Limiting Oxygen Concentration Research Articles

Modelling of opposed flame spread over thin electric wires: estimation of flame spread rates and limiting oxygen concentrations

A model of opposed flame spread along thin electric wires is developed to estimate the variation of flame spread rate ( V f ) with oxygen concentrations and oxidiser flow velocity. The length of pyrolysis zone ( L py ) and V f are treated as eigenvalues of the problem, and one-dimensional energy balance equations for the wire core and insulation are formulated to derive their solutions. To obtain a set of steady solutions for L py and V f , the macroscopic energy balance equation for the entire system is calculated from the one-dimensional energy balance equations with appropriate boundary conditions. Since the equations are nonlinear function of L py and V f , multiple solutions appear. The physical meaning of each solution is evaluated based on the deviation of energy from the equilibrium. Comparison of the temperature distribution along the wire with experimental data confirms that the model reproduces well the actual flame spread process. The variation of V f with oxygen concentration shows a C-shaped curve. The upper branch is the stable solution, and the lower branch is the unstable solution and the merging point of two branches correspond to the limit condition for flame spread. Therefore, the model can be used to estimate the limiting oxygen concentration based on the existence of a solution for V f . Furthermore, the variation of V f with oxidiser flow velocity shows O-shaped curve, and it is confirmed that radiative extinction under low flow velocity and blow-off under high flow velocity can also be estimated with the model. Mapping of variations of radiative extinction and blow-off extinction with oxygen concentration reveals the U-shaped flammability diagram. The predicted flame spread limits are in good agreement with the limiting oxygen concentrations measured in both microgravity and normal gravity, demonstrating the validity of using this model to predict flammability characteristics of electric wires under various oxidiser flow velocity.

Explosion characteristics of lithium-ion batteries vent gases containing dimethyl carbonate at elevated temperatures

Dimethyl carbonate (DMC) is a common component of lithium-ion batteries (LIBs) electrolyte, which is vented into the environment along with LIBs thermal runaway vent gases (BVG). This study used different ratios of DMC/BVG mixtures to simulate the combustible components vented from LIBs thermal runaway process. The explosion characteristic parameters of the DMC/BVG mixtures, such as the peak overpressure (Pex), the peak rate of pressure rise ((dp/dt)ex), lower flammability limits (LFL) and limiting oxygen concentrations (LOC), were investigated in an 8-L stainless steel cylindrical explosion vessel. The results indicated that as the percentage of DMC increased, maximum Pex, maximum (dp/dt)ex and LOC of the mixtures increased, while LFL showed a decrease trend. In addition, LFL decreased approximately linearly as increasing the initial temperature. The Britton correlation method can estimate LFL at varying initial temperatures. The research results are helpful to better understand the risk of the mixtures vent from LIBs and provide a reference for the explosion-proof design of LIBs’ transport containers and LIB energy storage stations.

Inertization parameters for alcohols and ketones with nitrogen and carbon dioxide

A flammable fuel/air mixture can be successfully prevented from entering the explosion range of concentration by the addition of an inert gas. This method of inertization is commonly used in industrial plants to keep processes safe. For this purpose, the oxygen concentration in the over-all mixture is often monitored, taking an appropriate safety margin into account. The mixture would not become flammable, independent of the amount of fuel added, while the oxygen content is below the so-called limiting oxygen concentration (LOC). The aim of this paper is to investigate the inertization-related characteristics of the two different inert gases nitrogen (N2) and carbon dioxide (CO2). The LOC of a series of alcohols and ketones was therefore measured. The experimental determination of the LOCs was carried out according to EN 1839 (2017) using the tube method at ambient initial pressure and suitable initial temperature to evaporate the liquid sample. Triangular diagrams, which represent the explosion ranges, were constructed from the results and additional inertization-related parameters derived: the minimum inert gas/air ratio (IAR) and the minimum inert gas/combustible gas ratio (ICR). It is well-known that carbon dioxide exhibits a stronger inerting effect than nitrogen. In agreement, the ratio LOC(CO2)/LOC(N2) was now determined to be a constant value of 1.33 ± 0.04 in the applied temperature range at ambient pressure. In inertization applications, this ratio in future helps to calculate LOC(CO2) from the much more often known LOC(N2).

