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.     

Fuzzy dynamic risk-based maintenance investment optimization for offshore process facilities

A methodology for maintenance planning is developed which helps in improving the reliability of the components and safety performance in process facilities. This methodology helps design an optimum safety maintenance investment plan by integrating the optimization techniques and a fuzzy dynamic risk-based method. Intuitionistic Fuzzy Analytic Hierarchy Process (IFAHP) is applied to deal with uncertain data. The proposed approach employs multi-experts’ knowledge which helps to optimize the maintenance investments. A separator system in an offshore process facility platform is selected as a case study to demonstrate the application of the proposed methodology. A practical example in the separator system is surveyed and potential failures and Basic Events (BEs) are identified. Finally, a risk-based maintenance plan is provided for future safety investment analysis. The results indicate that the developed methodology estimates the risk more accurately, which enhances the reliability of future process operations.     

固体和液体危险化学品仓库火灾风险分析方法探讨

固体和液体化学品仓库火灾是企业安全面临的经常性威胁之一,需考虑火灾中毒性燃烧产物释放和非燃烧产生的毒性物质释放。结合火灾风险分析方法,阐述火灾场景中各要素及相互关系,主要包括火灾场景、物质、燃烧速率、源项、毒性、扩散、概率和风险之间的关系,火灾场景考虑持续时间、面积和通风率的影响,物质中考虑平均结构式和燃烧方程,源项中考虑形成的产物、燃烧物质每千克的散发和活性物质百分比,毒性中考虑HCl,NO2,SO2和非燃烧产生的物质。基于储存物质平均结构式,建立燃烧关系方程。燃烧速率计算取决于可用的氧气量和需要的氧气量,分为面积受限的燃烧速率和氧气受限的燃烧速率。最后给出毒性燃烧产物HCl,NO2,SO2释放量和非燃烧产生的毒性物质释放量的计算方法,同时以毒性燃烧产物释放场景后果模拟为例说明仓库发生火灾的后果严重性,为仓库火灾风险分析提供借鉴。     

Advanced CFD modeling on vapor dispersion and vapor cloud explosion

The main objective of this study is to quantify the potential overpressures due to Vapor Cloud Explosions (VCEs) and the potential gas buildup by using Computation Fluid Dynamics (CFD) for onshore or offshore facilities.A series of CFD simulations and analyses have been performed for the various vapor dispersion scenarios, covering different release rates and release locations. The overpressure that could result from the potential VCE is assessed by CFD simulation for the largest explosive transient gas cloud. The results from the analyses also comprise an extensive picture of probable leak scenarios having the potential to make an explosive gas cloud.The CFD analysis results could be applied to provide input for detailed risk-based design and risk analysis, to find safe and cost-optimal design against explosions.     

Offshore safety case approach and formal safety assessment of ships

PROBLEM: Tragic marine and offshore accidents have caused serious consequences including loss of lives, loss of property, and damage of the environment. METHOD: A proactive, risk-based "goal setting" regime is introduced to the marine and offshore industries to increase the level of safety. DISCUSSION: To maximize marine and offshore safety, risks need to be modeled and safety-based decisions need to be made in a logical and confident way. Risk modeling and decision-making tools need to be developed and applied in a practical environment. SUMMARY: This paper describes both the offshore safety case approach and formal safety assessment of ships in detail with particular reference to the design aspects. The current practices and the latest development in safety assessment in both the marine and offshore industries are described. The relationship between the offshore safety case approach and formal ship safety assessment is described and discussed. Three examples are used to demonstrate both the offshore safety case approach and formal ship safety assessment. The study of risk criteria in marine and offshore safety assessment is carried out. The recommendations on further work required are given. IMPACT ON INDUSTRY: This paper gives safety engineers in the marine and offshore industries an overview of the offshore safety case approach and formal ship safety assessment. The significance of moving toward a risk-based "goal setting" regime is given.     

Revised fire consequence models for offshore quantitative risk assessment

Offshore oil and gas platforms are well known for their compact geometry, high degree of congestion, limited ventilation and difficult escape routes. A small mishap under such conditions can quickly escalate into a catastrophe. Among all the accidental process-related events occurring offshore, fire is the most frequently reported. It is, therefore, necessary to study the behavior of fires and quantity the hazards posed by them in order to complete a detailed quantitative risk assessment. While there are many consequence models available to predict fire hazards-varying from point source models to highly complex computational fluid dynamic models—only a few have been validated for the unique conditions found offshore.

In this paper, we have considered fire consequence modeling as a suite of sub-models such as individual fire models, radiation model, overpressure model, smoke and toxicity models and human impact models. This comprehensive suite of models was then revised by making the following modifications: (i) fire models: existing fire models have been reviewed and the ones most suitable for offshore conditions were selected; (ii) overpressure impact model: a model has been developed to quantify the overpressure effects from fires to investigate the possible damage from the hot combustion gases released in highly confined compartments; (iii) radiation model: instead of a point/area model, a multipoint grid-based model has been adopted for better modeling and analysis of radiation heat flux consequences. A comparison of the performance of the revised models with the ones used in a commercial software package for offshore risk assessment was also carried out and is discussed in the paper.     

