Explosion Protection Research Articles

Study on the Mechanism of Sparks Generated Mechanical Friction

In the field of explosion protection, measures must be taken to prevent ignition sources due to mechanical friction and impact. One of the most dangerous sources of ignition in methane-air mixtures is sparks, which are easily induced by friction and impact from light metals. In general, sparks and hot surfaces are coexistent in the friction processes of metal contacts. The questions are whether sparks are a truly effective ignition source and whether the nature of materials plays a decisive role in the ignition ability of sparks. Therefore, this research focuses on the temperature of hot surfaces and sparks generated by friction between pure copper, Q235A steel, and TC4 titanium alloy and the grinding wheel. The effect of the relative rotating speed on the friction temperature and friction spark characteristics is investigated. The result indicates that friction sparks are indeed easier to detonate gas than hot surfaces. Moreover, a mathematical model based on the heat transfer theory is used to prove that the sparks induced by friction from TC4 alloys are more hazardous than those induced by friction from copper and Q235A steel. The factors affecting the energy released by sparks are listed in the formula.

Testing of models of explosion protection system for highvoltage oil-filled electrical equipment

Explosions of high voltage oil-filled electrical equipment (OFEE) lead to a significant material damage. These explosions occur under action of an arc discharge (AD) which arises after internal short circuit. Modernization of OFEE design and protection systems is the possible way to achieve significant reduction of potential explosion and substantial reduction of material losses. Examination of perspective explosion-proof OFEE designs and new explosion protection systems demands the effective test methods. In present work results of development and application of an arcless source of pulse pressure (ASPP) are described. In ASPP the testing impulse is produced by the jet of powder gases (JPG) which arises at the combustion of explosive materials. In this work results of experimental researches of AD in transformer oil (TO) at conditions typical for AD initial stage have been presented: current rise time was 3-5 ms, the maximum arc current was up to 30 kA, AD burning time was 3-20 ms. The energy released in AD amounted to 0.1 MJ. It was established, that electric field strength in AD column was about 0.2 kV/сm, gas producing factor in AD was 110 l/MJ, growth rate of pressure in TO was about 0.3 MPa/ms. These results allowed to create an ASPP with demanded parameters. Experiments proved that TO flow under action of AD and JPG are similar given that the same influence duration of the energy released in AD is equalled enthalpy of JPG at liquid inlet. In this work the transformer fracturing behavior after explosion has been analyzed; and the requirements for protection systems have been formulated. By means of ASPP the breadboard model tests of two well-known OFEE explosion protection methods were carried out. In the first method it is assumed that the protection is reached due to fast dump of pressure inside of OFEE case when special membranes are opened. In the second protection method it is offered to establish porous coverings on internal surfaces of OFEE cases. Experiments were carried out on OFEE model with the characteristic size of 1 m at action energy up to 1.5 MJ. It was shown, that these systems cannot protect the transformer body from significant damages. The dynamic protection system of transformer (DPS) has been described. The efficiency of this new system using ASPP has been verified in experiments with autotransformer of 25 MW. It was shown that DPS protects the transformer from considerable damages at least at dynamic impulse of about 3 MJ.

Explosion behavior of methane-air mixtures and Rayleigh-Taylor instability in the explosion process near the flammability limits

Methane is the main component of natural gas and biogas, and it has been applied in various fields in daily life and industrial production. A better understanding of the explosion behavior of methane mixture can contribute to the safe usage of this fuel and developing advanced explosion protection technology and devices. The main purpose of this study is to investigate the explosion behavior and the Rayleigh-Taylor (RT) instability in the explosion process of methane-air mixtures using a 20 L bomb. Overpressure trajectories and flame images using high-speed schlieren technique are recorded for each experiment. Explosion behavior of methane-air mixtures is investigated at 280 K covering wide equivalence ratios (0.61–1.42) and initial pressures (50 kPa ∼ 250 kPa). By analyzing the explosion image data, flame speed and laminar burning velocity are then calculated. Results indicate that as initial pressure rises, the maximum explosion pressure increases, while the flame speed and the laminar burning velocity decrease. The effect of initial pressure and equivalence ratio (Ф) on the spherical flame is also presented and analyzed through the combination of image data and pressure data. It is suggested that mass of reactants per unit volume and fuel composition have a strong relationship to ignition feasibility and ignition delay time. When Ф is 1.42 and the initial pressure is less than 150 kPa, the dynamic ignition process is recorded. Fores (pressure gradient, density gradient) are generated at the position of the flame front due to combustion. The density of spherical flame zone (burned zone) is lower than the unburned zone, therefore the spherical flame moves upward. The moving density stratification of the flame surface changes the structure of the flame front, which induces the RT instability. Near the flammability limits (Ф = 0.61 or 1.42), the explosion pressure is weak and flame speed is slow (∼0.4 m/s). Due to the longer duration of forces, the effect of forces on the spherical flame becomes apparent. It is found that the RT instability leads to structural instability of the flame.

