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Vapor cloud explosions (VCEs) can cause significant damage to nearby buildings, facilities and infrastructure with potential loss of life and significant business interruption, so the accuracy of predicting blast loads on facility buildings is critical in estimating these losses. Closely spaced buildings and process equipment outside of the congested region of a VCE provide a complicated flow field for an expanding blast wave. Their presence can channel and shield the blast, resulting in significant effects on the blast load magnitude and waveform shape. Currently, the most common way to estimate applied blast pressures resulting from VCE's is to use simplified methods that account for the total energy from the stoichiometric portion of the vapor cloud, fuel reactivity, and level of congestion and confinement, such as the TNO Multi-energy, equivalent TNT, CAM, and BST methods. These simplified tools assume an unobstructed line-of-site condition, which can overestimate and/or underestimate blast loads. This paper illustrates the use of a fast-running Computational Fluid Dynamics (CFD) approach that can account for channeling and shielding effects without having to use a turbulent combustion model. This approach provides a convenient tool for designers and process safety planners to more accurately quantify the hazard from postulated VCE hazards that include site-specific channeling and shielding effects. The accuracy of the approach is demonstrated via comparisons of CFD simulations to experimentally measured waveforms. Computed pressure and impulse are also compared to the BST predictions for unobstructed and obstructed sites.

In the chemical process industry, flammable gases are handled or stored in many production- or storage facilities. They can cause a vapor cloud explosion (VCE) accident if they come free from their containment and there is an ignition. A knock-on effect propagation from a primary VCE to one or more subsequent VCE(s) forms the cascading effect of VCEs. A new methodology of probabilistic Petri-net (PPN), which is an extension of Petri-net, is proposed to model the cascading effect and estimate the probabilities of escalation VCEs. The definition of what is a PPN is provided and three types of probabilistic relationships based on PPN are modeled. Further, the VCE cascading analysis approach based on Petri-net reasoning (execution of transitions) is discussed. The approach is illustrated by an example analyzing a VCE cascading effect in atmospheric tanks containing gasoline.

A large vapor cloud explosion (VCE) followed by a fire is one of the most dangerous and high-consequence events that can occur at petrochemical facilities. As the size and complexity of facilities increase, designs must consider the potential adverse effects associated with vapor cloud explosions in large congested areas and understand the potential for more devastating deflagration-to-detonation transitions (DDTs) on these facilities. While the likelihood of DDTs is lower than deflagrations, they have been identified in some of the most recent large-scale explosion incidents including: 2005 Buncefield explosion, 2009 San Juan explosion, and 2009 Jaipur event. The consequences of DDTs can be orders of magnitude larger than deflagration because they have the ability to self-propagate outside the region of high congestion/confinement. Hence, it is critical to understand how a facility's geometry or equipment layout can affect explosion consequences and assist in their mitigation and/or prevention. Due to the inability to predict such devastating phenomena on the large scale, owners and designers cannot evaluate installations for risk of DDTs and provide “inherently safer” layout or mitigation measures to significantly reduce or eliminate such hazards. However, there is a lack of data at the large scale to validate the necessary design tools used to predict the risk of DDT. One of the main goals of this research project is to provide large scale DDT explosion data and validate the tools necessary to predict vapor cloud explosions in early design phase. This paper will present the results of large scale testing being conducted in a newly developed test rig of 50,000 ft3 (1500 m3) gross volume under award Subcontract 12121-6403-01 provided by the Research Partnership to Secure Energy for America (RPSEA). These tests involve evaluation of deflagrations and DDTs involving stoichiometric, lean and rich mixtures, with propane and methane fuels. The effectiveness of mitigation techniques such as solid inhibitors or deluge is evaluated for preventing DDTs.

In this article, a new concept is presented with the intent to suppress the generation of damaging overpressures during a vapor cloud explosion via triggering ignitions at additional locations within the vapor cloud immediately after the primary ignition has occurred. The resulting lower explosion overpressures would then be less damaging to buildings and their occupants. The results of early experimental work support the hypothesis underlying this new concept. © 2016 American Institute of Chemical Engineers Process Saf Prog 36: 54–61, 2017

This paper presents an analysis and simulation of an accident involving a liquefied petroleum gas (LPG) truck tanker in Kannur, Kerala, India. During the accident, a truck tanker hit a divider and overturned. A crack in the bottom pipe caused leakage of LPG for about 20 min forming a large vapor cloud, which got ignited, creating a fireball and a boiling liquid expanding vapor explosion (BLEVE) situation in the LPG tank with subsequent fire and explosion. Many fatalities and injuries were reported along with burning of trees, houses, shops, vehicles, etc. In the present study, ALOHA (Area Locations of Hazardous Atmospheres) and PHAST (Process Hazard Analysis Software Tool) software have been used to model and simulate the accident scenario. Modeling and simulation results of the fireball, jet flame radiation and explosion overpressure agree well with the actual loss reported from the site. The effects of the fireball scenario were more significant in comparison to that of the jet fire scenario.

Chemicals used in paint industry are generally comprised of toxic and inflammable substances; they may cause serious problems for humans and environment if safety conditions are neglected. In 2012, rupture of a toluene tank in a paint factory in Iran claimed lives of two workers near the tank. The present study is formulated in order to model the incident. The results showed the area prone to flash fire occurrence and extension. Furthermore, radiation was measured in terms of distance to the tank. A bund wall is also assumed around the vessel in order to determine its influence on evaporation in flash fire area, radiation, and maximum concentration of vapor cloud. The results provided important hints on minimum and required distance of electrical equipment or electrical enclosure (PLC) installation from vessels as well as suitable distance between the vessels. Finally, preventive recommendations were proposed to reduce the risk of potential accidents.

