Fire Suppression Performance Research Articles

Encapsulation of Hydrophobic-but-Not-Lipophilic Perfluoro Liquids Based on a Self-Assembled Double Emulsion Template via Solvent Evaporation Method.

The facile encapsulation of perfluoro liquids that are hydrophobic but not lipophilic into liposomes or microcapsules presents a significant challenge in the fields of biomedicine, dynamic optics, functional chemical applications, etc. This is due to their chemical inertness and physical immiscibility, particularly those with low boiling points. In this study, a novel strategy based on a double emulsion template via solvent evaporation is proposed after investigating the mechanism of three-phase emulsion systems. The perfluoro liquid droplets can be easily emulsified into a polymer solution as the second emulsion layer, where the polymer shell is formed during solvent evaporation in the continuum medium under proper processing controls. The morphology of particles is predictable and fits well with the linear model derived from Neumann's triangle in three-phase systems. Furthermore, a comprehensive study on the encapsulation of perfluoro ketone, which is widely used as a green fire extinguisher agent, is conducted as an example. The encapsulated perfluoro ketone showed instant thermal response upon heating while maintaining a good shelf life at room temperature. The remarkable fire suppression performance exhibited great potential for practical applications. This work offers more insight into the encapsulation of "naughty" perfluorinated chemicals and provides more possibilities for extended applications.

A new experimental method to study the flame inhibition performance of low concentration halogenated gas

The minimum fire extinguishing concentration is a key index for the development of next generation chemical clean fire extinguishing gases, which is usually got by the cup-burner. The fire suppression performance of low concentration of chemical gas is hard to be understood by the available methods. In this work, the fundamental acknowledgement of steady flame surface attacking mechanism by halon functional group is newly discussed by conducting a series of bench scale tests with a cylindrical channel under a varied fluorinated gases. The characteristics of flame propagation under differentiated air atmosphere environmental conditions is obtained. The influence of fluorine-containing gas flow rate on flame propagation speed is clarified. A dimensionless relationship including atomic radius, bond length, polarization degree, molar mass and molar volume are proposed to describe the influence of low concentration of fluorine-containing gas on flame propagation speed. It provides an insight for the understanding of the flame inhibition performance of low concentration halogenated gas.

Preparation of novel gel foam and its fire suppression performance against gasoline pool fires

The phenomenon of re-ignition after extinguishing tank fires poses a significant challenge for firefighting and rescue operations. In this study, a gel foam was prepared using linseed gum as the gelling agent and sodium tetraborate as the cross-linking agent. By analyzing the foaming performance of the gel foam, the optimal formulation for the gel foam was determined. Subsequently, microscopic structural observations and thermal stability tests were conducted on this material. A comparison of the firefighting performance between the gel foam and aqueous film-forming foam (AFFF) on extinguishing gasoline pool fires was also carried out. The results indicate when the foaming agent, consisting of coconut oil glucoside (APG0814) and fatty alcohol polyoxyethylene ether (AEO-9), is used in a 9:1 ratio with a mass fraction of 0.4 wt%. Furthermore, by introducing 0.35 wt% concentration of linseed gum and 0.02 wt% concentration of sodium tetraborate, the gel foam exhibits a foaming expansion ratio of 6.5, a half-life of 203 min, and a comprehensive value of 989.63, which represents the best performance. The gel foam and the AFFF exhibit relatively similar extinguishing effectiveness, with respective extinguishing times of 108s and 95s.Further analysis of the gel foam's resistance to re-ignition reveals that the gel foam demonstrates 25 % and 90 % ignition resistance times of 425s and 573s, respectively, representing a significant enhancement of 66.02 % and 104.64 % compared to the AFFF. These results indicate that the novel gel foam possesses excellent resistance to re-ignition, reducing the risk of fire rekindling in liquid fire scenarios. This research serves as a valuable reference for the development of environmentally friendly and re-ignition-resistant gel foam for extinguishing liquid fires.