Fireball and flame venting comparisons: Test data, CFD simulations, and industry standard prediction

Baker Engineering and Risk Consultants, Inc. (BakerRisk®) has performed vented deflagration testing of congested enclosures over a range of configurations, congestion levels, and fuels. This paper provides a comparison of the measured flame jetting distances to predictions made applying standard methods commonly used to calculate the associated hazard zone. These methods include the National Fire Protection Association Standard on Explosion Protection by Deflagration Venting (NFPA 68 (National Fire Protection Association, 2018, )), the British Standard's Gas Explosion Venting Protective Systems (EN 14994 (British Standard EN 14994, 2007)), and a computational fluid dynamics (CFD) analysis.Nine test series were carried out using BakerRisk's Deflagration Load Generator (DLG) test rig. The DLG is a rectangular steel enclosure measuring 48-feet wide × 24-feet deep × 12-feet tall, yielding a total volume of 13,800 ft3 (391 m3), and is enclosed by three solid steel walls, a roof, and floor. The rig vents through one of the long walls (i.e., 48-foot × 12-foot). The venting face was sealed with a 6-mil (0.15 mm) thick plastic vapor barrier for these tests to allow for the formation of the desired fuel air-mixture throughout the rig. Both slightly hyper-stoichiometric propane and lean hydrogen mixtures have been tested in the DLG. Congestion was provided by an array of vertical cylinders. A range of congestion levels and fill fractions were tested. DLG testing was performed with and without vent panels present.Flame jetting distances from the venting face of the DLG were measured using high-speed video. Flame jetting distances were predicted using the Fireball Dimensions calculation from NFPA 68 and the Flame Effects calculation from EN 14994. Blind (i.e., pre-test) simulations were also performed using the FLACS CFD code (Gexcon, 2014). The flame jetting distance in the CFD simulation was determined as the horizontal distance from the DLG vent to the location where the gas temperature dropped below a specified value; the predicted distance for the fuel concentration to drop below half the lower flammability limit (LFL) was also evaluated to assess jetting distance.

Comparative Study on the Damage Effects in the Deflagration Process of Typical Liquid Propellants

AbstractTo study the damage effects caused by accidental deflagration of liquid propellants during production, storage, transportation and use, the information of the deflagration processes and the shock wave hazards of three typical liquid propellants under external flame stimulation were obtained by a high‐speed camera and a shock wave pressure acquisition system. Additionally, in the same situation, the highest temperature of the surface fireball and the law of fireball of the thermal radiation were also studied by an infrared thermal imager and heat flux test system. High‐speed video results showed that the fireball of DT‐3 developed most violently of the three liquid propellants; anhydrous hydrazine took the second place and metallized gelled MMH was the weakest. The average TNT equivalents of 18 kg anhydrous hydrazine, 18 kg DT‐3, 120 kg anhydrous hydrazine and 120 kg DT‐3 were 0.724, 0.629, 0.000375 and 0.0293 respectively. The peak values of thermal radiation flux were in the order of DT‐3>anhydrous hydrazine>metallized gelled methylhydrazine. The corresponding death radius in the accident was supposed to be 20–30 m. Experimental results indicated that package design pressure of liquid propellant had a significant effect on the intensity of the reaction response to the action of flame stimulation. Within a certain range, the package design pressure of liquid propellant should be appropriately reduced to improve its security in storage and use. The study provided a theoretical guidance for the explosion protection of liquid propellant in case of accidental deflagration.

