Extinguishing Performance Research Articles

Inspiration from a thermosensitive biomass gel: A novel method to improving the stability of core-shell “dry water” fire extinguishing agent

“Dry water” (DW) material is the powder with hydrophobic nano silica particles as the shell and water droplets as the core. The water content in DW is higher than 90%, thus, it is an effective fire extinguishing material. However, when DW is compressed under external pressures, it will crack with the core-shell structure being destroyed. In this work, the water phase in the core is modified as gel phase to enhance the internal pressure resistance of DW powder and its stability. More specifically, the feasibility and optimum preparation conditions of carrageenan gel based dry water (CGDW) material are explored and its fire extinguishing performance is revealed using fire extinguishing experiments. The results indicate that the CGDW powder performs better in fire extinguishing than ordinary ABC dry powder. The CGDW materials are green and environmental friendly, and show broad potentials in various applications.

Wood crib fire tests to evaluate the influence of extinguishing media and jet type on extinguishing performance at close range

abstract This paper is intended to be the first study to discuss the fire suppressing performance of the four most common extinguishing media under the same reproducible conditions. The tests were performed in bench-scale and used standardized 5A wood cribs as well as a miniature extinguishing system with a liquid flow rate of 1.4 l min − 1 . The tests results present a consistent overview of the fire suppression efficacies of water, water with a foaming agent, nozzle-aspirated foam and compressed air foam. Depending on their jet types, the cooling capabilities of the extinguishing media water and water with a foaming agent were compared to the cooling capability of a full jet of wet, general and dry foams. The results show that compressed air foam suppressed fire most effectively under the test conditions. Because of the convoluted crib structure, water and water with foaming agents used from a distance are more effective in the form of a full jet rather than a spraying jet. At close range, spraying jets multiply their effectiveness. A slight difference can be observed in the cooling performance of extinguishing foams that use foaming agents from different manufacturers. The paper establishes a link between the foaming agent's cooling capability and its wetting power by relating the results of wood crib fire tests according to DIN EN 3–7 and findings from laboratory immersion tests compliant with DIN EN 1772.

Research on Abnormal Identification Technology of Circuit Breaker extinction based on wavelet analysis

Circuit breaker is the actuator of power network fault removal and operation mode conversion. If the circuit breaker itself cannot complete the breaking operation, it may cause the accident impact range to expand, or even cause more serious chain failure. The fault phase current is decomposed based on wavelet analysis and Fourier transform, and the unstructured recorded wave data is converted into structured fault characteristic quantity to realize the analysis of current mutation characteristics. The high frequency characteristic singular value at the occurrence of arc is obtained by wavelet transform, which provides the key characteristic quantity for the identification of abnormal arc extinguishing performance of circuit breaker and realizes the identification of abnormal arc extinguishing state of circuit breaker. Issue an alarm before abnormal expansion of circuit breaker or adverse impact, remind relevant personnel to timely check and deal with defects, reduce the occurrence of abnormal tripping circuit breaker phenomenon.

Synthesis and characterization of a novel surfactant used for aqueous film-forming foam extinguishing agent

Fluorocarbon surfactants are a key ingredient of aqueous film-forming foam (AFFF) extinguishing agent. As is well known, the most widely used fluorocarbon surfactants are perfluorooctane sulfonates (PFOS) and theirs derivatives. However, PFOS has been restricted due to its drawbacks such as toxicity, bio-accumulation and resistance to biodegradation, etc. Fortunately, the toxicity and bio-accumulation can be neglected if the fluorocarbon chain contained in the surfactants is less than or equal to 4. Therefore, synthesis of novel short fluorocarbon chain (≤ C4) surfactants has become a very important way to solve this problem. A novel fluorocarbon surfactant based on perfluorobutyl had been synthesized and its chemical structure had been confirmed by Fourier transform infrared spectroscopy, 1H nuclear magnetic resonance (NMR) and 19F NMR measurements in this work. Since the fluorocarbon surfactant mixed with appropriate hydrocarbon surfactant can reduce its dosage and cutting production costs, the surface tension and the critical micelle concentration (CMC) of the synthesized fluorocarbon surfactant and its equimolar mixtures with CH3(CH2)5NaO3S had been studied. The results show that CMC and the surface tension at CMC (γCMC) of the pure surfactant were 21.68 mmol/L and 17.08 mN/m, while the minimum surface tension and CMC could reach to 16.58 mN/m and 7.72 mmol/L for the mixed system, respectively. In addition, the foamability, spreadability and extinguishing performance of the equimolar mixed system has also been investigated. The foam expansion and the 25% drainage time are 9.8 and 313 s, respectively, and the extinguishing times are less than 65 s while the burnback times are more than 14.50 min for all the hydrocarbon oils studied in this work, indicating a great application prospect in AFFF.