Assessment of Halon-Free Agents for Fire Safety Application in Aircraft Propulsion System

Halon 1301 is an effective total flooding fire suppression agent which is widely employed in aircraft cargo and propulsion systems for emergency fire scenarios. The production of Halon 1301 was banned by the Montreal Protocol in 1994 due to its environmental impact on ozone depletion and long atmospheric lifetime. Thus, a credible alternative is required for fire safety application on-board aircrafts. This study forms a follow-up to the work published by A. Dinesh et.al and M. Diakostefanis et.al which studied halon-free fire suppression in aircraft cargo bay through CFD and experimental validation respectively. Due to constraints in cost and logistics of testing fire suppression in a gas turbine engine, a computer modelled fire zone of a hypothetical high-bypass turbofan engine was used to simulate and evaluate the fire suppression performance of three Halon-free agents - HFC-125, HFC-227ea and FIC-13I1. Halon 1301 was also simulated to provide baseline comparison to the alternative agents. The capacity to inert was based on the distribution of agent concentrations subjected to a heptane-based fuel fire. Simulations were conducted at ISASLS and 40,000 feet to represent the engine’s operating environment. Overall, it was found that HFC-125 and HFC-227ea satisfactorily suppressed fire at both ambient scenarios. It was found that agent density and suppression concentration significantly influenced the agent’s ability to mix with ambient air and flood the fire zone. Density of the agent combined with higher inertion concentrations also influenced formation of localised recirculation zones which influenced mixture distribution in the fire zone. The simulations enabled identification of individual changes to agent flow characteristics at different operating conditions and demonstrated the performance criteria of Halon 1301 along with the proposed alternative agents for successful fire suppression. Through this study, it was found that all the agents except FIC-13I1 passed the minimum suppression criteria making HFC-125 and HFC-227ea suitable agents for replacement of Halon 1301. The minimum concentration and simulation design in the engine fire zone were validated against the experimental tests conducted by NIST in Boeing 777’s dual-spool high bypass turbofan engine for Halon 1301 and HFC-125. The failure of FIC-13I1 was attributed to the complex design in fire zone and could be overcome by considering a higher factor of safety for this design and injecting higher mass flow rate of the agent into the fire zone. The outcome of this study proposes further work to be carried out through experimental validation of the CFD simulations which will be key to progress the technology to higher TRL and meet aviation certification requirements. Further work may also explore blended agent configurations to tailor the agent characteristics to meet suppression requirements for maintaining safety and reliability of the system.

A biphosphophenanthrene structure intumescent flame retardant with superior smoke suppression performance for epoxy resin

The intrinsic flammability and high smoke production are two major defects that epoxy resin (EP) must overcome during the practical application. However, few current studies have acknowledged in both fire resistance and smoke suppression performance, which is vitally interrelated with quality of char layers. Herein, a P/S-containing compounds (PODSE) was prepared via esterification and then supplemented with ammonium polyphosphate (APP) to develop an intumescent flame retardant for heightening the strength of char. With 20 wt% PODSE/APP, the peak of smoke produce rate (pSPR) and total smoke production (TSP) of EP3 reduced by 88.1 % and 87.0 %, respectively, indicative of superior smoke suppression performance. It attained a limited oxygen index (LOI) value of 40.0 % with V-0 rating during vertical burning test (UL-94) and the char residues at 700 °C increased from 15.8 % to 29.9 % compared with pure EP. More importantly, in order to figure out the reason for such highly-improved performance, the residual chars after cone calorimeter (CC) test were comprehensively investigated. The result showed that the internal chars of the samples modified by PODSE/APP exhibited honeycomb-like structure instead of irregular network structure of the one modified with single PODSE, endowing the char layers with higher expanded ratio and strength, which responded to excellent insulation effect. This finding provided theoretical and experimental basis for further exploration of P/S synergistic intumescent flame retardant.

