Vapor Cloud Explosion Research Articles

Safety Issues of a Hydrogen Refueling Station and a Prediction for an Overpressure Reduction by a Barrier Using OpenFOAM Software for an SRI Explosion Test in an Open Space

Safety issues arising from a hydrogen explosion accident in Korea are discussed herein. In order to increase the safety of hydrogen refueling stations (HRSs), the Korea Gas Safety Corporation (KGS) decided to install a damage-mitigation wall, also referred to as a barrier, around the storage tanks at the HRSs after evaluating the consequences of hypothetical hydrogen explosion accidents based on the characteristics of each HRS. To propose a new regulation related to the barrier installation at the HRSs, which can ensure a proper separation distance between the HRS and its surrounding protected facilities in a complex city, KGS planned to test various barrier models under hypothetical hydrogen explosion accidents to develop a standard model of the barrier. A numerical simulation to investigate the effect of the recommended barrier during hypothetical hydrogen explosion accidents in the HRS will be performed before installing the barrier at the HRSs. A computational fluid dynamic (CFD) code based on the open-source software OpenFOAM will be developed for the numerical simulation of various accident scenarios. As the first step in the development of the CFD code, we conducted a hydrogen vapor cloud explosion test with a barrier in an open space, which was conducted by the Stanford Research Institute (SRI), using the modified XiFoam solver in OpenFOAM-v1912. A vapor cloud explosion (VCE) accident may occur due to the leakage of gaseous hydrogen or liquefied hydrogen owing to a failure of piping connected to the storage tank in an HRS. The analysis results using the modified XiFoam predicted the peak overpressure variation from the near field to the far field of the explosion site through the barrier with an error range of approximately ±30% if a proper analysis methodology including the proper mesh distribution in the grid model is chosen. In addition, we applied the proposed analysis methodology using the modified XiFoam to barrier shapes that varied from that used in the test to investigate its applicability to predict peak overpressure variations with various barrier shapes. Through the application analysis, we concluded that the proposed analysis methodology is sufficient for evaluating the safety effect of the barrier, which will be recommended through experimental research, during VCE accidents at the HRSs.

Study on vapour dispersion and explosion from compressed hydrogen spill: Risk assessment on a hydrogen plant

Hydrogen produced from renewable resources is one of the cleanest fuels and could be used to store intermittent solar, wind and other energies. The main concern about using hydrogen is its hazards, such as high storage pressure, wide-range flammability, low mass density, and high diffusion. This study investigated the hazards of compressed hydrogen storage by developing a CFD model to understand the gas dispersion behaviour. The model was validated using the past experimental data and showed a good agreement, which could demonstrate the diffusion characteristics and gas stratification of a buoyant gas. A case study of an accidental release of compressed hydrogen from a storage tank was investigated to evaluate the risk of a hydrogen plant. A mathematical model of the jet spill was used to account for the choking effect from a high-pressure release to ensure the input velocity in CFD simulation is suitable for modelling gas dispersion using verified spatial and temporal scales, then the simulation results were used as inputs of vapour cloud explosions (VCEs) to investigate the potential overpressure effect. It was found the CFD model could predict a more reasonable flammable gas amount in cloud than using the bulk hydrogen release rate. The safety distance based on the overpressure prediction was reduced by 35%. The method proposed in this study can provide more validity for the consequence analysis as part of risk assessment.

Numerical Simulation of Chemical Storage Tank Area Leakage and Explosion Accident Based on FLACS

The large amount of oil storage tank possesses significant risks of leakage, and once leakage occurs, the combustible gas is prone to fire and explosion accidents. When the combustible gas cloud is exposed to the ignition source, there are possibilities of triggering the domino effect with more serious consequences. As one important kind of protective layers, the combustible gas detectors continuously monitor the leakage of combustible gas, guaranteeing the safety performance of the site. Using the computational fluid dynamics software FLACS as a tool, the impact of the consequences of the raw material leakage with a vapor cloud explosion accident in a large chemical fiber manufacturer's storage tank area is studied, and the risk of domino effect in the tank area during the course of the accident is predicted. The study shows that FLACS can be applied to the simulation study of gas diffusion explosion phenomenon in complex operation and storage areas, with the great capability of the explosion risk quantitative assessment and the reliable prediction to the risk of domino effects.