Comprehensive evaluation of low-temperature oxidation characteristics of low-rank bituminous coal and oil shale

The coexistence of coal and oil shale mining conditions exacerbates the complexity of coal spontaneous combustion (CSC) prevention, so conducting in-depth research on the spontaneous combustion characteristics of coal, oil shale, and their mixed samples is necessary. A programmed heating system simulated the low-temperature oxidation process of bituminous coal and oil shale under different air volumes. It was found that CO concentration, C2H4 concentration, and Graham's fire coefficient (R1, R2) can be used as indicator gases to predict the CSC process. Compared with oil shale and mixed samples, bituminous coal has a higher CO production rate, oxygen consumption rate, heat release intensity, and lower apparent activation energy during the slow oxidation stage. Meanwhile, bituminous coal also has lower peak values of minimum float coal thickness, lower limit oxygen concentration, and maximal air leakage intensity, which means that bituminous coal in the goaf is more prone to oxidation. However, the abundant free hydrogen bonds in oil shale can stabilize the hydrogen-deficient functional groups of bituminous coal, which weakens the oxidation ability of the mixed sample during the accelerated oxidation stage. In addition, the increased air volume fraction increases the oxygen adsorption efficiency of the mixed sample throughout the low-temperature oxidation process, which means that the M70 sample has a higher CSC risk. The results have enriched the research on the spontaneous combustion characteristics of coal, oil shale, and mixed samples, which may strengthen the management and control of CSC in coal and oil shale co-mining mines.

Investigation on the flammability limit and limiting oxygen concentration of propane/propylene mixture at elevated temperature and pressure

With the development of industrial technology, a new process has emerged for the production of acrylic acid using propane as a feedstock. There are few studies on the combustion characteristics of propane/propylene mixtures at elevated temperature and pressure. In this study, a flammability limit test system was used to determine the flammability limit and limiting oxygen concentration of propane and propane/propylene mixture at different initial temperatures (30–120 °C) and pressures (0.1–2 MPa). The results showed that with the increase of initial temperature and pressure, the flammability limit range expanded, and the limiting oxygen concentration reduced. In addition, the flammability limit range of the propane/propylene mixture is greater than that of propane, indicating that the addition of propylene increases the explosion risk. The empirical formula of the experimental gas was fitted to predict the combustion and explosion parameters under different conditions. In addition, the chemical reaction simulation of propane/propylene mixture was also investigated. The results showed that with the propylene ratio increased, the adiabatic flame temperature and adiabatic overpressure increased, the proportion of H-abstraction reaction decreased and the proportion of pyrolysis reaction increased significantly, which promoted the explosive reaction and the increase of explosion temperature.

Application of ISO 4589-4 to determine limiting oxygen concentrations for opposed-flow flame spread over thin electric wires and their comparison with microgravity data

High gas flow velocity oxygen index test, ISO 4589-4, for measuring the limiting oxygen concentration of flat specimens in opposed flow configuration is applied to electric wires and its applicability is examined. Furthermore, data obtained on the ground are compared with those obtained in microgravity to verify the validity of estimating the minimum limiting oxygen concentration from the high gas flow velocity oxygen index test. The wire samples used in this study consist of LDPE and ETFE insulation over metallic cores. The gas flow velocity is varied from 4 to 100 cm/s to obtain the flammability data in wide range of flow velocity. Limiting oxygen concentrations of wire samples are accurately determined by following ISO 4589-4. All samples tested in this study are more flammable under microgravity than normal gravity. It is also confirmed that the relationship between the limiting oxygen concentration acquired on the ground and in microgravity is well connected.