DROPLET SIZE DISTRIBUTION VARIATION OF PENDENT FIRE SPRINKLER SPRAY DEPENDING ON THE MEASUREMENT LOCATION

Droplet size of sprinkler sprays is related to the rate of evaporation and penetration of a fire plume. However, sprinkler sprays have various droplet sizes even at one location. Therefore, it is essential to examine the droplet size distribution depending on the location to predict the fire suppression performance of the sprinkler spray. To examine the droplet size distribution of spray from a pendent sprinkler head, acrylic plates were installed around the sprinkler head and a gap was made on one side of the wall. A charge-coupled device camera was installed to capture the droplet images both on a plane parallel to the sprinkler frame arm and on a plane perpendicular to the frame arm. Droplet information was obtained by deriving the image from the brightness and gradient images extracted from the original image. Large droplets, exceeding 1.5 mm in diameter, were observed in the mainstream of the spray. The probability of observing small droplets decreased as the droplets moved downstream. Spherical droplets were observed in the mainstream of the frame arm direction, while nonspherical droplets were observed in the perpendicular direction to the frame arm because of high velocity. The number-based cumulative distribution function (CDFs) fitted using the Rosin-Rammler distribution function provided the best fitting results. The volume CDFs fitted using the Rosin-Rammler distribution function yielded acceptable adjusted R<sup>2</sup> values. In this case, the coefficient m related to D<sub>v50</sub> and the coefficient n related to the width of the distribution increased with increasing radial and vertical locations.

Evaluation of Fire Suppression Performance for Multiple-Fire-Source Fire Using Water Mist-Type Fire-Suppression Equipment for Railway Passenger Cabin

The fire suppression performance of a mist fire-extinguishing system in railway passenger cabin was evaluated using a performance evaluation method based on multiple fire sources. Scenarios were analyzed for a simulated space in the railway vehicle cabin of the Daegu Urban Railway Line 3 using automatic fire-suppression system methods based on railway-vehicle technical standards. Three n-heptane fire pools were positioned inside the test space. When the spray fire-extinguishing equipment was operated at 10 and 20 bar after 30 s of ignition, the variations in the temperature of the test space and the fire-extinguishing characteristics, such as the time taken to stop the fire-extinguishing equipment, were analyzed. The experimental results showed that the internal temperature of the cabin initially increased after ignition. However, when the fire- extinguishing equipment was operated 30 s after ignition, the internal temperature of the cabin stopped increasing and started to decrease, satisfying the fire safety standard that the fire must be completely extinguished within 5 min. The temperature decreased more rapidly when the operating pressure was 20 bar than when it was 10 bar. In addition, the vertical temperature distribution analysis showed that the temperature of the upper part was higher than that of the lower part, owing to thermal buoyancy. However, the design of the nozzle location is critical because the temperature decreases more slowly far from the nozzle of the mist fire-extinguishing system, which can be dangerous.

Investigating correlations between physical properties and fire suppression performance of fluorinated and fluorine-free foams using a novel firefighting foam database

Aqueous film-forming foams (AFFF) contain fluorinated surfactants, a class of perfluoroalkyl substances (PFAS) which have been shown to cause damage to the environment and human health. This has necessitated their replacement on military sites by the year 2024. But to date, no fluorine-free replacement firefighting formulation has showed comparable performance to AFFF. Fire extinction performance is measured in tandem with formulation physical properties, but whether various physical properties and fire suppression are correlated is poorly understood. Herein, we present the curation of a large amount of physical property and fire suppression data collected in-house. Chemometric regression was used to ascertain correlations between the critical micelle concentration (CMC) of both individual surfactant solutions and multi-component formulations and their corresponding (1) solution surface tension, (2) interfacial tension with heptane, and (3) fuel-induced foam degradation using heptane and (4) gasoline. After evaluating several algorithms, promising correlations are found between CMC and foam degradation on heptane and gasoline using locally weighted regression (LWR), as indicated by a large R2 of cross-validation (R2CV) from ∼0.6–0.9. Solutions with CMCs from ∼0.01–0.1 wt percent (%) exhibit the longest degradation times, whereas solutions with CMCs outside of this range had considerably faster degradation. This correlation is new but explains only 90% or less of the variation in the data partly because foam degradation is induced by fuel, which the CMC does not consider. However, this work will serve as a basis for future machine learning endeavors to predict fire suppression performance based on chemical structure.