In the last two decades, several serious accidents at large-scale technological systems that have had grave consequences, such as that at Bhopal, have primarily been attributed to human error. However, further investigations have revealed that humans are not the primary cause of these accidents, but have inherited the problems and difficulties of working with complex systems created by engineers. The operators have to comprehend malfunctions in real time, respond quickly, and make rapid decisions to return operational units to normal conditions, but under these circumstances, the mental workload of operators rises sharply, and a mental workload that is too high increases the rate of error. Therefore, cognivitive human features such as situation awareness (SA)—one of the most important prerequisite for decision-making—should be considered and analyzed appropriately. This paper applys the SA Error Taxonomy methodology to analyze the role of SA in three different accidents: (1) A runaway chemical reaction at Institute, West Virginia killing two employees, injuring eight people, and requiring the evacuation of more than 40,000 residents adjacent to the facility, (2) The ignition of a vapor cloud at Bellwood, Illinois that killed one person, injured two employees, and caused significant business interruption, and (3) An explosion at Ontario, California injuring four workers and caused extensive damage to the facility. In addition, the paper presents certain requirements for cognitive operator support system development and operator training under abnormal situations to promote operators’ SA in the process industry.

In this work, the prediction of the overpressure resulting from a vapor cloud explosion (VCE) will be conducted from external area of a chemical process plant. Based on Feyzin Refinery disaster, this study will analyzed and focused on the spillage from a delayed ignition causing a VCE from the T61-443 sphere tank. TNT Mass Method and Baker-Strehlow models are used to estimate the overpressure of the explosion. The results are presented in the form of table and figures to compare the two methods and justify the overpressure predicted.

A devastating crude oil vapor explosion accident, which killed 62 people and injured 136, occurred on November 22, 2013. It was one of the most disastrous vapor cloud explosion accidents that happened in Qingdao's storm drains in China. It was noted that blast overpressure and flying debris were the main causes of human deaths, personal injuries and structure damages. Two months after the accident, it was reported that there were three contentious issues in the investigation report. First issue was the discrepancy between the temperature of the crude oil vapor explosive limits which were measured by the investigation panel and the temperature reported by the local fire department. Second issue was the contradiction between the upper explosive limit and vapor pressure of the crude oil vapor. The last issue was the location of the ignition source which led to the explosion. In the present study some specific features of this accident and various causes led to the explosion, high casualties and severe damages were analyzed. Three contentious issues in the official investigation report were investigated and tested in detail. The first element tested was the explosive limits and limiting oxygen concentration of the crude oil vapor at different temperatures. Based on theoretical analysis and field investigations, the last two elements in the report were analyzed from multiple perspectives. Based on the TNO Multi-Energy model and PROBIT equations, damage probability of affected people at the leaking site was also estimated. The investigation concluded with a result that precautions need to be taken to prevent flammable gas explosions in the drainage systems. Key steps were explicitly discussed for improving the hazard identification and risk assessment of similar accidents in the future.

A hydrocarbon Vapor Cloud Explosion (VCE) is one of critical hazardous events in offshore installations. Once VCE occurs in the ocean, it results in tremendous economic loss, casualties, and environmental impact. The combustion mechanism of VCE differs from HE in particular in complex geometries (e.g. offshore oil and gas production facilities) as there exist many objects which can trigger severe turbulences. Although many research efforts have been made to develop design provisions for blast resistant structures, most of those provisions are based on high-order explosives (HE) such as TNT (TriNiTrotoluene) in a free field. Therefore, typical blast resistant structural design standards were examined to address the weaknesses of standards in this study. Existing blast wave models which provide key design load parameters were also reviewed to address limitations of each approach. Finally, essential recommendations are discussed in this paper for future studies to improve blast resistant structural design provisions with the ultimate aim of protecting our lives, assets and environment from VCE in the ocean.

The common rift between academia and industry has existed in all fields of engineering. However, ultimately that can be seen as more of a lag; it is not so much a question of academia research, which ends up finding its way into the practical world of industry years if not decades later. On the topic of detonations or Vapor Cloud Explosions (VCE), this is indeed a true statement. A little more than a decade ago the common belief in the chemical process industry was that detonations were not possible unless you had some very reactive process materials such as hydrogen or acetylene. When some industry and consulting experts began to challenge this view, they soon found out that a more common and less reactive process material such as ethylene could in fact be made to detonate as well. The key was that the environment had to be just right for an ignited flame to accelerate and transition to a detonation. In fact, academia had known this since the early 1960s and so the question remains, what else can we learn? Industry has retuned itself and made use of a several common explosion modeling tools which for some can be made to predict detonations. In others, they must be inferred and only very knowledgeable users can determine detonations. This paper will review the basics of detonations, the academic perspective and the industrial applications. Additionally, several of the various and commonly used models for explosion prediction will be reviewed, in the light of detonation.

