Fire Experiments Research Articles

Modelling the heat release rate of PRISME experimental cable fires in a confined, ventilation controlled, environment using FLASH-CAT and FDS

Development of a Heat Release Rate (HRR) to represent a fire scenario with unknown parameters is challenging. A key step in any fire modelling approach is to define a HRR curve which accounts for the fuel type, quantities, and combustion behaviour. Without robust evidence to underpin the HRR definition, approaches must be adopted to address data uncertainty. This paper presents a methodology for defining the HRR of cable tray fires in a confined, ventilation controlled, environment. The HRR model has been developed during the PRISME-3 programme which has included both “open” and “blind” prediction exercises, giving the opportunity to develop and validate a fire growth rate model and address uncertainties. The model was developed from an existing, published, approach (FLASH-CAT, as outlined in NUREG CR-7010), which was modified, using sensitivity analysis, to better replicate experimental fire tests.The modified model, used in conjunction with the Computational Fluid Dynamics (CFD) based fire modelling tool NIST Fire Dynamics Simulator (FDS), provides comparison to experimental HRR and other HRR growth approaches, indicating the relative importance of HRR in fire model definition.

Features of turbulence during wildland fires in forested and grassland environments

Fire-induced turbulence and the feedback into the fire, following ambient changes, differ for forested (sub-canopy) and grassland environments. Here, we synthesize observations from multiple experimental surface fires: two sub-canopy backing fires, one sub-canopy heading fire, and a grassland heading fire. We identify and compare the most essential coherent structures and processes of each case from the turbulent momentum fluxes and turbulent kinetic energy (TKE) budget terms. In the sub-canopy burns, turbulent eddies are strongest near the canopy top: high streamwise turbulent flux accompanies low cross-stream turbulent flux and vice versa. In the grassland fire, both streamwise and cross-stream eddies strengthen simultaneously until a certain height, informing a vertical length scale for the fire-influence. Moreover, the forward sweep from streamwise eddies assists in the fire spread by pushing hot gases towards unburnt fuel. In the sub-canopy fires, shear production and buoyancy production are more substantial near the canopy top for more intense fires, while their magnitudes decrease with decreasing fire intensity. At mid-canopy-height scales, buoyancy production dominates shear production, becoming the key mechanism for vertical transport of TKE. In the grassland fire, shear production dominates buoyancy production near the surface and is insignificant beyond a certain height relative to the flame length, while buoyancy production increases with height, becoming substantial further away from the surface. Turbulent transport terms are also active in both environments. For intense sub-canopy fires, there is a loss in TKE due to its expulsion to the boundary layer aloft via the transport term, compensated by a reversal process: TKE influx via the transport term. In the grassland fire, the transport term mimics this behavior until a certain height. The insights into the relative significance of the respective turbulent fluxes and TKE budget terms in each environment can help simplify the complex system of equations governing fire physics.

A Critical Review of Fire Tests and Safety Systems in Road Tunnels: Limitations and Open Points

Fire tests are used to determine whether fire protection products meet the minimum performance criteria set out in codes and legislation, as well as to certify these products. Experimental large-scale fires are used to test the performance of safety systems in tunnels, which are confined environments with a high probability of accidents and significant consequences due to the evolution of the event and whether there is the capability of counteracting it by safety measures. In this study, we conducted a systematic literature review following PRISMA guidelines. We searched the Scopus and Web of Science databases for publications from 2013 to 2022, resulting in a selection of 72 articles. An analysis was conducted on the following main topics: tunnel fires, fire characteristics (measured variables, spread, and smoke), model-scale tests, automatic shutdown systems, and ventilation solutions. One of the most important contributions of this study is the suggestion that fire tests represent an effective method not only to prevent fire events in tunnels but also to ensure the resilience of the infrastructure. Based on this state-of-the-art literature review, future tunnels could be designed by linking new smart technology and artificial intelligence to create interactive and high-performing safety systems.

