Suppression of wood dust explosion by ultrafine magnesium hydroxide

Study on Explosion Characteristics and Mechanism of Electrostatic Spray Powder

In order to fully understand the explosion risk of electrostatic spraying powder, corresponding preventive measures are put forward. The explosion characteristics, ignition sensitivity, and flame propagation of three typical electrostatic spraying powders were tested using a 20 L spherical explosion test device, a G-G furnace test device, and a Hartmann tube test device, and the explosion process and mechanism of electrostatic spraying powders were discussed. The results show that the maximum explosion pressure and the maximum explosion pressure rise rate increase first and then decrease with the increase in mass concentration. The maximum explosion pressure and the maximum explosion pressure rise rate of acrylic powder coating are the largest, which are 0.75 and 85.4 MPa/s, respectively. The shortest burning time is 97.5 ms, and the highest explosion danger level is 23.46 MPa·m/s. The flame propagation of electrostatic spraying powder develops slowly; the flame front spreads linearly and the average flame velocity increases first and then decreases. The explosive development process of powder coating particles is concentrated in the three-phase system of solid particles, molten particles, and pyrolytic gasification combustible gas, which goes through the kinetic process of particle heating melting, cross-linking curing, pyrolytic gasification, combustion, and extinction.

Research on the Inhibition Effect of NaCl on the Explosion of Mg-Al Alloy Powder

A study was conducted on the explosion overpressure and flame propagation law of magnesium-aluminum (Mg-Al) alloy powder, and the suppression mechanism of sodium chloride (NaCl) on the explosion of magnesium-aluminum alloy powder was explored. Adding NaCl powder can effectively reduce the explosion pressure, flame front position, and flame propagation speed. The higher the amount of NaCl powder added, the lower the explosion pressure of magnesium-aluminum alloy powder, the slower the flame propagation speed, and the lower the flame brightness. NaCl adsorbed on Mg-Al alloy powder isolated heat transfer and played a cooling role. The Cl- produced by NaCl decomposition will react with the free radicals H+ and OH- in the reaction system, which will reduce the concentration of H+ and OH- in the combustion process and hinder the propagation and expansion of the flame. The research results provide theoretical guidance for the explosion prevention of Mg-Al alloy powder and the preparation of a physical-chemical compound explosion suppressor in the later stage.

Exceptional Performance of Flame-Retardant Polyurethane Foam: The Suppression Effect on Explosion Pressure and Flame Propagation of Methane-Air Premixed Gas

A self-built gas explosion testing platform was used to explore the quenching effect of flame-retardant polyurethane foam on a gas explosion. The effect of the foam's filling position and length on the explosion suppression performance was explored. The results demonstrate that polyurethane foam exhibits an excellent flame-quenching performance, with a minimum of a 5 cm length of porous material being sufficient to completely quench the flame during propagation. Furthermore, the attenuation function of this porous material on the pressure wave is insignificantly affected by the change in ignition energy. Compared with the explosive state of the empty pipeline, the best suppression effect is obtained when the polyurethane foam is 20 cm in length with a filling position at 1.8 m, and the maximum explosion pressure and maximum rise rate are attenuated by 86.2% and 84.7%, respectively. This work has practical significance for the application of porous materials in explosion suppression and explosion-proof technologies in the chemical industrial processing and oil (gas) storage fields.

Combustible wood dust explosions and impacts on environments and health - A review

