Minimum Ignition Temperature Research Articles

Systematizing risk assessment and responses to combustible dust from explosive characteristics

A systematic approach to defining dust explosion risks is presented, utilizing key parameters: minimum ignition energy (MIE), minimum ignition temperature of dust clouds (MITC), minimum explosion concentration (MEC), maximum explosion overpressure (Pmax), and the dust explosion characteristic index (Kst). These parameters form the basis for robustly assessing combustible dust explosion risks. Drawing on experimental findings, a safety evaluation method empowering plant operators to directly assess the safety of dust-handling processes was devised, ensuring effective dust explosion prevention. Evaluation of three common dust samples (aluminium, polyethene, and lycopodium) revealed varying explosion risks. Through comparative analysis with existing literature, this study aligns risk definitions, proposing a scoring method for process safety controls to effectively mitigate dust cloud explosion risks.

Influence of stearate dry coating on ibuprofen powder: What about the combustibility?

Dust explosion is one common type of process safety incident within the pharmaceutical industry. During powder processing, surface modification is widely used to increase dust flowability by alleviating inter-particle cohesion. However, it is currently unclear whether the addition of guest particles affects the combustibility of pharmaceutical powders. To investigate the explosion hazard of stearate-coated ibuprofen powder, this paper studied the ignition sensitivity and explosion severity of pure and coated ibuprofen by determining a series of explosion parameters in accordance with ASTM standards. The results indicated that the addition of stearate significantly reduced the minimum ignition energy of the mixture. Other parameters including the minimum ignition temperature, the minimum explosible concentration, the maximum explosion pressure, and the maximum rate of pressure rise were found to have less correlation with the improvement in dust flowability. Powder characterization through methods such as the Hausner ratio, scanning electron microscope, thermo-gravimetric analysis, and X-ray diffraction were employed to investigate chemical phase changes between coated mixtures and pure pharmaceuticals. The effects of improved dust flowability and dust dispersibility on the combustibility of ibuprofen dust were discussed to improve explosion-proof awareness in the pharmaceutical industry.

Experimental Study on Evaporation and Ignition Behavior of RP-3 Fuel with Different Leakage Volumes on Hot Surface

ABSTRACT Fire accidents caused by fuel leakage to hot surfaces are of significant concern in the aerospace domain due to their potential for severe consequences. This paper investigates the evaporation and ignition characteristics of fuel leakage to a hot surface through a series of experiments with different volumes of RP-3 droplets. The evolution patterns of evaporation lifetime, ignition position, and ignition delay time are examined. The results show that within the surface temperature range of 500–700°C, the fuel droplets of all volumes almost immediately reach the film boiling state upon contact with the hot surface. The droplets move erratically across the surface, changing shape from irregular to elliptical and finally to spherical. The evaporation lifetime decreases with increasing hot surface temperature. The occurrence of ignition is stochastic, and the ignition probability rises with the hot surface temperature, while the minimum ignition temperature decreases with the increase of fuel volume. The movement of the fuel droplets in the film boiling state leads to the irregularity of the ignition position. Additionally, the ignition delay time decreases with an increase in the temperature of the hot surface. The relationship between ignition delay time and surface temperature in the film boiling state is discussed in the context of the vapor plume model and boiling heat transfer analysis.

Spotting ignition of plastic foam by a fast-moving hot metal particle

Spotting ignition involves dynamic interaction between fuel bed and hot particles, but the scientific understanding of the ignition by a fast-moving hot particle is still limited. Herein, a hot steel particle with various horizontal velocities, temperatures, and sizes is shot to ignite vertically oriented low-density expandable polystyrene foam. A high-speed particle can directly get embedded into the foam to achieve flash-point, fire-point, or no ignition, while a low-speed particle bounces away from the foam without ignition. Results show that for a particle of 1150 °C, its minimum velocity for embedding is 12.00 m/s. Such a critical velocity for hot-particle embedded or ignition slightly decreases as particle temperature increases. Minimum ignition temperature of these high-speed particles is 200 °C higher than that of near-static or with a low free-fall velocity, due to the shorter residence time and insufficient to produce a flammable mixture. Moreover, when the particle is neither too slow to bounce away nor too fast to get embedded, it will be partially embedded on the sample surface to burnout the fuel, posing the biggest fire hazard. It deepens our knowledge of the complex interaction between hot moving particles and insulation foam to reduce spotting fire risk for building façade.

