Vapor Cloud Explosion Research Articles

Effect of separation distance on gas dispersion and vapor cloud explosion in a storage tank farm determined using computational fluid dynamics

Storage tank separation distance, which considerably affects forestalling and mitigating accident consequences, is principally determined by thermal radiation modeling and meeting industry safety requirements. However, little is known about the influence of separation distance on gas dispersion or gas explosion, which are the most destructive types of accidents in industrial settings. This study evaluated the effect of separation distance on gas dispersion and vapor cloud explosion in a storage tank farm. Experiments were conducted using Flame Acceleration Simulator, an advanced computational fluid dynamics software program. Codes governing the design of separation distances in China and the United States were compared. A series of geometrical models of storage tanks with various separation distances were established. Overall, increasing separation distance led to a substantial reduction in vapor cloud volume and size in most cases. Notably, a 1.0 storage diameter separation distance appeared to be optimal. In terms of vapor cloud explosion, a greater separation distance had a marked effect on mitigating overpressure in gas explosions. Therefore, separation distance merited consideration in the design of storage tanks to prevent gas dispersion and explosion.

Industrial system for mitigation of vapor cloud explosions

The oil industry operates installations and processes with important quantities of flammable substances within a wide range of pressures and temperatures. A particular hazard for this type of installations is an accidental release of a large quantity of flammable material resulting in a devastating vapor cloud explosion.Extensive research was conducted to assess the efficiency of chemicals for inhibition of flames. Especially alkali metal compounds (especially carbonates and bicarbonates of sodium and potassium) have shown to be one of the more efficient flame inhibitor species.In this paper, the principles of flame inhibition by alkali metal compounds are briefly explained. Based on these principles, a practical implementation of an industrial system for chemical inhibition of vapor cloud explosions is discussed. This implementation is based on the use of dry powders of carbonates and bicarbonates of sodium and potassium as flame inhibitor species.The efficiency of the final design of the inhibition system was tested and confirmed on a very large scale in Vapor Cloud Explosion tests in California (US) in September 2016. Several projects in TOTAL were identified in which the VCE inhibition technology is implemented (new cracker units in Daesan (South-Korea) and in Port Arthur (United States)).

Modeling detonation limits for arbitrary non-uniform concentration distributions in fuel–air mixtures

In most scenarios where detonations in fuel–air mixtures can present a hazard, such as in industrial accidents, or where they can be used for practical purposes, like detonative propulsion applications, the mixture is essentially non-uniform. For industrial accidents, it is important to understand what fraction of the mixture can detonate in order to limit the consequences of an explosion event by ensuring proper separation distances to critical facilities and personnel. For propulsion applications, mixture non-uniformities directly affect the performance of the device by limiting the detonable portion of the mixture. While it is known that detonation limits depend on mixture composition, geometry, and concentration gradients, these limits have only been defined for either uniform mixtures, or for detonation propagation in the direction of a smooth concentration gradient. In this study, a model is developed to generalize these classic detonation limits to consider arbitrary concentration distributions and is compared with experimental data for detonation propagation in non-uniform mixtures. The model is then applied to representative concentration distributions corresponding to two practical examples, a high-pressure hydrogen jet and a large-scale vapor cloud explosion (VCE). For both distributions, the model illustrates how a non-uniform mixture composition significantly limits the detonable portion of the flammable mixture created by a realistic release.

Risk assessment of an oil depot using the improved multi-sensor fusion approach based on the cloud model and the belief Jensen-Shannon divergence