Wood dust is the major wastes from timber and wood-based panel processing, including wood sawing, sanding, chipping, flaking, etc., which easily causes fire and explosions. The fine wood dust had risks of inhaling the dust air, causing problems to the respiratory system of workers, as well as the explosive risk of the wood dust-air mixture. Wood dust explosions occur worldwide, which have caused massive damages to equipment, buildings, and environments, killed people, and threatened human health. This study was aimed at exploring the causes, affecting factors, mechanisms, models of wood dust explosions, and their environmental/health impacts through reviewing and analyzing the collected data in order to minimize wood dust explosion risks by improving of safety procedures in the wood processing industry. To better understood and prevent wood dust explosion cases in the future, this review collected the explosion reports and analyzed the accident information through the following aspects: 1) Summarization of published review articles regarding wood dust explosions in Introduction, 2) Scrutinization of wood dust explosion cases and design of testing device, 3) Exploration of effects of wood dust properties and surrounding conditions on explosion and their mechanisms, 4) Investigation of methods for reducing wood dust explosion risks, 5) Modeling and simulation of wood dust explosions, 6) Examination of environmental and health impacts of wood dust explosions. Finally, the findings in this review were summarized in Conclusions. By collecting dust explosion reports, reviewing literature, and analyzing the collected data, wood dust explosions can be better understood. The results of this study can be useful for the design of equipment and dust absorption systems, as well as further suggestion of safety improvement procedures to minimize or eliminate risks of wood dust-related fire and explosion in the wood processing industry and mitigate its impacts on environments and health.

Preparation of Nano-Mg(OH)2 and Its Flame Retardant and Antibacterial Modification on Polyethylene Terephthalate Fabrics

The multifunctional polyethylene terephthalate (PET) fabrics were successfully prepared through a dip-coating technology to endow the flame retardant and antibacterial properties of PET fabrics, which are extensively used in many fields. The flame retardant and antibacterial agent was synthesized by a double drop-reverse precipitation method and surface-modified by the mixtures of titanate coupling agents and stearic acid to result in a good compatibility of the hydrophilic nano-Mg(OH)₂ and the hydrophobic PET fabrics. The results indicated that the suitable synthesis conditions of nano-Mg(OH)₂ are: Mg²⁺ concentration 1.5 mg/mL, reaction temperature 50 °C and reaction time 50 min, and the optimal modification conditions of nano-Mg(OH)₂ are: modifier ratio 5/5, modification temperature 70 °C and modification time 40 min. The flame retardant test and the antibacterial test showed that the multifunctional PET fabrics had excellent flame retardant and antibacterial properties.

The Effect of Magnesium Hydroxide Addition on the Extinguishing Efficiency of Sodium Bicarbonate Powders

This article analyzes the possibility of the modification of BC powder (a mixture of sodium bicarbonate and calcium carbonate) with magnesium hydroxide (Mg(OH)₂). Extinguishing efficiency as well as the influence of this additive on other physicochemical properties were determined by performing a 13B fire test, rheological measurements of the powders, thermal tests (thermogravimetry (TG) and differential scanning calorimetry (DSC) in combination with quadrupole mass spectrometry (QMS)) and microscopic observations of the powders’ surface (scanning electron microscope (SEM) with energy dispersive X-ray analysis (EDS)). It was found that the increase of the Mg(OH)₂ content causes deterioration of the rheological properties by increasing the slope angle of the flow curve in relation to the normal stress (the tangent of the flow curve slope varying from 0.258 for 5% of Mg(OH)₂ up to 0.330 for 20% of Mg(OH)₂). However, at the same time, the increased content of Mg(OH)₂ increases the total energy of the chemical decomposition reaction (from −47.27 J/g for 5% of Mg(OH)₂ up to −213.6 J/g for 20% of Mg(OH)₂) resulting in the desirable higher level of heat removal from the fire. The initial extinguishing effect of the fire becomes more effective as the hydroxide content increases (within the first 2 s), but at a later stage (from t = 63 s), the temperature is no longer sufficient (it is below 350 °C) for thermal decomposition of Mg(OH)₂. As such, the optimal content of Mg(OH)₂ is 10–15%. The obtained results allowed for the assessment of the impact of individual powder components on its extinguishing effect and will contribute to the development of science in the field of developing new types of extinguishing powders.