Experimental investigation on the impact of water immersion time and particle size on the ignition characteristics of coal dust

After drying, water-immersed coal is more prone to spontaneous combustion than raw coal. However, the influence mechanisms of particle size and water immersion duration on the physicochemical properties of coal dust, as well as the explosion and fire hazards of water-immersed coal dust, have not been sufficiently investigated. In this study, two particle sizes of coal dust were selected, and experiments were conducted using the Godbert-Greenwald furnace, Hartmann tube, Muffle furnace, and Fourier Transform Infrared Spectrometer. The study investigated the impact of different water immersion times, dust particle sizes, and dust concentrations on the sensitivity of coal dust fires and explosions, analyzed the process of functional group changes in coal dust particles in water and other mechanisms of transformation. The results indicated that the water immersion process increased the number of active functional groups on the surface of coal dust, significantly reducing the Minimum Ignition Temperature (MIT) and Minimum Ignition Energy (MIE) values for different samples, and also enhancing the ignition sensitivity and peak temperature of coal dust layer fires. This study contributes to a deeper understanding of the characteristics of coal dust and is of great significance for improving the prevention and control of coal dust fires and explosions.

Study of the Safety Characteristics of Different Types of Pepper Powder (Capsicum L.)

This research was aimed at comparing the fire characteristics of different types of pepper in the context of explosion prevention. The following characteristics were studied: explosion pressure Pmax and Kst at selected concentrations, ignition temperature of the deposited dust layer from the hot surface, and minimum ignition energy. The comparison of the chemical properties of the used types of pepper was performed using TG/DSC. The results of the measurements suggest that different types of peppers exhibit different explosion characteristics. Each sample reached the maximum value of the explosion pressure and rate of pressure rise at different concentrations. The volume of the explosion chamber used also influenced the explosion characteristics. It is a consequence of the fact that the explosion characteristics strongly depend on the mechanism of action of a particular igniter. The minimum effect on the safety characteristics was observed when measuring the minimum ignition energy and the minimum ignition temperature of the dust layer from the hot surface. The results of the measurements suggest that different types of peppers exhibit different explosion characteristics. This information should then be considered in explosion prevention.

Single-Use Vape Batteries: Investigating Their Potential as Ignition Sources in Waste and Recycling Streams

This study investigates the potential link between the increasing prevalence of single-use vapes (SUVs) and the rising frequency of waste and recycling fires in the UK. Incorrectly discarded Li-ion cells from SUVs can suffer mechanical damage, potentially leading to thermal runaway (TR) depending on the cells’ state of charge (SOC). Industry-standard abuse tests (short-circuit and nail test) and novel impact and crush tests, simulating damage during waste management processes, were conducted on Li-ion cells from two market-leading SUVs. The novel tests created internal short circuits, generating higher temperatures than the short-circuit test required for product safety. The cells in used SUVs had an average SOC ≤ 50% and reached a maximum temperature of 131 °C, below the minimum ignition temperature of common waste materials. The high temperatures were short-lived and had limited heat transfer to adjacent materials. The study concludes that Li-ion cells in used SUVs at ≤50% SOC cannot generate sufficient heat and temperature to ignite common waste and recycling materials. These findings have implications for understanding the fire risk associated with discarded SUVs in waste management facilities.

Experimental study on hydrogen–oxygen spontaneous ignition limits in supercritical water using a wall-cooled reactor

Hydrogen is a promising fuel for many industrial applications because of its carbon-free properties. The characteristics of hydrogen–oxygen reaction in supercritical water were thoroughly investigated using a newly constructed experimental facility. Three typical temperature profiles were obtained, representing different reaction states: mild oxidation, transition state, and intense combustion. The spontaneous ignition limit was mapped based on 42 experimental data points. The minimum ignition temperature decreases with increasing fuel concentration, reaching as low as 517 °C at a hydrogen concentration of 23.2 mol%. The reliability of the spontaneous ignition limit was confirmed by the first hydrogen hydrothermal flame images obtained. The initial reactor temperature and fuel concentration increase allows the hydrogen–oxygen reaction to transition from mild oxidation to intense combustion. The oxygen excess ratio does not affect the reaction states, but it affects the temperature profile and hydrogen conversion efficiency. The introduction of cooling water changes the concentration and temperature of the reactant mixture in the reactor, thus affecting the stability of the hydrothermal flame.