At present, enterprises have introduced the Internet of Things (IoT) technology to monitor and evaluate the safety status of oil depots, allowing for the collection of a substantial amount of multi-source monitoring data from factories. However, sensor monitoring data is often inaccurate and fuzzy. To improve the reliability of risk prevention and control based on multi-source sensor data, this study proposed a CM-BJS-DS model based on the cloud model (CM), the Belief Jensen-Shannon (BJS) divergence and Dempster-Shafer(D-S) evidence theory. First, the relevant evaluation factors of the accident and their threshold intervals of different risk levels were determined, and the fuzzy cloud membership functions (FCMFs) corresponding to different risk levels were constructed. Then, the sensor monitoring data were processed using the correlation measurement of the FCMF, and basic probability assignments (BPAs) were generated under the risk assessment frame of discernment. Finally, the BPAs were pre-processed by the improved evidence fusion model and the accident risk level was evaluated. Based on the monitoring data, a case study was performed to assess the risk level of vapor cloud explosion (VCE) accidents due to liquid petroleum gas (LPG) tank leaks. The results show that the proposed method presents the following characteristics: (i) The BPAs were constructed based on the monitoring data, which reduced the subjectivity of the construction process; (ii) Compared with single sensors, the multiple sensor fusion evaluation yielded more specific results; (iii) When dealing with highly conflicting evidence, the evaluation results of the proposed method exhibited a higher belief degree. This method can be used as a decision-making tool to detect potential risks and identify critical risk spots to improve the specificity and efficiency of emergency response.

Influencing factors of the chain effect of spherical gas cloud explosion

Flammable gases and liquids are widely used in industry and have serious leakage hazards. When a leaking gas cloud accidentally encounters an ignition source, it results in vapor cloud explosion accidents and multiple explosions. Pressure and flow field monitoring of a primary exploding spherical gas cloud and the secondary explosion of the gas cloud were conducted using the pressure acquisition system and schlieren system, and the impact of different influencing factors on exploding were analyzed. It was found that the larger the size of the primary exploding gas cloud, the smaller the distance between the primary exploding gas cloud and the secondary explosion gas cloud, and the larger the explosion intensity of the two gas clouds. Ignition on both sides of the primary exploding gas cloud was more likely to cause a blasting effect than was central ignition. The change in sparking ignition energy had no obvious effect on explosion propagation. When multiple gas clouds were exploding, the position of the primary exploding gas cloud had a considerable influence on the chain effect of exploding. If the primary exploding gas cloud was located in the middle of multiple gas clouds, interaction occurred between the primary exploding spherical gas cloud and the secondary explosion gas cloud because the angle formed by the secondary explosion gas cloud decreased, and the explosive intensity of the exploding gas cloud was higher. When the primary exploding gas cloud was on the side, the smaller the angle, the closer the lateral gas cloud was to the flame development path of the explosive gas cloud, which increased the likelihood of a blast and increased explosion intensity.

Investigating Vapour Cloud Explosion Dynamic Fatality Risk on Offshore Platforms by Using a Grid-Based Framework

The reliability of petroleum offshore platform systems affects human safety and well-being; hence, it should be considered in plant design and operation in order to determine its effect on human fatality risk. Methane Vapour Cloud Explosions (VCE) in offshore platforms are known to be one of the fatal potential accidents that can be attributed to failure in plant safety systems. Traditional Quantitative Risk Analysis (QRA) lacks in providing microlevel risk assessment studies and are unable to update risk with the passage of time. This study proposes a grid-based dynamic risk analysis framework for analysing the effect of VCEs on the risk of human fatality in an offshore platform. Flame Acceleration Simulator (FLACS), which is a Computational Fluid Dynamics (CFD) software, is used to model VCEs, taking into account different wind and leakage conditions. To estimate the dynamic risk, Bayesian Inference (BI) is utilised using Accident Sequence Precursor (ASP) data. The proposed framework offers the advantage of facilitating microlevel risk analysis by utilising a grid-based approach and providing grid-by-grid risk mapping. Increasing the wind speed (from 3 to 7 m/s) resulted in maximum increase of 21% in risk values. Furthermore, the integration of BI with FLACS in the grid-based framework effectively estimates risk as a function of time and space; the dynamic risk analysis revealed up to 68% increase in human fatality risk recorded from year one to year five.

