Graphdiyne (GDY) is an emerging two-dimensional carbon allotrope comprising unique sp(1) and sp(2) hybridisation, which has attracted extensive investigation into various applications, especially as battery component materials owing to its excellent electromechanical properties. However, GDY's thermal stability and oxidation behaviour have yet to be evaluated, which is crucial to safety in high-energy applications. The present study characterised the thermophysical properties of GDY via reactive molecular dynamics (MD-ReaxFF) and experimental measurement. The oxidation kinetics and decomposition behaviour were elucidated and benchmarked with graphene (GP) and graphyne (GY) to investigate the correlation between thermal stability and morphology of carbon nanomaterials. The simulation results revealed the initial oxidation mechanism of GDY sheets, where the cleavage of C-C bonds was observed at the acetylenic chain and could be identified as the weak spots of the structural stability. As for oxidation kinetics, GDY's experimental and numerical activation energy was found to be 173.1 and 133 kJ/mol, which is lower than 220.8 kJ/mol of GP. The current work pioneer investigated the thermal stability of GDY using both experimental and numerical approaches. Meanwhile, different oxidation mechanisms between GP and GDY were distinguished and demonstrated in detail.

Understanding exit choice behaviour is essential for optimising safety management strategies in building evacuations. Previous research focused on contextual attributes, such as spatial information, influencing exit choice, often using utility models based on monotonic functions of attributes. However, during emergencies, evacuees typically make rapid, less calculated decisions. The choice of context can significantly impact the evaluation of attributes, leading to preference reversals within the same choice set but under varying context conditions. This cognitive psychological phenomenon, known as context effects, encompasses the compromise effect, the similarity effect, and the attraction effect. While researchers have long recognised the pivotal role of context effects in human decision making, their incorporation into computer-aided evacuation management remains limited. To address this gap, we introduce context effects (CE) in a social force (SF) model, CE-SF. Evaluating CE-SF’s performance against the UF-SF model, which considers only the utility function (UF), we find that CE-SF better replicates exit choice behaviour across urgency levels, highlighting its potential to enhance evacuation strategies. Notably, our study identifies three distinct context effects during evacuations, emphasising their importance in advancing safety measures.

A biomass fire suppression gel foam (FSGF) with outstanding thermal stability and fire resistance performance was synthesised to improve the flame retardancy of foam agents on liquid fuel fires. The foam comprehensive index, microstructure, thermal stability, fire resistance and extinguishing properties of the FSGF were benchmarked against aqueous film-forming foam (AFFF). Subsequently, reactive forcefield (ReaxFF) molecular dynamics (MD) simulations were performed on the FSGF to study the thermokinetic properties. Based on the experimental results, a porosity layer was found on the external film of FSGF, which enhanced the thermal stability of the foam. The gelling mechanism of the foam is the formation of an O-Ca-O bond. Through MD simulations it was discovered that the remained calcium oxide/hydroxide species when deposited on fuel surfaces would promote char formation as they capture H/O atoms via dehydration. Alternatively, the foam showed better thermal stability than that of AFFF due to a lower weight loss rate and longer collapse time. The extinguishing performance tests demonstrated that the fire extinguishing time and resistance time of FSGF respectively are 72 s and 801 s, showing a significant potential to suppress the re-ignition of tank fires.

Given the growing demand for increased energy capacity and power density in battery systems, ensuring thermal safety in lithium-ion batteries has become a significant challenge for the coming decade. Effective thermal management plays a crucial role in battery design optimization. Air-cooling temperatures in vehicles often vary from ambient due to internal ventilation, with external air potentially overheating due to vehicle malfunctions. This article highlights the efficiency of lateral side air cooling in battery packs, suggesting a need for further exploration beyond traditional front side methods. In this study, we examine the impact of three different temperature levels and two distinct air-cooling directions on the performance of an air-cooling system. Our results reveal that the air-cooling direction has a more pronounced influence compared with the air-cooling temperature. By employing an optimal air-cooling direction and ambient air-cooling temperature, it is possible to achieve a temperature reduction of approximately 5 K in the battery, which otherwise requires a 10 K decrease in the air-cooling temperature to achieve a similar effect. Therefore, we propose an empirical formula for air-cooling efficiency under various conditions, aiming to provide valuable insights into the factors affecting air-cooling systems for industrial applications toward enhancing the fire safety of battery energy storage systems.