A Review of Safety Issues and Risk Assessment of Industrial Ammonia Refrigeration System

Several industries like cold storage and ice plants heavily rely on ammonia (NH3) due to its low cost, excellent thermophysical traits, and zero effects on the ozone layer. Despite its widespread use as a refrigerant, the hazardous nature of ammonia remains a significant health concern. Since the industrial revolution, ammonia leakage has led to numerous major accidents, including fire and vapor cloud explosions. This paper reviews the safety issues and the current practices of risk assessment with regard to the industrial ammonia used in refrigeration systems. In addition, previous works related to the risk analysis of ammonia-based industries are reviewed. The majority of ammonia refrigeration system-related works applied the traditional static tools for risk analysis such as fault tree, event tree, and bow-tie that are not suitable to handle common causes of failures or conditional dependencies, which are absolutely significant aspects for a reliable safety assessment. Thus, it is vital to maintain and improve the safety levels of diverse industries using ammonia-based refrigeration systems. Various characteristics of ammonia-based refrigeration systems and their safety issues related to industry, present development, and future trends are comprehensively underscored. This review may act as a guide to develop a better understanding of dealing effectively with the hazards of ammonia-based refrigeration systems and risk assessment, thus enhancing the overall safety of humans and the environment.

Firewater fuel tank integrity under blast loads from vapor cloud explosions

AbstractMany firewater systems employ diesel fuel pumps that require nearby diesel storage tanks. If a flammable release and subsequent vapor cloud explosion (VCE) occurs near a firewater pumping station, it is important to understand the impact that the blast load will have on the fuel tanks. This presentation describes an evaluation of the blast response of 350‐gal diesel fuel tanks 80% filled with water to simulate a nearly full diesel tank. The tanks were elevated 6 ft above grade. The deflagration load generator (DLG) test rig was used to impose blast loads of 1–10 psig and 50–180 psi‐ms on a 3 × 3 fuel tank array. Each row of three tanks was rotated to different orientations with respect to the blast load: parallel (face‐on), 45°, and 90° (side‐on). Pressure gauges and high‐speed video recorded the blast loads and dynamic response of the fuel tanks. The results indicate that, depending on orientation and blast load, the tank support structures may undergo plastic deformation and translate in space during loading, although the tanks were still functional post‐test under the blast loads imposed in these tests. A limited comparison between response predictions made using finite element analysis and the test data is provided.

Study on the characteristic of boiling expansion process of superheated LPG and its vapor cloud explosion

Liquefied Petroleum Gas (LPG) is stored in liquid form under high pressure conditions. Once the tank fails, LPG will leak in gaseous form hundreds of times its liquid volume. LPG inside the storage tank will undergo a violent boiling process leading to pressure rebound in the tank. In serious cases, boiling liquid expanding vapor explosion (BLEVE) will happen. And the leaking LPG will mix with air to form a flammable vapor cloud that can explode. Therefore, it is necessary to study the violent boiling process inside the LPG vessel after rupture, the leakage diffusion process in the surrounding environment and the vapor cloud explosion process. In this paper, CFD software FLUENT was used to conduct numerical simulation of the inter-phase transfer of mass and heat inside the vessel when LPG leakage happens, and the transient pressure inside the vessel was analyzed. The results obtained from the simulation are in good agreement with the experimental data under the same conditions which provides the validity verification of the phase transition during boiling process of LPG. A three-dimensional numerical model of LPG release process after the failure of a cylindrical vessel was established. The realizable k-ε model and eddy-dissipation model were used to simulate the explosion process of LPG after the release. The pressure, temperature and thermal radiation distribution of the explosion flow field were obtained so the damage range of LPG after explosion can be analyzed, which has certain guiding significance for the risk assessment of LPG.