Preparation of the Environmentally Friendly and High Stable Gel Foam Based on Biomass Xanthan Gum for Inhibiting Coal Spontaneous Combustion

ABSTRACT In order to improve the environmental friendliness of inhibiting coal spontaneous combustion, a new environmentally friendly biomass gel foam was successfully prepared by using xanthan gum (XG), aluminum citrate (Alcit), gluconate-δ-Lactone (GDL), alkyl glycoside (APG), and tea saponin (TS). When the concentrations of XG, Alcit, GDL and biomass composite foaming agent were 4, 4, 0.4, and 0.3 wt%, respectively, the gel foam had a half-life of up to 27 days. The gel foam water retention study showed that the water loss rate of its was 60% lower than that of water and 58.6% lower than that of foam after heating at 60°C for 10 h. The temperature-programmed experiment showed that the gel foam could delay the accelerated oxidation temperature of coal from 90°C to 140°C. The fire extinguishing experiment showed that the gel foam could extinguish coal fire quickly, the temperature of coal rapidly dropped from 960°C to 121°C within the first 20 min and the reburning of coal fire was not observed after the extinguishment. This study is useful for the development of environmentally friendly gel foams for inhibiting coal spontaneous combustion.

The partial fire protection of steel members: a comparative study

PurposeThis paper provides a summary of the issues in the passive fire protection of steel structures. Types of passive fire protection and the material properties of protection members and steel members are described. The paper deals with the possibility of partial fire protection for secondary steel beams, in cases where, due to possible membrane action, it is not necessary to apply passive protection to the entire beams.Design/methodology/approachStudies of partially fire-protected steel structures are compared, and results from studies with different input data are summarized. A fire experiment was conducted to investigate the effect of partial passive protection in a small-scale furnace. Based on the findings of the experiment, numerical models were prepared using Ansys Mechanical.FindingsThe results are summarized, and a partial fire protection length of 500 mm is recommended. Various partial fire protection lengths were compared, and the temperature development of the steel contactors was compared using a protection length of 500 mm. At the end of the paper, options for partial passive protection of steel beams are presented.Originality/valueExtended paper from ASFE2021 based on selection.

Scaling Study of Smoke Spread from Building Integrated Photovoltaic (BIPV) Double Skin Façade Fire for Achieving Sustainable Buildings and Cities

Due to the shift to sustainable design of buildings and cities, the building integrated photovoltaic (BIPV) is getting more attention. However, this technology may bring new challenges to safety in buildings and cities, i.e., fire safety issues regarding BIPV fire induced smoke propagation in double skin façades (DSF). To study this phenomenon, it is essential to conduct experiments, in which full-scale fire experiments are often inefficient regarding economics and safety. To cope with these issues, this study proposes a new scaling method, which applies the helium sub-scale tests to replace full-scale fire smoke tests for buildings with DSF during BIPV fires. To verify this scaling method, three groups of cases are defined and simulated by fire dynamic simulator (FDS), i.e., full-scale with fire (FSF), small-scale with fire (SSF) and small-scale with helium (SSH). Then, a small-scale experimental model is constructed to validate the FDS model. At last, the simulation results are compared among SSH, SSF and FSF cases, which show acceptable agreement. Therefore, the new scaling method of smoke spread from BIPV DSF fires is justified, which can be applied to the study of BIPV DFS fires induced smoke control in urban scale.

Progressive collapse of steel structures exposed to fire: A critical review

A state-of-the-art review is presented on design and research related to progressive collapse of steel structures under fire conditions. The influence of load ratios, strength of structural members, fire scenarios on the collapse behavior of structures is comprehensively reviewed. The corresponding mitigation measures and quantitative assessment methods are summarized. The existing experimental works are limited to low-rise buildings, plane frames or scaled models due to cost and safety issues, while numerical works involve high-rise buildings, three-dimensional models, full scales and various influencing factors. It is found that these influencing factors as well as fire protections and bracing systems significantly affect whether, how and when a structure collapses. Whether a structure collapses in fire essentially depends on the location of fire, heating rates, peak temperatures and duration of fire. Three collapse modes of global lateral drift collapse, global downward collapse and combined lateral-downward collapse are concluded for steel framed structures in fire. Three-dimensional models are recommended to make an accurate prediction of collapse modes of structures exposed to various fire scenarios. The determination of collapse time of structures under fire is a complicated process, and it is suggested to divide it into safe, alert, dangerous and collapse stages. This can provide three collapse warning levels of stay in, ready to evacuate and must evacuate. Further work is still needed on fire experiments considering collapse purpose, large structural scale and realistic fire conditions (cooling phase and fire spread) to achieve the real fire-induced collapse mechanism of structures and validate numerical models.