The myth of episodic deflagration in large, unconfined vapor clouds

AbstractReports and reviews issued by the Health and Safety Executive (HSE) have a wide‐ranging influence that extends well beyond the United Kingdom. One such recent document, RR1113 Review of Vapor Cloud Explosion Incidents, discusses explosions arising from the ignition of large vapor clouds. The report proposes a mechanism called “Episodic Deflagration” which has been proposed as an alternative to Deflagration to Detonation Transition (DDT). Here, we examine the concept and the assumptions behind this mechanism in detail. We examine fundamentals purported to characterize this mechanism such as the so‐called cumulative build‐up of pressure over time, an assumed stationary flame state and the radiant heating mechanism proposed as the basis for this postulated phenomenon. We show that the concept is fundamentally flawed and built on unrealistic assumptions, leading to the conclusion that this phenomenon should be ignored.

Study on Risk Evaluation of Acetochlor Production Process

To scientifically evaluate the danger of acetochlor production process, this article identifies and analyzes dangerous and harmful factors in a company’s factory from dangerous and hazardous substances, equipment, and places, etc, fire, leakage and explosion are the main risk factors of the plant. Taking the ethanol storage tank leakage in the storage area as an example, the FLUENT software was used to simulate the leakage of ethanol, and it was found that the leakage outlet emitted a concentration of more than 8% and migrated to the windward side, which was extremely prone to vapor cloud explosion. Then, the TNT equivalent explosion model was used to calculate that the vapor cloud explosion may cause the death radius, severe injury radius, and minor injury radius to reach 57.27m, 138.39m, and 252.21m. At the same time, the radius of explosion damage under other overpressures was calculated. Based on this, suggestions for targeted safety countermeasures can be provided, which can provide a reference for accident prevention and emergency treatment.

Mechanisms of vapor cloud explosion and its chain reaction induced by an explosion venting flame

This experimental study focused on vapor cloud explosion and its chain reaction induced by an explosion venting flame. Two vapor clouds were installed in front of the explosion venting container along the horizontal direction. Explosion flame evolution process was recorded by a high-speed camera and a schlieren system. Pressure sensors at different locations were used to acquire the pressure data. The temperature data were collected by a high-speed infrared thermal imager and three thermocouples. The changes in flame propagation characteristics, flame temperature, and pressure distribution were determined, and the mechanisms of the vapor cloud explosion and its chain reaction induced by the venting flame were deeply analyzed. Results indicate that the venting flame could induce vapor cloud explosion and set off a chain reaction, leading to the high explosion intensity. As for the ignition condition, the venting flame directly came in contact with the vapor cloud and provided the required energy for the ignition. The pressure first increased and then decreased as the distance from the venting port increased, and the highest pressure appeared in the central region of the vapor cloud. The temperature distribution also presented a similar phenomenon.

Comparison of explosion models for detonation onset estimation in large-scale unconfined vapor clouds

Although industrial denotations in semi-open and congested geometries are often neglected by many practitioners during risk assessment, recent studies have shown that industrial detonations might be more common than previously believed. Therefore, from the explosion safety perspective, it becomes imperative to better assess industrial detonation hazards to improve robustness of explosion mitigation design, emergency response procedures, and building siting evaluation. Having that in mind, this study aims to review current empirical vapor cloud explosion models, understand their limitations, and assess their capability to indicate detonation onset for elongated vapor clouds. Six models were evaluated in total: TNO Multi-Energy, Baker-Strehlow-Tang (BST), Congestion Assessment Method (CAM), Quest Model for Estimation of Flame Speed (QMEFS), Primary Explosion Site (PES), and Confinement Specific Correlation (CSC). Model estimations were compared with large-scale test data available in the open literature. The CAM model demonstrated good performance in indicating deflagration-to-detonation transition (DDT) for test conditions experiencing detonation onset without any modification in the methodology. Some suggestions are provided to improve simulation results from PES, BST and QMEFS.