Numerical modelling of wind-influenced above sea gas dispersion and explosion risk analysis due to subsea gas release on multileveled offshore platform

Above-sea gas dispersion due to subsea release could lead to explosion on nearby offshore facility. Less congested single-deck offshore platform has been considered in past for numerical modelling of above-sea gas dispersion and deflagration. Offshore platforms are designed compactly and comprise of multiple decks due to space restrictions. The approaching flammable gas may disperse differently at each deck, and high overpressures could develop in event of explosion in confined decks causing severe damages. Therefore, investigating effect of above-sea gas release and dispersion and resulting vapour cloud explosion on equipment damage and human fatality in complex multi-deck platform is worth investigating. This paper presents above-sea gas dispersion and explosion modelling on realistic multileveled fixed offshore platform under varying wind speeds using FLACS. Simplified steps are provided to model gas release from large area sea surface gas pool along with atmospheric dispersion and subsequent explosion in FLACS. It was found that generally, lower decks had near-stoichiometry concentrations thus being most susceptible to explosion consequences. High wind speed increased flammable cloud accumulation, where 50-60% of decks were filled at 3m/s wind speed whereas 100% filled under 7m/s. It is suggested to have adequate ventilation on lower platform decks specially under high wind circumstances to avoid possible explosion hazard due to cloud accumulation. Congested and confined regions with low flammable concentration produced more overpressure than the areas with same concentration but no or low congestion and confinement. Stoichiometric concentration together with congestion produced incredibly high localised overpressure reaching 3.55-4 barg. The probability of equipment damage and human fatality was reaching 1 for explosions at base and deck 2 under 7 m/s wind speed. Since roof was open, the probability of equipment damage and human fatality was least.

Quantitative Risk Analysis on Rail Transportation of Hazardous Materials

The hazardous nature of the chemical materials is of significant concern in the economic viability of rail transportation globally. The potential risks of these materials to cause severe health impairments and catastrophic accidents have been widely studied and reported. Moreover, several models have been employed for assessing the risks associated with transporting hazardous materials by rail. However, a more holistic, quantitative, and robust model should incorporate more potential risk-triggered criteria, especially those causing severe health loss and devastating consequences like vapor cloud explosion. This study develops a risk assessment model by incorporating potential health risk factors and the obstacle circumstances. The potential risk factors are population density, route distance from residential areas, and the availability of sensitive third parties for health consequences. The proposed model utilizes Bayesian networks for causality modeling of the material release scenarios and fuzzy set theory for estimating the health effects and severity impact coefficient. Finally, individual risk curves and safe distances from the railway are developed. A real rail system for gasoline transportation in Tehran is investigated to evaluate the model’s effectiveness. The study provides panoramic leverages for risk-managed decision-making for safely transporting hazardous material by rail.

CFD implementation to mitigate the LNG leakage consequences: A review of explosion accident calculation on LNG-fueled ships

Liquefied Natural Gas (LNG) has a significant benefit in reducing air pollutants such as sulfur oxide, nitrogen oxide, and particulate matter emitted by Diesel Oil or Heavy Fuel Oil. The International Maritime Organization (IMO) regulates these pollutants in MARPOL Protocol Annex VI. It was implemented by establishing an Emission Control Area (ECA) in 2010 that restricts exhaust gas of ships. This regulation has resulted in new shipbuilding orders or conversions to adopt the LNG-fueled systems. Besides the benefits of LNG fuel, storing, transporting, and distributing this fuel has a different problem with conventional fuels. LNG is volatile, and it has a low flashpoint that could lead to spontaneous ignition. To assess the safety and mitigation for LNG-powered ships, Computational Fluid Dynamics (CFD), such as Kameleon Fire Ex (KFX) and Flame Acceleration Simulator (FLACS), is considered to simulate the LNG release. This technical measure is taken to observe the possible damage or loss due to the cryogenic effect, the extreme temperature of the jet fire, or Vapor Cloud Explosion (VCE). These consequences could happen sequentially that known as the “Domino Effect”. The effect of the leak and environment-related parameters could influence the severity of the damage. The applications of CFD for the LNG release cases are discussed and highlighted in this review.