Flame ignition and extinction modelling using infinitely fast chemistry in large eddy simulations of fire-related reacting flows

Large eddy simulations with the use of infinitely fast chemistry, focusing on flame ignition and extinction modelling, are presented within the context of fires. A dynamic approach with respect to turbulence, combustion and radiation modelling is employed in the simulations. Flame ignition is modelled based on an ignition temperature, which varies with the local sub-grid scale strain rate, while flame extinction is modelled based on the concept of a critical flame temperature, which varies with the local mixing time scale. Validation of the approach is made by considering four different experiments, involving both no-extinction and extinction scenarios. Focus is put on the predictive capabilities of the simulations, with respect to different grid sizes, by comparison to experimental data involving both first and second order statistics, and data available in the literature for different grid sizes and for the different fuels considered. The predicted flame temperatures and combustion efficiencies with the proposed approach agree fairly well, both qualitatively and quantitatively, with the experiments and data for the limiting oxygen concentration from the literature.

Flammability of complex hydrocarbon mixtures in air and nitrogen diluted atmosphere at ambient conditions and at elevated pressures

An innovative experimental method was introduced to study flammability limits and limiting oxygen concentration of complex hydrocarbon mixtures simulating crude oil vapour composition. Flammability experiments were conducted in a 10L spherical vessel at 25 °C and initial pressures of 100 kPa, 1100 kPa and 2600 kPa in air with additional nitrogen. Based on the experimental data, applicability of selected empirical methods and two calculated adiabatic flame temperature based methods was validated for ambient initial conditions. The experimental results confirmed relative decrease below 6.5% for lower flammability limit and below 3% for limiting oxygen concentration with increasing pressure within the examined range. The upper flammability limit increased with initial pressure. Vapour-liquid equilibrium was found to be a constraint in the fuel-rich region at elevated pressures to keep the constant initial composition of the vapour phase. At ambient conditions the calculated adiabatic flame temperature based methods were able to approximate the experimental data well. Empirical mixing rules showed accuracy highly dependent on source literature data.

Revealing the role of limiting oxygen concentration test for a wick flame in characterizing the liquid fuel flammability

A two-dimensional numerical model was established to simulate the wick combustion system for determining the limiting oxygen concentration (LOC) of organic solvents, called the wick-LOC method. The ethanol wick flame under forced flow with decreased oxygen concentrations in normal gravity was studied numerically. Three simplified reaction mechanisms, 1-step, 2-step, and quasi-global mechanisms of ethanol were employed in the simulations for comparison with experimental results. The responses of flame height and edge flame standoff distance to the oxygen decrease were analyzed for validation. As the oxygen concentration was reduced to the stability limit of the full flame, the blow-off of the edge flame can be observed. By comparing the simulated LOCs and near-limit stabilized flame structures, the 2-step mechanism can reproduce the wick-LOC well, while the quasi-global mechanism can provide a more detailed flame structure. Further investigation into flame blow-off processes revealed that the reaction rate in fuel-lean conditions is more important for determining the wick-LOC, and the local flow velocities at the flame kernel are almost constant until blow-off occurs. By combining the flame stabilization theory with simulations, the physical meaning of the wick-LOC value can be explained as the oxygen concentration where the local flow velocity can be balanced with critical edge flame speed (more fundamentally, the critical laminar burning velocity) in a certain fuel-lean equivalence ratio. Further applications of the wick-LOC method are expected to examine the simplified reaction mechanisms of other liquid fuels.

Effects of water immersion and pre-oxidation on re-ignition characteristics of non-caking coal

Coal spontaneous combustion (CSC) in waterlogged goafs has become an essential threat to coal mine safety production, so it is necessary to comprehensively and deeply evaluate the re-ignition characteristics of residual coal after water immersion and pre-oxidation. The re-ignition process of non-caking coal under the influence of water immersion and pre-oxidation was tested using a temperature-programmed test system (TPTS), and the spontaneous combustion characteristic parameters and limit characteristic parameters of low-temperature oxidation were calculated. The results show that the spontaneous combustion characteristic parameters such as CO production rate, oxygen consumption rate, and heat release intensity positively correlate with temperature. The minimum float coal thickness and lower limit oxygen concentration show a trend of increasing and then decreasing with the temperature increase, while the maximal air leakage intensity is the opposite. In addition, the expansion of pores and cracks caused by water immersion and pre-oxidation processes and the increase of unstable functional groups promote the oxygen consumption and heat generation of immersed and oxidized coal, which reduces the characteristic temperature, and activation energy, and limit characteristic parameters. Meanwhile, water immersion and pre-oxidation can synergistically accelerate the low-temperature oxidation process of non-caking coal, which significantly increases the CSC risk of coal O140I30 and coal O90I30. The results enrich the research on the characteristics of water immersed and oxidation coals re-ignition, which may be applied to prevent CSC in the future.