A model for predicting vapor cloud explosion blast loads is described extending a previously developed model. The model considers the contribution of a Primary Explosion Site (PES) as well as the bulk effect of the total flammable cloud. The model results are then compared with historical accidents and other commonly used models considering a single PES. Four historical events are examined: the Flixborough accident of 1974, the Texas City accident of 2005, the Phillips 66 accident of 1989, and the Buncefield incident of 2005. It is found that the combined model produced pressure and impulse values consistent with the damage observed. If the contribution of the total cloud is not considered, the far field pressure, which included overpressures up to 0.35 bar, was underpredicted and impulse was significantly underpredicted. The other methods, produced, in general, significantly lower overpressures and impulses when compared with the damage indicators seen in the explosion accidents. © 2014 American Institute of Chemical Engineers Process Saf Prog 34: 147–153, 2015

Fire risk of gas pipeline leakage is high.The factors contributing to gas pipeline leakage most are third party damage, corrosion, design and incorrect operation. The accident consequences of gas pipeline leakage and quantitative risk assessment method of gas pipeline leakage consequence are analyzed. In order to achieve quantitative fire risk assessment of gas pipeline leakage, flash fire model, vapor cloud explosion model and thermal radiation damage criterion are analyzed. Firstly, the gas leakage quantity is estimated. Then, the heat radiation estimate flux, the thermal dose and damage range are got by using flash fire model, vapor cloud explosion model and the thermal radiation damage criterion respectively.Combined with an example of gas pipeline, damage ranges of different disaster patterns are estimated according to different gas pipeline leakage pattern. Through comparing the accident consequences of gas pipeline leakage, this paper provides some reliable scientific references for gas pipeline management departments.

Owner/operators of chemical processing and petroleum refining sites often ask whether unconfined hydrogen vapor cloud explosions (VCEs) can actually occur. This question normally arises during the course of a consequence-based facility siting study (FSS) or a quantitative risk assessment (QRA). While it is generally recognized that a hydrogen release within a process enclosure could lead to an explosion, the potential for an external hydrogen release to cause a VCE is not as widely recognized and is often questioned. This uncertainty appears to stem from the impression that a hydrogen release always ignites quickly and near the point of release such that a flammable cloud does not have time to develop prior to ignition and/or that a hydrogen release never produces a flammable cloud of any significant volume due to its positive buoyancy. Unfortunately, neither impression is correct. Hydrogen releases are actually susceptible to delayed ignition, and hydrogen releases can form significant flammable gas clouds near grade level. Unconfined hydrogen VCEs can and do occur. Furthermore, given the potential for rapid flame acceleration associated with hydrogen, the consequences of a hydrogen VCE can be severe. Consideration of such events in FSS and QRAs is, therefore, warranted. Prior accidental hydrogen VCEs are reviewed to establish that such events do occur. Selected hydrogen VCE tests are also discussed to establish the potential severity of such events. Moosemiller and Galindo [10th Global Congress on Process Safety, 2014 Annual AIChE Meeting, New Orleans, LA, March 30–April 2, 2014] reviewed the ignition characteristics of hydrogen relative to the potential for a delayed ignition, and only the conclusions from that article are presented here. Example dispersions, using both simplified dispersion and computational fluid dynamics methods, are presented to illustrate the flammable gas volumes that can be created by hydrogen release scenarios. Blast load predictions are presented to illustrate the range of loads that could result from a hydrogen VCE due to such a release. © 2014 American Institute of Chemical Engineers Process Saf Prog 34: 36–43, 2015

This paper analyzes the fire explosion risk of liquefied petroleum gas (LPG) storage tank through methods of model calculation and simulation. A large crude oil reserves library in Tianjin is the main study object in this paper, the fire process for the storage tank pool fire is simulated using the fire simulation software FDS, which produces the development of fire and the change of the radiation intensity in the case of fire. And the damage degree of explosion accident consequences has been calculated quantitatively by the vapor cloud explosion model, which obtains the casualties radius and property damage. Study results provide reference data and theoretical guidance for fire protection design and fire fighting tactics in LPG storage tank area.

API Recommended Practice 752 is one of the most referenced practices for evaluating vapor cloud explosion (VCE) impacts to site occupied buildings. This reference introduces generic VCE frequencies for different types of process units that are based on VCE incidents database. Although these reported VCE frequencies are not capable of illustrating all parameters that affect explosion likelihood, they are widely used in risk analysis studies and software packages. This paper delineates the structure of a more realistic method for estimation of local VCE frequencies for independent congested spaces or units as a function of process, site, and meteorological variables. Compared to traditional methods for VCE frequency estimation, the new proposed approach is supported by an obviously more populated and precisely categorized database of leakage frequencies and features a multi-variable functionality of process/plant conditions. Contrary to previous procedures that aimed at finding the frequency of occurrence for a single VCE incident, this proposed methodology characterizes each congested space with a local VCE frequency. This frequency is an integration of the frequencies pertaining to VCE's that are likely to be initiated by each congested space. This new VCE frequency can also be used to determine the level of explosion hazard in each unit and in risk matrix analysis.

It is very important and necessary to perform quantitative hazard analysis for possible accidental leakage from an underground gas storage cavern in salt rock. An integrated quantitative hazard analysis method for natural gas jet release from salt caverns is presented in this paper, which was constituted by a revised model for gas leakage rate calculation, a consequence analysis and a model of probability assessment for harm. The presented method was validated by comparing the analytical results with the data collected from the real accidents (including the leakage, jet fire, fireball and vapor cloud explosion). It is indicated that the proposed method was more accurate than the TNT equivalence method for vapor cloud explosion and gave more reasonable results when applied to the consequence analysis for the thermal radiation from jet fire and fireball.