Solid Fire Suppression Performance and Mechanism of a Novel Environmental-Friendly Hydrogel

ABSTRACT The types of solid fires are diverse and the suppression highly depends on the adhesion and surface cooling effects of the extinguishing agent. In order to overcome the disadvantage of low adhesion and improve the efficiency of water in suppressing fires, a novel environmental-friendly thermal gelation hydrogel was prepared with hydroxypropyl methylcellulose (HPMC), sodium n-dodecyl sulfate (SDS), and super absorption resin (SAR) as the main raw materials. Ammonium polyphosphate (APP) and aluminum hydroxide (ATH) were added to enhance the fire-suppressive properties of the hydrogel. Then, cone calorimetry experiments were carried out to investigate the suppression effects differences between the hydrogels and water. According to response surface methodology, the optimal composition of hydrogel is the amount of HPMC, SDS, and SAR was 1.28 wt%, 1.50 mM, and 0.20 wt%, respectively. By adding APP and ATH flame retardants in combination, the hydrogel exhibited a reduced gelation temperature and an improvement in viscoelasticity, making it more effective in suppressing fires. Compared with water, solid fuel samples covered with hydrogel presented longer time to ignition. The maximum heat release rate was reduced by 53.27 kW/m2 and total smoke production exhibited a reduction of 12.23%. The hydrogel generated a fireproof and dense char layer on the solid surface, which acted as a barrier against heat and mass exchange, effectively suppressing the development of fire. The results of this study can provide guidance for the development of hydrogel extinguishing agents.

Modeling of Sprinkler skipping for the suppression of large-scale rack-storage fires

A sprinkler skipping model is developed and implemented into FireFOAM. The model considers spray impingement and water accumulation on the sprinkler thermal link. A sub-grid spray impingement model is developed assuming a simplified link geometry, i.e., a sphere. Both the impinged cold water and the water evaporative cooling reduce the sprinkler thermal response. The model is calibrated with the plunge tunnel tests in the presence of water mist sprays and validated against a large-scale fire suppression test using Class 2 commodity. The skipping model improves the sprinkler activation prediction. With the skipping model, the second sprinkler activation is delayed, and the activation time is close to the test. The predicted number of activations and the activation pattern also show good agreement with the measurement, which improves the prediction of the fire suppression performance. The model is applied using different rack array heights (7.6, 10.7 and 13.7 m) under a 15.24 m high ceiling at two injection pressures. The model predicts that the highest array at the low injection pressure has several sprinklers skipped, which causes the failure of fire suppression.

Launch Dynamic Simulation of a Compressed-Air Launcher for Fire Suppression

This paper focuses on improving fire suppression performance through the use of compressed-air launching technology. A launch dynamics calculation model of a compressed-air launcher is presented, developed using VC++ programming, to simulate the acceleration process of a fire-extinguishing bomb in a barrel. By analyzing the influences of various structural and initial parameters on interior ballistics variations, the effectiveness of the calculation model and program in accurately simulating the launching process is demonstrated. The calculation results indicate that the bore pressure follows a similar trend to that of traditional gunpowder launching. Additionally, it is found that specific structural parameters, such as nozzle diameter and gas cylinder volume, have a direct impact on interior ballistics variations. Notably, the nozzle diameter positively affects the peak pressure, muzzle velocity, gas transfer efficiency, and launch efficiency. To ensure an optimal launch effect and efficiency, the nozzle diameter should be selected to be more than half of the launcher caliber. Similarly, the gas cylinder volume positively influences the peak pressure and muzzle velocity while negatively affecting the gas transfer efficiency and launch efficiency. Furthermore, the initial pressure in the gas cylinder exhibits a positive linear relationship with both the peak pressure and muzzle velocity but a negative linear relationship with the gas transfer efficiency and launch efficiency. The loading position minimally impacts the peak pressure and muzzle velocity but slightly enhances the gas transfer efficiency and launch efficiency. Finally, it is observed that launch angles do not affect the interior ballistic process. The research findings provide valuable theoretical guidance for determining the working parameters of compressed-air accelerated fire-extinguishing bombs.