Numerical investigation on fire-extinguishing performance using pulsed water mist in open and confined spaces

This article is an attempt to reveal the fire extinguishing mechanism under the action of pulsed water mist system using the method of Large Eddy Simulation (LES). The fire extinguishing performances with continuous and pulsing discharge modes were numerically investigated by measuring gas temperature, oxygen concentration and fire-extinguishing time. The simulation results presented that the pulsed water mist has no obvious advantage over the continuous water mist in the open space, but has a considerable extinguishment performance by optimizing the interval of the pulsing discharge mode in the confined space. The optimum pulse interval was obtained. Moreover, the oxygen dilution effect of pulsed water mist plays an important role in fire extinguishment. The numerical simulations conducted in this work can provide global information on the fire-extinguishing time under different discharge modes as well as spatially-resolved information on the advantages of pulsed water mist extinguishment based on oxygen concentration and water vapor concentration. The results suggested that the best suppression performance of pulsed water mist was achieved when the oxygen concentration around the flame base was diluted. The above results can provide a significant reference for the optimal design of water mist fire suppression system.

Discharge Characteristics of a Portable Compressed Air Foam System

Existing portable foam extinguishers generate fire-fighting foam at high pressures with the aid of an air aspirating nozzle. This system could encounter several limitations at the point of application such as poor foam quality due to the use of fire contaminated air for foam generation and insufficient momentum to reach the seat of fire. Research has shown that by incorporating compressed air into a portable foam system, the integrated foam system could generate superior quality foam with high momentum when properly installed with the right components. Several studies had been conducted on the extinguishing performance of compressed air foam systems on multiple fire types, both for small and large fires. Compressed air foam systems mitigate exposure of the operator to heat and provides faster knockdown of the fire plume as compared to air-aspirated foam because of its stronger stability and rheology. Since the expansion ratio of the foam can be regulated to combat specific fire types and sizes, compressed air foam systems can be utilized in protecting a variety of equipment of varied sizes.The aim of this study is to investigate the discharge characteristics of a portable compressed air foam at low pressure. For this study, the requirements of NFPA 10 and CAN/ULC-S508 for a new system were used to determine the feasibility of the system.The effect of air pressure on the expansion ratio of the foam was investigated with foam concentrate ranging from 2% to 4% for three different hoses with lengths of 1-m, 2-m and 3-m. Pressure used ranged from 1.72 bar to 5.52 bar. The 3% and 4% solution for the 2-m hose and 3-m hose exhibited similar trend of a rise and fall with pressure by generating fluid foam of medium expansion ratio in the range of 19 to 28. However, the expansion ratio of 3% solution and 4% solution for the 1-m hose increased monotonically with increasing pressure and generated wet foam of low expansion ratio in the range of 8 to 15. While low expansion foams are effective in extinguishing liquid pool fires, medium expansion foams are used for structural protection due to its slow drainage time and its ability to adhere to sloped, vertical, horizontal and slippery surfaces.Discharge range tests were conducted to investigate the horizontal projection of the foam from the nozzle at a height of 0.9m above the ground. The test was conducted in an open space with little interference of wind. Visual record of the maximum discharge range was taken at intervals. The foam from the 1-m hose projected from 1 m at 2.42 bar to 2.4 m at 5.52 bar while the foam from the 2-m hose projected from 1.8 m at 2.42 bar to 4.5 m at 5.17 bar. Likewise, the foam from the 3-m hose with an initial discharge of 1.85 m at 2.41 bar increased progressively to above 4.5 m at 4.83 bar. The tests demonstrated the relationship between pressure and the momentum of the foam, showing that an increase in pressure leads to an increase in the range covered. Furthermore, flow rates at different pressures were investigated using 3% foam solution with a 2 m hose. The flow rate of the foam ranged from 8 g/s to 20 g/s at 1.93 bar and 5.24 bar respectively, indicating linear progression with pressure. The flow rates correspond to application times of 244 and 102 seconds respectively for the 2-liter solution. Overall, all foams tested met the requirements of the CAN/ULC-S508 standard.