Simulation of Natural Gas Dispersion and Explosion in Vented Enclosure using 3D CFD FLACS Software

Natural gas is used as fuel in industries, power plants, commercial installations, and households. In its application, natural gas leaks can be considered as a major hazard because of its flammable and explosive nature. In addition to fuel, heat and oxygen sources, fires and explosions can occur if the concentration of natural gas in the air is between Low Flammable Limit (LFL) and Upper Flammable Limit (UFL). If the release of natural gas is not ignited, it will immediately form a Vapor Cloud Explosion (VCE) that can cause an explosion if it meets ignition point. Therefore, a research on dispersion patterns in a particular area or space is needed to minimize hazards and to develop safety procedures and regulations. This research aims to determine the external parameters that affect the dispersion and explosion caused by natural gas by using FLACS software from PT. Gexcon Indonesia. This software can display overpressure graphs of time and 3D visuals of simulations. The external parameters consist of vent size (5.4 m2 and 2.7 m2), wind direction, lighter position (center and back), day and night condition, and the presence of a obstacle (with and without obstacle). From the research results by the simulations, it is obtained that the highest overpressure value when there is an obstacle with a vent size of 2.7 m2; wind direction from the north; night condition, and back ignition point is 0.503 bars at 40, 835 s which can cause most buildings to collapse and the death rate to increase.

Accident modeling of toxic gas-containing flammable gas release and explosion on an offshore platform

Toxic gas-containing flammable gas leak can lead to poisoning accidents as well as explosion accidents once the ignition source appears. Many attempts have been made to evaluate and mitigate the adverse effects of these accidents. All these efforts are instructive and valuable for risk assessment and risk management towards the poisoning effect and explosion effect. However, these analyses assessed the poisoning effect and explosion effect separately, ignoring that these two kinds of hazard effects may happen simultaneously. Accordingly, an integrated methodology is proposed to evaluate the consequences of toxic gas-containing flammable gas leakage and explosion accident, in which a risk-based concept and the grid-based concept are adopted to combine the effects. The approach is applied to a hypothetical accident scenario concerning an H2S-containing natural gas leakage and explosion accident on an offshore platform. The dispersion behavior and accumulation characteristics of released gas as well as the subsequent vapor cloud explosion (VCE) are modeled by Computational Fluid Dynamics (CFD) code Flame Acceleration Simulator (FLACS). This approach is concise and efficient for practical engineering applications. And it helps to develop safety measures and improve the emergency response plan.

Dynamic vulnerability assessment of process plants with respect to vapor cloud explosions

Vapor cloud explosion (VCE) accidents in recent years such as the Buncefield accident in 2005 indicate that VCEs in process plants may lead to unpredicted overpressures, resulting in catastrophic disasters. Although a lot of attempts have been done to assess VCEs in process plants, little attention has been paid to the spatial-temporal evolution of VCEs. This study, therefore, aims to develop a dynamic methodology based on discrete dynamic event tree to assess the likelihood of VCEs and the vulnerability of installations. The developed methodology consists of six steps: (i) identification of hazardous installations and potential loss of containment (LOC), (ii) analysis of vapor cloud dispersion, (iii) identification and characterization of ignition sources, (iv) explosion frequency and delayed time assessment using the dynamic event tree, (v) overpressure calculation by the Multi-Energy method and (vi) damage assessment based on probit models. This methodology considers the time dependencies in vapor cloud dispersion and in the uncertainty of delayed ignitions. Application of the methodology to a case study shows that the methodology can reflect the characteristics of large VCEs and avoid underestimating the consequences. Besides, this study indicates that ignition control may be regarded as a delay measure, effective emergency actions are needed for preventing VCEs.

Feasibility Evaluation of Designated Quantities for Chemicals Requiring Preparation for Accidents in the Korean Chemical Accident Prevention System.

To prevent chemical accidents, the United States (US), the European Union (EU), and the Republic of Korea operate legal systems, such as risk management plans (RMP) and process safety management (PSM), to prevent chemical accidents inside and outside the workplace. The duty to implement chemical accident prevention systems and the criteria for being a target workplace are dependent on the designated quantities of chemicals handled. A chemical accident prevention system is obligatory for storage and handling of legally declared chemicals in the workplace. Benzene, toluene, xylene, methyl ethyl ketone, and ethyl acetate are all flammable materials that are commonly used as solvents in the chemical industry. These substances are grouped into flammable substances groups in the US and the EU, and are managed with the same designated quantities. However, in Korea, the designated quantities are: benzene, 10,000 kg; toluene, xylene, and methyl ethyl ketone, 200,000 kg; and ethyl acetate, 20,000 kg. In order to evaluate the validity of the chemical quantities, fire explosion scenarios during chemical accidents were modeled using two modeling programs, Areal Location of Hazardous Atmosphere (ALOHA) and Korea Off-Site Risk Assessment Supporting Tool (KORA) software, under the same conditions. Similar damage radii were found for the five flammable materials with both pool fires and vapor cloud explosions (VCE). Based on these damage radii, the designated quantities of five substances were calculated and included in the range (10,000 to 13,500 kg). The results show that current designated quantities underestimate chemical substances, and for the prevention of accidents and post-management after chemical accidents, it is necessary to manage flammable substances under one grouping.