Wood Dust Flammability Analysis by Microscale Combustion Calorimetry

To study the practicability of a micro combustion calorimeter to analyze the calorimetry kinetics of wood, a micro combustion calorimeter with 13 heating rates from 0.1 to 5.5 K/s was used to perform the analysis of 10 kinds of common hardwood and softwood samples. As a microscale combustion measurement method, MCC (microscale combustion calorimetry) can be used to judge the flammability of materials. However, there are two methods for measuring MCC: Method A and Method B. However, there is no uniform standard for the application of combustible MCC methods. In this study, the two MCC standard measurement Methods A and B were employed to check their practicability. With Method A, the maximum specific heat release rate, heat release temperature, and specific heat release of the samples were obtained at different heating rates, while for Method B, the maximum specific combustion rate, combustion temperature and net calorific values of the samples were obtained at different heating rates. The ignition capacity and heat release capacity were then derived and evaluated for all the common hardwood and softwood samples. The results obtained by the two methods have significant differences in the shape of the specific heat release rate curves and the amplitude of the characteristic parameters, which lead to the differences of the derived parameters. A comparison of the specific heat release and the net calorific heat of combustion with the gross caloric values and heating values obtained by bomb calorimetry was also made. The results show that Method B has the potentiality to evaluate the amount of combustion heat release of materials.

Experimental study and mechanism model on the ignition sensitivity of typical organic dust clouds in O2/N2, O2/Ar and O2/CO2 atmospheres

To reveal and improve our understanding of the ignition behavior and mechanism, G-G furnace experiments of three typical organic dusts were performed to investigate the minimum ignition temperature (MIT) in O₂/N₂, O₂/Ar and O₂/CO₂ atmospheres with oxygen mole fraction from 8.4% to 50%. The experimental results were presented in oxygen-lean and oxy-fuel atmospheres to evaluate the ignition sensitivity of dusts in different atmospheres. It was found that CO₂ is the strongest in terms of lowing the ignition sensitivity of the three dusts, and the dust explosion risk increases significantly with increasing O₂ mole fraction for the three dusts through a logarithmically and significantly reducing MIT. However, for different dusts, inert gases show different suppression effects. In addition, a modified steady-state homogeneous ignition model was proposed and successfully applied to oxygen-lean atmospheres, and in oxy-fuel atmospheres, this model has also been improved to estimate the ignition mechanism. This ignition mechanism model could be used to successfully predict the minimum ignition temperature of high volatile dust under different inert atmospheres controlled by homogeneous ignition, which will provide a reference for the ignition hazard assessment of dust on hot surfaces.

Transient reaction process and mechanism of cornstarch/air and CH4/cornstarch/air in a closed container: Quantitative research based on experiments and simulations

Both dust/air explosion and flammable gas/dust/air explosion are common forms of energy release. Experiments and simulation models with a multi-step chemical reaction mechanism were used to study the intensity parameters and mechanism of the CH₄/air explosion, cornstarch/air explosion and CH₄/cornstarch/air explosion in a closed container. Results showed that the peak overpressure, maximum flame temperature, and average flame propagation speed of the stoichiometric CH₄/air explosion reach 0.84 MPa, 2614 K and 3.5 m/s, respectively. The optimal concentration of cornstarch explosion is 750 g/m³, and its peak overpressure, maximum flame temperature and average flame propagation speed are 0.76 MPa, 2098 K and 1.77 m/s, respectively. For a three-components system, adding methane can significantly increase the explosive intensity and combustion performance of cornstarch. The explosive intensity parameters (peak overpressure, maximum flame temperature, average flame propagation speed) of a certain concentration of cornstarch first increase and then decrease with the increase of methane concentration. The maximum explosion intensity parameters of a three-components system with a certain concentration of lean-methane/air are higher than that of single-phase, but always lower than that of the stoichiometric methane/air. Moreover, the mutual coordination of dust and combustible gas in energy release and the mutual competition mechanism in oxygen consumption are described.

An Intelligent Fire-Protection Coating Based on Ammonium Polyphosphate/Epoxy Composites and Laser-Induced Graphene

