EcoSmart Fire as Structure Ignition Model in Wildland Urban Interface: Predictions and Validations

The window glass ignition temperature is one of the main factors that determine the Heat Release Rate (HRR) of passenger rail car. In order to reveal the influence of window glass ignition temperature on the HRR of China Railways High-speed (CRH) passenger rail car, the HRR, ignition temperature and other thermal parameters of the individual materials and component assemblies of the CRH passenger rail car, are measured with the Cone Calorimeter, burning temperature tester and other instruments, as the input parameters of Fire Dynamics Simulator (FDS), and according to the different window glass ignition temperatures ,4 fire scenarios have been designed to obtain the HRR vs. time curves of CRH passenger rail car. The comparison results show that the window glass ignition temperature exerts a significant influence on the HRR of passenger rail car; if the ignition temperature is lower than 415°C, during the fire process the windows near the ignition source will be broken, and the back draft phenomenon will take place, resulting in the extremely high second peak HRR, about 22.6MW; if the ignition temperature is higher than 470°C, during the fire process all the windows will not be broken; and so it is suggested that the window glass ignition temperature in the passenger rail car should be higher than 520°C.

Numerical modeling of flexible polyurethane foam combustion under two ignition modes

This study validates numerical models for mixed polymer combustion in a B-707 aircraft cargo compartment against Federal Aviation Administration test data. A simplified approach using a predefined mass loss rate was compared with a detailed model coupling in-depth heat transfer and pyrolysis kinetics based on the assumption of negligible co-pyrolysis effects. Both approaches reliably captured smoke dynamics and light transmission. The detailed model predicted the mass loss rate with high accuracy, matching the experimental value of 0.11 g/s at 200 s after the ignition. However, it significantly overpredicted the heat release rate with a peak value of 8 kW versus 5 kW in the experiment. This discrepancy was examined through a sensitivity analysis of key parameters: the radiative fraction, heat of combustion, turbulence model, and pyrolysis kinetics. The Smagorinsky model best captures the growth pattern of the heat release and mass loss rates, despite its larger deviation from the experimental data compared to other models. The analysis revealed that the radiative fraction and the activation energy of high heat-of-combustion materials like high-density polyethylene are the most influential parameters. One possible solution to the overestimation is the calibration of the activation energy and heat of combustion values for high-energy materials like HDPE. The results confirm the detailed model’s physical realism for fire spread modeling and highlight a path for improving its heat release rate predictions. Further investigation is required across a wider range of computational cases with varying sample mass fractions, compositions, geometries, and boundary conditions to establish the broader applicability of this approach.

In this paper two observations are emphasized with regard to flame radiation in luminous turbulent jet flames: (a) the radiant fraction in turbulent buoyant jet flames is a weak function of the fuel sooting tendency as expressed by the laminar smoke-point heat release rate; and (b) moreover, for very sooty fuels, the radiant fraction saturates to a constant value which is independent of the laminar smoke-point heat release rate, although it depends on the adiabatic flame temperature. These observations can be explained by considering that cooling of the flames is enhanced and the effective radiation temperature drops as soot increases and thus radiant losses increase, until for very sooty fuels flame extinction in the upper part of the flames occurs. The physics of flame radiation phenomena are discussed in the light of a global similarity analysis for flame radiation together with the use of extensive experimental data. In the analysis, complementary to the usual hydrodynamic length scale for combustion, a new radiation length scale is introduced which characterizes the effects of radiant losses on the flow. Scaling relationships of the turbulent radiant fraction in terms of the laminar smoke-point heat release rate are developed first for turbulent buoyant jet flames, wherein flow effects are small, and then extended to momentum-dominated turbulent jet flames. The present results have direct practical significance (a) Tor predicting radiant fractions in fires, and (b) for the design of enhanced flame radiation burners. The physics presented here for soot concentration and radiant cooling can be incorporated in detailed k-ε-g or other turbulence models.