Experimental Study on Flammability Limits Behavior of Methane, Ethane, and Propane with Dilution of Nitrogen.

The dilution inerting process of multi-component flammable gaseous mixtures is an important emergency disposal technology that has been widely applied in the explosion-proof field of flammability gases (vapors). In this study, we examined the flammability limits (LFLs and UFLs) of mono and binary alkane mixtures of methane, ethane, and propane when nitrogen is used for dilution inerting. The HY12474B explosion limit test device was used to determine the flammability limits, and the obtained data were compared with the literature data and Chatelier's law. Additionally, the sensitivity coefficient of the chemical reaction chain for LFLs and UFLs of the binary alkane mixtures was analyzed. The minimum inerting concentration (MIC) of methane was found to be sequentially higher than that of ethane and propane when using nitrogen for dilution inerting, and the MIC of the binary alkane mixtures follows the rule of methane/ethane > methane/propane > ethane/propane. Chemical kinetics calculation revealed that the maximum positive sensitivity coefficient of methane/ethane, methane/propane, and ethane/propane are both R5 H + O2 ↔ O + OH, and the reaction with the maximum negative sensitivity coefficients are both R34 H + O2(+M) ↔ HO2(+M) and R43 CH3 + H(+M) ↔ CH4(+M), respectively. The limiting oxygen concentration (LOC) for both mono alkane and binary alkane mixtures ranged between 10 and 13%. The region of the triangular flammability diagram for methane and ethane was greater than the regions for methane/ethane and methane/propane. In contrast, propane had a smaller region compared to other mono alkane or binary alkane mixtures.

Экспериментально-аналитические исследования пожарной опасности материалов, применяемых в оборудовании с обогащенными кислородом средамипри повышенных давлениях, и пути снижения их горючести

Introductio n. Sealed equipment (hereinafter referred to as hermetic chambers) is used in various branches of economy. Atmospheres enriched with oxygen (in some cases under variable pressure conditions) are used. It was shown that the main reason of the fires in the pressurized chambers was the unregulated use of the electrical equipment, as well as combustible substances and materials on the basis of organic compounds included in the materials used in the pressurized chambers. Objective. To find ways to decrease combustibility of materials used in pressurized chambers and to study fire risk parameters of pressurized chambers with high oxygen content and increased pressure. Obje ctives. To determine the boundary conditions of applying materials with increased values of temperature, oxygen content and pressure and analyze the results of experimental studies of combustibility of materials used in sealed chambers. Research met hods. Investigation of the characteristics of the combustion process of non-metallic materials under increased pressure was carried out on an original setup represented by a stainless steel vessel with a height of 750 mm and an inner diameter of 155 mm. A spiral of nichrome wire was used to ignite the sample. The pressure was fixed with a manometer. Results and th eir discussion. As a result of experimental research of fire hazard of construction and construction materials in oxygen-enriched media and under increased pressure the ways of increasing the oxygen concentration limit (OCL) and reduction of combustibility of materials were determined: application of heat-removing surface, incombustible shell; putting inhibitors in their composition and structure; surface treatment with different fire protective compositions and impregnations. When studying the parameters of fire hazard (flame propagation velocity, heat of combustion, autoignition temperature) of materials under the conditions of changes in the composition of nitrogen-oxygen atmosphere and pressure, it was found that the OCL for all materials decreases at higher pressures. Conc lusions. It is found that the limiting oxygen concentration depends on the geometrical dimensions of the sample, as well as on the speed of the gas flow. At higher pressures the OCL for all the materials decreases. The presence of a heat-removing surface also leads to higher OCL, which increases with increasing substrate thickness and decreasing thickness of the material on it. For materials not containing substances that inhibit the combustion reaction, a decrease in the LOC value with an increase in the number of hydrogen atoms in the polymer macromolecule is characteristic.