Gas dispersion and explosion dynamics can be very complex. Blast effects in the far field are less sensitive to the local dynamics of an explosion event, and simplified techniques have been developed to roughly estimate the amount of fuel involved (i.e., energy released) in an explosion based on the observed damage in the far field. However, these simple techniques are not suitable to predict the complex explosion dynamics that occur in the near field. The phenomena that drive explosions and resulting damage in the near field are complex in nature, as they depend on non-linear interactions between multiple variables (e.g., ignition location, flame accelerations due to object interaction, fuel reactivity, geometry of the facility regarding confinement and interconnected rooms, vent areas, etc.). Furthermore, the damage created in the near field by overpressure development, blast wave reflections and focusing, pressure impulse, pressure piling, blast wind and ensuing drag forces, may be difficult to interpret using simple methods. The origin of an explosion may, in fact, differ from the intuitive epicenter determined from oversimplified assumptions and may lead to incorrect conclusions regarding the cause and origin or initiating events of the accident. State-of-the-art 3D modeling tools, such as FLACS, are typically required to understand and evaluate complex explosions. FLACS was specifically developed to predict the consequences associated with complex explosions, especially in the near field, and has been extensively validated against hundreds of full-scale experiments. Therefore, FLACS simulations can be used to investigate the chain of events of the explosion and provide a more complete understanding of the evidence, including near-field blast damage. This paper presents the findings of how FLACS was used to help determine the explosion origin in the explosion that occurred at an ink and paint manufacturing facility in Danvers, Massachusetts, on November 22, 2006. This paper is not intended to provide complete investigation findings and will only provide the necessary background material to follow the explosion origin analysis.

Hydrocarbon gas explosion is one of the critical hazards resulting in huge environmental impact as well as loss of valuable assets and lives as observed from the historical disasters in the oil and gas industry. In response to these events, stronger international rules and regulations have been made to ensure safety of these structures. Hence, considerable effort has been devoted to quantify accidental design loads for flammable gas based on probabilistic approaches which requires extensive computational fluid dynamic simulations. Also, demand for 3D nonlinear dynamic finite element structural simulations has increased significantly with rapid progress in computer performance. Some of the major issues and difficulties in structural design and evaluation for probabilistic design loads are discussed in this paper. Uncertainties in explosion hazard analysis which cause large variations in probabilistic explosion responses are reviewed. Some gaps between provisions for design load estimation based on probabilistic approaches versus current structural design and analysis schemes are compared. Finally, it is concluded that there is an urgent need for reliable guidelines for risk-based structural design and simulation for probabilistic explosion design loads.

An analysis was completed of the hazards distance of hydrogen accidents such as jet release, jet fire, and vapor cloud explosion(VCE) of hydrogen gas, and simplified equations have been proposed to predict the hazard distances to set up safety distance by the gas dispersion, fire, and explosion following hydrogen gas release. For a small release rate of hydrogen gas, such as from a pine-hole, the hazard distance from jet dispersion is longer than that from jet fire. The hazard distance is directly proportional to the pressure raised to a half power and to the diameter of hole and up to several tens meters. For a large release rate, such as from full bore rupture of a pipeline or a large hole of storage vessel, the hazard distance from a large jet fire is longer than that from unconfined vapor cloud explosion. The hazard distance from the fire may be up to several hundred meters. Hydrogen filling station in urban area is difficult to compliance with the safety distance criterion, if the accident scenario of large hydrogen gas release is basis for setting up the safety distance, which is minimum separation distance between the station and building. Therefore, the accident of large hydrogen gas release must be prevented by using safety devices and the safety distance may be set based on the small release rate of hydrogen gas. But if there are any possibility of large release, populated building, such as school, hospital etc, should be separated several hundred meters.

The main objectives of this study are to analyze the leaked gas dispersion and quantify the potential overpressures due to vapor cloud explosions in order to identify the most significant contributors to risk by using Computational Fluid Dynamics (CFX & FLACS) for gas fuelled ships. A series of CFD simulations and analyses have been performed for the various gas release scenarios in a closed module, covering different release rates and ventilating methods. This study is specially focused on the LNG FGS (Fuel Gas Supply) system recently developed for the propulsion of VLCC crude oil carriers by shipyards. Most of work presented is discussed on the gas dispersion from leaks in the FGS room, and shows some blast prediction validation examples.

Butadiene is a kind of important material in the chemical engineering, and it is inflammable and explosive. Once it leaks to the air, fire and explosion accident may happen. In the current experiment, the Butadiene tank in a chemical plant was taken as the example to analyze the potential hazards that the tank may cause. Some mathematical models, such as the UVCE（the Unconfined Vapor Cloud Explosion） and the BLEVE（the Boiling Liquid Expanding Vapor Explosion）, were used to describe the results that the hazards may lead to，so that it could provide some scientific criteria to the similar companies, and help the companies to take measures to keep away from these dangers, and reduce the casualty and loss in the end.

Based on the tunnel environment and the characteristic of flammability and explosion of liquefied petroleum gas (LGP), the leak of LPG tanker can induce heavy casualties and property loss in the tunnel. In order to study quantitative risk of LGP transportation in road tunnel, the data of 599 accidents and 659 accidental vehicles are collected. From these data, the proportion of LGP tanker accident in the total accident vehicles and million vehicles kilometer (MVK) tanker accident rates are obtained. By analyzing the leakage scene of LGP tanker, the possible accident types of the LGP transportation were analyzed, such as boiling liquid expanding vapor explosion (BLEVE), vapor cloud explosion (VCE), flash fire and jet fire, etc. The impact of leak time to various ranges of injury is studied in the condition of LGP continued leakage. The slight injury, serious injury and death radius of LGP leakage accidents are calculated in tanker loaded with different LGP quantity. In view of the accidental analysis, the countermeasures will be proposed to reduce the risk of LGP transportation in road tunnel.

CNG cylinder is a sort of used storage device in CNG filling stations. As a gas storage container with high-pressure, it will lead to harmful consequences if failure occurs. The explosion consequences after its leakage are analyzed in this article. The vapor cloud explosion (VCE) quantitative evaluation model is compared with API pub 581 consequences evaluation model. And the comparison of the consequences of the explosion bteween two evaluation models is also made based on an example with a set of CNG cylinders.

