Fire Experiments Research Articles

The use of multi-zone modelling for tunnel fires

This paper introduces the use of a multi-zone modelling approach for analysing smoke spread in tunnels. The approach suggested in this paper is based on an existing model, i.e., the Multi-Zone Fire model developed for large spaces. The Multi-Zone Fire model has been adapted and modified for tunnel fire scenarios by including features that consider longitudinal ventilation flow, tunnel gradient and tunnel section representations. An evaluation of the model has been conducted through benchmarking against experimental data from the BeNeLux tunnel experiments and the Runehamar tunnel fire experiments. The results from the Multi-Zone Fire model results were also compared against results from the Fire Dynamics Simulator. The results of the benchmarking exercise indicate that the multi-zone approach can be a time-efficient and useful tool for studying tunnel fire dynamics. The Multi-Zone Fire model performs well 50–200 m from the fire for heat release rates of 5–20 MW and moderate longitudinal ventilation flows. The model results are more conservative for the studied scenario with a higher heat release rate.

Impact of partial encapsulation on the fire dynamics of an open‐plan compartment with exposed timber ceiling and columns:CodeRed #04

AbstractThe use of mass timber in construction is becoming a compelling option when faced with the high carbon footprint of traditional concrete and steel production. However, fire safety standards are yet to evolve to support these designs. Encapsulation is commonly used to protect all, or some, of the timber surfaces and reduce the risks introduced. This paper presents the results fromCodeRed #04, the final experiment of theCodeRedexperimental campaign. This experiment was carried out inside a purpose‐built facility to capture fire dynamics in large compartments with exposed timber.CodeRed #04had identical characteristics toCodeRed #01with the exception that ~50% of the cross‐laminated timber (CLT) ceiling was encapsulated. The experiments were intentionally similar to the traveling fire experiments,x‐ONEandx‐TWO, which had a non‐combustible ceiling to enable a direct comparison. The overall fire dynamics experienced inCodeRed #04, intersect the characteristics observed inCodeRed #01andx‐ONEandx‐TWO.1. InCodeRed #04, there was a delay in the ignition of the CLT ceiling as the CLT directly above the crib was encapsulated. Once the CLT ceiling ignited, the fire spread rapidly throughout the compartment. The peak heat release rate (HRR) was estimated to be approximately 100 MW, a 17% decrease fromCodeRed #01. Following CLT ignition the resulting fire duration, maximum temperatures, and heat fluxes were broadly similar toCodeRed #01. Flame heights of approximately 1.5 m were observed from the windows while flame heights of 2.5–3 m were observed inCodeRed #01. Therefore, flame heights were found to be comparable tox‐TWO.1, though over a greater number of windows, reflecting the greater extent of simultaneous burning within the compartment. The average charring depth of the exposed CLT panels was ~25 mm, which is similar to that measured inCodeRed #01‐suggesting that the fire severity near the ceiling was not strongly impacted by the 50% encapsulation of timber. No charring was observed where the ceiling was encapsulated and loaded service fixings installed through the encapsulation were found to be less likely to fail than when attached directly to the exposed timber. Smoldering was observed after the cessation of flaming and, in a few locations, was observed to progress through the thickness of the CLT panel and continue behind the encapsulation. This illustrates that, while encapsulation can succcessfully prevent flaming, it cannot be completely relied on to avoid smouldering. The findings fromCodeRed #04contribute to the development of evidence‐based fire safety design methodologies for exposed mass timber buildings.

