With the upgrading of fire safety requirements and the tightening of environmental protection policies, foam fire extinguishing agents, as key materials for fighting flammable and combustible liquid and solid fires, have become the industry focus for performance optimization and green development. This paper systematically reviews the development history of foam fire extinguishing agents at home and abroad, focuses on sorting out the research and development progress of current new products, conducts an in-depth analysis of the research status of basic theories of foam fire extinguishing agents, and looks forward to the future development trends of foam fire extinguishing agents towards environmental protection, high efficiency and intelligence.

In view of the performance requirements that ideal chemical gas fire extinguishing agents need to meet, such as environmental friendliness, high fire extinguishing efficiency, stable storage, safety and low toxicity, this paper summarizes in detail the rapid evaluation methods for the application performance parameters of new gas fire extinguishing agents, deeply analyzes the influence law of the molecular structure of chemical gas fire extinguishing agents on their application performance. Explore the quantitative structure-activity relationship between molecular structure and application performance, the prediction model of key performance parameters of gas fire extinguishing agents, and the molecular optimization technology, so as to achieve rapid targeted optimization of massive potential fire extinguishing agents and guide the efficient research and development of new chemical gas fire extinguishing agents with market application potential.

The effects of polymer addition on the rheological properties of compressed air foam and the pressure drop characteristics of foam flow in horizontal pipeline were investigated. The results show that the viscosity of the foaming solution changes significantly with polymer type and concentration. At the same polymer concentration, the non-Newtonian behavior of the Xanthan Gum (XG)-based foaming solution is more pronounced than that of the sodium Carboxymethyl Cellulose (CMC)-based one, which is attributed to stronger molecular interactions within the XG chains. Furthermore, both the type and concentration of the polymer substantially influence the rheological properties of the foam. As the polymer concentration increases, the consistency coefficient of the foam increases, while its flow behavior index decreases. Based on the rheological experimental results, a pressure drop prediction model for annular foam flow of compressed air foam was developed by incorporating the friction factor between the foam and the pipe wall, as well as the entrainment effects of the gas core and the foam layer on the fluid. The errors between the pressure drop values predicted by the proposed theoretical model and the corresponding experimental data are within 25%, indicating that the model exhibits satisfactory predictive performance.

In order to optimize the extinguishing efficiency of traditional foam extinguishing agent, a new type of efficient and environmentally friendly foam extinguishing agent was synthesized from AES, SLES, SDS and BS-12 surfactants. Firstly, foam analysis method and droplet profile analysis method were used to systematically characterize the intermediates and products. Four factors and three levels orthogonal experiments were designed to optimize the ratio and determine the best combination scheme. Then, molecular dynamics simulation was used to study the synergistic effect of their combination. The results indicate that there is a significant synergistic effect between the four surfactant molecules, which significantly enhances the surface activity of the mixed system. The critical micelle concentration (CMC) of the composite system was ultimately measured to be 0.16% using fluorescence spectroscopy experiments. Its surface tension is 28.24 mN/m, and its performance is significantly better than that of a single surfactant. Then add foam stabilizer (xanthan gum, sodium alginate) and cosolvent (urea, propylene glycol, glycerin) to make foam concentrate. Then, the formula was used to prepare fire extinguishing foam using the double syringe technology and tested. The test results showed that the 25% liquid separation time was 274 s, and the viscosity was 25 mm2/s. Finally, the fire extinguishing experiment was conducted in a well ventilated environment, with extinguishing time of only 18 s, which meets the national standard requirements.

This study fully leverages the excellent foaming performance of hydrocarbon surfactants and the superior spreading ability of organosilicon surfactants. Guided by the carbon-silicon synergistic effect, we developed a novel anionic, fluorine-free foam fire extinguishing agent, composed of α-olefin sulfonate (AOS) and polyether-modified heptamethyltrisiloxane (SILWET L-77) as surfactants, with xanthan gum (XG) as a key functional component. We further investigated the foam formulation design, foam performance, and fire extinguishing efficacy. The results indicate that the optimal formula was AOS with a mass fraction of 2.75%, SILWET L-77 with a mass fraction of 1%, and XG with a mass fraction of 0.275%. Tests over a wide temperature range (20~80 °C) showed that both foam viscosity and surface tension decrease exponentially with increasing temperature (R²>0.98). In a 0.25 m² standard oil pan fire test, the new fluorine-free foam exhibited an average foaming ratio of 6.1, an average 90% fire control time of 34.3 s, an average extinguishing time of 82 s, an average burn-back resistance of 401 s, and an average maximum cooling rate of -8.67 °C/s at the monitoring point. These results provide valuable guidance for the formulation and performance optimization of novel fluorine-free foam fire extinguishing agents.