Biomass inertization to increase minimum ignition temperature

In the past years, the use of biomass has significantly increased and, therefore, so has the number of accidents related to its storage, transport, and use. To prevent these accidents, it is essential to properly know their flammability and explosion characteristics so their behaviour can be addressed as a first stop for preventing accidents. The present work studies the inertization with solid inerts of biomass layers and clouds (biomass powder suspended in air) as a possible solution to reduce their ignition tendency. To do so, two biomass samples were studied: wood pellets and dried sewage sludge; mixed with two different inert materials: recycled glass and sodium bicarbonate. In particular, the inert materials were mixed with biomass at three different concentrations (30%, 50% and 70%) and the ignition of the mixtures was studied, determining the minimum ignition temperature of layer and cloud (MITL and MITC) for each mixture, and detecting the needed concentration for avoiding the ignition. Additionally, samples were tested using TGA and DSC techniques to analyse their thermal behaviour and to determine the influence that the inert material has in the energetic power of the biofuel.Different behaviours were observed depending on the different inert materials, showing that not only the amount of inert added is important but also its physico-chemical properties. If the results for a layer and a cloud are compared, it was noticed that inertization effect differs between biomass and test. Regarding TGA and DSC results, it was concluded that smaller percentages of inert material should be considered, as they substantially modify the energetic value.

Research on the inerting mechanism of sucrose dust explosion by sodium bicarbonate

Sucrose dust is prone to explosion accidents during the production process. This research utilized sodium bicarbonate (NaHCO3) to prevent the explosion of sucrose dust. Based on the minimum ignition temperature of sucrose dust cloud (MITc), combined with thermogravimetric analysis-differential scanning calorimetry (TG-DSC) and pyrolysis-gas chromatography-mass spectrometry (PY-GCMS), the differences of combustion processes and combustion products between sucrose dust and sucrose-NaHCO3 mixed dust were comprehensively compared. Also, the mechanisms of sucrose dust explosion and NaHCO3 inerting sucrose dust were systematically studied. It showed that NaHCO3 powder contributed to a higher MITc of sucrose dust and activation energy of sucrose oxidation reaction, with a reduction in exothermic enthalpy and entropy changes. NaHCO3 interfered with the entire burning process of sucrose dust by playing an important role in physical inhibition, and producing sodium-containing compounds to capture free radicals from the bond breakage of sucrose. It limits the reaction pathway and progress of sucrose pyrolysis and therefore against burning. Additionally, the mass fraction and particle size of NaHCO3 impact the inerting ability by increasing the amount and accelerating the procedure rate of products, respectively. The increase in mass fraction works better in macroscopic phenomena, while the decrease in particle size is more significant in reaction kinetics and thermodynamic parameters.

Minimum ignition temperature of gas–liquid two-phase cloud

Minimum ignition temperature of gas–liquid two-phase cloud

Prevention and suppression of coal dust explosion in underground coal mines: Role of rock dust type, particle size, proportion, concentration, and thermal properties

Rock dust inertant is commonly used for prevention and suppression of coal dust explosion in underground coal mines. The effects of rock dust type, proportion, particle size, thermal conductivity, and specific heat capacity on minimum ignition temperature (MIT) of coal-rock dust mixtures and intensity of explosion propagation under different experimental conditions were examined using Godbert-Greenwald furnace integrated with a high-speed camera. MIT of coal-rock dust mixtures significantly increased with increase in rock dust proportion. With decrease in particle size from < 850 to < 75 µm, the mean MIT increased from 616 to 657 °C and 627 to 665 °C for dolomite and limestone dust, respectively. With increase in dust concentration from 500 to 3000 g/m3, the ignition temperature (IT) of coal-rock dust mixtures decreased by 28 % and 30 % for dolomite and limestone dust, respectively. Moreover, the MIT significantly increased with increase in thermal conductivity and specific heat capacity of coal-rock dust mixtures. Limestone dust proved to be a better explosion suppressant compared to dolomite dust.