Pupae survival following fire in the frosted elfin (Callophrys irus)

Abstract The frosted elfin (Callophrys irus) butterfly inhabits landscapes that may be subject to frequent fire to be sustained. Frosted elfins pupate primarily in leaf litter, at the soil surface, or just below it, and may suffer high mortality rates when fires occur. Gathering better information on this source of mortality is critical to planning prescribed fire operations in a manner conducive to the long‐term survival of the species. We buried lab‐reared frosted elfin pupae (n = 61) at 0.75 cm (n = 31) or 1.75 cm (n = 30) below the ground and conducted two experimental fires that mimicked typical prescribed fires. Eighteen of 30 (60%) buried at 1.75 cm survived 4 weeks postburn; no pupae buried at 0.75 cm survived. Most (n = 17) of the pupae that survived successfully enclosed the following year. Surviving pupae encountered lower maximum temperatures and were exposed to shorter durations of above‐lethal temperatures compared to those that died. Our data demonstrate that high mortality rates can be expected due to fire, yet fire remains a critical tool for maintaining the habitat. Fire practitioners should mitigate losses by using ignition patterns and suboptimal burn conditions to reduce fire intensity, or burn in a mosaic pattern across the landscape to ensure enough survival to perpetuate frosted elfin populations.

Pyrophilic Plants Respond to Postfire Soil Conditions in a Frequently Burned Longleaf Pine Savanna.

AbstractFire-plant feedbacks engineer recurrent fires in pyrophilic ecosystems like savannas. The mechanisms sustaining these feedbacks may be related to plant adaptations that trigger rapid responses to fire's effects on soil. Plants adapted for high fire frequencies should quickly regrow, flower, and produce seeds that mature rapidly and disperse postfire. We hypothesized that the offspring of such plants would germinate and grow rapidly, responding to fire-generated changes in soil nutrients and biota. We conducted an experiment using longleaf pine savanna plants that were paired on the basis of differences in reproduction and survival under annual ("more" pyrophilic) versus less frequent ("less" pyrophilic) fire regimes. Seeds were planted in different soil inoculations from experimental fires of varying severity. The more pyrophilic species displayed high germination rates followed by species-specific rapid growth responses to soil location and fire severity effects on soils. In contrast, the less pyrophilic species had lower germination rates that were not responsive to soil treatments. This suggests that rapid germination and growth constitute adaptations to frequent fires and that plants respond differently to fire severity effects on soil abiotic factors and microbes. Furthermore, variable plant responses to postfire soils may influence plant community diversity and fire-fuel feedbacks in pyrophilic ecosystems.

Numerical Study of the Effect of the Ignition Procedure on the Front of a Surface Fire from a 3D Numerical Model

In instrumented prescribed fires, the ignition procedure requires much attention. In this paper, we investigate the effects of two ignition procedures on the fire head using a 3D numerical model. The first procedure is to ignite the fire from the edges of the fire line towards the centre of the line. The second procedure consists of igniting the fire from the centre of the fire line to the edges of the line. The 3D numerical model used is based on the modelling of the fuel layer from Lagrangian particles, and the fire propagation is based on a two-phase model. The model was tested on an experimental fire in a wheat field in southern Australia. The model predicted the experimental fire front well. Analysis of the impact of the ignition procedure on the fire head showed that the quasi-steady-state rate of fire spread was the same for both procedures. However, before the quasi-stationary state, the front of the first procedure spread faster than that of the second procedure. The fire front in the first procedure was wider than in the second procedure. It was also found that the length of the head fire in the first procedure remained the same as that of the ignition line. In the second procedure, the length of the head fire was one-third of that of the ignition line.

Experimental fire performance assessment of a new type of prestressed composite circular precast concrete columns

The purpose of this paper is to study the fire resistance of a new type of prestressed composite circular precast concrete column (PCCPCC) consisting of a prestressed precast concrete hollow pipe and cast-in-place core concrete filled in the hollow section through a combined numerical and experimental approach. The potential advantages of PCCPCCs lie in their low manufacturing costs and high construction efficiency. A series of fire tests were conducted on PCCPCCs with consideration of different precast concrete strengths, rebar layouts, and axial loads, where the column damage patterns, fire exposure time, and vertical displacements of all the specimens were experimentally examined. Their post-fire residual strengths were also determined via uniaxial compression tests. Finite element (FE) simulations were also conducted and the obtained results were compared to the corresponding test outcomes. The results show that the fire resistance of PCCPCCs is largely dependent on the imposed axial loading, and an effective thermal isolation effect from the prestressed precast concrete hollow pipes was identified. The further research on this new column form is necessary for the possible future wide adoption.