Thermo‐responsive fluorine‐free foam stabilized by PEO–PPO–PEO triblock copolymer (EO)100(PO)65(EO)100 for pool fire suppression

AbstractResearch and development of novel fluorine‐free materials to replace fluorinated aqueous film‐forming foam (AFFF) are crucial for improving pool fire suppression performance and protecting the environment. In this study, we report the thermo‐responsive fluorine‐free foam stabilized by triblock PEO–PPO–PEO copolymers (EO)100(PO)65(EO)100 for pool fire suppression. Small‐angle X‐ray scattering (SAXS) and reflected light interferometric techniques are conducted to study the molecular self‐assembly in bulk and film thinning behavior, and the foaming kinetics of copolymer solution and thermophysical properties of the liquid foam are studied by dynamic surface tension and oscillatory rheology analysis. At room temperature, the amphipathic structure of PEO–PPO–PEO makes it possible to absorb at the air–liquid interface forming large‐scale liquid foams containing the mobile films with a detergent state. Upon heating to the surface cooling temperature of burning oil, the mobile films can be actively switched into mechanically strong films with rigid surfaces. The in situ switching of the two interfacial states leads to the significant enhancement of the foam stability, especially under the dual defoaming effects of heat and oil. What's more, it is observed that the confinement of organized copolymer micelles in the Plateau borders and micellar self‐layering in film confinement induce drainage delay of foam and film's stepwise thinning phenomenon, further increasing film thickness and enhancing the thermal stability of the foam. In standard fire‐fighting tests, it is proved that the burnback performance exhibited by thermo‐responsive copolymer foams is three times better than that for classical fluorine‐free foams and almost 1.5 times higher than that for commercial AFFF.

The suppression performance of fluorinated cooling agents on the Lithium-ion Batteries fire based on the Accelerating Rate Calorimeter (ARC)

Lithium-ion Batteries (LIB) fire has attracted a wide attention since it threatens the application limitation of LIB. The combustible gases are producted during the LIB thermal runaway. When the immersion cooling technology is used for LIB thermal management, the mixiture of combustible gases and fluorinated cooling agents in a confined space could result in a big explosion due to the LIB thermal runaway. With an aim to have a deep understanding regarding the influence of fluorinated immersion cooling agents on the fire suppression performance, a series of tests were conducted to obtain the profile of critical temperature and pressure based on the accelerating rate calorimeter (ARC). Duing the tests, the cylindrical 18,650 LIB is heated under insulated environment firstly. Then several typical fluorinated cooling agents are selected to clarify the fire suppression performance of LIB thermal runaway. The results and discussion indicate that the utilization of HT (hexafluoropropene trimer) agent has a peak pressure 0.6 Mpa and a peak temperature 823 ℃ during LIB thermal runaway. The suppression results varying seven typical fluorinated cooling agents are discussed. BTP (2-BroMo-3,3,3-triflouro propene) shows an obvious suppression effect because it results in a low pressure ratio.The suppression mechnasim of agents on the LIB thermal runaway is discussed and presented. It could provide a insight into the development of new fluorinated agents for suppression.