Assessment of a clean and efficient fire-extinguishing technique: Continuous and cycling discharge water mist system

Abstract As the succedaneum of halon extinguishing agent, water mist is absolutely green, harmless, and sustainable which does not cause the ozone depletion. In order to investigate the fire extinguishment performance of water mist system with both continuous and cycling discharge modes, a series of full-scale pool fire suppression experiments (including gasoline and diesel) with the two discharge modes were conducted in a confined compartment (3 m × 3 m × 3 m) under different mechanical exhaust rates. Some characteristic parameters, such as the smoke temperature, radiative and total heat flux, fire-extinguishing time, and carbon monoxide and oxygen concentration under the influences of both water mist and mechanical ventilation, were obtained, and their variation mechanisms were analyzed in detail. The experimental results show that pool fires could be extinguished more quickly using cycling water mist with shorter turn-off time. The reduction coefficient of carbon monoxide concentration increases exponentially, while the extinguishing time of both gasoline and diesel pool fires decreases first and then increases with the ventilation rate. With cycling discharge mode, the smoke temperature and heat flux both fluctuate with alternate activation of water mist. The application of cycling discharge mode substantially improves the fire suppression efficiency, especially in the condition that the pool fire is difficult to extinguish utilizing continuous discharge mode. The cycling discharge water mist system can be applied in some ventilated spaces when mechanical ventilation is unavoidable, and is helpful for personnel security and evacuation.

Experimental Study on the Extinguishing Efficiency of Compressed Air Foam Sprinkler System on Oil Pool Fire

Abstract In order to evaluate the impact of foam qualities and foam application rates on the extinguishing efficiency of compressed air foam sprinkler system on oil pool fire, a series of large-scale gasoline fire extinguishment experiments have been conducted under different expansion ratios and foam application rates. The consumed foam solution dosages to control and extinguish the pool fire have been calculated out respectively. The result showed that foam qualities significantly affect the extinguishing efficiency and burn back resistance performance of compressed air foam sprinkler system. The optimal expansion ratios of compressed air foam was about 10:1 comprehensive considering the extinguishing performance, re-ignition resistance, burn back protection and economical efficiency. It was found that as the foam application rate increases, the fire extinguishing and burn back protection performances of compressed air foam can be evidently improved. The most economical and efficient foam application rate on gasoline pool fire was 3.48 L/ (min· m2), and the minimum foam solution dosage to 90% control and entirely extinguish the fire were 0.99 L/ m2 and 2.38 L/ m2 respectively. The research results are vital to the engineering application of compressed air foam sprinkler system.

Experimental Study on Fire Extinguishing Properties of Compound Superfine Powder

Abstract In this paper, the existing fire extinguishing powder was improved with magnesium hydroxide as additive to prepare the compound superfine powder. And the fire extinguishing performance of the compound powder was tested by the modified cup-burner, being compared with the commercial dry powder and the superfine powder. The advantages of the compound superfine powder were explained from the aspects of minimum extinguishing concentration, temperature and extinguishing time. The experimental results showed that the minimum extinguishing concentration of compound superfine powder was much lower than the other two, and the temperature drop rate was greater in the process of suppressing flame. Although the compound superfine powder was slightly lower than the superfine powder in the average extinguishing time, the standard deviation results showed that the composite powder had better stability. In addition, the experimental results showed that the fray-out of flame was very fast and the time only accounted for 17.5% in the fire extinguishing process.