Hydrogen explosions in sprinkler systems

AbstractThis study analyzes the cause of two explosions that occurred during maintenance on a sprinkler system to examine the risk of such an explosion. In both incidences, the explosion occurred after the system was drained into the water‐collecting tank and shortly after the work began. Sprinkler systems in Korea generally use galvanized pipes to prevent corrosion and extend their lifetime. Zinc is the most common element used as a coating material. Although such a system is not usually perceived as dangerous, our study shows that it can contribute to a build‐up of hazardous factors, which ultimately can lead to accidents. As a common metal oxidation reaction, zinc produces hydrogen gas while oxidizing within the water‐filled pipes. Such hydrogen gas can become explosive when stagnating inside the water‐collecting tank as the sprinkler pipes are drained. In both explosion cases, the automatic water level control system of the water‐collecting tank is suspected to have acted as an ignition source for hydrogen gas explosion by electrical contact. By understanding these two cases, we can provide better safety standards for explosion protection for sprinkler systems that are already installed in buildings and those that will be installed in the future.

Problems of Explosion Protection at Oil аnd Gas Facilitiesin the Russian Federation

The fundamental problems of statutory and technical regulation of oil and gas facilities explosion safety in Russia are considered. The main tasks that need to be solved by companies operating facilities with explosive zones to ensure safety are identified.

Study on explosion resistance process simulation and blast fracture failure of Ti[sbnd]6Al[sbnd]4V titanium alloy sheet

The application of high-strength and high-toughness titanium alloy in armour protection is increasing with its excellent properties. However, there is little research on titanium alloy in explosion protection, especially the dynamic response process under localised explosion load and finite element simulation of the explosion resistance process of titanium alloy sheet. In this paper, the deformation and fracture failure features of the 1.6 mm thick Ti6Al4V titanium alloy sheet during the blast loading process were studied by combining LS-DYNA finite element simulation and air explosion experiments. The error of the overpressure peak value of explosion shock wave between the value obtained by improved theoretical empirical formula calculation of cylindrical charge and the value obtained by numerical simulation is only 0.2%. By studying the influence of explosive shape and air domain mesh size on the overpressure value in the process of detonation wave propagation, the Structured Arbitrary Lagrangian-Eulerian (S-ALE) algorithm was selected for finite element simulation. When the air domain mesh size is 1 mm, the tensile failure criterion was introduced into the finite element simulation process. The results show that the numerical simulation results of the full-scale model and the test results were consistent. The destruction morphology of the target showed severe asymmetry. Under 50 g TNT blast load, the 1.6 mm thick Ti6Al4V titanium alloy target was damaged seriously, and the central area of the target was completely torn. The failure features were mainly petal-shaped warping tearing cracks and localised plastic deformation. The tensile stress is the main stress mode of the target failure. Therefore, dynamic tensile strength should be used as one of the selection criteria for explosion-resistant titanium alloy sheets. The target failure mode is dominated by adiabatic shear fracture.

Numerical simulations of trajectories of shock wave triple points in near-ground explosions of TNT charges

To accurately predict the locations and trajectories of shock wave triple points in near-ground explosions, this study determined the propagation law of shock waves after the initiation of a detonator using a schlieren system. Moreover, it established a numerical simulation model using the Autodyn software and verified the accuracy of the model through a detonator explosion experiment. The propagation law of shock waves of TNT charges (1, 10 ​kg and 100 ​kg) at different heights of burst(0.5, 1.0, 1.5, 2.0 ​m,and 2.5 ​m) was studied through numerical simulations, and the triple point trajectories were fitted to an empirical formula. The results show that the maximum simulation error relative to the schlieren images of detonator explosions did not exceed 4 ​mm. As the scaled height of burst decreased, the positions of generated triple points were closer to the vertical projection of the explosion center and rose faster. As the scaled distance increased, the scaled height of triple points rose exponentially. The average error of triple point trajectories between the values predicted in this study and the experimental values was 4.1%, indicating that the accuracy of the fitted formula is acceptable. This study revealed the overpressure distribution law of shock waves and will provide a reference for shock wave overpressure measurements and explosion protection.