Experimental investigation of coal particle size on the kinetic properties of coal oxidation and spontaneous combustion limit parameters

Investigating the behavior of coal spontaneous combustion (CSC) is of great significance to the prevention of coal mine fires. and the dangerous area. In this paper, we firstly analyzed the CO concentration variation at different coal sample particle sizes based on the programmed heating experiments, and initially determined the critical temperature (TC) and xerochasy temperature (TX), the two key characteristic temperatures in the CSC process. Afterwards, the three oxidation stages of the coal spontaneous combustion process were divided as per TC and TX, and the apparent activation energy of the corresponding stages was obtained. Conclusively, the variation patterns of the coal spontaneous combustion limit parameters (minimum float coal thickness hmin, upper limit air leakage intensity Qmax and lower limit oxygen concentration cmin) were analyzed. It was found that the smaller the particle size, the greater the CO concentration, oxygen consumption rate and exothermic intensity of the coal samples. An exponential function was fitted between the exothermic intensity and the coal temperature. The apparent activation energy of the oxidation kinetic parameter increases as the coal spontaneously combusts, and is positively correlated with the particle size. This is mainly due to the fact that the larger the particle size, the smaller the contact area between the coal and oxygen and the corresponding reduction in the active material in the coal, resulting in a greater apparent activation energy required for the coal oxygen reaction. Grain size plays a non-negligible role in the spontaneous combustion limit parameters of coal. The smaller the particle size, the smaller the minimum floating coal thickness and the lower oxygen concentration limit, and the greater the upper air leakage intensity. The relationship between coal spontaneous combustion limit parameters and grain size is not only a quadratic function, but also an exponential function. The smaller the grain size of the relict coal in the mining area, the greater the risk of coal spontaneous combustion. The content of this study can provide some support for predicting and preventing the risk of coal spontaneous combustion.

Calculating limiting oxygen concentration of gas mixtures

The limit values for the fuel concentration in the air-flammable fuel mixture are LEL (lower explosive limit) and UEL (upper explosive limit). The addition of an inert component to the fuel / air mixture determines the increase and decrease of the LEL, until no explosion occurs. The maximum oxygen quantity of the non-combustible - air - inert fuel mixture is LOC (limited oxygen concentration), an important safety property. Investigation of a comprehensive set of data on the flammability at high temperature and ambient pressure obtained from documented sources was carried out for systems containing nitrogen, carbon dioxide and water (steam) such as inert ingredients. Determining the LOC for gas mixtures with different ratios requires step-by-step testing. To solve that problem, the author used Lechateler calculation method to calculate LOC for the ratio of gas mixture and compared the results of experimental equipment.

Effects of N2 and CO2 on the flammability of 2,3,3,3-tetrafluoropropene at elevated temperatures

The flammability characteristics of refrigerants are affected by environmental factors, making them prone to flammability and explosion accidents in cooling systems. In this paper, the flammability characteristics of R1234yf–air mixtures with N2 and CO2 were investigated comparatively at temperatures between 20 and 50 °C at 80% relative humidity. The lower and upper flammability limits of R1234yf were measured. The limiting oxygen concentration (LOC), critical flammable ratio (CFR), and critical flammable concentration (CFC) of the R1234yf–air mixtures with inert gases were investigated. The paper developed a linear formula between the flammability limit of R1234yf and the temperature. The changes in CFC with different temperatures were negligible for R1234yf. Furthermore, the mixed refrigerant had both non-flammability and the lowest vapor pressure when the CFR of the R1234yf/CO2 mixture was 2.9. The experimental results were used to propose a new prediction model to estimate the flammability limits of R1234yf. Finally, molecular simulation explained the effect of inert gases on the flammability of R1234yf from a microscopic point of view. The research aimed to provide valid evidence and data for preventing flammable and explosive refrigerant incidents.