A Study on the Evaluation of Fire Extinguishing Performance of a Synthetic Surfactant Compressed Air Foam with Scaled Model

A Study on the Evaluation of Fire Extinguishing Performance of a Synthetic Surfactant Compressed Air Foam with Scaled Model

Dissociative adsorption of environment-friendly insulating medium C3F7CN on Cu(111) and Al(111) surface: A theoretical evaluation

SF6 is extensively used in electrical applications because of its excellent insulation and arc extinguishing performance, but its strong greenhouse effect has negative impact on the atmosphere. The excellent performance of C3F7CN in greenhouse effect, insulation ability, safety, and thermal stability has been demonstrated, indicating that this compound can replace SF6 in electrical applications. However, little information is available on the compatibility of C3F7CN with metals, such as copper and aluminum, in devices. Material compatibility between new gas mixtures and materials used in Gas Insulated Switchgear (GIS) should be investigated to determine the long-term behavior of materials. In this paper, dissociative adsorption of C3F7CN on Cu (1 1 1) and Al (1 1 1) surfaces were analyzed based on density functional theory. Adsorption energy, charge transfer, density of states, and electron density difference of interaction between C3F7CN and two metals were analyzed. It was found that the adsorption energy of C3F7CN adsorbed on Cu (1 1 1) and Al (1 1 1) is both below 0.8eV. This value indicates that the interaction between them is not very strong. In addition, the dissociation reaction path of gas molecules after adsorption requires certain activation energy. Therefore, C3F7CN and copper or aluminum have certain compatibility and the compatibility of C3F7CN with aluminum is better than that of copper. Related results provide a reference for predicting the aging mechanism of equipment and the selection or modification of major materials for equipment.

Experimental Study on Effect of Foam Stabilizers on Aqueous Film-Forming Foam

Aqueous film-forming foam (AFFF) is widely used in both military and civilian applications as an effective method to suppress flammable liquid fires. The present study focuses on identifying the contribution of different foam stabilizers to performance of AFFF. Carboxymethylcellulose, xanthan gum, triethanolamine and lauryl alcohol, are chosen as foam stabilizers of AFFF to synthetize AFFF formulation concentrates, and their mass concentration in AFFF is varied in the range of 0–2%, 0–0.4%, 0–4%, and 0–3%, respectively. Subsequently, the properties of AFFF aqueous solutions, including surface tension, interfacial tension, film-forming property, viscosity and foaming ability are measured. In particular, a new apparatus is established to evaluate the effect of foam stabilizers on foam drainage and foam spreading property. Finally, fire extinguishing tests and burn-back tests of AFFF containing different foam stabilizers are performed with a circular pan, 0.25 m2 in surface area. The results indicated that film-forming property and foam spreading property are decreased by the addition of the foam stabilizers. Foam stability of AFFF can be enhanced by the addition of carboxymethylcellulose and xanthan gum but reduced by the addition of triethanolamine and lauryl alcohol. The AFFF containing 0.4% xanthan gum shows the optimal foam stability, but the AFFF containing 0.3% xanthan gum shows the optimal fire extinguishing performance. This indicates that fire extinguishing efficiency is affected by multiple factors. In selecting foam stabilizers we need to be trading off factors such as film-forming property, foam stability and foam spreading property.

Evaluation of SF6-alternative gas C5-PFK based on arc extinguishing performance and electric strength

C5-PFK (C5-perfluoroketone, C5F10O) is under wide consideration as an environmentally-friendly alternative gas to SF6 in high-voltage applications, because of its superior insulation performance. The aim of this work is to study theoretically the arc extinguishing performance and electric strength of C5-PFK.The arc extinguishing performance of C5-PFK was evaluated by analyzing and comparing the thermophysical properties of C5-PFK, SF6, CF4, CO2 and N2 plasmas. It was difficult to obtain the species formed in C5-PFK plasmas because of the complex C5-PFK molecular decomposition process. In this work, the decomposition process of C5-PFK and the related species were analyzed by the bond energy analysis method. For the species for which parameters such as the partition function and the enthalpy of formation were not available, computational chemistry methods were used to obtain the required data. The collision integrals were calculated using the phenomenological potential model. Using these results, the local thermodynamic equilibrium composition at temperatures from 300 to 30 000 K at 1–10 atm of pure C5-PFK was calculated by the method of minimization of the Gibbs free energy, and the corresponding transport coefficients were calculated by Chapman–Enskog method. Through the comparison of the thermophysical properties, it was found that C5-PFK had similar characteristics to SF6, with large peaks in specific heat below 4500 K, indicating potentially good thermal interruption capability. However, the specific heat peak at 7000 K corresponding to CO decomposition may detract from the thermal interruption capability. Specific heat peaks at higher temperatures are associated with the breaking of double or triple bonds, and should be avoided if possible in the new alternative gases.The electric strength of C5-PFK was assessed using the molecular electrostatic potential, which can be accurately calculated or measured, and gives strong insights into important characteristics of the molecule. Based on the analysis of the molecular surface electrostatic potential and electric strength of C5-PFK, SF6, CF4, CO2, and N2, it is found that the positive potential area of the molecular surface has a strong correlation with the electric strength and is expected to be one of the predictors of electric strength. To verify this phenomenon, 36 kinds of particles were used for the correlation analysis. The correlation coefficient between the positive potential area and electric strength is up to 0.9 which means strong correlation.