Fire-protection coatings with a self-monitoring ability play a critical role in safety and security. An intelligent fire-protection coating can protect humans from personal and property damage. In this work, we report the fabrication of a low-cost and facile intelligent fire coating based on a composite of ammonium polyphosphate and epoxy (APP/EP). The composite was processed using laser scribing, which led to a laser-induced graphene (LIG) layer on the APP/EP surface via a photothermal effect. The C–O, C=O, P–O, and N−C bonds in the flame-retardant APP/EP composite were broken during the laser scribing, while the remaining carbon atoms recombined to generate the graphene layer. A proof-of-concept was achieved by demonstrating the use of LIG in supercapacitors, as a temperature sensor, and as a hazard detection device based on the shape memory effect of the APP/EP composite. The intelligent flame protection coating had a high flame retardancy, which increased the time to ignition (TTI) from 21 s to 57 s, and the limiting oxygen index (LOI) value increased to 37%. The total amount of heat and smoke released during combustion was effectively suppressed by ≈ 71.1% and ≈ 74.1%, respectively. The maximum mass-specific supercapacitance could reach 245.6 F·g⁻¹. The additional LIG layer enables applications of the device as a LIG-APP/EP temperature sensor and allows for monitoring of the deformation according to its shape memory effect. The direct laser scribing of graphene from APP/EP in an air atmosphere provides a convenient and practical approach for the fabrication of flame-retardant electronics.

Synergistic Effects of Graphene and Ammonium Polyphosphate Modified with Vinyltrimethoxysilane on the Properties of High-Impact Polystyrene Composites

Ammonium polyphosphate (APP) was modified with a silane coupling agent (vinyltrimethoxysilane, Si-171), and then the synergistic flame retarding effect of graphene and surface-modified APP (APP@Si-171) on high-impact polystyrene (HIPS) was investigated. Surface modification and thermal stability characterization of APP were analyzed by Fourier transform infrared spectroscopy (FTIR), energy dispersive spectrometer (EDS), scanning electron microscopy (SEM) and thermogravimetric analysis (TGA). The results showed that surface-modified APP (APP@Si-171) exhibited significantly better dispersion and less agglomeration tendencies compared with pure APP. A series of target HIPS composites containing different mass fractions of the two flame retardants were prepared by melt blending. TGA and cone calorimeter tests (CCT) were conducted to quantitatively investigate the thermal and flammability properties of the composites, respectively. Results from TGA and CCT demonstrated that the addition of the flame retardants delayed the onset and peak temperatures in differential thermogravimetry (DTG) curves and weakened the peak heat release rate (PHRR) and total heat release (THR). Moreover, the synergistic effect index (SE) was employed to quantify the synergistic behavior between the two fillers, and the results showed that APP@Si-171 and graphene had a synergistic effect on improving the thermal stability and flame retardancy of HIPS.

Investigation on thermokinetic suppression of ammonium polyphosphate on sucrose dust deflagration: Based on flame propagation, thermal decomposition and residue analysis

In this investigation, ammonium polyphosphate (APP) is applied to suppress the deflagration of sucrose dust. Through the systematic research on flame propagation images and temperature, decomposition behavior of powder samples and the compositions of deflagration residue, the suppression performance and mechanism of APP on sucrose deflagration are profoundly summarized. Timing diagrams show that APP contributes to reduce deflagration flame brightness, increases ignition delay time and flame fault area. The minimum inerting concentration of APP for sucrose deflagration is determined to be 8 %. From the collected deflagration flame temperature curves, it is confirmed that APP can delay peak temperature arrival time, weaken temperature fluctuation, and decrease peak values of flame temperature and temperature rising rate. Through the analysis on thermal decomposition of samples and deflagration residue, it is reflected that APP has superior composite suppression effect. It can not only absorb reaction heat, but also decrease deflagration exotherm to improve thermal stability of sucrose particles. Thus, the easily oxidized components in sucrose are protected, and deflagration intensity is effectively weakened. This work provides a new solution for prevention and suppression deflagration of dust waste in sugar industry.

Nacre-like graphene oxide paper bonded with boric acid for fire early-warning sensor

Boric acid-modified graphene oxide (GO-BA) paper is prepared by a green and facile water evaporation-induced self-assembly method, and its application as an early fire-alarm sensor is investigated. The nacre structure is constructed by assembling graphene oxide (GO) and boric acid (BA) as brick and mortar, respectively. Compared with pure GO paper, improved thermal-oxidative stability is obtained for GO-BA. GO nanosheets are bonded with BA molecules by forming hydrogen bonds between hydroxyl in BA and the rich oxygen-containing functional groups on GO. Notably, the insulating GO-BA paper can be rapidly thermally reduced to conductive reduced graphene oxide under flame exposure, thus providing an ideal fire-alarm response with a quick flame-detection time of ∼0.8 s. In addition, boron oxide formed under flame attack covers the surface of GO, inhibiting further oxidation of GO paper, and effectively extending the duration time of GO-BA under combustion. These results indicate that the GO-BA paper prepared has a broad prospect in the field of fire early-alarm.