From the perspective of improving the formulation of foam extinguishing agents, this study investigated the effects of gel addition method and reaction-to-gel method on enhancing the thermal protection performance of foam. The influence of gel additive, as well as the amount of gelling agent and cross-linking agent, on the thermal protection performance of foam was also studied. The experimental results showed that under a heat radiation intensity of 15 kW/m2, the addition of 1.4% xanthan gum using the gel addition method could increase the thermal protection time of conventional aqueous film-forming foam from 248 s to 335 s, achieve an improvement of 35.1%. However, the gel foam obtained using the reaction-to-gel method exhibited superior thermal protection performance. When the amount of guar gum was 1.0% and the amount of cross-linking agent was 1.0%, the thermal protection time could be significantly increased to 888.5 s, achieve an improvement of 258.3%. It was found that after the water evaporated, the gel foam formed an expanded solid film, which continued to exert a certain thermal protection effect. The reaction-to-gel method not only improved the stability of the foam liquid film but also enhanced the protective ability of the foam after its own water evaporated, significantly extending the thermal protection time of the foam.

To develop highly stable fluorine-free foam extinguishing agents, this study used a base system consisting of a nonionic organosilicon surfactant (LS-408L) and a zwitterionic hydrocarbon surfactant, dodecyl dimethyl betaine (BS-12). Nonionic water-soluble polymer guar gum (GG, 0.2%) and hydrophilic fumed silica (SiO₂, 1.5%) nanoparticles were introduced as foam-stabilizing modifiers to construct four fluorine-free foam mixed systems. The surface tension and electrical conductivity of each mixed solution were systematically characterized, foam stability was analyzed, and the evolution of the rheological behavior of both the foam mixed liquids and the foam phase under thermal action from 25 ℃ to 75 ℃ was thoroughly investigated. The results showed that the addition of either GG or SiO₂ alone increased the surface tension and electrical conductivity of the LS-408L/BS-12 system, whereas their combination exhibited a synergistic effect, characterized by reduced surface tension and a continuously increased electrical conductivity. Both GG and SiO₂ delayed the foam drainage process, and their combination achieved the best foam-stabilizing performance. All four foam mixed liquids exhibited typical shear-thinning non-Newtonian fluid behavior. The systems containing SiO₂ displayed viscoelastic solid-like characteristics with a relatively high yield stress, whereas the SiO₂-free system behaved as a viscoelastic fluid. The modified fluorine-free foams showed an elastic response before the crossover point of the viscoelastic moduli and transitioned to a viscous response after the crossover point. Increasing the temperature generally reduced the viscoelastic moduli of the foams; nevertheless, the composite system maintained the best thermal rheological stability and retained good shear resistance even at the maximum temperature of 75 °C. Within the linear viscoelastic region, the complex modulus of system A-3# was 16.60 Pa, the highest among the four systems. This study elucidates the synergistic regulation mechanism of the GG and SiO₂ combination on the thermal rheological behavior of fluorine-free foam, achieving superior foam-stabilizing ability with a relatively low SiO₂ concentration. These findings provide experimental evidence and theoretical support for component optimization and formulation design of highly stable fluorine-free foam extinguishing agents.

To address the practical issue of lacking suitable foam solutions for training and equipment testing in non-firefighting scenarios (such as daily drills) for fire rescue teams, an eco-friendly and economical foam concentrate has been developed to meet personnel training and equipment testing requirements. Test results indicate that under standard testing conditions, this product achieves a foam expansion of 8~9 times with a 25% drainage time of 4~5 min, accurately simulating the foam characteristics of fire extinguishing foam agents. Application tests using typical dispensing equipment like foam nozzles and foam monitor yielded results similar to those of fire extinguishing foam agents, further verifying the product's reliability. Additionally, this product contains no PFAS or other harmful persistent organic pollutants, demonstrates a 28-day biodegradation rate >99%, and shows a 96 h LC50 value for zebrafish exceeding 3 000 mg/L, exhibiting excellent environmental performance that significantly reduces post-use environmental risks.