Performance evaluation of guar gum and conventional binders based fire‐extinguishing aerosol‐forming composites

AbstractPyrotechnic‐based firefighting systems have been found to be effective in a wide variety of firefighting applications. Binders in pyrotechnic mixtures play a significant role as they consolidate the ingredients, provide excellent mechanical strength and increase the storage life. The rise in health and environmental safety concerns in recent years has directed our research towards natural binder systems of biological origins. Therefore, in this work, galactomannan, also called guar gum, was comparatively investigated against four different types of conventional binders, phenol–formaldehyde resin, ethyl cellulose, hydroxyethyl cellulose and carboxymethyl cellulose sodium salt, which are being used in aerosol‐forming pyrotechnic mixtures for firefighting application. It was found that the nature of the binder in an amount of 3% by weight significantly influences the combustion behaviour, fire suppression performance, mechanical and thermal characteristics of gallic acid–KNO3–KClO3 tertiary aerosol‐forming pyrotechnic mixture for fire fighting application. The safety and performance characteristics of these formulations were evaluated by conducting analyses specific to pyrotechnic formulations, that is, burn rate measurement, heat of combustion, TGA/DSC thermal analysis, hygroscopic study, compression test and n‐heptane pool fire suppression test. It can be inferred from the values obtained from these analyses that guar gum is a preferred binder to the other four‐binder systems for the gallic acid–KNO3–KClO3 pyrotechnic mixture.

Inhibitory effects of water mist containing alkali metal salts on hydrogen–natural gas diffusion flames

Fire extinguishing technologies of fine water mist containing additives have good application prospects. Additives that are efficient, nontoxic, nonpolluting, widely used, economical and reliable provide a reference for the application and promotion of fine water mist fire extinguishing systems containing alkali metal salts. In this paper, six potential alkali metal salt additives were selected: potassium carbonate (K2CO3), sodium carbonate (Na2CO3), potassium oxalate (K2C2O4·H2O), potassium acetate (CH3COOK), potassium chloride (KCl), and potassium bicarbonate (KHCO3); these additives were delivered into the fires as mists of their solutions at certain concentrations, the extinguishing time was recorded, and the minimum fire extinguishing concentration (MEC) of fine water mist containing alkali metal salt was tested by using a cup burner experimental apparatus. In addition, different types of alkali metal salts were compared to determine the anions and cations with better fire suppression performance levels. The suppression efficiencies of different ratios of additive packages for hydrogen-doped natural gas diffusion flames were studied to determine a specific ratio of additive packages. Based on the results of the experiment, in contrast to the pure water mist, the suppression efficiency of alkali metal salt greatly improved. The cation extinguishing ability was K+>Na+, and CO32- and CH3COO− were better than other anions in alkali metal salts. An efficient compound additive was identified as 1.5% K2CO3 + 0.5% CH3COOK. With increasing hydrogen addition, the MEC of fine water mist with additives increased.

Experimental study on fire suppression performance of the high pressure water mist in the engine room of an offshore platform

The total flooding application water mist system is a new type of environmentally-friendly fixed extinguishing system. The optimizing design can improve its fire extinguishing performance. At present, the water mist fire extinguishing system in the engine room of the offshore deepwater semi-submersible support platform has not attracted sufficient attention. In this paper, the water mist in the engine room of a deepwater semi-submersible support platform was studied. It contains the effect of water mist on the heat absorption and oxygen insulation of diesel pool fires. The applicable parameters of the water mist fire extinguishing system were also determined. Moreover, based on the shielding of the fire source in the engine room and the different requirements for water mist extinguishing parameters, a hierarchical multi-parameter combined high-pressure water mist fire extinguishing system was proposed. In the full-scale experimental engine room model, according to the fire extinguishing experiments for diesel pool fires with different areas, this kind of hierarchical multi-parameter water mist system is very effective on shielded and non-shielded fires. In addition, it is still effective even in a non-closed environment coupled with smoke exhausting.