Layout optimization for safety evaluation on LNG-fueled ship under an accidental fuel release using mixed-integer nonlinear programming

The Liquefied Natural Gas (LNG)-fueled ship is an alternative solution to deal with the Emission Control Area (ECA) issued by the International Maritime Organization (IMO). LNG fuel has eco-green characteristics since sulfur oxide and particulate matter are eliminated. The equipment sitting on the Fuel Gas Supply System (FGSS) layout needs a good arrangement to prevent the domino effect. This study’s scopes are to establish the feasible FGSS layout based on the equipment position and conduct an accidental LNG release that adopts the Computational Fluid Dynamics (CFD). Mixed-Integer Nonlinear Programming (MINLP) is provided as an optimization tool. The MINLP framework is written in the Python programming language. The minimum separation distance, deck size, and non-overlapping functions of equipment are included as the MINLP constraint. The separation distances are provided based on the Center of Chemical Process Safety (CCPS) recommendation. Also, several options of the separation distance are added that consist of 5.0, 6.0, and 7.0 m to observe the congestion effect. The total pipe length is considered as the MINLP objective that can be used to estimate the pipe cost. The proposed MINLP framework is designated to generate a feasible layout that has an adequate separation distance and minimum cost of the pipe. CFD results show that the increase of separation distance can reduce the gas accumulation effectively which eventually reduces the severity of other consequences. Finally, the feasible layout is proposed based on a series of several consequences under an accidental LNG release, such as gas dispersion, fire, and vapor cloud explosion.

Cause analysis and damage mechanism of explosive destruction with case investigation involving LPG tank trailer

Identifying causations and failure analysis at the onset holds a key to ensure LPG (liquefied petroleum gas) tank trailer transport safety state and prevent similar failures. Current study presents an unexpected accident by LPG tank trailer, which triggered a massive LPG dispersion and destructive explosion. After the post-accidental scene reconstruction by computational approach, the occurrence of pressurized tank burst and continuous dispersion were detected as an active failure analysis. Macroscopic investigation of the explosion phenomenon involving LPG tank trailer suggested that the causation was responsible for vapor cloud explosion. Hazardous parameters regarding the LPG release, dispersion, explosion shock wave and thermal radiation were represented to identify the mechanisms of potential damages by obtaining at multi-directional area. The visual graphics of flammable gaseous mixtures dispersion showed that the ambient factors imposed great influence on explosive energy reserve in different areas, which were not in accordance with the actual accident scene. The results revealed that the reflected and disturbed effects significantly increased the shock wave, causing more severe structural damage with dense obstacles and elevated flame. A large amount of released gaseous mixtures accumulated, resulting in much higher thermal intensity formed by fireball. This study proposed a failure analysis and classifications of LPG tank trailer accident by explosive destruction integrated with damage mechanism, which contributes to improve the hazard identifications and emergency response under LPG transportation accident sequences.

A risk assessment framework considering uncertainty for corrosion-induced natural gas pipeline accidents

Corrosion degradation is one of the main causations of natural gas pipeline failure, which poses a severe threat to human life, assets, and the environment. This paper develops a methodology to assess the risk of corrosion-induced natural gas pipeline accidents considering the uncertainties in incident escalations. This approach can capture both the uncertainties in corrosion failure likelihood and the impact of pipeline leak accidents. A pair of limit state functions are established to estimate the corrosion failure probability of the pipeline. The pipeline accident from gas release to vapor cloud explosion (VCE) is modelled using empirical models. Subsequently, the uncertainties in gas pipeline corrosion failure accidents, reflected by some uncertain parameters, e.g., basic pipeline parameters, corrosion defect and environmental conditions et al., are identified. These identified parameters are discretized and described using a set of probability density functions. Eventually, Monte Carlo (MC) method is utilized to solve the established models. Besides, sensitivity analysis is conducted to study the effect of uncertain parameters on the likelihood and impact of a pipeline accident. A practical case is used to test the methodology, proving a valuable tool for risk assessment of corrosion-induced natural gas pipeline accidents.

Improvement of Charge Strength Guideline for Multi-Energy Method by Comparing Vapor Cloud Explosion Cases

Improvement of Charge Strength Guideline for Multi-Energy Method by Comparing Vapor Cloud Explosion Cases

Study on Overpressure Propagation Law of Vapor Cloud Explosion under Different Building Layouts.