Refueling of LH2 Aircraft—Assessment of Turnaround Procedures and Aircraft Design Implication

Green liquid hydrogen (LH2) could play an essential role as a zero-carbon aircraft fuel to reach long-term sustainable aviation. Excluding challenges such as electrolysis, transportation and use of renewable energy in setting up hydrogen (H2) fuel infrastructure, this paper investigates the interface between refueling systems and aircraft, and the impacts on fuel distribution at the airport. Furthermore, it provides an overview of key technology design decisions for LH2 refueling procedures and their effects on the turnaround times as well as on aircraft design. Based on a comparison to Jet A-1 refueling, new LH2 refueling procedures are described and evaluated. Process steps under consideration are connecting/disconnecting, purging, chill-down, and refueling. The actual refueling flow of LH2 is limited to a simplified Reynolds term of v · d = 2.35 m2/s. A mass flow rate of 20 kg/s is reached with an inner hose diameter of 152.4 mm. The previous and subsequent processes (without refueling) require 9 min with purging and 6 min without purging. For the assessment of impacts on LH2 aircraft operation, process changes on the level of ground support equipment are compared to current procedures with Jet A-1. The technical challenges at the airport for refueling trucks as well as pipeline systems and dispensers are presented. In addition to the technological solutions, explosion protection as applicable safety regulations are analyzed, and the overall refueling process is validated. The thermodynamic properties of LH2 as a real, compressible fluid are considered to derive implications for airport-side infrastructure. The advantages and disadvantages of a subcooled liquid are evaluated, and cost impacts are elaborated. Behind the airport storage tank, LH2 must be cooled to at least 19K to prevent two-phase phenomena and a mass flow reduction during distribution. Implications on LH2 aircraft design are investigated by understanding the thermodynamic properties, including calculation methods for the aircraft tank volume, and problems such as cavitation and two-phase flows. In conclusion, the work presented shows that LH2 refueling procedure is feasible, compliant with the applicable explosion protection standards and hence does not impact the turnaround procedure. A turnaround time comparison shows that refueling with LH2 in most cases takes less time than with Jet A-1. The turnaround at the airport can be performed by a fuel truck or a pipeline dispenser system without generating direct losses, i.e., venting to the atmosphere.

Modeling of turbulent deflagration behaviors of premixed hydrogen-air in closed space with obstacles

The propagation of premixed hydrogen-air deflagration flames in a closed duct with different shapes of obstacles was investigated using large eddy simulation (LES). The turbulent flame wrinkling factor in the LES subgrid turbulent combustion model is dynamically modeled based on Charlette's power-law model. The LES results obtained by the dynamic flame surface density (DFSD) model can accurately match the experimental data quantitatively and qualitatively. Numerical results show that the triangular obstacle induces a higher peak overpressure, 7% and 30% higher than that in the square and circle, respectively. The formation of juxtaposed tulip flames is discovered, and the topological analysis of the velocity vector field reveals that the vortex at the tail of the obstacle is the main inducing factor for its formation. Additionally, the Karlovitz number is used to quantify the degree of turbulence-flame interaction, and the transition of deflagration flame from "wrinkled flame" to "thin reaction zone" is observed. The research helps to understand the mechanism of deflagration flame propagation induced by obstacles and provides critical information for safety planning and explosion protection.

A fuzzy multi-objective optimisation model of risk-based gas detector placement methodology for explosion protection in oil and gas facilities

A flammable gas detection system is one of the critical control strategies of catastrophic events such as fire and explosion. While gas detector technology has improved significantly, adopting a methodology for optimal placement of gas detectors is still an issue, especially when integrated with a risk-based approach. An enhancement of a risk-based approach is proposed to optimise the placement of flammable gas detectors by integrating a formulation of fuzzy multi-objective mixed-integer linear programming with the goal of minimising the residual risk and total number of detectors for effective explosion protection. The proposed methodology primarily begins with the identification of critical leak scenarios that require detection followed by the prediction of a targeted gas cloud and dispersion analysis using a computational fluid dynamic model. Risk analysis is conducted to identify high risk areas that need flammable gas detectors protection, which is the input for the mathematical model. The proposed risk-based model was tested using a case study involving a natural gas liquids (NGL) recovery unit, and the results were compared to a published greedy algorithm (GA) formulation. By using mixed-integer linear programming (MILP) formulation, the number of detectors needed are lower with higher risk reductions compared to the GA formulation. Additionally, a sensitivity analysis was performed to determine the proposed model’s response to parameter variations.

