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.     

A multivariable approach for estimation of vapor cloud explosion frequencies for independent congested spaces to be used in occupied building risk assessment

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.     

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 an accidental vapour cloud explosion: Lessons from the Indian Oil Corporation Ltd. accident at Jaipur,India

On 29 October 2009, at 19:30 IST, a devastating vapour cloud explosion occurred in a large fuel storage area at the Indian Oil Corporation (IOC) Depot in Jaipur, India, generating significant blast pressure. As a consequence of this explosion, the entire installation was destroyed, buildings in the immediate vicinity were heavily damaged, and windowpane breakages were found up to 2 km from the terminal. The IOC estimated that the total loss from the fire and explosion was approximately INR 2800 million.Ironically, as a storage site, the Jaipur terminal was not highly congested, and thus was not considered to have adequate potential for a vapour cloud explosion (VCE). Nevertheless, the prima facie evidences indicate that this was a case of VCE. Therefore, the main objective of this study is to quantify the potential overpressures due to vapour cloud explosions (VCEs) using the Process Hazard Analysis DNV Norway based PHAST 6.51 Software. The results are validated by the extent of the damage that had occurred. The estimation of the VCE shows that a maximum 1.0 bar overpressure was generated in the surrounding area. The initial assessment of the accident data roughly estimates the release mode, time, and amount of vaporized fuel. A more accurate estimate has been obtained by modelling the dispersion of vapour clouds in the surrounding atmosphere, which reveals trends and relationships for the occurrence of vapour cloud explosions.     

Measurement of gas detonation blast loads in semiconfined geometry

The ignition and explosion of combustible vapor clouds represents a significant hazard across a range of industries. In this work, a new set of gas detonations experiments were performed to provide benchmark blast loading data for non-trivial geometry and explosion cases. The experiments were designed to represent two different accident scenarios: one where ignition of the vapor cloud occurs shortly after release and another where ignition is delayed and a fuel concentration gradient is allowed to develop. The experiments focused on hydrogen-air and methane-oxygen detonations in a semiconfined enclosure with TNT equivalencies ranging from 9 g to 1.81 kg. High-rate pressure transducers were used to record the blast loads imparted on the interior walls of a 1.8 m × 1.8 m × 1.8 m test fixture. Measurements included detonation wave velocity, peak overpressure, impulse, and positive phase duration. A comparison of the pressure and impulse measurements with several VCE models is provided. Results show that even for the most simplified experimental configuration, the simplified VCE models fail to provide predictions of the blast loading on the internal walls of the test fixture. It is shown that the confinement geometry of the experiment resulted in multiple blast wave reflections during the initial positive phase duration portion of the blast loading, and thus, significantly larger blast impulse values were measured than those predicted by analytical models. For the pressure sensors that experienced normally-reflect blast waves for the initial blast impulse, the Baker-Strehlow and TNT equivalency models still struggled to accurately capture the peak overpressure and reflected impulse. The TNO multi-energy model, however, performed better for the case of simple normally-reflected blast waves. The results presented here may be used as validation data for future model or simulation development.     

A multivariable model for estimation of vapor cloud explosion occurrence possibility based on a Fuzzy logic approach for flammable materials

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.     

A societal risk study for transportation of class-3 hazmats – A case of Indian state highways

United Nations Class-3 hazardous materials (hazmats) are basically liquid products and transported in road tankers under ambient temperature and atmospheric pressure. They are mostly flammables and some of them are toxic (e.g. benzene) as well. The spillages due to collision related incidents involving the road tankers, carrying such hazmats through highways, pose not only flammability hazards due to pool fire, flash fire and vapor cloud explosion (VCE), but create substantial toxic hazards also. The paper presents the risk-based study of route evaluation of two state highways and one urban city road in western India on account of transportation of class-3 hazmats, namely benzene, toluene, p-xylene, methanol, cyclohexane and acetone. A comparative evaluation of study routes was undertaken based on their societal risks presented in terms of F–N curves and assessed against HSE, UK as well as VROM, The Netherlands risk acceptance criteria. Societal risks contribution of cyclohexane to the overall flammability risk mainly VCE is found to be the highest followed by acetone and benzene compared to other study hazmats. This is due to highly explosive nature of cyclohexane resulting into vapor cloud explosion. While acetone and methanol pool fires are likely to cause larger area of damage compared to others, benzene supersedes others as far as toxicity risk is concerned and larger evacuation area is encountered, as it poses greater Immediately Dangerous to Life or Health (IDLH) distance than others. Besides, study of initial isolation distance following an accident in case of benzene tanker found that benzene spillage requires larger initial isolation distance than others and so are the day and night protective action zone distances.     

Analysis and assessment of the Qingdao crude oil vapor explosion accident: Lessons learnt

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.     