Extensive Gaseous Emissions Reduction of Firewood-Fueled Low Power Fireplaces by a Gas Sensor Based Advanced Combustion Airflow Control System and Catalytic Post-Oxidation

In view of the tremendous emissions of toxic gases and particulate matter (PM) by low-power firewood-fueled fireplaces, there is an urgent need for effective measures to lower emissions to keep this renewable and economical source for private home heating available in the future. For this purpose, an advanced combustion air control system was developed and tested on a commercial fireplace (HKD7, Bunner GmbH, Eggenfelden, Germany), complemented with a commercial oxidation catalyst (EmTechEngineering GmbH, Leipzig, Germany) placed in the post-combustion zone. Combustion air stream control of the wood-log charge combustion was realized by five different control algorithms to describe all situations of combustion properly. These control algorithms are based on the signals of commercial sensors representing catalyst temperature (thermocouple), residual oxygen concentration (LSU 4.9, Bosch GmbH, Gerlingen, Germany) and CO/HC-content in the exhaust (LH-sensor, Lamtec Mess- und Regeltechnik für Feuerungen GmbH & Co. KG, Walldorf (Germany)). The actual flows of the combustion air streams, as calculated for the primary and secondary combustion zone, are adjusted by motor-driven shutters and commercial air mass flow sensors (HFM7, Bosch GmbH, Gerlingen, Germany) in separate feedback control loops. For the first time, the residual CO/HC-content (CO, methane, formaldehyde, etc.) in the flue gas is in-situ monitored with a long-term stable AuPt/YSZ/Pt mixed potential high-temperature gas sensor, which allows continuous estimation of the flue gas quality with an accuracy of about ±10%. This parameter is not only an essential input for advanced combustion air stream control but also provides monitoring of the actual combustion quality and logging of this value over a whole heating period. By many firing experiments in the laboratory and by field tests over four months, it could be demonstrated that with this long-term stable and advanced automated firing system, depression of the gaseous emissions by about 90% related to manually operated fireplaces without catalyst could be achieved. In addition, preliminary investigations at a firing appliance complemented by an electrostatic precipitator yielded PM emission depression between 70% and 90%, depending on the firewood load.

Herbaceous vegetation responses to experimental fire in savannas and forests depend on biome and climate.

Fire-vegetation feedbacks potentially maintain global savanna and forest distributions. Accordingly, vegetation in savanna and forest ecosystems should have differential responses to fire, but fire response data for herbaceous vegetation have yet to be synthesized across biomes. Here, we examined herbaceous vegetation responses to experimental fire at 30 sites spanning four continents. Across a variety of metrics, herbaceous vegetation increased in abundance where fire was applied, with larger responses to fire in wetter and in cooler and/or less seasonal systems. Compared to forests, savannas were associated with a 4.8 (±0.4) times larger difference in herbaceous vegetation abundance for burned versus unburned plots. In particular, grass cover decreased with fire exclusion in savannas, largely via decreases in C4 grass cover, whereas changes in fire frequency had a relatively weak effect on grass cover in forests. These differential responses underscore the importance of fire for maintaining the vegetation structure of savannas and forests.