25 JAHRE ZONENEINTEILUNG IN DEN USA

n the area of explosion protection, the publication of Article 505 in the 1996 National Electrical Code (NEC®) was seen as a giant step toward global harmonization. It allowed for the implementation of the Zone system for explosive gas atmospheres (gases, flammable liquid-produced vapors, and combustible liquid-produced vapors) in the United States to co-exist with the traditional North American Class/Division system.

Оценка эффективности способов обеспечения пожаровзрывобезопасности транспорта на водородном топливе

PURPOSE. The paper examines the issue of switching to hydrogen as motor fuel in terms of fire and explosion safety. Taking into account the peculiarities of various hydrogen storage methods, the specifics of emergency situations development and insufficiency of the existing methods of passive and active fire and explosion protection for vehicles running on the given gas are discussed. METHODS. Analysis of available scientific data on hydrogen as motor fuel storage methods used in transport has been carried out. An assessment of the possibility to use a nitrogen fire engine for the described options for ensuring explosion safety has been made. FINDINGS. The insufficiency of existing methods for passive and active fire and explosion protection of vehicles running on hydrogen has been shown. To solve the identified issues, it is proposed to use a nitrogen fire engine to create local gaseous extinguishing environment around a hydrogen-powered damaged vehicle, as well as portable toximeters to control atmosphere explosion risk. RESEARCH APPLICATION FIELD. The results are applicable to ensure fire and explosion safety of vehicles and transport infrastructure. CONCLUSIONS. It is shown that the existing methods of passive and active fire and explosion protection for hydrogen-powered vehicles do not fully ensure their fire and explosion safety. In fire departments tactics in relation to such objects, actions under the threat of explosive hydrogen-air environment have not been worked out, there are no methods of mobile assessment for hydrogen level in the atmosphere. One of the options for ensuring explosion safety of hydrogen-air environment can be using a nitrogen fire engine to create local gaseous extinguishing environment around a hydrogen-powered damaged vehicle. Portable toximeters can be used to quickly determine hydrogen level in the atmosphere, which allow getting quick results and controlling potential environment hazard by combustible substance concentration.

Blast Resistance of 240 mm Building Wall Coated with Polyurea Elastomer.

Enhancing the blast resistance of building walls is a research hotspot in the field of anti-terrorism and explosion protection. In this study, numerical simulation and experimental verification were combined to analyze the failure phenomenon of brick masonry wall and sprayed polyurea-reinforced brick wall under contact explosion and determine the failure response parameters of the wall. The failure limit, mode, and mechanism of a 240 mm wall without reinforcement and strengthened with polyurea elastomer under different strength loads were investigated. Under contact explosion, the increase in the size of the blasting pit of the 240 mm wall gradually slowed down after the dose was increased to higher than 0.5 kg. Thereafter, the energy of the explosive load was released by splashing wall fragments as well as by deflecting and movement of the wall. The results show that the 240 mm walls sprayed with polyurea elastomer had outstanding anti-explosion performance because it wraps the damaged area and fragments of masonry wall inside the polyurea layer. When the thickness of the polyurea layer increases to 8 mm, the damaged area of the masonry wall decreases by 55.6% compared with that without reinforcement. The numerical simulation results were in good agreement with the experimental results.

Maintenance of on-premise test equipment for high quality tests

The use of equipment in areas where flammable substances may be released requires explosion protection for them. Explosion protection must be confirmed in the certification process, which in addition to assessment also requires testing. The tests to which equipment must be subjected to confirm explosion protection are regulated by specific standards, depending on the type of protection adopted. This paper focuses on the issues involved in ensuring the quality of test results for low current equipment. For the quality assurance of test results the required aspects are: proficiency testing, use of certified reference materials, repetition of tests using the same methods, retesting of retained items, correlation of test results for different characteristics of a product and control chart where applicable. Another important aspect is the conditions of use and operating condition of the equipment. Thus, maintenance, periodic inspection and interim checks of laboratory equipment are an essential part of ensuring the quality of results. An important conclusion of the work is that the important aspect for quality assurance of test results is proficiency testing, which confirms not only the suitability of the equipment used but also the conformity of the test procedures.