To investigate the inhibitory effect of the mixture of perfluorohexanone and 2-bromo-3,3,3-trifluoropropene (2-BTP) on hydrogen fluoride generation, a cup-burner-based experimental platform was established in this study. By measuring the amount of hydrogen fluoride generated, the suppression efficiency of different mixing ratios on hydrogen fluoride production was examined. Combined with quantum chemical calculations and Monte Carlo simulations, the pyrolysis pathway of perfluorohexanone and the hydrogen fluoride generation behavior under various mixing ratios were analyzed. The results indicate that when the volume fraction of 2-BTP ranges from 25% to 30%, the inhibitory effect on hydrogen fluoride is the most significant. Due to the low bond dissociation energy of the C—C bond adjacent to the carboxyl group, perfluorohexanone is prone to pyrolysis. The optimal inhibitory effect on hydrogen fluoride generation is achieved when the ratio of perfluorohexanone to 2-BTP is 2∶1.

To address the issues of insufficient instantaneous cooling capacity and secondary temperature rise during the suppression of thermal runaway in lithium-ion batteries by perfluorohexanone (Novec 1230), this study designs composite agents comprising Novec 1230 and three fluorinated gases—R236fa, R227ea, and R116—based on the characteristics of thermal runaway propagation and intermolecular interaction theory. Suppression experiments were conducted on 18650-type lithium-ion batteries undergoing thermal runaway. The results indicate that all three composite agents outperform pure Novec 1230 in reducing peak temperatures and delaying thermal diffusion. Among them, the Novec 1230/R227ea combination exhibited the highest cooling rate (10.6 ℃/s), maintained stable temperatures in the later stages, and effectively avoided secondary temperature rise, demonstrating the best overall temperature control performance. Furthermore, density functional theory (DFT) calculations were performed using Gaussian 16 to investigate the intermolecular interactions and structural stability of the composite systems. The results show that the Novec 1230/R227ea system has the highest intermolecular interaction energy (-33.62 kJ/mol). Non-covalent interaction (NCI) analysis reveals pronounced van der Waals forces, indicating a stronger synergistic effect and greater structural stability, which provide a microscopic explanation for its superior fire suppression performance.

Aiming at the critical challenge in handling lithium iron phosphate battery thermal runaway jet fires—where flames are easily controlled but prone to rapid re-ignition—this study conducts comparative experiments using pure water, aqueous film-forming foam(AFFF), fluoroprotein foam, F-500 water-based additive, and three-phase foam. The flame extinction time during the specified spraying process and post-extinction reignition characteristics after cessation of spraying are recorded, while simultaneously analyzing the dynamic responses of flame zone and battery surface temperatures, heat release rate (HRR), and CO2 and CO volume fractions. Results indicate that pure water and AFFF failed to fully extinguish the flames during the spraying phase. Fluoroprotein foam, F-500, and three-phase foam successfully achieved flame extinction, with three-phase foam exhibiting the shortest extinguishing time (7.56 s), followed by F-500 (13.05 s); fluoroprotein foam achieved extinction at the end of spraying but the flame reignited after 13.27 s of pause. Temperature and combustion characteristic analyses reveal that instantaneous cooling intensity during spraying does not fully represent overall fire suppression performance; although all agents reduce thermal feedback, post-extinction reheating rate and other factors determine whether reignition occurs. Based on comprehensive evaluation of combustion intensity, cooling dynamics, and anti-reignition capability, three-phase foam demonstrates superior suppression performance, followed by F-500. This study elucidates the differences in cooling mechanisms and oxygen-blocking anti-reignition behaviors among various water-based fire suppressants under jet flame conditions, confirming that constructing a durable physical barrier can effectively interrupt heat accumulation.

To improve the thermal stability and coal spontaneous combustion inhibition effect of gel foam, SiO₂ nanoparticles were used as reinforcing agents in this study. The effects of SiO₂ nanoparticles on gel foam solution were systematically investigated through foam mixture property characterization, foaming performance test, thermal stability experiment and simultaneous thermal analysis experiment. The reinforcement mechanism of SiO₂ nanoparticles on the thermal stability of gel foam was revealed, and the inhibition characteristics of modified gel foam on coal spontaneous combustion were analyzed. The results showed that SiO₂ nanoparticles had a significant regulatory effect on the properties of gel foam solution. With the increase of its concentration, the surface tension of foam solution increased first and then decreased, while the conductivity and viscosity decreased first and then increased. SiO₂ nanoparticles reduced the foaming performance of gel foam, and the higher the concentration, the more obvious the attenuation of foaming performance. When the mass fraction of SiO₂ nanoparticles was 1.5%, the volume attenuation and drainage process of gel foam under thermal action could be effectively delayed, the thermal insulation performance of foam was significantly improved, and thus its thermal stability was enhanced. The gel foam modified by 1.0% SiO₂ nanoparticles could significantly increase the characteristic temperatures of coal samples, effectively weaken the heat release intensity in the coal oxidation process, reduce heat accumulation, and significantly inhibit the low-temperature oxidation and thermal decomposition stages of coal spontaneous combustion through physical inhibition. This study provides experimental basis and theoretical support for the application of nanoparticle-reinforced gel foam in the field of coal spontaneous combustion prevention and control.