Performance Analysis and Optimization of Fuel Tank Ground-Based Washing Inerting on Unmanned Aerial Vehicles

In this study, a ground-based washing inerting (GBWI) method was proposed, and the application of GBWI in the field of fire prevention and explosion suppression of unmanned aerial vehicle (UAV) fuel tanks was studied using a volume of fluid (VOF) two-phase flow model at a given typical flight envelope. The variation in oxygen concentration in tank ullage during flight was calculated considering the entrance of ambient air and the escape of dissolved oxygen from the fuel. The results indicate that the oxygen concentration in the ullage increases with increasing initial oxygen concentration in the ullage and the initial fuel load after GBWI. In the climb and cruise stages, the oxygen concentration in the ullage increases slowly, while in the tactical descent stage, the oxygen concentration in the ullage increases rapidly, easily exceeding the limiting oxygen concentration (LOC) of aviation fuel combustion. To expand the application range of GBWI, an optimization scheme of nitrogen filling protection was proposed so that the GBWI could meet the requirements of an inert tank at different fuel loads and initial oxygen concentrations in the ullage. Compared with a traditional on-board inert gas generation system (OBIGGS), the optimized GBWI method could greatly reduce the fuel compensation loss and improve the maneuverability of UAVs at the same time.

Experimental investigation of methane content on the oxidation characteristics and spontaneous combustion limit parameters of coal

ABSTRACT The methane contained in a coal seam is closely related to the oxidative properties of the coal and serves as an important basis for accurately evaluating the coal spontaneous combustion (CSC) behavior. In this paper, programmed temperature rise experiments were conducted on three coal samples with different methane contents. The sensitivity of oxidation products, olefin products, and their production rates to methane content were investigated. Also, the contribution made by methane content to the characteristic temperature point and CSC limit parameters were qualitatively assessed. When the methane content is 2.7 cm3/g, 4.5 cm3/g, and 6.8 cm3/g, the critical temperatures (CT) are 70°C, 80°C, and 100°C, respectively, and the dry cracking temperatures (DCT) are 100°C, 110°C, and 130°C, respectively. The higher the methane content, the greater the CT and DCT points during coal oxidation, which is because high concentration of methane will inhibit coal oxygen chemical reaction. The methane content is positively correlated with the minimum floating coal thickness (h min) and the lower limit oxygen concentration (C min), while the upper limit air leakage intensity (Q max) decreases with the increasing methane content. Coal samples with high methane content can withstand higher safe float thicknesses and oxygen concentrations and require less air leakage to carry away the heat accumulated by the residual coal in the mining area, making the CSC risk lower.

Opposed-flow flame spread over carbon fiber reinforced plastic with different carbon fiber orientations

Herein, carbon fiber reinforced plastic (CFRP) sheets with different carbon fiber (CF) orientations were combusted in an environment of variable opposed-flow velocity (Vg) and oxygen concentration, and the effects of the CF orientation angle (θ) on the flame spread characteristics were studied. The limiting oxygen concentration increased with θ and linearly decreased with increasing Vg. The flame spread rate (Vf) was the highest when the CF orientation corresponded to the flame spread direction (i.e., θ = 0 deg.) and increased with Vg. Conductive heat transfer sideways became more significant as θ increased, which signifies increased heat loss. Thus, the net heat transfer rates that directly contributed to the flame spread decreased, leading to low flammability and weak flame spread. Vf was calculated using our previous CFRP flame spread model. The calculated Vf was higher than the measured Vf, and the difference between them increased as Vg increased. This is because the flame height (Hf) decreased considerably with increasing Vg, resulting in high heat transfer rate from the flame and high Vf. The Hf model was thus revised based on the dataset of the opposed-flow flame spread tests; then, the calculated Vf agreed well with the measured Vf. The Vf for the buoyant-flow flame spread assuming Vg = 35 cm/s was also calculated using the flame spread model with the original and revised Hf models, and no significant difference was noted between the calculated and measured Vf. Thus, this study succeeded in improving the CFRP flame spread model to deal with both the opposed-flow flame spread and the buoyant-flow flame spread. This revised model will help understand the physics of the flame spread over CFRP sheets and assess the fire risk of CFRP products for fire safety.