To determine and optimize the emergency evacuation path of personnel in the case of vapor cloud explosion caused by pipeline leakage and improve the safety control measures in the high-consequence areas of gas pipelines, this study was conducted. This work mainly studied two questions: whether various research methods applicable to the solid explosive explosion are also applicable to vapor cloud explosion and the influence of different building layouts on the overpressure propagation law of vapor cloud explosion. First, the applicability of several empirical models and computational fluid dynamics (CFD) methods in vapor cloud explosion overpressure prediction is systematically compared and analyzed. Second, the finite element models based on the fluid–structure interaction are established to study the overpressure propagation law under the influence of different building layouts. Finally, based on the overpressure propagation law, the determination and optimization principle of the emergency evacuation path of personnel when an accident occurs are given. The results show that the CFD method and empirical model based on equivalent assumption between trinitrotoluene and combustible gas are not suitable for the study of gas-phase explosion, while the mixed gas method based on CFD is more suitable for exploring the overpressure problem of vapor cloud explosion. Buildings arranged perpendicular to the direction of blast wave have the most obvious enhancement and weakening effect on overpressure, and the maximum increase rate and decrease rate are about 90%. The maximum increase rate of overpressure between two vertical layout buildings is more than 60% higher than that between two horizontal layout buildings. When determining the emergency evacuation path, the non-explosive side of the building perpendicular to the shock wave layout should be given priority. If it is necessary to pass through the building gap, the gap between the two horizontal layout buildings should be preferred to ensure that the damage of overpressure to personnel is minimized. The research results can provide a theoretical basis for the improvement of personnel safety control measures in high-consequence areas of the gas pipeline.

Vapor cloud explosions in various types of confined environments: CFD analysis and model validation

In the current work, three different types of vapor cloud explosion experiments are simulated. The purpose of the simulations is twofold: firstly, to evaluate a recently developed CFD model and secondly to analyze the involved phenomena with the help of the simulation results. The proposed model, which has been implemented in the ADREA-HF CFD code, utilizes the RANS method using the Kato and Launder modification of k-e model. Combustion is modelled by taking into account the main mechanisms that contribute to the phenomenon such as chemistry, turbulence generated from the obstacles in front of the flame front, flame instabilities and turbulence generated by the flame-front itself. The CFD model is evaluated against different types of explosions in different geometries and with various fuels. Uniform premixed fuel-air mixture is considered in all cases. A large scale vented deflagration experiment in a 10 m length enclosure is firstly simulated using methane as fuel. The external explosion effect is apparent in this case. Then, a hydrogen deflagration experiment in a 78.5 m tunnel is simulated. Four mock-up cars are placed in the premixed region. Finally, propane and methane explosions inside a 1.5 m tube with obstacles and intense turbulence are simulated. Two different obstacle configurations are studied. The model predicts the overpressure values satisfactorily in all the examined cases. The factors that contribute to the pressure rise in each stage of each experiment are discussed based on the simulation results.

Investigation and modeling of the LPG tank truck accident in Wenling, China

In this study, the liquefied petroleum gas (LPG) accident in Wenling, Zhejiang Province, China, on June 13, 2020, was analyzed and simulated. An LPG tank truck overturned and collided with the concrete guardrail; the subsequent explosion of the tank released 25.36 t LPG. Shortly afterward, the LPG tank was shot into the air, and the gas cloud ignited, thereby triggering a fire and vapor cloud explosion (VCE). This accident killed 20 people, injured 175 people, and caused significant property loss. The accident timeline was established based on multiple accident images, and the accident process was discussed in detail. The distribution of tank debris, evaporation and spreading of the LPG pool, dispersion of the LPG gas cloud, and VCE were simulated with the EFFECTS and ALOHA software. The images of the accident scene helped to determine and analyze the accident process. In the particular case in which a tank is shot into the air with a continuous two-phase jet, the actual flight distance of the tank is much greater than the prediction of the debris distribution model. The gas cloud distribution simulated with the SLAB model approximately corresponds to a major part of the severely damaged zone. In this accident, the TNO multi-energy method and ALOHA provide relatively consistent predictions with the actual building damage distribution when models use a specific confined explosive mass.