A violent, episodic vapour cloud explosion assessment: Deflagration-to-detonation transition

A large vapour cloud explosion (VCE) followed by a fire is one of the most dangerous and high consequence events that can occur in petrochemical facilities. The current process of safety practice in the industry in VCE assessment is to assume that all VCEs are deflagration. This assumption has been considered for nearly three decades. In recent years, major fire and VCE incidents in fuel storage depots gained considerable attention in extreme high explosion overpressure due to the transition from Deflagration to Detonation (DDT). Though the possibility of DDTs is lower than deflagrations, they have been identified in some of the most recent large-scale VCE incidents, including Buncefield (UK), 2005, San Juan explosion (US), 2009, and IOCL Jaipur (India), 2009 event. Such an incident established the need to understand not only VCE but also the importance of avoiding the escalation of minor incidents into much more devastating consequences.Despite decades of research, understanding of the fundamental physical mechanisms and governing factors of deflagration-to detonation transition (DDT) transition remains mostly elusive. An extreme multi-scale, multi-physics nature of this process uncertainly makes DDT one of the “Grand Challenge” problems of typical physics, and any significant developments toward its assured insistence would require revolutionary step forward in experiments, theory, and numerical modelling. Under certain circumstances, nevertheless, it is possible for DDT to occur, and this can be followed by a propagating detonation that quickly consumes the remaining detonable cloud. In a detonable cloud, a detonation creates the worst accident that can happen. Because detonation overpressures are much higher than those in a deflagration and continue through the entire detonable cloud, the damage from a DDT event is more severe. The consideration of detonation in hazard and risk assessment would identify new escalation potentials and recognize critical buildings impacted. This knowledge will allow more effective management of this hazard.The main conclusion from this paper is that detonations did occur in Jaipur accident at least part of the VCE accidents. The vapour cloud explosion could not have been caused by a deflagration alone, given the widespread occurrence of high overpressures and directional indicators in open uncongested areas containing the cloud. Additionally, the major incident has left many safety issues behind, which must be repeatedly addressed. It reveals that adequate safety measures were either underestimated or not accounted for seriously. This article highlights the aftermath of the IOCL Jaipur incident and addresses challenges put forward by it.

Assessment of Cascading Accidents of Frostbite, Fire, and Explosion Caused by Liquefied Natural Gas Leakage

Liquefied natural gas (LNG) leaks often lead to cascading accident disasters, including vapor cloud release, explosion, fire, and toxic gas release. The origin and evolution of each accidental disaster must be considered when assessing safety. This paper discusses the safety assessment project of an LNG gas storage station in Xuzhou, China. Multiple conceivable disasters due to the leakage of LNG storage tanks are simulated and analyzed using the computational fluid dynamic software FLACS. We studied different wind speeds interacting with the flammable vapor cloud area and creating frostbite in areas of low temperature. Diffusion simulations of vapor cloud explosion (VCE), thermal radiation, and the distribution of toxic substances were performed. The overpressure‐impulse criterion was used to calculate the influence range of VCE. Heat flux, heat dose, and heat flux‐heat dose criteria were used to calculate the safe distance for personnel in the event of fire. Based on the calculation results of the three latter criteria, this paper recommends using the heat flux criterion to evaluate fire accidents. The danger zone of each accident was compared. VCE accidents yielded the largest area.