Electric Field and Current Density Performance Analysis of Sf6, C4f8 and CO2 Gases As An Insulation

SF6 gases are not only widely used as an insulating component in electric power industry but also as an arc extinguishing performance in high voltage (HV) gas-insulated circuit breaker (GCB). SF6 gases is generally used in the production of semiconductor materials and devices. Though these gasses is widely used in many application, the presences of temperature hotspot in the insulations may affect the insulation characteristics particularly electric field and current density. Therefore, it is important to determine the relationship between electric field and current density of gasses used in the insulator in the presence of hotspot. In this paper, three types of gases in particular Sulphur Hexafluoride (SF6), Octafluorocylobutane (C4F8), and Carbon Dioxide (CO2) was used in the insulator for gas insulation with the presence of two hotspots. These two hotspost were detected by referring the rising temperature in the insulator which are 1000 and 2000 Kelvin temperature for hotspot 1 and hotspot 2, respectively. From the simulation results, it can be concluded that Sulphur Hexafluoride (SF6) is the best choice for gas insulation since it had the lowest current density and electric field compared to Octafluorocylobutane (C4F8), and Carbon Dioxide (CO2). It is observed that the maximum current density and electric field for SF6 during normal condition are 358.94 × 103 V/m and 0.643 × 109 A/m2, respectively. Meanwhile, during temperature rising at hotspot 1 and hotspot 2, SF6 also had lowest current density and electric field compared to the other gasses where the results for Emax and Jmax at hotspot 1 are 322.34 × 103 V/m and 1.934 × 109 A/m2, respectively; While, Emax and Jmax at hotspot 2 are 259.77× 103 V/m and 2.824 × 109 A/m2. The results of this analysis can be used to find the best choices of gas that can be used in the insulator.

Application of water@silica core-shell particles for suppressing gasoline pool fires

A new type of dry powders with capsular structure was fabricated for fire suppression, in which the content of water approached 60%. The capsules with the size of 3–5μm consisted of liquid core and solid shell, where the core was water droplet and the shell was assembled silicon dioxide particles with surface hydrophobic modification. The shell of close-packed silica particles surrounding each water droplet provided the structural rigidity of the capsules and enabled their application as powder fire suppressants. Two different scaled real fire tests showed that thus-prepared solid powders could extinguish 0.21MW gasoline pool fire in 2.0s with agent mass of 0.055kg, and 1.0MW gasoline pool fire in 5.0s with agent mass of 0.49kg. Such fire extinguishing performance greatly outperformed the conventional monoammonium phosphate (ABC) powders, neat silica powders and water mist, with significantly reduced fire extinguishing time and mass of agent consumed. Mechanism of the core-shell particles in fire suppression was discussed based on established theories and experimental results.

Examination on Liquid Pool Fire Extinguishment Performance of Twin-fluid Nozzle

Examination on Liquid Pool Fire Extinguishment Performance of Twin-fluid Nozzle

Active substances study in fire extinguishing by water mist with potassium salt additives based on thermoanalysis and thermodynamics

The active substances during the process of fire extinguishing by water mist with potassium salt additives was studied. The minimum extinguishing concentration (MEC) experiment results showed that K2CO3 have the most benefit in improving the fire extinguishing efficiency of pure water with the improving rate of 37.6%, 47.2% and 64.8% which the mass percent was 1%, 2% and 5%, respectively. Other potassium salt additives followed the order by: K2C2O4>CH3COOK>KNO3>KCl>KH2PO4, and the reason attributed to the different active substances decomposed from flame temperature by different kinds of potassium salt additives. Thermoanalysis and characterization of the pyrolysis products of potassium salt solutions at flame temperature were analyzed through TG-DSC, XRD, and SEM, the results showed the KOH was the main product in the high extinguishing performance of potassium salts in flame chemical reactions. Thermodynamics analysis by HSC CHEMISTRY showed the K2CO3 could provide 4.85% KOH in equilibrium substances, which well above other potassium salts, and other active substances good for fire extinguishing benefited from the intermediate product during the process of the KOH reacted with the flame free radicals.