Prediction of the minimum ignition energy of dust clouds based on heat transfer and particle reaction kinetics

A numerical model for the calculation of the minimum ignition energy (MIE) of dust clouds is developed based on heat transfer and particle reaction kinetics. The model is an update of previous models relying on the experimental minimum ignition temperature (MIT) of dust clouds. Gas and particle temperature profiles during the spark ignition processes are studied in detail to generate dust cloud MIE prediction. For the 20 dusts studied, with the updated model, the average calculated MIE over experimental MIE ratio is 81.6%, a significant improvement compared with the ratio of 48.1% using a previous model with the MIT. A strong correlation is found between the dust cloud MIE and the MIE of the nearest particle to the spark center in the dust cloud: for all the studied dusts, the latter accounts for over 85% of the dust cloud MIE. Moreover, the minimum spark ignition temperature of a dust particle (SITP) can be defined, which also strongly correlates with the dust particle MIT (MITP) calculated using the Semenov theory. Based on these correlations, simple MIE predictive equations are derived and validated by comparing their MIE predictions with the experimental MIE data.

A journey through space and time in the Godbert-Greenwald furnace: The evolution of a dust cloud particle size distribution

Minimum Ignition Temperature (MIT) characterizes the ignition sensibility of a dust cloud. This work assesses the role of a standard Godbert-Greenwald furnace in the agglomeration/deagglomeration and fragmentation phenomena. Several organic powders and different dispersion pressures were tested. The average residence time varied from 120 to 330 ms according to the amount of powder injected and the pulse pressure. Entanglement was observed for coarser cellulose particles, while surface cohesion forces characterised the agglomerates of finer cellulose, glucose and ascorbic acid. The latter was characterised by fragmentation, especially at 0.5 and 1 bar(g). Biot, Pyrolysis and Damköhler numbers were used to analyse the effects of cellulose agglomeration and deagglomeration. At 600 K, the pyrolysis is the rate-limiting step, but from 700 K, the external heat transfer becomes the rate-limiting step, which would not happen without agglomeration. Due to the particle size distribution evolution, but also to turbulence and residence time variation, MIT can vary by 50 °C.

Effect on ignition sensitivity of combustible dust particle size reduction due to dispersion in the 20-L chamber

This work simulates the particle breakage process caused by the dispersion of several typical combustible dusts in a 20-L chamber. Some operations in the process industry that involve gas turbulence and particle interactions can cause dust particles to break, resulting in a decrease in minimum ignition energy (MIE) and minimum ignition temperature (MIT). Particle breakage classification should attempt to correlate changes in D3,2 (Sauter mean diameter) values with the brittleness index. The descending order of particle breakage severity is as follows: ascorbic acid > anthraquinone > tobacco > nicotinic acid > lignite. The percentage decrease in MIE and MIT values is generally proportional to the degree of particle breakage. However, the decrease in MIT values was not as significant as in MIE values. This is because of the various dust-ignition source interaction patterns between a dust cloud and an ignition source.

Influence mechanism of dispersion and agglomeration characteristics of micron/nano carbon dust on its combustion kinetics and explosion process

Due to the widespread use of lithium-ion batteries, evaluations of the flammability and explosive characteristics of carbon dust materials as anodes require attention. Carbon dust often reaches the micron/nano scale, and dust particle state and explosion risk generated in different industrial scenarios are different, which is in urgent need of research. Nanoscale dust has relatively static coagulation properties and shows characteristics of dispersion and reagglomeration under a certain airflow. The particle size characteristics affect its thermodynamic characteristics and various consequence parameters of dust explosion. The oxidation and combustion characteristics are mainly affected by dust particle size distribution characteristics. The apparent activation energy is mainly affected by the proportion of small and medium-sized particles and pre-exponential index factor is mainly affected by the dust overall average particle size and specific surface area. The explosion consequence parameters are affected by the thermodynamic parameters, by the disturbance state, particle distribution degree of dust cloud and other factors, which affect the heat radiation and heat transfer process to some extent resulting in different explosion consequence parameters. Due to the agglomeration characteristics of nano-level dust, the minimum ignition energy and minimum ignition temperature of nano-level dust are generally smaller than that of micron level dust.