Urban Spatial Risk Assessment of Fire from Fueling Stations on Buildings Case Study: Lubaga Division, Kampala City, Uganda

The discovery of oil and gas in Uganda has attracted many investors, leading to increase in fuel/gas distributing companies and fueling stations creating rapid demand for land to locate the stations compared to available open urban land. Because of the explosive and combustion characteristics of fuel stored and dispensed at stations, several studies have been conducted on different fires at fueling stations such as static fire, jet fire, vapor cloud explosions, open fires, etc. but there was need to assess spatially the risk of fire from stations, its consequences and sovereignty on buildings surrounding them. This was done basing on seven parameters—proximity of buildings to stations, building materials, distance between buildings, wind speed, temperature, slope and vegetation. Analytical hierarchy process and pairwise comparison were used to weight the parameters based on their relative importance. Weighted sum tool was applied to generate the fire risk maps for the quarters—December to February, March to May, June to August, and September to November from 2008 to 2013. The parameters were overlaid with the buildings in each risk zone for all the four quarters and their influences determined. The highest contributors were proximity of the buildings to stations, building materials and separation between buildings. Most of the affected buildings were made of rusted corrugated iron sheets and wood; the separation distance from one building to another ranged from 0 - 4 m. Most of buildings located within 100 m from stations were at moderate risk level and within 50 m were at highest risk level. The period of December to February and June to August had the highest risk. The findings can be used to guide planners and policy makers on building location vs. material vs. separation. It can also guide developers on where, when and how to carry out their developments.

Research on Safety Spacing of Chemical Storage Tanks Based on Accident Consequence and Risk Analysis

The placement of chemical storage tanks is an important topic in industrial safety, and its placement method is based on the study of the safety spacing of storage tanks. This paper takes LPG and LNG storage tanks as examples. It uses vapor cloud explosions, pool fires, pressure vessel explosions, boiling liquid expansion vapor explosions and other fire and explosion accident consequences models and risk probability analysis methods to analyze. It is proved that the transfer of storage tanks from ground to underground can significantly reduce the scope of impact of explosion accidents, thereby increasing the utilization rate of industrial land.

Experimental investigation of potential confined ignition sources for vapour cloud explosions

Electrical control boxes are common on high vapour cloud hazard sites, and in the case of the Buncefield explosion the ignition source was inside such a box, that was sited in an emergency pump house building. There has, however, been relatively little previous research into this type of ignition mechanism and its effect on the explosion severity. Commercially available electrical control boxes measuring 600mm high, 400mm wide and 250mm deep were used to explore the pressure development, venting processes and flame characteristics of stoichiometric propane/air explosions using aluminium foil and the supplied doors as vent coverings. In some tests, the boxes were empty in order to establish a baseline for the effect of the internal congestion of the boxes. In other tests a congestion array was added. It was found that, in both the empty and congested box tests, the door produced a flat petal shaped flame, which differed drastically from the mushroom flame shape and associated rolling vortex bubble venting that is traditionally observed with large orifice vented explosions.

Failure analysis integrated with prediction model for LNG transport trailer and thermal hazards induced by an accidental VCE: A case study

An unexpected explosion accident of an LNG transport trailer occurred in China on April 23, 2019, resulting in a massive vapor cloud explosion (VCE) fireball. The outstanding thermal damage induced by the LNG VCE’s fireball is enhanced in open space, which impose a serious threat on injured workers, building destruction, and even raise safety alarm about a potential second catastrophe. According to post-accident investigations of the present accident case, an integrated analysis of the fireball’s characteristics and thermal damage during the explosion accident are performed. Previously, an optimized model for the fireball’s characteristics have been developed based on full-scale experimental validation. It is found that the optimized model can facilitate better predictions in detailed parameters from the LNG VCE’s fireball in this study. Meanwhile, the numerical approach relating PHAST is applied to rebuild real accident scene, and the simulations involved fireball’s thermal hazards and damage radius on human and environment. Comparative research show that a near 100% fatality range is expected within a radius of 162.7 m and there is a harmless area with an ellipse distance of 893.9 m. It aims to bring a new development to predicted model, thereby improving performance of risk assessment on VCE fireball’s thermal damage duo to LNG transport process failure.