New Books across the Disciplines

New Books across the Disciplines

Пожарная опасность и приоритетные области пожаробезопасного применения композитных материалов на основе арамидных волокон

The article is devoted to topical issues of research on the fire hazard of composite materials in particular the materials based on the aramid fibers. Preliminary analysis of possible areas of their application showed the need for conducting hazard studies. For fire-resistant fabrics considering the operating conditions, research and test methods were justified and selected to determine and evaluate the indicators of flammability, smoke-generating ability, toxicity of combustion products, specific emission of some toxic gases and oxygen consumption, burnout rate. For this purpose, both standard methods and a separate experimental method of complex testing were used. Based on the results of these studies, the new experimental data were obtained, which indicate the fireproof properties of composite materials and fabrics based on the aramid fibers. So, for example, the tested samples belong to the groups (classes) of materials D1 (with low smoke-forming ability), T1 (low-hazardous) in terms of toxicity of combustion products, B1 (hard to ignite) in terms of flammability. The experimental fire hazard data analyzed in the work allow to draw conclusions about the possibility of using the tested composite materials based on the aramid fibers with virtually no restrictions. This is especially true for air support structures of various functional purposes.

Pyrodiversity trade-offs: A simulation study of the effects of fire size and dispersal ability on native mammal populations in northern Australian savannas

Maximising the spatiotemporal variability of prescribed fire (i.e. pyrodiversity) is often thought to benefit biodiversity. However, given mixed empirical support, the generality of the pyrodiversity hypothesis remains questionable. Here, we use a simulation experiment to explore the effects of spatiotemporal fire patterns on the population trajectories of four mammal species in a northern Australian savanna: northern brown bandicoot (Isoodon macrourus), northern brushtail possum (Trichosurus vulpecula arnhemensis), grassland melomys (Melomys burtoni), and northern quoll (Dasyurus hallucatus). Underpinned by data from a landscape-scale fire experiment, we simulated mammal population trajectories under three scenarios of fire size (ambient, small/dispersed fires, large/clumped fires) and three levels of dispersal ability (low, moderate, high) over a 21-year period across the Kapalga area of Kakadu National Park. The simulated population size of all four species declined markedly, regardless of fire spatial pattern and dispersal ability. However, the predicted final population size (i.e. number of individuals in the final timestep of the simulation) for the northern brown bandicoot, northern brushtail possum and grassland melomys were significantly influenced by fire size, with declines most severe under the small/dispersed fire scenario. Our results suggest that maximising the dispersion of small fires at the expense of disturbance refugia (such as less-frequently burnt areas) may exacerbate the severity of mammal decline. This highlights the importance of considering trade-offs between spatial (i.e. fire dispersion) and temporal (i.e. fire frequency) aspects of pyrodiversity, and the potential risks when applying fire management for biodiversity conservation without a firm understanding of the requirements of the target species.

Droplet group combustion model improvement for sodium spray fire pre-combustion analysis

Sodium spray fire could happen in sodium-cooled fast reactor, which will cause the rapid rise of temperature and pressure in the vessel. In this paper, based on the droplet pre-combustion model, droplet motion model, multi-node spray fire combustion model and flow field model, a one-dimensional sodium fire combustion analysis code NAFCALX is developed. Its original droplet group combustion model and other inadequacies are improved, coupling the change of droplet with the movement of droplet during droplet combustion. The improved model is used to simulate the ABCOVE and KAERI sodium spray fire experiments. The predicted temperature and pressure peaks and the trend of temperature changing with time were in good agreement with the experimental values, which is much better than that from the original model. Through the comparison and analysis of the calculation results, the accuracy of the improved model is verified.

Deep learning health management diagnostics applied to the NIST smoke experiments

Fire is one of the most important hazards that must be considered in advanced nuclear power plant safety assessments. The Nuclear Regulatory Commission (NRC) has developed a large collection of experimental data and associated analyses related to the study of fire safety. In fact, computational fire models are based on quantitative comparisons to those experimental data. During the modeling process, it is important to develop diagnostic health management systems to check the equipment status in fire processes. For example, a fire sensor does not directly provide accurate and complex information that nuclear power plants (NPPs) require. With the assistance of the machine learning method, NPP operators can directly get information on local, ignition, fire material of an NPP fire, instead of temperature, smoke obscuration, gas concentration, and alarm signals. In order to improve the predictive capabilities, this work demonstrates how the deep learning classification method can be used as a diagnostic tool in a specific set of fire experiments. Through a single input from a sensor, the deep learning tool can predict the location and type of fire. This tool also has the capability to provide automatic signals to potential passive fire safety systems. In this work, test data are taken from a specific set of the National Institute of Standards and Technology (NIST) fire experiments in a residential home and analyzed by using the machine learning classification models. The networks chosen for comparison and evaluation are the dense neural networks, convolutional neural networks, long short-term memory networks, and decision trees. The dense neural network and long short-term memory network produce similar levels of accuracy, but the convolutional neural network produces the highest accuracy.