This report documents a series of full-scale fire experiments conducted at the National Institute of Standards and Technology (NIST) to characterize the performance of select wildland-urban interface (WUI) eave vents exposed to fire from noncombustible steel sheds of different sizes and fuel loads (wood cribs). The experiments were conducted indoors under the 20 MW exhaust hood in the National Fire Research Laboratory (NFRL) with the noncombustible steel sheds at varying fuel loads and structure separation distances (SSDs) from the target structure. The target structure included an assembly of an exterior residential wall, a roof, and an eave vent. A range of measurements were taken during the experiments including heat release rate, heat flux, temperature, gas flow velocity, and gas species concentration using open-path absorption spectroscopy. Video and infrared cameras recorded the experiments. Thermal exposures from different types of sheds with different fuel loadings were found to be very repeatable when quantified in terms of heat release rate (HRR), heat fluxes and temperatures measured at the eaves. In the case of thermal exposures from the noncombustible steel sheds, ignition of the eaves was a function of flame jetting from the door opening and sustained incident peak heat flux at the eaves. Higher fuel packing density in the shed resulted in focused flame jetting and increased the likelihood of an eave ignition. The same fuel loading in different types of sheds resulted in different thermal exposures on the target structure. Thermal exposures to the target structure increased linearly with the fuel mass, however, the eave ignition was a function of flame jetting. Eave ignition started with glowing ignition in thermally vulnerable locations including sharp edges, corners, and joints of the rafters. The performance of three commercially available fire-resistant eave vents was assessed when subjected to much larger fire exposures (1.5 MW to 2.5 MW) compared to the fire exposure (300 kW) specified in the existing test methods. The vent performance was assessed primarily for flame penetration and temperature rise on the unexposed side of the vent. Amongst the commercially available vents tested in this experimental series, the performance of the intumescent coated baffle vents was superior compared to the intumescent coated honeycomb core vents during very high thermal exposures. Intumescent coated honeycomb core vents that comply with ASTM E2886 and are listed as WUI compliant products, failed to prevent flame penetration when exposed to large thermal exposures, particularly when eave ignition occurs. The current standardized eave vent test methods may not adequately expose the eave vents to real-WUI fire type of exposures. The knowledge generated from this experimental series will inform standards development organizations to consider revising the existing test methods for qualifying the vents for usage in WUI constructions. The exposure quantification data generated from this experimental series will be useful for hazard mitigation and reducing structure ignitions from large thermal exposures. The exposure quantification information will be useful in managing thermal exposures from auxiliary fuels and other exposures, particularly in WUI communities.

Wood and wood-based products are abundantly used, especially in structural applications, due to the impetus for sustainable development. The present work helps highlight the fire performance of plywood, one of the most used wood-based laminated structural components, under three different heat fluxes of 35 kW/m2, 50 kW/m2, and 65 kW/m2. The effects on the various fire reaction properties, namely, time to ignition, heat release rate, peak heat release rate, time to peak heat release rate, time to flameout, total burn time, and mass loss, were observed and reported. The times to ignition (42.2% and 35.4%), peak heat release rate (27.7% and 18.9%), flameout (22.2% and 28.6%), burn time (10.6% and 16.1%), and residual mass (25% and 53.3%) were reduced with the increase in heat flux from 35 kW/m2 to 65 kW/m2, respectively, whereas the peak heat release (21.7% and 2.4%) and ignition temperature (6.5% and 6.6%) were observed to increase. The vertical burning test (UL-94) illustrated the plywood samples to have a V-1 rating, with self-extinguishing capabilities. A numerical predictive model has also been developed based on the Fire Dynamics Simulator to predict the time to ignition, time to flameout, and heat release rate trend along with the peak heat release rate—it is shown to have good agreement with the experimental results, with an average correlation coefficient of 0.87.

Passive houses are becoming more and more popular due to energy efficiency requirements. An important aspect is their airtightness, i.e., they have a very low leakage. The present paper describes a preliminary numerical study on fire-induced pressure variations in a structure that resembles a passive house compartment. The configuration without ventilation system is considered in this paper. The fire source used in the experiment consists of wood cribs that have been simulated in the Fire Dynamics Simulator (FDS), version 6.5.2, as a cube with a prescribed heat release rate (HRR) curve (based on experimental measurements). The grid sensitivity study is conducted by using different mesh cell size and comparing the results of pressure variation. A cell size of 0.1 m is considered sufficient in this preliminary study. The maximum over-pressure obtained without ventilation reached up to 870 Pa in the experiment. Such high over-pressure will definitely hinder the escape of occupants. The structural integrity may also be affected by the over-pressure. Using a constant leakage area, which is the default option, the pressure difference without ventilation rises up to 2027 Pa in the simulation. A good agreement with the experimental data can only be achieved if the simulated leakage area is not kept constant when the room pressure rises. Tuning the leakage pressure exponent in FDS significantly reduces the deviation between the simulation and experimental results. The default setting of reference pressure difference in FDS is used to examine the influence of this parameter on the pressure prediction. When applying the default reference pressure difference, a smaller leakage pressure exponent is needed to reproduce experimental results. Therefore, the reference pressure difference has a certain influence on leakage area and should be set according to the pressure used in determining the reference leakage area during experiments. The overall pressure evolutions are qualitatively well captured in the FDS simulations, as these strongly depend on the fire heat release rate evolution, which was prescribed to match the experimental profile. However, in order to improve the current level of accuracy and address the general validity of the observations made in the present study, more experimental and numerical work need to be carried out.