The first edition of the CCPS book Guidelines to Evaluating Vapor Cloud Explosions, Flash Fires and BLEVEs was published in 1994. The second edition was completed in October 2010. It is a major revision of the Guideline with contents completely reorganized, recent research results added, revised and new prediction methods inserted, with sample problems worked for each prediction method. The treatment of pressure vessel burst was expanded and placed in a dedicated chapter, resulting in a new name for the second edition of the Guideline. © 2011 American Institute of Chemical Engineers Process Saf Prog, 2011.

Vapor cloud explosions (VCEs) cause considerable problems in the chemical and petrochemical industries. They generate damaging levels of overpressure and the possibility of human injury/death, and building/equipment damage. Predicting the possible consequences of VCEs is important to ensure the safe design of existing and new structures. Prediction of the overpressures resulting from a VCE is typically done using simplified (empirical) models, phenomenological models, and computational fluid dynamics models. The focus of this article is on two of the most frequently used simplified prediction methods: TNO multienergy and Baker–Strehlow–Tang models. These models are compared in terms of structural response and vulnerability of damage caused by an explosion. © 2010 American Institute of Chemical Engineers Process Saf Prog, 2011

Quantifying the size of flammable vapor cloud hazards associated with an accidental release of Liquefied Natural Gas (LNG) into a spill containment system supported by narrow drainage trenches has posed a modeling challenge since the inception of the LNG industry. Early attempts to treat the vapors evolving from the trenches included using line-source Gaussian models, and the use of the DEGADIS model by modeling “segmented” trench elements and adding the contributions from each trench segment at a specified downwind distance. These approaches often are only reasonable for a select set of conditions (e.g., winds perpendicular to the trench) and have no ability to simulate many of the conditions that might result in a larger potential impact (e.g., winds blowing parallel to the trench).

Fire and explosion hazards in ammonia plants include releases of flammable materials. The distinction between fire and explosion scenarios is often whether the fuel ignites promptly upon release or has delayed ignition. Prompt ignition prevents formation of a flammable vapor cloud and, thereby, averts a VCE. Syngas contains a significant amount of hydrogen, a fuel that is easily ignited. Industry experience with accidental releases of syngas has been that it promptly ignites. Literature was reviewed for test and accident data for syngas and hydrogen to estimate the probability of prompt versus delayed ignition. No instances of syngas VCEs were found in literature; however, numerous test and accidents were reported for hydrogen. The probability of delayed ignition varied with the release conditions. A conservative estimate of the probability of delayed ignition was developed. © 2010 American Institute of Chemical Engineers Process Saf Prog, 2010

Effective safety measures to prevent and mitigate the consequences of an accidental release of flammable LNG are critical. Water spray curtain is currently recognized as an effective technique to control and mitigate various hazards in the industries. It has been used to absorb, dilute and disperse both toxic and flammable vapor cloud. It is also used as protection against heat radiation, in case of fighting vapor cloud fire. Water curtain has also been considered as one of the most economic and promising LNG vapor cloud control techniques. Water curtains are expected to enhance LNG vapor cloud dispersion mainly through mechanical effects, dilution, and thermal effects. The actual phenomena involved in LNG vapor and water curtain interaction were not clearly established from previous research. LNG spill experiments have been performed at the Brayton Fire Training Field at Texas A&M University (TAMU) to understand the effect of water curtain in controlling and dispersing LNG vapor cloud. This paper summarizes experimental methodology and presents data from two water curtain tests. The analysis of the test results are also presented to identify the effectiveness of these two types of water spray curtains in enhancing the LNG vapor cloud dispersion.

A few years ago, there was an explosion in a reactor at the XYZ Chemical Company. The reactor was a block copolymerization reactor where butadiene and styrene monomers were added in a semibatch manner. The heat of reaction was removed by means of a refrigeration system. The incident occurred when the reactants were not added in the sequence or quantity required. The resulting runaway reaction overpressurized the reactor system and caused an expansion joint to rupture. The hydrocarbons released formed a vapor cloud that exploded, causing the death of two workers, serious injury to three others, and significant damage to the facility. The contributing causes of the incident include: (a) lack of information about the hazards of the chemicals in the process, (b) lack of information about the equipment in the process and inadequate equipment, (c) inadequate or no PHA, (d) inadequate training, (e) confusing operating procedures, (f) failure to use management of change procedures, (g) failure to perform a prestartup safety review, (h) failure to have an adequate contractor safety program, and (i) failure to investigate previous near misses and incidents and take corrective actions. This article describes this accident, the root causes, and the major plant deficiencies. The following expresses my opinion of the events that led to this explosion as testified to in open court. Others may have different opinions. © 2009 American Institute of Chemical Engineers Process Saf Prog, 2010

The Baker-Strehlow-Tang (BST) vapor cloud explosion model is one of the most common methods used to estimate overpressures for the purpose of locating buildings in relation to process units. This model suffers from a problem common to all simplified explosion models: the user is required to pick the “strength” of the explosion using one or more simple parameters. In the BST model, the fuel reactivity, flame expansion, and obstacle density parameters are used to select a flame speed from a limited matrix of possible values. This article presents the Quest Model for estimation of flame speeds (QMEFS), a systematic approach to estimating flame speed that does not rely on the BST categories. It provides for a continuous range of flame speeds that can then be used with the existing BST blast curves to calculate the characteristics of the vapor cloud explosion. The QMEFS approach provides the user with a method for describing a vapor cloud explosion that is more detailed than the BST model, and establishes a more refined system for predicting the consequences of vapor cloud explosions. © 2008 American Institute of Chemical Engineers Process Saf Prog, 2009