In recent years, the utilisation of bio-based materials in flame retardants (FRs) has been widely advocated due to significant recyclability, flame retardancy and cost-effectiveness. For example, carbon derived from peanut shells (CPS) with sheet-like structures are natural FRs with rich carbon sources for epoxy resins (EP). In this study, we hybridised CPS with black phosphorous (BP) via the ball milling method and embedded it in EP to exploit their synergistic effects. CPS enhances the formation of a durable char layer, complemented by BP's dual action in scavenging radicals in the gas phase and promoting char formation in the condensed phase. The modified EP (EP/BP/CPS) has offered excellent flame resistance towards pinewood that 3 wt% addition of EP/BP/CPS can significantly reduce the peak heat release rate (pHRR) and total heat release (THR) and total smoke reduction (TSR) by 45 %, 14 %, and 28 % compared to pure EP coated pinewood. Importantly, we proposed a numerical framework that can be fully utilised to integrate the fire field model, reconstruct the fire scene and predict the fire development stages by coupling pyrolysis kinetics with computational fluid dynamics (CFD). The combustion behaviour of pinewood coated with EP/BP/CPS was characterised. In particular, the burning characteristics such as pHRR, time to ignite (TTI) and burning duration were well-predicted. This work has proven that the hybridised EP/BP/CPS is an effective and sustainable FR coating for timber structure buildings, while its combustion behaviour can be numerically characterised for large-scale fire safety assessment.

The cellular automata (CA) model has been a meaningful way to study pedestrian evacuation during emergencies, such as fires, for many years. Although the time step used in the CA model is one of the most essential elements, there is a lack of research on its impact on evacuation time. In this paper, we set different time step sizes in an extended cellular automaton model and discuss the effect of time step size on the overall evacuation time under different emergency types and levels. For a fixed step time mode, the larger the time step, the longer the evacuation time. In each time step size, the evacuation time gradually increases with the increase of emergency level, and there is a sharp increase when the time for pedestrians to move one step is exactly an integer multiple of the time step. When there is no friction between pedestrians, the evacuation time at each time step first decreases slightly with the increase of emergency level and then remains unchanged; the larger the time step, when the evacuation time remains unchanged, the lower the emergency level and the greater the evacuation time. For the variable time step model, when the friction between pedestrians approaches infinity, the total evacuation time does not change with the emergency level; when the friction between pedestrians is reduced, the total evacuation time slightly decreases with the increase of the emergency level. The less friction there is, the more significant the reduction. The results of previous actual experiments are also reflected in the simulation at a lower emergency level. The result shows that the time step size significantly impacts the evacuation simulation results of the CA model, and researchers should choose carefully to obtain more realistic simulation results.

Evidence suggests that in the event of a fire accident, a certain number of building occupants escape through smoke-filled environments. Consequently, evaluating the corresponding evacuation performance under such life-threatening conditions is important for advancing fire safety analyses. This study aimed to develop a fire-integrated evacuation model to consider the effects of spreading fire hazards (i.e., radiation, temperature, toxic gas, visibility) on evacuees in a room fire evacuation scenario. Furthermore, a novel quantitative approach was introduced to evaluate evacuees’ local fire risks and stress levels according to their egress paths. The escape characteristics at various stages of fire development were studied as well. The results demonstrate that evacuation performance varies considerably depending on the severity of evacuees’ confronted fire hazard conditions, which emphasizes the importance of minimizing the pre-evacuation time in fire evacuation emergencies.

Modern buildings and structures are commonly equipped with fire safety detection and protection systems. Owing to the complexity in building architectures, performance-based fire engineering designs are often applied to achieve safety compliance criteria in stipulated fire events. With the uprising popularity of computer simulation fire predictive models benefited by the rapid improvement in computing speed and modelling techniques, the use of computational fluid dynamics (CFD) based fire field models has become an integrated component in fire tenability and assessment studies. This article delivers a comprehensive review on the history, past developments, and current state-of-the-art of CFD models for enclosure fires, as well as providing an in-depth review on the advancement in other sub-modelling components including turbulence, combustion, radiation, and soot models. Additionally, two types of multiphase modelling approaches involving solid-gas and liquid-gas phase models are reviewed. As for the preceding, the consideration of the solid phase combustibles is generally achieved via pyrolysis modelling under the context of CFD. Recent advancements in CFD-based pyrolysis studies are extensively discussed, including the consideration of porous media, charring layer formation, and kinetics search algorithms to describe the solid decomposition and charring processes. Meanwhile, fire suppression models involving the discrete phase model (DPM) approach are reviewed. This includes previous developments in simulation methods of water droplets, coupling approaches with the fire dynamics in the large eddy simulation (LES) framework. Finally, a future perspective regarding the need to develop a melting/dripping sub-model for building materials is discussed, whose reaction kinetics can be supported by molecular dynamics (MD).

In this study, a multiphase pyrolysis model has been proposed under the large eddy simulation (LES) framework incorporating moving boundary surface tracking, char formation, and detailed chemical kinetics combustion modelling. The proposed numerical model was applied to simulate the cone calorimeter test of two kinds of materials: (i) pinewood (charring) and (ii) low-density polyethylene (non-charring). Using a cone calorimeter setup, good agreement has been achieved between the computational and the experimental results. The model is capable of predicting the formation of the char layer and thus replicating the flame suppressing thermal and barrier effects. Furthermore, with the application of detailed chemical kinetics, the fire model was able to aptly predict the generation of asphyxiant gas such as CO/CO2 during the burning process. However, the pinewood experiments showed significant CO/CO2 emissions post flame extinguishment attributed to char oxidation effects, which were not considered by the fire model. Despite the limitation, the fully coupled LES model proposed in this study was capable of predicting the fluid mechanics and heat transfer for the turbulent reacting flow, solid-phase decomposition, and gaseous products under flaming conditions. In the future, it can be further extended to include char oxidation mechanisms to improve predictions for charring materials.