Investigation of dust ignition sensitivity and co-pyrolysis properties of biomass and plastic waste during resource utilization

This study investigated the sensitivity of dust to ignition and the co-pyrolysis properties of biomass-plastic composites (BPCs) during resource utilization process. A model of co-pyrolysis process for four BPCs was developed using a BP neural network algorithm. The addition of polyethylene increased the biomass powder's tendency to pyrolyze. In the main pyrolysis stage, the lignin and polyethylene fractions significantly impact the synergistic effect more than the other fractions. Corn stalk/polyethylene and rice husk/polyethylene are synergistic during the pyrolysis process making these BPC products relatively promising for utilization. However, more attention should be paid to the dust explosion hazard posed by the BPCs. PE increases the ignition sensitivity of the biomass powder. Compared to other BPCs, minimum ignition temperature (420 °C) and minimum ignition energy (21 mJ) values for rice husk/polyethylene composites are the lowest. The volatile fraction of biomass content is one of the most influential factors affecting the ignition sensitivity of BPCs.

Flammability and explosion characteristics of softwood dust

In technical terms, wood is a natural composite material with a polymer matrix, reinforced with fibres made of uniaxially oriented longitudinal cells. Due to the ease of obtaining and relatively low technological requirements related to its processing, wood is a common material used for various types of construction materials. An experimental investigation was carried out to determine the evolution of the ignition sensitivity and the explosion of three types of softwood dusts. Two of those dusts come from conifers and one from a deciduous tree. Complete fire characteristic requires several parameters describing wood dust behaviour under fire conditions including heat release rate (HRR), ignition time, or fire growth index. To determine those parameters, a cone calorimeter was used. Explosion characteristic was tested for representative wood as a dust sample in 20-L spherical vessel. Minimum ignition energy (MIE) was tested on MINOR II apparatus, which is a modified Hartman’s tube. Minimum ignition temperatures were tested with the use of layer ignition temperature apparatus and Godbert–Greenwald apparatus for minimum ignition temperature of a dust layer and dust cloud (MIT), respectively. Dust with the highest KST value, lowest MIE in the widest concentration range, and lowest MIT was pine wood dust. It also shows the shortest ignition time and a timespan between ignition and HRR peak.

Experimental Research on Combustion, Pyrolysis Characteristics, and Kinetics of Three Different Coal Samples in China.

Coal thermal and kinetic parameters are important for the design of combustion reactors and risk assessment. Two methods were employed to investigate such key parameters of lignite, bituminous, and anthracite coal samples from China. With thermogravimetry (TG) and differential scanning calorimetry (DSC) methods, two distinct transitional stages were found in all coal samples combustion, but reaction intervals shifted to higher temperatures from lignite to anthracite and varied between 317 and 665 °C depending on the sample nature. Compared to the other two coal types, the pyrolysis of anthracite was less sensitive to increasing temperature, and its combustion process occurred at a much higher temperature. The results indicated that anthracite is difficult to ignite but has a considerable heat of reaction of 22.6 kJ/kg if ignited, which is close to that of bituminous. The basket heating method was used to obtain the kinetic data. Sample activation energies varied in the ranges of 38-51 kJ/mol from TG analysis and 49-67 kJ/mol from basket heating tests. Both results were comparable and consistent with the reference data. Due to its higher activation energy, anthracite poses a lower risk of thermal runaway than other coal types. This conclusion was validated by performing a minimum ignition temperature determination of a dust layer (MITL). In contrast, lignite and bituminous should be handled with greater safety precautions in coal-related process industries. The data presented will be used for hazard analysis and for designing more efficient combustion reactors in power plants. The data collected led to an extension of the current data for coal dust, as found in the literature.

Comparative Analysis of Fire and Explosion Properties of Lycopodium Powder

Lycopodium (L.) clavatum powder, due to its uniform particle size distribution and low equilibrium moisture content, is often used as a reference material and a calibration benchmark for dust combustion and dust explosion studies. The aim of the study was to determine its fire and explosion parameters, compare them to values obtained in the previous literature findings, and assess the appropriateness of using lycopodium powder as a reference material. The research included the determination of minimum ignition temperatures of dust layer and dust clouds, spontaneous ignition behavior, and explosion characteristics of dust clouds including maximum explosion pressure, maximum rate of explosion pressure rise, and the lower explosion limit of the air/dust mixture. The results reveal that the maximum equipment temperature used with lycopodium dust should not exceed 215 °C for dust thickness up to 5 mm. In order to eliminate the risk of lycopodium dust ignition, the temperature of the equipment surfaces that can come into contact with the dust cloud should not exceed 300 °C. In order to prevent explosions, the concentration of lycopodium dust in air should not be greater than 15 g/m3. Based on the obtained results, it can be seen that lycopodium fire and explosion parameters vary slightly, and its usage as a benchmark is considered legitimate.