© 2014 Elsevier Ltd. In this paper, a new method based on Fuzzy theory is presented to estimate the occurrence possibility of vapor cloud explosion (VCE) of flammable materials. This new method helps the analyst to overcome some uncertainties associated with estimating VCE possibility with the Event Tree (ET) technique. In this multi-variable model, the physical properties of the released material and the characteristics of the surrounding environment are used as the parameters specifying the occurrence possibility of intermediate events leading to a VCE. Factors such as area classification, degree of congestion of a plant and release rate are notably affecting the output results. Moreover, the proposed method benefits from experts' opinions in the estimation of the VCE possibility. A refrigeration cycle is used as the case study and the probability of VCE occurrence is determined for different scenarios. In this study, sensitivity analysis is performed on the model parameters to assess their effect on the final values of the VCE possibility. Furthermore, the results are compared with the results obtained using other existing models. publisher: Elsevier articletitle: A multivariable model for estimation of vapor cloud explosion occurrence possibility based on a Fuzzy logic approach for flammable materials journaltitle: Journal of Loss Prevention in the Process Industries articlelink: http://dx.doi.org/10.1016/j.jlp.2014.11.003 content_type: article copyright: Copyright © 2014 Elsevier Ltd. All rights reserved. ispartof: Journal of Loss Prevention in the Process Industries vol:33 pages:140-150 status: published

This chapter reviews two massive and powerful unconfined vapor cloud explosions. One occurred in Buncefield, Hertfordshire near London, England and is well documented with public reports. The other incident occurred in Amuay, Venezuela. The Amuay incident has multiple reports that have some major differences in the cause but not in the consequences. Government reports say that the Amuay incident was the result of sabotage; others say it was lack of maintenance. Each incident resulted in a large blast with major damages to the nearby residential areas or adjacent commercial facilities. Each incident occurred in a tank farm area and not within a refinery process area. The British were fortunate that it occurred on a Sunday morning when few people were working in the nearby commercial buildings. In Venezuela, the blast killed an estimated 47 people and only one was a refinery worker. A number of casualties were National Guard and their family members.

In the early 1960s a number of sizable explosions and fires occurred in the oil and petrochemical industries. A light hydrocarbons plant in Louisiana suffered a vapor cloud explosion. This phenomenon, although it had occurred before, was largely unrecognized in industry. At about the same time, the process industries were moving toward the "jumbo" plants. Formerly, ammonia was produced in multiple plants of 100 to 300 tons/day capacity with multiple parallel lines of reciprocating compressors. However, in the early 1960s ammonia plants having capacities of 750, 1000, and 1500 tons/day with centrifugal machines were rolling off the designers boards. Large, single-train olefin plants, with capacities of 1.5 billion pounds per year, were also being designed and erected. As a response to these trends, a number of people from industry and insurance put together a symposium to explore ways to improve loss prevention in the process industries. This symposium contained six sessions and was held at the AIChE National meeting in Houston in 1967. Attendance was excellent and a committee was formed to prepare annual symposia on the topic. These symposia are still held at AIChE National meetings with the 40th Loss Prevention Symposium being held this year. This paper will discuss some of the highlights of these symposia and some of the people that have made them so successful over the years. Language: en

At approximately 1:20 p.m. on Wednesday, March 23, 2005 a series of explosions and fire occurred at the BP Texas City oil refinery during the start-up of an isomerization (ISOM) process unit. Fifteen workers were killed and about 170 other people were injured. Many of those killed were working in or around office trailers located near a blowdown drum and stack open to the atmosphere. The U.S. Chemical Safety and Hazard Investigation Board (CSB) found that because of problems that began during the ISOM process unit start-up, a sudden, geyser-like release of flammable hydrocarbon liquid and vapor discharged from the atmospheric vent stack. This release created a flammable vapor cloud, which ignited, causing as many as five explosions and fire in and around the ISOM unit. CSB identified multiple possible ignition sources in and around the blowdown drum area, including idling vehicles; however, the exact ignition source remains unknown. CSB deployed a team of investigators to BP Texas City to conduct a root-cause investigation immediately after the incident. This team examined blast patterns to determine the explosion origin; reviewed the design of the isomerization unit equipment; and examined plant safety and operating procedures, past accidents, maintenance procedures, and oversight and inspection. Investigators also reviewed the adequacy of applicable regulations and industry standards for the placement of temporary structures such as trailers in refineries. This article presents the preliminary findings from the CSB investigative team regarding the technical and underlying causes of the incident and discusses three urgent recommendations issued by the CSB stemming from the BP incident. © 2006 American Institute of Chemical Engineers Process Saf Prog, 2006

The Baker–Strehlow–Tang vapor cloud explosion (VCE) blast load prediction methodology uses flame speed as a measure of explosion severity. In previous publications, guidance has been presented for selecting flame speeds as a function of congestion, confinement, and fuel reactivity. These recommended values were based on empirical data available from the literature. Over the last 5 years, a series of medium-scale VCE tests have been conducted through a joint industry program to better understand vapor cloud explosions and to allow a more accurate definition of the flame speed applicable to a given combination of congestion, confinement, and fuel reactivity. These tests have demonstrated that the previously published flame speeds are not conservative for all configurations for the case of no confinement (3-D flame expansion). This paper provides an overview of the tests along with an update to the flame speed table where the previously published guidance was not conservative. © 2005 American Institute of Chemical Engineers Process Saf Prog, 2005

Two recent, tragic events remind us that the broad topic of high-energy release events encompasses more than vapor cloud explosions and reactive chemical incidents. Dust explosions also have potential for causing catastrophic harm to personnel and facilities. This paper describes recent, major dust explosions with a particular focus on learnings related to a commonly underconsidered aspect of facility operations—housekeeping. © 2004 American Institute of Chemical Engineers Process Saf Prog 23: 175–184, 2004