A set of numerical analyses was conducted to investigate the effect of fuel location of dual burners in an under-ventilated ISO9705 compartment room. Moreover, the influences of the burner separation displacement on the fire development, the evolution of thermal layers, the distribution of toxic gas species were comprehensively studied. The simulations were conducted using a novel in-house large eddy simulation (LES) based fire field model comprised of subgrid-scale (SGS) turbulence, detailed chemical kinetics of combustion, soot and radiation models. The first part of the simulation focused on 3 different fuel distributions: single centre burner (SCB), single rear burner (SRB) and two distributed burner (TDB). Alternative configurations were considered for dual burners with 4 different distances between the dual burners, to study the influence towards air flow at the doorway, internal temperature profile and major chemical species (i.e. CO/CO2) distributions. The numerical outcome states that fuel distribution has a minor effect on heat release rate and the total CO2 amount but noticeable differences in CO's generation and distribution. Overall, the temperature and gas field predictions were almost identical for all dual burner cases, while significant differences were observed at the rear section of the compartment, especially temperature, CO/CO2vol fraction and soot concentration.

Numerical assessment on a large-scale compartment buoyant fires was performed to investigate the effect of exit door width on the flame tilting behaviour, evolution of the thermal layer and formation of combustion species. The simulations were performed using an in-house large eddy simulation (LES) based fire field model incorporating subgrid-scale (SGS) turbulence, detailed chemical kinetics combustion, soot and radiation models. A comprehensive set of simulation case studies have been carried out with various doorway opening sizes, to investigate the influence of the incoming air entrainment towards the deflection angle of the flame. In addition, the changes in the thermal interface, neutral plane and major chemical species profiles (i.e. CO/CO2) are also studied in detail. The fire model was validated against experimental measurements. It was found that increasing the door width elevates the neutral plane height and its correlated layer height of concentrated toxic gases. In addition, there is a critical door width (4/6) that produced the minimum fire tilting angle, deviation from the minimum door width results in an increase in flame tilting angle. It was discovered the centre fire have a range of titling angle between 58 degrees to 75 degrees, with a variation of 25% from 2/6 to 8/6 doorway sizes. This also totally affects the dynamics of the CO2 profiles with the compartment room, in which the concentrated toxic gas layer ascends as the fire is more ventilated. In general, it was discovered that having a large doorway size is mainly contributing to reduce the potential fire hazards in a one-opening compartment room fire scenario. The relation of compartment fire tilting can be critical especially for the design of fire protection systems. (C) 2020 Elsevier Ltd. All rights reserved.

With recent developments in the design and manufacturing process of water-based fire suppression systems, more advanced technologies such as water mist systems have expanded in their building application. In this article, the critical fire suppression mechanisms of water mist systems and conventional fire sprinklers are investigated and compared, with emphasis on the influence of water droplet sizes on the fire suppression mechanisms. Applying computational fluid dynamics (CFD), a fully ventilated fire compartment room has been considered where a methane pool fire was placed at the centre. The considered fire suppression systems were placed directly upon the fire. Thermocouple and gas probes were applied in the computational domain to identify different stages of the fire suppression process, as well as to evaluate the suppression performance. The velocity field was analyzed to examine the penetration effect of suppression systems. Relative humidity and oxygen concentration data obtained by gas analyzers were also studied to further understand the droplet/fire interaction behavior. It was found that latent cooling, volumetric displacement, and dilution of oxygen and fuel were the main suppression mechanisms for water mist systems, as smaller droplets evaporate more efficiently compared to larger ones. On the other hand, for sprinklers, heat extraction by water droplets from the fire was found to be the main suppression mechanism, and the evaporation effect is not as significant as in water mist systems. According to in-depth parametric studies of water droplet sizes, recommendations for the optimal running conditions have been provided for both systems.

This paper numerically examines the characterisation of fire whirl formulated under various entrainment conditions in an enclosed configuration. The numerical framework, integrating large eddy simulation and detailed chemistry, is constructed to assess the whirling flame behaviours. The proposed model constraints the convoluted coupling effects, e.g., the interrelation between combustion, flow dynamics and radiative feedback, thus focuses on assessing the impact on flame structure and flow behaviour solely attribute to the eddy-generation mechanisms. The baseline model is validated well against the experimental data. The data of the comparison case, with the introduction of additional flow channelling slit, is subsequently generated for comparison. The result suggests that, with the intensified circulation, the generated fire whirl increased by 9.42 % in peak flame temperature, 84.38 % in visible flame height, 6.81 % in axial velocity, and 46.14 % in velocity dominant region. The fire whirl core radius of the comparison case was well constrained within all monitored heights, whereas that of the baseline tended to disperse at 0.5 m height-above-burner. This study demonstrates that amplified eddy generation via the additional flow channelling slit enhances the mixing of all reactant species and intensifies the combustion process, resulting in an elongated and converging whirling core of the reacting flow.