Study on the effect of tunnel dimensions on the smoke layer thickness in naturally ventilated short tunnel fires

This study is part of an ongoing project on modeling vegetation fires and their impacts on dwellings at wildland-urban interfaces. As a first step, fire tests were conducted at laboratory scale on both wooden wool litter and rockrose non-natural hedge. To this end, a 0.5 m x 0.5 m x 1 m hedge reconstituted from rockrose branches was burned under a Large Scale Heat Release (LSHR) apparatus. A litter of wooden wool was used before and under the hedge to mimic an ignition from an underneath burning herbaceous layer. These fire tests provided experimental data for mass loss and heat release rate, which were used as a basis for comparison with the simulations performed by using the Wildland-urban interface Fire Dynamics Simulator (WFDS). To numerically model the rockrose hedge, the distribution of the different particle classes (leaves, twigs of various diameters) was determined as well as their physicochemical properties. The comparison of the experimental data and predicted quantities showed a good agreement, whether for wooden wool burnings alone or mixed wooden wool and rockrose hedge.

Valencia bridge fire tests: Validation of simplified and advanced numerical approaches to model bridge fire scenarios

Wildfires in the urban-forest interface constitute a civil protection emergency, causing considerable personal injury and damage to properties. The potential impacts of wildfires on buildings can be minimized by reducing the surrounding fuel and the use of structural materials with low flammability. However, the costs associated with implementing these actions and the responsibility for maintenance usually present conflicts with the property owners. This study aimed to identify minimum safety distances in wildland-urban interfaces within priority areas. The priority areas were identified based on the integration of fire risk and fuel hazard. Radiant heat is a variable in the behavior of fire that directly influences the definition of safety distances. In this research the radiant heat transfer was calculated based on the potential fire behavior for each study area. A comparative study of the horizontal heat transfer method and the radiant heat flux model was carried out. The horizontal heat transfer method indicated the highest vegetation-free distances, ranging from 23 m to 32 m. Some safety distances were validated using experimental fires and wildfires. The findings from the experimental fires and wildfires emphasize the need for a progressive fuel load reduction to mitigate radiant heat transfer. This may include both the removal of surface fuel and removal of trees to mitigate against crown fires. Our findings provide relevant information for decision-making on the effectiveness and efficiency of safety distances at the wildland-urban interface.