Design Fire Methodology for Vehicle Spaces Onboard Ships

The purpose of this paper is to contribute towards establishing procedures of assessment of the fire safety of Ro–Ro ship cargo spaces, by employing suitable design fires. Data collected from fire experiments involving vehicles are utilized in order to deduce representative heat release rates for common types of passenger cars and heavy goods vehicles (HGVs). An existing mathematical scheme for generating parametric heat release rate curves is extended for handling vehicle fire scenarios. The methodology is demonstrated through a case study. In particular, the Fire Dynamics Simulator (FDS) code is used for investigating fire propagation on the vehicle deck of a Ro–Ro ship, initiated from a single HGV. On this deck are assumed to be transported a combination of cars and HGVs. The evolution of the fire is assessed assuming different ventilation conditions. The circumstances for spreading to adjacent vehicles are examined. Human survivability and the time that the deck remains accessible are evaluated by considering the International Maritime Organization (IMO) life safety performance criteria.

Effect of protective cladding on the fire performance of vertically loaded cross-laminated timber (CLT) wall panels

ABSTRACT Cross-laminated timber (CLT) is a sustainable engineered wood product which is utilised in modern multi-storey timber buildings. The fire behaviour of timber structures is often a concern due to their combustible nature. In this paper, experimental fire testing of CLT panels made of Irish spruce was performed. This series of tests consisted of four vertically loaded CLT wall panels which were tested under Standard fire curves in the Structural Laboratory of Munster Technological University, Cork (MTU). To improve the fire performance of CLT panels, different types of protective claddings were used. The effectiveness of each system of protection has been stated particularly in terms of the delay in the start of charring of the CLT panels. The location of joints in the protective cladding was also analysed and was found to be a key factor in the fall-off time of the protective claddings. The results show that protective claddings made with Fireline gypsum plasterboard and a combination of plywood and Fireline gypsum plasterboard delayed the charring of CLT panels by as much as 30 and 44 min respectively. This paper analyses the detailed results of experimental fire testing and measures the charring rate and temperature distribution across the panels.

Short-Term Effects of Experimental Fire on Physicochemical and Microbial Properties of a Mediterranean Cambisol

Little is known about the bonfire impact on microbial properties in soil. This work aimed to study moderate- to high-severity experimental burning (250 °C) compared to unburned Cambisol in a natural Mediterranean environment (Croatia) on selected soil properties. The soil was sampled immediately and 1, 2, 4, and 6 months after the fire. The fire increased the mean weight diameter, water stable aggregates, and water repellence in different soil fractions, and the observed effect was the strongest immediately after the fire. It also altered soil pH, electrical conductivity, total nitrogen carbon, and sulphur content, and completely destroyed carbapenem-resistant bacteria, but did not significantly affect the soil’s mineralogical properties. Six months after the fire, most microbial properties (save for pH) returned to near control values. Heterotrophic, sporogenic, and phosphate-solubilising bacteria started to recover after a month, whereas the population of carbapenem-resistant bacteria was destroyed initially, but recovered by the fourth month after the fire. Dehydrogenase activity was not significantly affected, but proper recovery started four months after the fire. Even though Cambisol showed some resilience to fire and its properties mostly returned to normal by the sixth month, and a full recovery is expected to occur later, as vegetation returns.