In September 1997, an LPG release occurred at the Hindustan Petroleum Corporation, Ltd. refinery in Visakhapatnam, India. The resulting explosion and fire destroyed most of the facility's administrative buildings, numerous LPG storage vessels, processing units, and an adjacent petroleum liquid storage terminal. Fifty-six people were declared dead, but the fatality number could have been as high as 3 times the official estimate. Property damage was estimated at US $15 million. It is known that a leak occurred during receipt of LPG cargo from a pressurized ship. The subsequent vapor cloud spread throughout the refinery tank farm, administrative complex, utilities area, and at least one process unit before eventually finding an ignition source. The investigation team developed numerous release theories. However, none of these theories could be substantiated by first hand witnesses' testimonies since all personnel directly involved in the tank filling operation were killed. Vapor cloud dispersion computer modeling was used to evaluate the credibility of various release scenarios. This paper discusses the events leading up to the explosion, the damages sustained, and compares quantitative dispersion modeling results to the physical damage and witness testimony obtained during the investigation.

The damage to equipment and facilities found after an industrial explosion can be used to identify the most probable scenario leading to the explosion. Here, a method for using this information along with a computational model, which simulates the vapor cloud explosion (VCE) process and object damage, is described. The process uses a collection of damaged items that are first analyzed to determine the blast load needed to produce the damage. This information is used with the VCE simulation tool in which several candidate explosion scenarios are modelled. The tool uses a detailed, three-dimensional representation of the scenario. A range of candidates in terms of vapor cloud size and location are analyzed. The results show that only one candidate scenario generates all the witnessed damage and suggests it to be the most probable.

This paper covers the development of the design blast loads for buildings in petroleum refineries and petrochemical plants as reported by the ASCE Task Committee on Blast Resistant Design. It briefly discusses the overall design process for such buildings and the considerations and methods for predicting the blast loading from vapor cloud explosions. The main focus is on determining the building component loads once the incident blast overpressure is defined.

Past accidents have demonstrated that vapor cloud explosions (VCEs) are the most severe threat to refining and petrochemical industries. In order to estimate the air blast parameters at any given distance from a possible explosion source, a variety of prediction methods have been developed. A brief description of these prediction methods is first presented. Then, the focus of this paper is on an engineering method based on blast curves, which is the most frequently used prediction method. Knowledge of blast effects from vapor cloud explosions has greatly improved due to the efforts of investigators in many countries during the last three decades; however, blast curves have not been reexamined. One of the aims of this paper is to present a new set of blast curves which have been validated with available experimental results and analytical solutions. Another aim is to present a comprehensive set of blast curves including blast parameters for both positive and negative phases. The new blast curves, which are a modification of the Baker-Strehlow curves, improve the prediction for detonations and supersonic deflagrations as well as for subsonic flames. By changing the slope of the blast pressure versus distance curve, the overly consserative blast pressure predictions by the previous Baker-Strehlow curves at large standoff distances for detonations and supersonic deflagrations are reduced. By clarifying the labeling of the flame. Mach number for each blast curve, the overly conservative pressure and impulse preditions for subsonic flames are also avoided. The new blast curves have been validated against VCE experiments including detonations, fast deflagrations, and slow deflagrations. Particular attention was given to large scale deflagration experiments, which became available only recently. Good agreement is shown between the new blast curves and the experimental blast data for vapor cloud detonations and subsonic deflagrations. For supersonic deflagrations, the blast curve predictions are overly conservative in that blast pressure decays more rapidly with distance in experiments than the calculated curves.

When considering the consequences of gas explosions in petro-chemical installutions simple methods are used such as TNT-equivalenc methods and the Multi-Energy method. These methods howewr, do not take into account directional effects, focusing effects, factors related to the source of the explosion (initial strength, shape) and reflections. FLACS, a 3-D CFD tool, allows for all factors mentioned including focusing on effects and reflections near buildings. A comparison of the CFD-method including the two traditional prediction methods for a practical case demonstrates the application areas of the FLACS method as well as the limitations of the traditional methods.

The Baker-Strehlow methodology was developed to provide an objective approach to prediction of blast pressures from vapor cloud explosions. The complete methodology was first published in 1994 [1]. Since then, it has evolved through ongoing research and use in VCE hazard analyses, facility siting studies and accident investigations. This article gives a brief overview of a paper on recent developments in the Baker-Strehlow methodology presented at the 31st Loss Prevention Symposium in Houston on March 9-13, 1997. Because the entire paper is too lengthy to be presented here, the following discussions may be lacking in some details. A copy of the complete paper can be obtained from the American Institute of Chemical Engineers (AIChE). Since the Baker-Strehlow method was first published, it has been used extensively in VCE hazard assessments in refineries and chemical plants. As expected, many practical lessons have been learned during the course of the hazard assessments, and the Baker-Strehlow method has evolved as a result. The changes have been evolutionary, not revolutionary. In keeping with the goals of the original study in which the methodology was developed, all changes have been incorporated with the intent of achieving an objective methodology to provide consistent prediction of VCE blast effects. The revisions to the Baker-Strehlow method resulting from experience gained during plant walk-downs and hazard assessments include: Systematic identification of “potential explosion sites” or “PESs,” Selection of the level of confinement for mixed zones of 2D and 3D confinement, Deciding on flame expansion when confinement is elevated above the vapor cloud, Selecting the reactivity for a fuel that is a mixture of fuels with differing reactivities, Predicting blast loads when there are multiple PES's within a vapor cloud considering different ignition source locations.