Wildfire risks are projected to increase in the future due to climate change, coupled with increased exposure along the wildland-urban interface (WUI) due to population growth and growing cities.This research presents a modelling framework for simulating potential risks posed by wildland fires to urban areas across the WUI via a multi-stage, loosely coupled approach:Stage 1 - Wildfire: Using Spark, user-defined equations determine fire spread behaviour (Miller et al. 2015). To calculate Rate of Spread (RoS) and Fireline intensities for New Zealand vegetation types, equations from Pearce (2005) are applied. These, along with localised climate data for current and future conditions, create wildfire scenarios. Flame heights and radiant heat flux (RHF) are spatially analysed at each time-step to assess risks to transport networks, critical infrastructure, and buildings near or outside urban areas along the WUI.Stage 2 – Building-to-building fire: With ignition points at urban boundaries defined, the second stage of the modelling framework uses a physics-based building-to-building fire spread model like that outlined in Himoto (2022) to simulate urban fire propagation over time. This, combined with wildfire model outputs, informs the risk assessment and micro-scale evacuation model.Stage 3 – Ensemble risk assessment:  Fire exposure from previous stages is used to assess risks to infrastructure and transportation networks. A method, adapted from Butler and Cohen (1998), defines RHF values and maps it to the transport network. This data informs the evacuation model, defining safe zones and low-risk evacuation corridors.Stage 4 – Evacuation modelling:  Building on work by Evans et al. (2020), the evacuation model integrates hazard outputs with micro-scale transport models to simulate evacuee movement under extreme scenarios. By incorporating movement restrictions and evacuee behaviours, it assesses risks to evacuees navigating the network.Together, these four stages provide a comprehensive risk assessment of wildfires and key insights for refining evacuation planning strategies.AcknowledgementThis project has received funding from the European Union's Horizon Europe research and innovation programme under the grant agreement number 101147385. Views and opinions expressed are however those of the authors only and do not necessarily reflect those of the European Union or CINEA. Neither the European Union nor the granting authority can be held responsible for them.ReferencesButler, W, B., Cohen, D, J. (1998). Firefighter Safety Zones: A Theoretical Model Based on Radiative Heating International Journal of Wildland Fire 8(2) 73 – 77. https://doi.org/10.1071/WF9980073Evans, B., Chen, A.S., Djordjevic, S., Webber, J., Gómez, A.G., and Stevens, J. (2020). Investigating the 421 effects of pluvial flooding and climate change on traffic flows in Barcelona and Bristol. Sustainability, 422 12(6), 2330. https://doi.org/10.3390/su12062330Himoto, K. (2022). Large Outdoor Fire Dynamics – Fire Spread Simulation (pp 333 – 367). 1st Edition. CRC Press. http://dx.doi.org/10.1201/9781003096689-10Miller, C., Hilton, J., Sullivan, A., Prakash, M. (2015). SPARK – A Bushfire Spread Prediction Tool. In: Denzer, R., Argent, R.M., Schimak, G., Hřebíček, J. (eds) Environmental Software Systems. Infrastructures, Services and Applications. ISESS 2015. IFIP Advances in Information and Communication Technology, vol 448. Springer, Cham. https://doi.org/10.1007/978-3-319-15994-2_26Pearce, G. H. (2025). Appendix 3: Sub-contracted Report: Fuel Load and Fire Behaviour Assessments for Vegetation within LCDB2

An investigation of the effects of burner exit Reynolds number (9,400–19,000) on the relative effects of burner geometry (circular and elliptic with an aspect ratio 2–4) in a propane jet flame is presented. Circular and elliptic burners of the equivalent area of a circular burner of diameter 5.02 mm were studied. Air entrainment into the nonreacting jets, emission indices of NO, NO2, and CO, visible flame length, flame temperature profiles, radiative fraction of heat release, and soot concentration were measured. Results show that an increase in Re decreases the benefits of higher air entrainment into the flame due to elliptic burner geometry. Similarly, the effects of changes in NO and CO emission indices level off at higher burner Re. The measurements of visible flame length, radiative fraction flame heat release, temperature profiles, and soot concentrations corroborate and offer the explanations for the observed emission index results.

Transparent wood is a modern bio-renewable material with great potential for both science and industrial applications. However, the fire hazard of transparent wood is still almost unexplored. This study aims to investigate the impact of pristine basswood modification to epoxy-based transparent wood on the fire hazard and to train neural networks for the prediction of heat release rate from mass loss rate of pristine basswood, epoxy-based transparent wood, and epoxy resin. Transparent wood was prepared by lignin modification in pristine small-leaved basswood (Tilia cordata Mill.) and subsequent vacuum infiltration by epoxy resin. The fire hazard of the samples was determined by the cone calorimeter at four heat fluxes of 20–50 kW m−2. The fire hazard of investigated materials was compared based on the critical heat flux, ignition temperature, heat release rate, effective heat of combustion and time to flashover. Transparent wood showed higher resistance to ignition (higher critical heat flux and ignition temperature) than pristine wood. However, other parameters (heat release rate and effective heat of combustion) were higher (worse) and the time to flashover was lower (worse) for transparent wood than for pristine wood. Trained neural networks for predicting heat release rate from the mass loss rate of wood (both pristine and transparent) and epoxy resin showed coefficients of determination from 0.70 to 0.92. Trained neural networks with a coefficient of determinations above 0.90 are usable for low-cost heat release rate measurements in both science and industrial applications.

Why are cooktop fires so hazardous?