Dopamine-modified poly(styrene) nanospheres as new high-speed adsorbents for copper-ions having enhanced smoke-toxicity-suppression and flame-retardancy

Polydopamine-coated polystyrene (PS@PDA) nanospheres which are prepared by self-polymerizing of dopamine on the surfaces of polystyrene (PS) nanospheres show excellent Cu²⁺ adsorption capacity. The Cu²⁺ adsorption capacity of PS@PDA can even reach 178 mg/g in about 6 min, which is superior to the other adsorption materials reported in literatures. Through linear fitting, it can be seen that Cu²⁺ is chemisorption covered by multilayers on the surface of PS@PDA, with less affect by temperature. The PS@PDA nanosphere with good adsorption capacity is first applied as the Cu²⁺ adsorbent and then recycled to preparation of PS nanocomposite with enhanced flame retardancy, great smoke and toxic gases suppression properties. To overcome the drawbacks of evaluation methods reported before, a new evaluation system of analytic hierarchy process is first applied to comprehensively analyze fire safety of samples. The average value of smoke production rate of PS@PDA absorbed 5 mg/L Cu²⁺ (PS 2) reduces by about 10%, and the average and total yield of carbon monoxide of PS 2 decrease by 15.7% and 18.1% compared with that of neat PS, respectively. PS 2 with the highest score of 86.75 has the best comprehensive fire safety performance among all samples. This work provides a guideline for green flame-retardant chemistry.

Nacre-biomimetic graphene oxide paper intercalated by phytic acid and its ultrafast fire-alarm application

A novel nacre-like flame-retardant paper based on graphene oxide (GO), and phytic acid (PTA) is fabricated via evaporation-induced self-assembly. This facile method is time saving and low energy consuming. A facile approach is proposed to improve thermal oxidative stability of GO paper by in situ phosphorus doping during flame exposure. Then fire-alarm system is designed based on the high-temperature thermal reduction characteristic of GO. The GO paper functionalized with PTA (GO-PTA) can provide ultrasensitive, reliable and longtime fire early-warning signal. Fire alarm can be triggered at approximately 0.50 s when GO-PTA samples are attacked by fire. Phosphorus atoms are in situ doped into graphene layers during fire exposure, endowing GO-PTA paper with outstanding thermal oxidative stability, and thus alarm duration time of GO is greatly improved. The work develops advanced fire detection and early-warning sensors that provide reliable and continuous signals, which provide more available time for fire evacuation.

Insight into suppression performance and mechanisms of ultrafine powders on wood dust deflagration under equivalent concentration

Flame propagation characteristics of wood dust deflagration and suppression mechanism of ultrafine powders are investigated systematically. The deflagration reaction intensity of wood dust increases firstly and then decreases with the increase in dust cloud concentration. This is due to factors such as oxygen supply, positive feedback among flame characteristic parameters. Thus, there is an equivalent dust concentration for greatest deflagration intensity. Nano-sized ultrafine zirconium hydroxide (Zr(OH)₄) and silicon dioxide (SiO₂) powder are introduced to suppress wood dust deflagration at the equivalent concentration. It is found that Zr(OH)₄ has a suppression effect of endothermic decomposition to generate zirconia (ZrO₂), dilution of oxygen and absorption of free radicals; while SiO₂ exerts suppression effect due to its high melting point and heat absorption. The suppression performance of Zr(OH)₄ is better than that of SiO₂. This is because that Zr(OH)₄ and ZrO₂ have a catalytic carbonization effect. It can not only improve thermal stability of wood particles by catalyzing production of high-temperature resistant residuals, but also promote the formation of catalytic sites to reduce crystallite size of carbon layer on wood particles surface, weakening heat and mass transfer between particles.