The well-known Yellow Book, nickname for the publication by the Dutch Ministry of Social Affairs and the Environment contains a number of models for prediction of the effects following an accidenial release of hazardous materials. TNO was involved in a complete revision of this Yellow Book. One of the models that has been completely revised is the blast prediction model for vapor cloud explosions. The Multy-Energy model was selected as the new model to be incorporated in the revision. The concept of the Multy-Energy model is widely accepted as a better alternative to TNT equivalence methods although a practical application is hampered by a lack of guidance for application in practice. Guidance for application is given in the revision, though it still leads to conservative solutions. This paper describes how the method should be applied according to the revised Yellow Book. The motivation for the guidance for application given is discussed by comparison with guidance given in other publications and with experimental results obtained from some large scale experimental programs. Present efforts in an ongoing research program by TNO to obtain more detailed and sound guidance is presented as well.

The leakage of high-pressure natural gas pipeline can lead to serious accidents and pose a significant threat to people and buildings in the vicinity of the failure location. This paper examines the harm effect distances of different consequences based on harmful criteria. And possible consequences caused by pipeline leakage are assumed and their subsequent harm effect distances are computed using the software EFFECTS. Harm effect distances evaluation was performed considering jet fire and vapor cloud explosion (VCE) as the worst-case scenarios. Results show that for pipeline leakage, the jet fire produces longer harm effect distances, so the jet fire scenario should be considered as the limiter for harm effect distances evaluation. Based on the analysis of this paper, harm effect distances caused by the leakage of a high-pressure natural gas pipeline can be evaluated, which will not only be useful to prevent and control natural gas pipeline leakage accidents, but also provide a good reference to design of new constructed pipelines.

A key component of explosion hazard evaluations is the determination of standoffs to given blast overpressure values. Many such evaluations use a simplified methodology that assumes that the blast wave propagates from the explosion source to the target location without interacting with intervening buildings or structures (i.e., without blast wave shielding). This is obviously a perfectly acceptable approach for a screening study, but blast wave shielding effects can be significant in certain circumstances (e.g., within a building group). A methodology was proposed by the UK Health & Safety Laboratory (HSL) in 2001 to account for blast shielding due to buildings/structures between the explosion source and target location. The HSL methodology is based on the blast waves generated by high explosives (HE). This paper extends the blast shielding evaluation to blast waves generated from pressure vessel bursts (PVB) and vapor cloud explosions (VCE). The influences of blast wave shape parameters (overpressure, duration and rise time) on blast wave shielding are examined. The results indicate that the degree of blast shielding is strongly dependent on the source of the blast wave (i.e., on the blast wave shape parameters) and that the shielding factors obtained with HE blast waves are not always directly applicable for PVB and VCE blast waves.

The diverse historical surveys on accidents involving domino effect have been analyzed to identify their significance and their most important features. From these data, the importance of domino effect among all accidents in the process industry and in the transportation of hazardous materials has been highlighted. The characteristics of this type of accidents have been studied with a statistical approach: origin and causes of domino effect, materials most frequently involved and effects and consequences of accidents. The significance of the diverse domino sequences have been assessed by using the relative probability event tree. Finally, four relevant cases have been discussed, corresponding to the following initiating events: two vapor cloud explosions (Buncefield, 2005 and Naples, 1985), one jet fire (Valero, 2007) and one accident associated with dust explosion.

This paper introduces a new method (now commonly referred to as the Baker-Strehlow Method) for estimating pressure and impulse generated by vapor cloud explosions. Strehlow's blast curves and concepts from the Multi-Energy method for determination of explosion energy are applied in this technique. New correlations for maximum flame speed based on obstacle density, fuel reactivity, and cloud confinement allow selection of the appropriate blast curve. Application of these correlations removes much of the subjectivity present in existing explosion estimates.

On November 7, 1975 a violent vapor cloud explosion occurred within a naphta cracker installation located at Beek in The Netherlands. The explosion resulted in several fatalities, destroyed the installation, resulted in severe damage in the direct surroundings of the installation and window breakage up to 4.5 km from the installation. The explosion was investigated, in detail, concentrating on the cause of the release of flammable gas and the explosion effects. The results were published in an official report by the Dutch authorities (Ministry of Social Affairs). In addition, a summary of accident descriptions were published by Lees and Gugan. Early in the 1980`s Christian Michelsen Research started developing a numerical tool which allows one to predict the effects of gas explosions in complex geometries. The first version of this tool (FLACS=FLame ACceleration Simulator) was issued in 1986. A second version was issued in 1989 and recently a third version was issued. The tool has been validated against numerous experiments on small- and medium-scale (maximum volume 50 m{sup 3}). The main application of the tool is prediction of explosion effects in offshore geometries but the tool has also been used for prediction of effects of explosions in landbased installations. Themore » tool appears to reproduce scaling effects (from small- to medium-scale) very well. The major uncertainty is, however, whether this range of scales is representative for industrial plants. No full-scale experimental data exist, hence scaling is a matter of some concern when FLACS results are used. Full-scale experiments are very expensive to perform and to shed some light on this question it was decided to simulate a well-documented accident. To this end the vapor cloud explosion accident which happened at Beek was chosen. Simulation of such an accident would at least show the possibilities of the use of FLACS for such large landbased installations. 14 refs., 9 figs., 3 tabs.« less

Within the project “MERGE”, an acronym for Modelling and Experimental Research into Gas Explosions, eight institutes from five different European countries co-operated to increase the understanding of vapor cloud explosions and to improve the sophisticated computerized prediction techniques that were, until this project, under separate development at several institutes. The objectives of the project were: to provide a consistent set of data on the influence of obstacles on flame propagation in initially quiescent mixtures at various geometrical scales; to improve, compare and validate numerical models for vapor cloud explosion simulation; to validate scaling techniques for explosion experiments; to investigate and to model jet explosions. The second item is discussed in this report.