A phenology-driven fire danger index for northern grasslands

Background Directly after snowmelt, northern grasslands typically have highly flammable fuel-beds consisting of 100% grass litter. With green-up, the addition of high-moisture foliage leads to progressively decreasing fire hazard. Aims Our aim was to create a fire-danger index for northern grasslands that incorporated grass phenology. Methods We made use of 25 years of Swedish wildfire data and 56 experimental fires conducted during one full fire-season, merged with established models for moisture content and flame spread rates. Refined data on equilibrium moisture content of grass litter were obtained through laboratory tests. Key results The RING (Rate of spread In Northern Grasslands) model uses cumulative air temperature as a proxy for growing season progression. Three independent functions account for impact of wind, moisture content and the damping effect of live grass, respectively. The latter results in exponentially decaying rate of spread (ROS) with the progressing season. Following the field experiments, green grass proportion as low as 10–20% (live/dead dry-mass) resulted in model-ROS so reduced that the grassland fire season could effectively be considered over. Conclusions The model, calculated from standard meteorological data only, matches the experimental results and separately performed validation tests, as well as wildfire dispatch data. Implications RING has been used in Sweden since 2021 and is likely applicable to other northern regions as well.

Improved logistic models of crown fire probability in Canadian conifer forests

Background Crown fires are an ecologically necessary but hazardous process in conifer forests. Prediction of their behaviour in Canada has largely depended on the Canadian Forest Fire Behaviour Prediction System, in which fire weather indices drive primarily fixed fuel type models. The Crown Fire Initiation and Spread (CFIS) system presents a more flexible approach to predicting crown fire occurrence than fixed fuel type models. Aims Using a multi-decadal database of experimental fires carried out in conifer plots (1960–2019, n = 113), our aim was to develop updated models based on the CFIS system approach, fitting crown fire occurrence models to fire environment variables using logistic regression. Methods We tested alternative fuel moisture estimates and compared various model forms using repeated cross-validation. In two-storeyed stands, crown fire occurrence was defined as the involvement of lower canopy stratum fuels. Key results Final models based on wind speed, fuel strata gap, litter moisture and surface fuel consumption predicted crowning events correctly in up to 92% of cases in training data (89% in cross-validation). Conclusions and implications These new models offer improved accuracy and flexibility that will help users assess how competing environmental factors interact under different fuel treatments and wildfire scenarios.

Review of Parameters Correlated with the Maximum Heat Release Rate in Flames of Polyurethane Foams of Various Cuboid Shapes

The heat release rate is an important physical quantity that can quantitatively analyze the scale and intensity of fires. Recently, studies have been conducted to analyze the correlation between various parameters of combustibles and the maximum heat release rate measured in fire experiments, and to predict the maximum heat release rate of combustibles through correlation equations. However, the suitability of various parameters of combustibles that can be applied in the correlation has not yet been fully investigated. In this study, fire experiments were conducted using polyurethane (PU) foams of various shapes. Besides, the correlations between various combustible parameters and the maximum heat release rate were quantitatively compared and analyzed. The results confirmed that by appropriately using the combustible parameters, the relative error of the maximum heat release rate predicted by the correlation equation could be reduced from 34% to 12%.

Application of FDS to Predicting Fire Spread in a Horizontal Cable Tray

With regard to cable tray fires, comparing the prediction results obtained through fire simulations with the measurement results from fire experiments conducted under real-life conditions is essential to ensure the predictive reliability of the model. In determining the validity of the calculation process and procedure performed in a specific fire experiment, the result may vary depending on the user’s capability. This is because of the high user dependence due to the characteristics of the fire model. In this study, we examined whether the actual spread of fire could be similarly predicted when the physical quantities of cable tray fires suggested by previous studies were applied. We also applied a fire modeling method considering the arrangement of cables to predict appropriate fire spread in a nuclear power plant and then performed a comparative analysis of the results and the experimental results. The prediction results, in terms of the fire spread time, varied depending on the arrangement type (whether loosely and tightly arranged) of cables. Finally, we devised a process of accurately predicting the heat release rate (HRR) curve as compared to the experimental results by using a sensitivity analysis of the input parameters (density, specific heat, and thermal conductivity) corresponding to the physical properties considered in the fire model.