The inhibition effect of various thermal insulation materials, such as glass fibre, super cotton and alumina silica gel, on the thermal runaway propagation of the battery is investigated through the thermal runaway propagation experiment of 280 Ah lithium iron phosphate battery. The results show that all the materials can retard the thermal runaway propagation, among which the super cotton (with the thickness of 2.3 mm) performs the best, which can achieve the propagation blocking, and the highest thermal insulation efficiency reaches 74.5%. Heat transfer analysis showed that the low thermal conductivity and porous structure of the super cotton material had a significant shielding effect on heat. In contrast, glass fibre and aluminium oxide silica gel have a relatively weak inhibiting ability. In addition, although the thermal insulation structure can block the heat propagation, it is also easy to lead to the intensification of heat accumulation inside the first thermal runaway battery, and the thermal runaway reaction is more intense.

LiNixCoyMnzO2 (NCM, x+y+z=1) is considered a promising cathode material due to its low cost and high energy density. However, with the increase of Ni content, the material will have serious Li/Ni mixing and interface side reactions, which will affect its stability. In this paper, LiNi0.90Co0.05Mn0.05O2 (NCM90), a high nickel cathode material, was coated with phosphotungstic acid (PTA) in different ratios by surface coating technology to explore the mechanism of improving its properties. Through the system characterization, electrochemical performance test and thermal safety test, it was found that PTA coating can promote Li+ diffusion and reduce electrochemical impedance, and form a WO3-Li3PO4 composite protective layer on the surface of the material, effectively isolating the side reaction between the cathode and the electrolyte, while maintaining the structural inte⁃grity of the material. Thus, the electrochemical performance and thermal stability of NCM90 are significantly improved. Among them, 0.5%PTA-NCM sample has the best performance, its specific discharge capacity is increased by 34.58 mAh/g compared with the original NCM, and the heat release is reduced by 194.56 J/g compared with the original NCM. In summary, PTA coating can effectively improve the electrochemical performance and thermal safety of NCM90. The research method and coating material may be applied to other high-nickel ternary cathode materials, which provides an important theoretical basis and practical guidance for the optimization of cathode properties.

When a subway train is forced to stop in an interval tunnel due to an emergency, passengers inside the carriages may need to evacuate in place using the side platforms. Considering the influence of fire source on passenger movement behavior, this paper introduces a static field and a fire source field to describe the attractive effect of exits and the repulsive effect of the fire source on passengers, respectively, and develops a cellular automaton model for passenger evacuation in subway tunnel train fire scenarios. Based on this model, the effects of factors such as fire source power, fire source location, door opening/closing status, and evacuation direction on the evacuation efficiency using side platforms are investigated. The results show that, compared with non-fire scenarios, evacuation time in subway train fire scenarios is generally prolonged, and the difference between the two increases with the number of evacuees. As the parameter Kf, which characterizes fire source intensity, increases, the evacuation time first decreases slightly and then increases continuously, with the growth rate increasing as Kf rises. When passengers evacuate unidirectionally toward the front of the train, the evacuation time gradually increases as the fire source location moves from the rear to the middle of the train. After closing the two doors closest to the fire source, the evacuation time in the train-middle fire scenario is reduced by approximately 40%. Furthermore, when a fire occurs in the middle of the train, the evacuation time under bidirectional evacuation is only one-third of that under unidirectional evacuation toward the front in a train-head fire scenario.

This study addresses the controversial issue in current codes regarding the combined use of vehicular cross passages as pedestrian cross passages. Through a comparison of relevant codes, functional positioning analysis, and practical engineering experience, the feasibility and applicability of different cross passage configuration schemes are systematically examined. The study first reviews relevant technical codes and identifies discrepancies in requirements such as configuration methods and fire separation measures. Then, from the perspective of disaster prevention design, and based on the differences in evacuation and rescue scenarios for personnel and vehicles, it concludes that pedestrian and vehicular cross passages should be functionally separated. The study compares and analyzes the implementation effects of three schemes: "combined use" "shared use" and "separate". The results indicate that while the "combined use" scheme offers spatial feasibility, it suffers from unclear functional positioning of the cross passage and insufficient reliability of fire separation facilities. The "shared use" scheme, although adopting an adjacent but separated configuration, significantly increases structural width and construction costs. The "separate" scheme, by independently configuring pedestrian and vehicular cross passages, demonstrates comprehensive advantages in evacuation efficiency, smoke control, and operation and maintenance. The study recommends that the separate layout of pedestrian and vehicular cross passages is a more rational approach for the disaster prevention design of underground road tunnels.

