensionless size of brash ice and brash ice content. In order to explore the brash ice melting behavior in pool fire burning, a dimensionless correlation was proposed to describe the melting rate. This work provides basic experimental data and understanding of burning behavior for pool fire with brash ice, which can inform more practical in-situ burning applications in ice-covered areas.

Fire Resistance of Fire-Protected Reinforced Concrete Beams Strengthened with Externally Bonded Reinforcement Carbon Fibre-Reinforced Polymers at the Full Utilisation Degree.

The fire resistance of reinforced concrete (RC) beams strengthened with externally bonded reinforcement carbon fibre-reinforced polymers (EBR CFRP) depends on the load level and degree of strengthening. Design guides for this type of structure recommend strengthening limits to prevent collapse of the structure due to vandalism, damage or fire. In practice, however, it is not uncommon to exceed the proposed limits. This necessitates protection of the CFRP adhesive against high temperatures, namely glass transition temperature levels. This paper presents the results of 10 full-scale experimental fire resistance tests of reinforced concrete beams with EBR CFRP strengthening, with and without fire protection and under various load levels including full utilisation. It was demonstrated that in cases where CFRP strengthening was not needed to carry load in an accidental fire scenario, test specimens with and without it achieved the same fire resistance. It was also proven that in cases where CFRP failure influenced the failure of the entire beam, fire protection was crucial for maintaining the beam's load-bearing capacity and its thickness had to be substantial. A fire resistance rating of over 4 h was achieved, nevertheless.

Fire spread in a large compartment with exposed cross-laminated timber and open ventilation conditions: #FRIC-01 – Exposed ceiling

Exposing cross-laminated timber (CLT) structures in buildings is increasingly popular in modern buildings. However, large timber surfaces, window facades, and different geometries can change the fire dynamics in a compartment. The effect of those parameters, therefore, needs to be studied. Two large-scale CLT compartment fire experiments (95 m2) have consequently been performed. The experiments were designed to represent a modern office building with an open-plan space and large window openings. In this experiment, #FRIC-01, the ceiling was exposed. The wood crib fire developed slowly and travelled approximately 1.5 m before the ceiling ignited at 32.5 min. Thereafter the fire spread rapidly across the ceiling and wood crib before it shortly after retracted. Three such cycles of rapid spread followed by a retraction occurred within 13 min, whereby the wood crib fire grew larger for each cycle. After the flames extended through the compartment for the fourth time, the fire remained fully developed. After a short period of intense burning, the CLT self-extinguished while the wood crib fire was still burning. The compartment withstood full burnout, and no reignition occurred despite some delamination and using an adhesive that lacks a demonstrated resistance against glue-line integrity failure.

Experimental study on combustion characteristics of pool fires in a sealed environment

The results of a series of bench-scale pool fire experiments to explore the burning characteristics under a sealed environment are presented in this work.Although the oxygen fraction in the space gradually decreases by burning consumingin comparison to open conditions, the transient heat release rate can still be calculated using the PER approach using the in-situ measured oxygen fraction. The dimensionless flame height can still be calculated using the McCaffrey's model for open conditions, but a greater coefficient should be used because the flame burns in a ‘hunger’ mode when the oxygen fraction is low. The current non-sealed fire model for centerline temperature rise of pool fires is unsuitable for the sealed environment: the centerline temperature rise decreases more quickly than that predicted by Nasr's model developed for cases with a limited ventilation in the middle and later stages of the fire. A new engineering model has been developed in this study by curve fitting sealed fire test results. Pagni's law can still be suitable to describe the relationship between the frequency of flame oscillation and the diameter of a pool fire in a sealed environment, but the modified coefficients are required.