배전반 수분유입에 따른 화재 위험성과 제도개선 방안

Fires in the fire switchboard are constantly occurring and efforts are being made to improve them. Most of the causes of fire in switchboards are due to poor contact at terminals, dust and water inflow. Among them, we have checked the possibility of fire caused by water inflow through fire cases, installation status, and combustion experiments. We have also confirmed that there are no specific criteria regarding electrical equipment, although the technical standards of the Ministry of Trade stipulate that “the structure would not allow water to permeate into the distribution box.” Therefore, this study warns of fire hazard caused by water inflow switchboard through the results of fire reproducibility experiment, and it expects that the supplementation of laws to improve the environmental factors that bring moisture into switchboard. We hope that the fire investigation will develop from the center of ignition source and factor to the center of fire prevention measures and contribute to fire prevention.

Mineralogical and Physicomechanical Characterization of Kaolinitic Clay from Moshi, Northern Tanzania for Potential Ceramic Utilization

Kaolin clay from Moshi, northern Tanzania has been characterized for potential ceramics productions. Clay samples taken from three different levels of the deposit were analysed by XRD and XRF. Firing experiments were carried out on experimental briquettes at a maximum temperature of 1300 °C at the rate of 100 °C/hour. The results revealed dominance of kaolinite and illite in the raw clay. The samples were composed majorly by silica (36.88–41.62%), alumina (30.83–32.40%) and hematite (9.29–12.70%). Granulometric analysis showed that the amount of clay decreased with deposit depth. The physicomechanical properties of the clay fired at the optimal temperature of 1300 °C included shrinkage (22.06–30.72%), water absorption (18.23–20.15%), bulk density (1.834–2.182 g/cm3) and modulus of rupture (2.957–6.313 MPa). Mullite was the key component responsible for mechanical strength. Clay sample from the top level showed the best properties. The parameters were of satisfactory quality and comparable to other ceramically suitable clays. High levels of Fe2O3 (> 9%) could adversely affect the translucency of whitewares. These findings indicate that the investigated kaolin has potential of being used in the ceramic industry for making materials such as non-vitreous tiles, bricks and various high-temperature products that do not require high brightness specifications.
 Keywords: Clay mineralogy, firing temperature, microstructure characterization, ceramic properties, Tanzanian kaolin.

Examination of effects of indoor fires on building structures and people

The scientific study of the harmful effects of indoor fires on building structures and on the environment is a top issue today. Indoor fires frequently occur all over the world. The goal of our research is to examine the effects of an average room fire on the survival possibility of a trapped person and on the building structure, taking into account features of the Eastern European architecture. First, a computational fluid dynamics (CFD) simulation was performed to examine the change of temperature, oxygen, and carbon monoxide concentration in a selected room in a vacant building used for military training. Based on the results, a 1:1 scale fire experiment was carried out with the parameters used in the simulation. The experiment was repeated once with the same settings. It was observed that without the intervention of firefighters, the temperature in the experiment could have rapidly reached 400 °C, as suggested by the simulation, which could have caused structural damage to the building. Furthermore, after 3 min the carbon monoxide concentration reached 400 ppm in both experiments and the simulation, which is a harmful level to people trapped inside the room. Also, in the experiment there was sufficient oxygen at the ground level with what people can survive 3 min.

Research on multi-detector real-time fire alarm technology based on signal similarity

Accurate and timely fire detection is the focus of fire prevention, fire control and fire safety. However, fire detectors have a high false alarm rate in structures. To effectively realize real-time fire monitoring, a multi-detector fire detection model based on the asynchronous spatiotemporal signal similarity of different detectors was developed in this study. Firstly, the correlation coefficients of prediction signals and correlation signals were calculated based on the Pearson-Derivative dynamic time warping method. Secondly, a real-time fire detection model based on the signal correlation coefficient was constructed to realize the early detection of fire warnings. Besides, a calculation rule of the correlation coefficient for multi-detector signals was proposed, and the alarm threshold values in fire detection under different numbers of responding detectors were determined by the Support Vector Classification (SVC) algorithm. Finally, the effectiveness of the proposed fire detection model was verified by the fire experiment data from the National Institute of Standards and Technology (NIST) and the kitchen cooking nuisance tests.