COMPARED: A solvent vapor explosion in Germany and a combustible dust explosion in the United States

AbstractCombustible dust explosions and gas/vapor explosions have many features in common—but there are important differences. We take the opportunity to look at two recent industrial explosions and explore the similarities and the differences between solvent vapor and dust cloud explosions as a means of improving our understanding of both dust and vapor explosions.

How to Determine the Dangerous Potential of Accidents to Domino Effect Detonation in a Hydrocarbon Processing Area?

The crude oil industry has been developed in recent decades due to the uses of this product, as well as its derivatives. One of the worst consequences phenomena that can occur in the process industry is the called domino effect. The domino effect or cascade effect occurs when an initiating event, such as a pool of fire or a vapor cloud explosion, causes a new number of accidents. Moreover, due to the importance of avoiding this phenomenon, the European Commission considers the domino effect analysis as mandatory for industrial facilities. There are methodologies in the specialized literature focused on quantifying the existing risks in the storage and processing of hydrocarbons. However, there is a tendency to develop new procedures that increase the risk perception of these accidents. In addition, it is necessary to develop a method that allows visualizing clearly and concisely the dangerous potential of fire and explosion accidents for the occurrence of the domino effect. Precisely, this research aims to predict the dangerous potential of fire and explosion accidents for the occurrence of the domino effect. For this purpose, a methodology consisting of three fundamental stages is developed. Finally, hydrocarbon storage and processing area is selected to apply the proposed methodology. Overall, the development of graphs that summarize information and show the dangerous potential regarding the escalation of fire and explosion accidents is vital in risk analysis. For the case study, the effectiveness of the same was demonstrated, since after its realization it was possible to increase the risk awareness of workers, technicians, and managers of the area taken as a case study.

Procedure for determining design accidental loads in liquified-natural-gas-fuelled ships under explosion using a computational-fluid-dynamics-based simulation approach

ABSTRACT Liquefied natural gas (LNG)-fuelled ships provide a good option for the air pollution problem. However, safety and reliability have to investigate in the design process. A hypothetical LNG-fuelled ship model is used as the target ship. The gas explosion parameters include the gas cloud volume for determining the gas cloud size and the gas cloud centre of gravity for specifying the gas cloud position and ignition point. Previously reported gas dispersion results are utilised to establish these parameters regarding both frequency and physical data. The Latin hypercube sampling is used to generate 50 gas explosion scenarios. The blast overpressure of vapour cloud explosion (VCE) is simulated by the ExSim computational fluid dynamics (CFD) code, and software validation is provided. Finally, the gas explosion frequency can be compiled with blast overpressure to produce the exceedance frequency diagram. Subsequently, this diagram can be used to determine the design accidental loads under VCE.

Evaluation protocols for flammable and toxic dispersion models

AbstractThe siting of liquefied natural gas (LNG) facilities requires several types of hazards to be quantified so that the risk to the public and public property in areas surrounding each facility can be properly assessed. In order to quantify the hazards from potential accident scenarios, computational tools must be used. Given the multiplicity of tools available, ranging from empirical models to 3D computational fluid dynamics packages, the agency responsible for reviewing the hazard analysis may not have the methodologies or protocols necessary to determine the suitability of a given model to a certain scenario, its accuracy, and any other setup requirements. The Pipeline and Hazardous Materials Safety Administration (PHMSA) commissioned Blue Engineering and Consulting and the Gas Technology Institute to develop a set of model evaluation protocols (MEPs) that will allow the review of modeling tools for several different hazards, including flammable and toxic dispersion, source terms for dispersion models, vapor cloud explosions, and boiling liquid expanding vapor explosions (BLEVEs). The project will provide PHMSA with the means to properly evaluate modeling tools for these hazards, which are required to be evaluated in an LNG facility siting study. It will also provide clarity to LNG plant developers and their safety consultants on which models may be used and which safety factors need to be applied, and will increase the public's confidence in the regulatory review process of LNG facilities. This article discusses the first two MEPs completed as part of this project, which are focused on evaluating flammable dispersion and toxic dispersion models, respectively. This article describes the evaluation methodology, including the information to be submitted by the model proponents and the review process, and the model validation databases compiled for each protocol.