氯乙烯储罐的事故后果分析

氯乙烯具有毒性和易燃易爆性,如果泄漏至空气中,可能产生中毒或爆炸事故。笔者以某化工厂氯乙烯储罐为例,分析氯乙烯储罐可能发生的事故;对其主要事故危害,即中毒、蒸气云爆炸、扩展气体沸腾蒸气爆炸3种事故进行后果模型分析;计算出发生3种事故对人员伤亡和设备损坏造成的危害区域,并提出建议和对策。该研究结果可为同类企业进行安全管理提供科学依据和参考,有助于企业制定防范措施以及事故应急救援预案,从而减少人员伤亡及财产损失。     

Fire and explosion hazard analysis during surface transport of liquefied petroleum gas (LPG): A case study of LPG truck tanker accident in Kannur,Kerala, India

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.     

基于主成分分析法的液体管道泄漏后果综合评价模型

基于主成分分析和后果评价模型,提出了一种液体管道泄漏后果综合评价方法。将液体管道泄漏后果划分为火灾、爆炸和中毒3大类14个基本指标,建立后果评价指标体系。在VCE等后果模拟计算的基础上得到初始数据,运用SPSS软件处理相关数据,使用主成分分析法得到各指标相互独立的综合评价模型。选择天津港某码头进行实例分析,运用该方法对该港口储运的15类有代表性液体危险化学品进行综合评价,得到了各化学品的综合评价值以及按照其发生泄漏后危险性大小的排序。结果表明,该方法适用于评价港口码头等储运多种液体危险化学品的行业。     

重大事故后果模拟法在天然气场站安全评价中的应用

场站是气田集输的枢纽,也是高风险存在和集中的场所。本论文采用重大事故后果模拟分析法建立天然气泄漏速率估算模型、蒸气云爆炸模型,并以陕北某一天然气场站为例,借助Risk System软件对天然气泄漏速率和泄漏量以及蒸气云爆炸最大事故进行数值模拟。模拟分析结果有助于对天然气场站可能发生的各种事故进行风险评价,也有助于对各类风险大的危险危害因素提出对应的安全对策措施,确保安全生产。     

A study of the blast wave shape from elongated VCEs

Elongated congestion patterns are common at chemical processing and petroleum refining facilities due to the arrangement of processing units. The accidental vapor cloud explosion (VCE) which occurred at the Buncefield, UK facility involved an elongated congested volume formed by the trees and undergrowth along the site boundary. Although elongated congested volumes are common, there have been few evaluations reported for the blast loads produced by elongated VCEs. Standard VCE blast load prediction techniques do not directly consider the impact of this congested volume geometry versus a more compact geometry.This paper discusses an evaluation performed to characterize the blast loads from elongated VCEs and to identify some significant differences in the resulting blast wave shape versus those predicted by well-known VCE blast load methodologies (e.g., BST and TNO MEM). The standard blast curves are based on an assumption that the portion of the flammable gas cloud participating in the VCE is hemispherical and located at grade level. The results of this evaluation showed that the blast wave shape for an elongated VCE in the near-field along the long-axis direction is similar to that for an acoustic wave generated in hemispherical VCEs with a low flame speed. Like an acoustic wave, an elongated VCE blast wave has a very quick transition from the positive phase peak pressure to the negative phase peak pressure, relative to the positive phase duration. The magnitude of the applied negative pressure on a building face depends strongly on the transition time between the positive and negative phase peak pressures, and this applied negative phase can be important to structural response under certain conditions. The main purpose of this evaluation was to extend previous work in order to investigate how an elongated VCE geometry impacts the resultant blast wave shape in the near-field. The influence of the normalized flame travel distance and the flame speed on the blast wave shape was examined. Deflagration and deflagration-to-detonation transition regimes were also identified for unconfined elongated VCEs as a function of the normalized flame travel distance and flame speed attained at a specified flame travel distance.     

工业过程爆炸事故模式及其破坏效应探讨

从工业生产中的介质类型出发,通过对内装固体的、液体的及气体的介质装置可能发生的爆炸事故和破坏效应进行分析预测,编制了相应的分析流程图。结果表明:无论从哪种介质进行分析,最终的爆炸事故模式只有凝聚相爆炸、气云爆炸、沸腾液体扩展蒸气云爆炸及各类形式的容器爆炸。简要分析了几种事故模式破坏效应的最佳计算模型和应用实例,证明了所做的分析预测和编制的流程图,可以很好地应用于判断事故模式中爆炸源性质及其破坏效应,是对爆源的一个定性分析方法,同时为爆炸能量计算的重要依据。工业过程爆炸事故模式及其破坏效应的研究对企业的安全生产及爆炸事故的预防具有一定的实用价值。     