An experimental and numerical analysis of the fire resistance of concrete elements incorporating ROBOVOID void formers

Disposal of plastic waste poses a significant scientific challenge due to its non-biodegradable properties, increasing volume of production, and low recycling rate. One potential solution is its’ manufacture into void formers for use in concrete building elements. However, plastics soften and decompose when exposed to high temperature fire which poses a challenge for fire safety design and certification of construction elements. A combined experimental and numerical study is presented to determine the fire resistance of concrete building elements that incorporate a novel recycled plastic void former (ROBOVOID, US patent No. 11,352,789). Multiple experimental fire exposure tests are performed to determine fire resistance and assess thermally induced damage for various building elements incorporating ROBOVOID. The fire resistance of the voided elements increased as the concrete content increased, or the fire intensity or exposure duration decreased. A finite element model is presented that can predict the thermal response of the building elements when subject fire representative of the Australian Standard Bushfire Attack Level (AS 1530.8.1), Building-to-Building (AS 5113) and Fire Resistance Level (AS 1530.4) conditions. The analysis indicates that polymer-based void formers can be incorporated into concrete structures while maintaining a high level of fire resistance for a variety of fire conditions.

Integrating microfossil records from livestock dung burned as fuel in Menorca, Balearic Islands

Interdisciplinary microarchaeological approaches including integrated studies of plant and faecal microfossils are fundamental to identify and interpret fuel remains within combustion installations such as hearths and ovens which are common across the Mediterranean. This is particularly critical in cases when other sources of archaeobotanical evidence such as charred macroremains are partially uninformative or absent, in order to assess the nature of burnt fuel, as similar plant records may derive from plant-based fuels and other fuel types including animal dung.The current research illustrates the contribution of integrated analytical methods in archaeobotany to interdisciplinary approaches on the identification, seasonality, and the impact of fuelling on modern livestock dung. The focus is on pollen, phytoliths, and calcitic dung spherulites embedded within cattle, sheep and pig faeces collected in different seasons of the year and farms from UNESCO Biosphere Reserve Menorca, Balearic Islands, Western Mediterranean. Experimental firing reference records provide modern comparative datasets on factors affecting the microfossil content and preservation of animal faeces used as a fuel source, as well as on the range of natural and anthropogenic pathways influencing these which are critical to identify and accurately interpret fuel remains. The results reported here are also compared to laboratory-controlled experimental datasets as well as ethnoarchaeological records including firing measurements (time and temperature) from cooking installations that have followed a similar integrated methodological approach.Experimental and ethnoarchaeological records provide fundamental information on taphonomic issues that are understudied, such as variation in the production and its integrity among different animal defecators, as well as on seasonality of plant and faecal microfossils that are embedded within the dung, and the impact of fire on these as a result of fuel use, as an important combustion material which is still commonly overlooked.

Study on smoke propagation in tunnel construction of a hydropower station: A full-scale fire experiment

In this study, full-scale fire experiments were conducted in a hydropower station to investigate smoke propagation during tunnel construction. The flame height, smoke temperature and stratification, smoke descent and spread velocity were analyzed via measurements and on-site observations. The initial combustion stage was largely affected by ignition source during tunnel construction for diesel pool fire, and the average flame height in the fully developed stage could reach 1.4–2.1 m in experimental fire scenarios. The gradient of the smoke temperature evolution near the fire was the opposite for the upstream and downstream regions. The longitudinal temperature distribution was concentrated in a small range at the heights of the smoke layer, and gradually decreased by air entrainment as the height decreased, while further increasing in the lower half of the tunnel height in the near-fire region under heat radiation from the fire source. Moreover, distinct and stable smoke stratification formed during the fully developed combustion stage, and the smoke layer interface was at approximately half the tunnel height. Smoke descent was aggravated in the decay stage of combustion, and the fire risk remained high after the fully developed period. The smoke front spread velocity was empirically determined for the full-scale tunnel fire scenarios. Conclusions from full-scale experiments can support smoke control design and on-site fire emergency response plans for hydropower stations.