Respiratory function under anaesthesia

General anaesthesia can affect every aspect of ventilation. It produces dose dependent depression of control of respiration. Carbon dioxide response curve is shifted to the right. Muscle tone is reduced and the airway can get obstructed. One of the most prominent changes is reduction in functional residual capacity (FRC) with the adoption of supine function and induction of anaesthesia. The closing capacity increases with age. The atelectasis that occurs consequent to the fall in FRC and increasing age is compounded by the use of high concentrations of oxygen, cephalad movement of the diaphragm, residual effect of muscle relaxants and inadequate analgesia after thoracic or abdominal surgery. One of the important causes of ventilation perfusion mismatch during anaesthesia is atelectasis. This has been shown to contribute to hypoxia as well as increased postoperative pulmonary complications. A lot of research is being conducted as to reduce the effects of atelectasis during anaesthesia, including the best ventilator strategy during anaesthesia. Most inhalation anaesthetics are good bronchodilators. Inhalation anaesthetics depress hypoxic pulmonary vasoconstriction (HPV) beyond 1 MAC. The movement of ciliary movements is reduced with the use of dry gases. All these can increase postoperative pulmonary complications which are important causes of postoperative morbidity. Appropriate preoperative preparation has to be combined with optimal management of ventilation intraoperatively to minimise postoperative pulmonary complications. The role of lower tidal volume, use of positive end-expiratory pressure, limiting oxygen concentrations and the utility of recruitment manoeuvres are increasingly being recognised and have been the topics of recent research.

Finding a way through the “misty” evaluation of the flammability and explosivity of kerosene aerosols

• JetA1 mist flammability and explosivity are assessed in a confined explosion vessel. • Influence of initial conditions on explosion sensitivity and severity is studied. • JetA1 mists with a small droplet size have a higher rate of pressure rise. • The MIE of JetA1 mist may be lower than that of vapors at low temperatures. • The vapor/liquid ratio of a mist is a key parameter of its explosion severity. In the context of assessing hydrocarbon mist ignition sensitivity and explosion severity, an original test method is proposed, focusing on kerosene JetA1 mists but is applicable to other hydrocarbons. Experiments were carried out in a modified apparatus based on the 20L explosion sphere. Fine control of the gas/liquid ratio and flow rates, the mist concentration, and the ignition energy and duration, was ensured by a specifically customized control system guaranteeing the flexibility and compliance of the test apparatus. The droplet size distribution (DSD) and the level of turbulence of the JetA1 mist cloud were first determined by an in-situ laser diffraction sensor and by Particle Image Velocimetry, respectively. The lower explosive limit (LEL), the minimum ignition energy (MIE), the limiting oxygen concentration (LOC), the maximum explosion overpressure (P max ), and the maximum rate of pressure rise (dP/dt max ) were then determined for different mist concentrations, ambient temperatures, initial turbulence levels, energies, and DSD. Tests showed that the LEL mist of JetA1 mists of an average diameter of 8 µm is around 94 g/m 3 , a value which increases to 220 g/m 3 with increasing DSD. This value also tends to decrease considerably with increasing temperatures. Moreover, at a JetA1 concentration of 125 g/m 3 , P max and dP/dt max as high as 6 bar and 192 bar/s respectively were reached, the latter increasing to about 480 bar/s at T = 60 °C. These mists were shown to be ignitable using energies as low as 200 mJ, which is lower than that of vapors at low temperatures, and a limiting concentration of oxygen of 15.8 % v/v . The potential presence of hydrocarbon mist should therefore be an element that requires reconsidering the classification of hazardous areas. Finally, to stress the influence of the vapor-liquid ratio present in the cloud before ignition on the combustion kinetics, an evaporation model based on the d 2 -law was developed estimating the evaporation time and the vapor quantity at different initial temperatures or droplet diameters. Findings were shown to be well coherent allowing the proposition of a new technique for determining hydrocarbon mist safety criteria. Finally, results have shown that JetA1 mists can ignite at temperatures below the liquid’s flashpoint under varying turbulence levels and droplet size distributions.