Physical scaling of water mist fire extinguishment in industrial machinery enclosures

Froude-based scaling relationships had previously been theoretically extended to, and experimentally validated in the laboratory for, water mist suppression of fires in open environment and in enclosures, which were shown applicable to gas, liquid and solid combustible fires. Before applying these relationships to real-world settings, their applicability needs to be further evaluated for the intended protection. This paper presents such an evaluation on scaling water mist fire extinguishment in an industrial machinery enclosure. In this evaluation exercise, a full-scale water mist protection set-up tested for a 260-m3 machinery enclosure was selected as the benchmark. A ½-scale machinery enclosure test replica was then constructed, together with a ½-scale nozzle whose orifices were geometrically similar to those of the full-scale nozzle. Spray measurements indicated that the ½-scale spray closely met the scaling requirements, in terms of discharge K-factor, water mist flux, droplet velocity and droplet size distribution. Two spray fires and one pool fire, which were scaled with the respective full-scale fires, were used to challenge the water mist protection in the ½-scale enclosure. At least five replicated tests were conducted for each of the four tested fire scenarios. Overall, the instantaneous local gas temperature and oxygen concentration measured inside the ½-scale enclosure for each fire scenario agreed reasonably well with those measured at the corresponding locations inside the full-scale enclosure, meeting Froude modeling's requirement that scalar quantities be preserved in different scales. The fire extinguishment times obtained from the ½-scale tests for each fire scenario were also statistically consistent with that observed in the corresponding full-scale test. Based on the obtained results, it is concluded that, for machinery enclosures and other similar occupancies, the previously laboratory-validated scaling relationships for water mist fire suppression can be used to determine the fire extinguishing performance of a full-scale water mist protection in a ½-scale test facility.

Improvement of Fire Extinguishing Performance by Decentralized Supply of Fire-Fighting Agents

One of the central problems in fire safety science and technology is to reduce damage caused by both fires and fire-fighting processes. This paper provides a potential solution to the problem, and it derives from decentralization of fire-fighting agents. In particular, this paper investigates fire extinguishing performance when a fire-fighting agent is supplied to a fire from one direction with one extinguisher and from two directions with two extinguishers. The two methods are called the centralized supply and the decentralized supply, respectively, in this paper. It is demonstrated that the decentralized supply reduces damage caused by both fires and fire-fighting processes. This follows from the facts that fire extinguishment by the decentralized supply is more certain than the centralized supply, and that the decentralized supply requires less total amount of a fire-fighting agent than the centralized supply for fire extinguishment.

A study on the fire extinguishing characteristics of deep-seated fires using the scale model experiment

NFPA 18 is used as a standard for the performance evaluation of wetting agents used in fire fighting. The performance evaluation of the wetting agent involves three tests: a wood crib fire test, a deep-seated fire test, and a wood fiberboard penetration test. In this study, a scale model experimental device, which can evaluate both extinguishing performance and penetration performance at once, was prepared to evaluate the performance of a wetting agent in various types of porous materials. Then, this result was compared with the results of an NFPA 18 test to validate the result of the novel test. Three types of commercial fire-fighting solutions and water were used as extinguishing agents in the experiment. The experimental materials used in this performance evaluation were wood crib which is used in the existing class A fire test and wood flour from New Zealand pine trees which has 75% of the domestic market share in wood cribs. The discrimination of the study result used in this study to determine penetration and extinguishing performances was found to be equivalent to the results of the NFPA18 test. Moreover, the study established the validity of the scale model that could check on both penetration and extinguishing performance, permitting a more economical and efficient performance evaluation of wetting agents.