Review of fire experiments in mass timber compartments: Current understanding, limitations, and research gaps

AbstractThe use of mass timber in buildings instead of non‐combustible materials has benefits in sustainability, aesthetics, construction times, and costs. However, the uptake of mass timber in modern construction for medium and high‐rise buildings is currently hindered by uncertainty regarding safety and structural performance in fire. We attribute this to a lack of data. Insufficient understanding means that for building designs beyond the current range of experiments the fire performance is unknown. To address this uncertainty, we review the available data in the scientific literature from 63 compartment fire experiments with timber, the majority of which use cross‐laminated timber (CLT). We found that most experiments reached temperatures 80–180°C greater than in non‐combustible compartments. Timber ceilings have on average a 16% lower char rate than timber walls. The heat release rate contribution of timber has a positive linear relationship with charring rate, however is susceptible to significant uncertainty and variability. There are limits to the data available, particularly in large open‐plan compartments of floor areas larger than 100 m2 where a wider range of heating conditions occur. Other topics where further understanding is required are compartments with exposed timber areas greater than 75%, compartments with smaller opening areas, and the hazard of smouldering following the flames. Therefore, additional research is needed to design beyond the limits, specifically in compartment size, ventilation, and timber exposure. This paper identifies correlations in the current body of experimental research to improve fire‐safe design of timber buildings.

The performance of vertically perforated clay block masonry in fire tests predicted by a finite-element model including an energy-based criterion to identify spalling

Fire tests on masonry are one of the most expensive experiments in developing new vertically perforated clay block geometries. Numerical simulations might be a reasonable substitute for such experiments, leading to a significant cost reduction in the development phase. However, the prediction of such tests with numerical modeling concepts is challenging due to large temperature and stress gradients, highly non-linear material effects, and the complex geometry of the blocks. Herein, we present a finite-element-based concept, including thermal and mechanical simulations, a unit-cell approach, a smeared damage model, and a novel energy-based spalling criterion to describe the structural and material behavior of a masonry wall in a fire experiment. We could predict the obtained spalling times of longitudinal webs and the total endurance of a masonry wall without any empirical fitting parameters in good agreement with experimental data. These results show that we can use our modeling approach for simulating such fire tests, enabling a much cheaper and more efficient development of block geometries.

Rethinking “BLEVE explosion” after liquid hydrogen storage tank rupture in a fire

The underlying physical mechanisms leading to the generation of blast waves after liquid hydrogen (LH2) storage tank rupture in a fire are not yet fully understood. This makes it difficult to develop predictive models and validate them against a very limited number of experiments. This study aims at the development of a CFD model able to predict maximum pressure in the blast wave after the LH2 storage tank rupture in a fire. The performed critical review of previous works and the thorough numerical analysis of BMW experiments (LH2 storage pressure in the range 2.0–11.3 bar abs) allowed us to conclude that the maximum pressure in the blast wave is generated by gaseous phase starting shock enhanced by combustion reaction of hydrogen at the contact surface with heated by the shock air. The boiling liquid expanding vapour explosion (BLEVE) pressure peak follows the gaseous phase blast and is smaller in amplitude. The CFD model validated recently against high-pressure hydrogen storage tank rupture in fire experiments is essentially updated in this study to account for cryogenic conditions of LH2 storage. The simulation results provided insight into the blast wave and combustion dynamics, demonstrating that combustion at the contact surface contributes significantly to the generated blast wave, increasing the overpressure at 3 m from the tank up to 5 times. The developed CFD model can be used as a contemporary tool for hydrogen safety engineering, e.g. for assessment of hazard distances from LH2 storage.