氨分解装置中液氨储罐火灾爆炸危险性分析

以某金属处理企业氨分解装置中液氨储罐罐区为例,对液氨泄漏后火灾爆炸事故及其伤害范围进行了研究,用池火、蒸气云爆炸和沸腾液体扩展蒸气爆炸模型进行计算分析,给出火灾、爆炸事故的人员伤害和财产损失范围。结果表明:围堤堤内池火或罐内池火时,罐区建构筑物内的汽化器、管道等设备会因直接过火或热辐射导致损坏,建筑内人员死亡,但难以波及罐区之外;蒸气云爆炸产生相当于1192.72kgTNT爆炸的当量,爆炸的后果严重,应重点防范,防范的重点为液氨泄漏、点火源;沸腾液体扩展蒸气爆炸的火球半径56.1m,持续时间8.7s,死亡半径27.2m,其源于储罐受热或系统突然失效,液体瞬时泄漏汽化并遇点火源而发生,具有突发性且后果严重,企业应高度重视并严格储罐及系统的定期检验与校验、密切关注系统的有效运行。     

汽油介质储输运过程火灾爆炸危险性研究

由于汽油特殊的物化性质,在储输运过程中一旦发生泄漏极易造成火灾、爆炸事故, 从而导致重大人员伤亡及财产损失.针对汽油池火灾、流淌火灾及受限空间蒸气爆炸3种事 故形式,深入分析研究了它们的特点、特性参数及危险程度,为汽油储输运事故应急抢险方案的制定和具体实施提供参考.     

Study of the explosion parameters of vapor–liquid diethyl ether/air mixtures

The knowledge of the vapor–liquid two-phase diethyl ether (DEE)/air mixtures (mist) on the explosion parameters was an important basis of accident prevention. Two sets of vapor–liquid two-phase DEE/air mixtures of various concentrations were obtained with Sauter mean diameters of 12.89 and 22.90 μm. Experiments were conducted on vapor–liquid two-phase DEE/air mixtures of various concentrations at an ignition energy of 40.32 J and at an initial room temperature and pressure of 21 °C and 0.10 MPa, respectively. The effects of the concentration and particle size of DEE on the explosion pressure, the explosion temperature, and the lower and upper flammability limits were analyzed. Finally, a series of experiments was conducted on vapor–liquid two-phase DEE/air mixtures of various concentrations at various ignition energies. The minimum ignition energies were determined, and the results were discussed. The results were also compared against our previous work on the explosion characteristics of vapor–liquid two-phase n-hexane/air mixtures.     

井喷失控点火时间与方位探讨

利用计算流体力学方法(CFD)对井喷失控后天然气扩散过程进行研究,在有限元基础上建立模型,采用κ-ε紊流模型求解得出井喷失控后可燃性蒸气云随时间、风速变化的影响情况,求出稳态以后易爆区域的蒸气云形状。取5.0%和15%作为甲烷的爆炸上、下限,在不同区域进行点火求解爆燃结果,通过比较给出推荐的点火时间和点火方位。该研究成果可对井喷失控蒸气云爆燃危害性进行预测,有助于指导井喷失控进行点火放喷工作,避免爆燃事故的发生。     

LPG船液货泄漏事故风险评估系统研究

通过对液化石油气(LPG)船舶液货舱泄漏事故危险度因素分析,建立液化气液体货物泄漏源强、蒸气释放源强和蒸气扩散计算模型,并制定泄漏事故风险评价流程,基于VB语言编写泄漏事故风险评估系统。利用该系统能够计算得出泄漏事故发生后蒸发气在不同时刻不同区域的蒸发气浓度、爆炸或火灾后对生命财产的伤害半径以及伤害程度等相关参数。对某航行状态下的LPG实船进行模拟分析,结果表明能够对LPG船舶泄漏事故进行有效风险评估,并能对船舶航行安全应急预案的制定和事故后海事鉴定提供一定的技术帮助。     

天然气管道泄漏爆炸实验分析

天然气管道失效造成泄漏爆炸给周围人员带来非常严重的危害,对其危害范围的研究对输气管道设计和运行具有重要的意义。常见的天然气管道泄漏爆炸伤害半径计算方法有蒸气云爆炸(VCE)定量评价模型、TNO多能法评价模型、API pub 581定量后果评价模型和炸药爆炸经验公式。为验证不同评价模型在受限空间的预测效果,利用天然气爆炸试验台进行了受限空间爆炸实验,得到最大压强与距离经验关系,计算出天然气浓度为7%、9%和11%情况下爆炸死亡半径。计算结果与不同经验模型预测结果比较,表明当天然气浓度为7%~11%时,蒸气云爆炸(VCE)定量评价模型和炸药爆炸经验模型与实验结果最为接近,误差分别为-113%和189%,TNO多能法评价模型和API pub 581定量后果评价模型预测结果偏小。结论对有限空间天然气管道爆炸研究具有实际意义。