The analysis method of combining hot smoke test and FDS simulation was used to compare and analyze the smoke temperature, smoke propagation speed and smoke layer height of the mechanical smoke exhaust system in the operation depot of subway vehicle base under two different smoke discharge conditions, so as to determine the feasibility and accuracy of using FDS for smoke simulation research. On this basis, the smoke exhaust volume of the mechanical smoke exhaust system in the operation depot is optimized, and the FDS smoke simulation of full-scale train fire is carried out. The research results show that: the building scale of the operation depot of subway vehicle base is usually large, with high clearance and good smoke storage capacity. When the smoke exhaust volume per unit area of the operation depot is designed to be no less than 20 m³/（h·m²）, the smoke layer can be controlled at a higher height to ensure the safe evacuation of personnel and fire fighting and rescue.

This paper addresses the specific fire protection requirements for vehicle depot superstructure development projects. In accordance with the mandatory requirement in the Standard for fire protection design of metro that the fire resistance rating of floor slabs should not be less than 3.00 h, a fire resistance performance test was conducted on reinforced concrete roof slabs using a passenger vehicle depot superstructure development project as a case study. Three types of reinforced concrete slab specimens with varying dimensions and span-to-thickness ratios were designed. Using a scaled-down load method under standard heating conditions, tests evaluated their load-bearing capacity, integrity, and thermal insulation. Test results indicate: All specimens withstood the 181 min standard fire test without failure. Among them, the two-way slab specimen demonstrated optimal performance, with a maximum average temperature rise at the unexposed side of 47.5 ℃ and a maximum deflection of 91.1 mm, significantly below code limits. Although unidirectional slab specimens exhibited greater deflection (310.3 mm) during testing, their deformation rate remained within limits, and the single-point temperature rise at the unexposed side (148.1 ℃) still met code requirements. This study confirms that under specific design parameters (slab thickness ≥170 mm, protective layer thickness 35 mm, load ratio approximately 71%), this type of reinforced concrete roof slab can meet the 3.00 h fire resistance rating requirement. Its superior performance is primarily attributed to the substantial slab thickness, protective layer thickness, and the film effect formed in the two-way slab.

How to take effective means to evaluate the fire emergency lighting and evacuation indication system used in the project, and verify the healthy operation of the system correctly and efficiently, has always been an urgent problem for the fire on-site supervision and law enforcement team of fire protection. In view of the problems such as the difficulty of sampling and the difficulty of sending for inspection of fire emergency lighting and evacuation indication systems in engineering applications in supervision and spot checks, with reference to the product standard GB 17945—2024 and technical standard GB 51309—2018, this paper develops an on-site detection device for fire emergency lighting and evacuation indication system products, which can quickly detect emergency time, battery capacity, surface brightness, illumination, emergency conversion function, conversion time, key technical parameters such as equipment communication status can be used to evaluate the operation health of the fire emergency lighting and evacuation indication system, and the results are presented in the form of records and reports, which can provide reference for the later maintenance work of the system when the project is put into use, and can effectively guide fire supervision and law enforcement.

Fire smoke extraction is crucial for firefighting and rescue operations as well as for ensuring the safety of personnel on site. Hydraulic ventilation smoke extraction is a method that utilizes high-velocity water jets from fire nozzles to entrain and remove smoke. It offers advantages such as high flexibility and no need for additional equipment; however, systematic experimental research and theoretical support are currently lacking. This study focuses on hydraulic ventilation smoke extraction technology and employs a controlled variable method to investigate the effects of the distance from the nozzle to the window (ranging from 223 mm to 1 437 mm), spray angles (45° and 60°), and convection conditions on smoke extraction performance. A lux meter was used to monitor real-time changes in smoke concentration, enabling quantitative evaluation of smoke extraction efficiency. The results show that the highest smoke extraction efficiency is achieved when the nozzle is positioned 667 mm from the window, with the water jet diameter not exceeding the window area (i.e.,when the spray angle is 60°) . The experimental findings indicate that the nozzle-to-window distance, spray angle, and convection conditions are key factors influencing the effectiveness of hydraulic ventilation smoke extraction. Reasonable optimization of these parameters can significantly improve smoke extraction efficiency, providing theoretical support and practical guidance for smoke extraction in fire scenes.