Particular aspects of the tests for ignition of small components

The use of flammable substances in the industry means that the installations that process them generate explosion hazard zones in the proximal space. Equipment installed and operated in such hazardous areas must not ignite an explosive atmosphere. Confirmation of how equipment is adapted for use in an explosive atmosphere is named explosion protection. Explosion protection is confirmed by testing together with evaluation. For low-current equipment, the situation in which the hazardous atmosphere can be ignited by small components should be considered. The first part of the paper was devoted to the presentation of the explosion hazard and a brief presentation of the classification of equipment intended for use in explosive atmospheres. In the second part, the test methodology for ignition from small components is presented and in the last part, the results of ignition tests from small components are presented. The resulting main conclusion underlines the importance of test conditions.

Evaluation of equipment used in Ex atmospheres - interdisciplinary field

The risk of explosion becomes significant when, in the industrial field, flammable substances such as gases, vapours, mists, dusts, lint and fibres may be present. If they are present in sufficient quantity, the risk of explosion is imminent. On the other hand, the measure of shutting down the technical equipment, in the context of the presence of explosive atmospheres, is not an acceptable measure in all situations. As examples are the parts of installations that have safety functions: ventilation installations, installations for monitoring the concentration of flammable substances and other safety parameters. Explosion protection of technical equipment shall be evaluated and tested in order to validate it. The testing process of the technical equipment for the purpose of explosion protection certification is situated at the confluence of several engineering fields: mechanical, electrical, chemical, etc. The first part of the paper deals with the risk of explosion and presents the explosion protection of the technical equipment. The systematized presentation of the technical equipment tests is performed in the second part of the paper. Among the conclusions it is mentioned that although the field of tests in explosion atmospheres is an interdisciplinary one, its coherence is ensured by the specific standards.

Explosion risk assessment for already installed equipment

The equipment of installations for the processing, transport or storage of flammable substances which may generate an explosive atmosphere, in or around them, must be assessed in terms of the risk of explosions, both when they are put into operation or when the installation is modified and periodically for verify that the initial level of protection is maintained. The purpose of the assessment is to establish appropriate protective measures to prevent sources of ignition that could initiate explosive atmospheres. Explosion risk assessment is an obligation of the employer who must draw up an explosion protection document, as regulated in GD 1058/2006 transposing European Directive 1999/92/EC. The explosion risk assessment process focuses primarily on the formation of explosive atmospheres and then on the presence and activation of ignition sources. The principle of explosion protection is to reduce the probability of an ignition source occurring at the same time as the explosive atmosphere, to a minimum acceptable level according to the applicable norms and standards. The paper presents some aspects regarding the evaluation of the risk of explosions to already installed equipment, assembled in an installation, depending on the specific conditions.

Explosion prevention and mitigation in plants which process, generate and store combustible dusts

Combustible dusts which are present in workplaces are a significant hazard which cannot be ignored by the plant owners, managers and workers. Combustible dust deflagrations and explosions have caused large numbers of deaths and catastrophic property damages in various industries, ranging from pharmaceutical plants to sugar factories. One may say that dust explosions in process industries always start inside process equipment such as mills, dryers, filters. Such events may occur in any process in which a combustible dust is handled, produced or stored, and can be triggered by any energy source, including static electricity, friction and hot surfaces. For any combustible dust type, several important parameters have to be taken into account when designing and using protective systems: i.e. the ease with which dust clouds ignite and their burning rates, maximum explosion pressure, maximum rate of explosion pressure rise. These parameters vary considerably depending on the dust type, their knowledge being a first step for carrying out a proper explosion risk assessment in installations which circulate combustible dusts. The paper presents the main aspects concerning explosion protection which have to be taken into account when designing protective systems intended to be used in explosive atmospheres generated by combustible dusts and the importance of selecting the proper explosion protection technique.