Fire-suppression performance of high-pressure water mist system inside scaled-down road tunnel section

Fire-suppression performance of high-pressure water mist system inside scaled-down road tunnel section

Containment and Suppression of Class A Fires Using CO2 Hydrate

This paper presents the experimental findings on fire containment and suppression by dropping CO2 hydrate granules and tablets on burning solid materials. We used the combustible materials typical of compartment fires—wood, linoleum, and cardboard—to determine the volume and mass of gas hydrate powder necessary for the effective fire suppression. Gaseous emissions were recorded from the combustion with and without fire suppression using hydrates. Conditions were specified in which a fire can be extinguished with minimum air pollution. We also identified the conditions for effective fire containment and suppression using hydrates as compared to water spray, snow, and ice. The necessary volume of hydrate was determined for effective fire suppression in a compartment filled with various materials. Experimental data show that the impact of temperature on the CO2 hydrate decomposition is highly nonlinear. The carbon dioxide hydrate exhibited a much better fire suppression performance than water spray in the course of total flooding of solid combustible materials. It was established that fine water spray failed to reach the lower levels of multi-tier crib fires. Finally, key patterns of total flooding with CO2 hydrate powder were identified when applied to fires.

Crystallization of sodium metaborate on the surface of layered double hydroxide imparts high flame retardancy properties to epoxy coatings

To address the phenomenon of rapid fire spread in high-rise steel buildings, this paper used the in situ growth method to crystallize sodium metaborate (SMB) on the surface of layered double hydroxide (LDH) and grafted Ti-O onto LDH@SMB hybrid material by hydroxyl action. The synthesized LDH@SMB@Ti (LST) hybrid material was then doped into epoxy resin (EP) to prepare a composite coating. The fire test showed that the LST/EP coating makes the steel plate reach a stable temperature in a shorter time, so that the plate temperature did not continue to rise, and the temperature on the back side of the plate was stabilized at 172.9 °C, which was 87.4 °C lower compared to pure EP. This proves that the LST material gives the coating stronger fire retardant properties upfront and strengthens the continuous insulation ability of the char layer. Cone calorimeter tests showed that the total heat release rate (THR) of LST/EP was reduced by 47.3% and the total smoke release rate (TSR) was reduced by 45.4%, proving the excellent fire and smoke suppression performance of LST/EP. In the expansion performance test, the expansion height and expansion rate of LST/EP reached 29.90 mm and 23.36 respectively, and the expansion of char layer was more uniform. This indicates that the addition of LST hybrid material can improve the mechanical strength of char layer and attenuate the heat transfer rate in the vertical direction. The residual char of LST/EP was 33.2% by thermogravimetric analysis, indicating that the addition of LST could reduce the volatilization of volatile components and improve the thermal stability of EP.

Double-Layered Polymer Microcapsule Containing Non-Flammable Agent for Initial Fire Suppression.

Fire in energy storage systems, such as lithium-ion batteries, has been raised as a serious concern due to the difficulty of suppressing it. Fluorine-based non-flammable agents used as internal substances leaked through the fine pores of the polymer outer shell, leading to a degradation of fire extinguishing performance. To improve the durability of the fire suppression microcapsules and the stability of the ouster shell, a complex coacervation was used, which could be microencapsulated at a lower temperature, and the polymer shell was coated with urea-formaldehyde (UF) resin. The outermost UF resin formed elaborate bonds with the gelatin-based shell, and thus, the structure of the outer shell became denser, thereby improving the loss resistance of the inner substance and thermal stability. The double-layered microcapsules had an average particle diameter of about 309 μm, and a stable outer shell formed with a mass loss of 0.005% during long-term storage for 100 days. This study confirmed that the double-layered microcapsules significantly improved thermal stability, resistance to core material loss, core material content and fire suppression performance compared to single wall microcapsules. These results indicated that the double-layered structure was suitable for the production of microcapsules for initial fire suppression, including highly volatile non-flammable agents with a low boiling point.