Validation study of sodium pool fire modeling efforts in MELCOR and SPHINCS codes

Discharge of sodium coolant into containment from a sodium-cooled fast reactor vessel can occur in the event of a pipe leak or break. In this situation, some of the liquid sodium droplets discharged from the coolant system will react with oxygen in the air before reaching the containment. This phase of the event is normally termed the sodium spray fire phase. Unreacted sodium droplets pool on the containment floor where continued reaction with containment atmospheric oxygen occurs. This phase of the event is normally termed the sodium pool fire phase. Both phases of these sodium-oxygen reactions (or fires) are important to model because of the heat addition and aerosol generation that occur. Any fission products trapped in the sodium coolant may also be released during this progression of events, which if released from containment could pose a health risk to workers and the public. The paper describes progress of an international collaborative research in the area of the sodium fire modeling in the sodium-cooled fast reactors between the United States and Japan under the framework of the Civil Nuclear Energy Research and Development Working Group. In this collaboration between Sandia National Laboratories and Japan Atomic Energy Agency, the validation basis for and modeling capabilities of sodium spray and pool fires in MELCOR of Sandia National Laboratories and SPHINCS of Japan Atomic Energy Agency are being enhanced.This study documents MELCOR and SPHINCS sodium pool fire model validation exercises against the JAEA’s sodium pool fire experiments, F7-1 and F7-2. The proposed enhancement of the sodium pool fire models in MELCOR through addition of thermal hydraulic and sodium spreading models that enable a better representation of experimental results is also described.

Experimental study on vertical temperature distribution of the two-layer smoke flow in tunnel during construction

For a tunnel fire during construction, the formation of two-layer smoke flow underneath the ceiling accelerates the smoke descent threatening the personnel evacuation. As an important indicator of smoke diffusion, the gas temperature distribution inside tunnel is worthy of analysis in depth. However, the vertical temperature profiles within this kind of two-layer smoke flow inside tunnel have not been experimentally studied. To fill the gap, this paper conducts a series of fire experiments in a 1/20 reduced-scale tunnel model. Multi-variables including fire heat release rate, fire position, lifting-up height of fire source, inclined shaft slope, are considered. The visible flame shape, O2 volume fraction and gas temperature are recorded and measured. The burning of the propane gas persists steadily for 20 mins without the occurrence of self-extinction. The structural evolutions of the smoke layer are predicted by FDS simulation and traced by the laser sheet. The smoke descent process in the main tunnel is divided into three stages. The effects of fire source position, inclined shaft slope, fire heat release rate and lifting-up height on the gas temperature distributions inside tunnel are analyzed. The measured temperature rise and the perpendicular distance from the ceiling are normalized by ΔTmax and LT, respectively. At various longitudinal positions (1.82 ≤ │X-dm│/Hef ≤ 10.68), the normalized temperature distributions follow the same curve, independent of the values of Qm, dm and hm. The self-similarity of the vertical temperature distribution within the two-layer smoke flow are sufficiently proved. It is found that ΔT/ΔTmax with z/LT shows a two-regional variation. Based on over 1,740 temperature data from 36 experimental cases, an experimental equation is proposed to describe the gas temperature rise in the region between the fire source and the closed end. The proposed model shows good agreement with the measured data, which can help the researchers to better assess the smoke layer height inside tunnel.

Scheme design of the optimal background clutter suppression for impulse radio ultrawide band radar in complex fire environment: a simulation and experimental study

Impulse radio ultrawide band (IR-UWB) radar possesses several advantages, such as heat flow insensitivity, high resolution, great penetration, good mobility, and lightweight, making it a promising technology for detecting and rescuing individuals trapped in fire scenarios. However, reliable detection and extraction of vital signs of trapped people in the presence of complex fire environment, such as water droplets, smoke, wall occlusions, and reflections, require an optimal background clutter suppression scheme designed specifically for fire scenarios. This study comprehensively evaluates 20 background noise suppression schemes using an exhaustive approach that involves constructing radar echo simulation signals and designing an evaluation method for algorithms. The practical applicability of the improved design solutions was evaluated by conducting small-scale fire experiments in an acrylic chamber. The results indicate that the designed scheme is effective in overcoming the background interference from the combustion environment and is capable of supporting subsequent trajectory identification and vital sign extraction in the fire scene environment.