The study of burning behaviors and quantitative risk assessment for 0# diesel oil pool fires

The liquid fuel safety issues on fuel storage, transportation and processing have gained most attention because of the high fire risk. In this paper, some 0# diesel pool fire experiments with different diameters (0.2–1 m) were conducted with initial fuel thicknesses of 2 cm and 4 cm, respectively, to obtain liquid fuel combustion characteristics. Some key parameters including mass burning rate, flame height and the flame radiative heat flux, associated with fire risk, were investigated and determined. Subsequently, a detail quantitative risk assessment framework for 0# diesel pool fire is proposed based on the 0# diesel burning characteristics. In the framework, the probability of personal dead and the facility failure are calculated by the vulnerability models, respectively. In the end, 10 special tank fire scenarios were selected to show the whole risk calculation process. The tank diameter and the distance to pool fires were paid more attention in the cases. The safety distances in the cases are provided for the persons and nearby facilities, respectively. The paper enriches the basic experimental data and the provided framework is useful to the management of 0# diesel tank areas.     

Risk-based siting considerations for LNG terminals – Comparative perspectives of United States & Europe

Siting regulations and industrial standards for liquefied natural gas (LNG) terminals are evolving along different paths within Europe and the United States (U.S.). The 49 Code of Federal Regulations (CFR), Part 190 continues to delineate the United States process to adopt and revise safety regulations pertaining to LNG terminals and peak shaving plant sitting.¹ Embodied in these regulations are rich legal and regulatory traditions that are unique to the U.S. perspective. For example, the public is encouraged to petition existing regulations and to comment on regulatory proposals. Litigation within the U.S. court system is another means by which industry and the public may seek regulatory change. This approach promotes public involvement in governmental oversight and creates a distinctive obligation and accountability for U.S. regulatory agencies, which uniquely shape technical, safety, risk mitigation, and societal risk perspectives for siting LNG terminals.European traditions shape siting regulations for LNG terminals as well. Though American siting guidance includes references to the National Fire Protection Association’s NFPA 59A and 49 CFR, Part 193, European developers also apply the guidance within EN 1473 – a risk-based case-by-case analysis directive.^{2, 3 and 4} The NFPA 59A standard is applied for a basis to examine property line spacing as they pertain or may relate to off-site hazard impacts. The European approach applies the assessment and suitability of code compliance and the application of accepted engineering practices. In addition the approach incorporates the application of empirical risk assessments and computational modeling to reach an understanding of risk exposures. European policies set limits on the population’s cumulative exposure to facility risks and require LNG facility developers not to exceed established risk criteria.This paper describes how the U.S. and Europe site LNG terminals, identifies key differences in their risk-based approaches, and explains why these differences exist. This discussion also examines historical precedents that have influenced regulations and approval processes for siting LNG terminals within each continent.     

Quantitative risk analysis of fire and explosion on the top-side LNG-liquefaction process of LNG-FPSO

Since the massive use and production of fuel oil and natural gas, the excavating locations of buried energy-carrying material are moving further away from onshore, eventually requiring floating production systems like floating production, storage and offloading (FPSO). Among those platforms, LNG-FPSO will play a leading role to satisfy the global demands for the natural gas in near future; the LNG-FPSO system is designed to deal with all the LNG processing activities, near the gas field. However, even a single disaster on an offshore plant would put the whole business into danger. In this research, the risk of fire and explosion in the LNG-FPSO is assessed by quantitative risk analysis, including frequency and consequence analyses, focusing on the LNG liquefaction process (DMR cycle). The consequence analysis is modeled by using a popular analysis tool PHAST. To assess the risk of this system, 5 release model scenarios are set for the LNG and refrigerant leakages from valves, selected as the most probable scenarios causing fire and explosion. From the results, it is found that the introduction of additional protection methods to reduce the effect of fire and explosion under ALARP criteria is not required, and two cases of the selection of independent protection layers are recommended to meet the SIL level of failure rate for safer design and operation in the offshore environment.     

基于RBI与多米诺效应的输气站场设备定量风险评价

针对目前输气站场设备风险评价方法仅以单个设备为评价对象,并未考虑设备间相互影响的特点,提出将多米诺效应分析引入输气站场设备风险评价当中,再结合RBI(基于风险检测方法)对输气站场设备进行定量风险评价。首先,计算所评价设备的失效概率与危险指数,得到设备固有风险;然后对设备的多米诺效应风险进行计算;最后,得到设备总风险。实例分析表明,考虑多米诺效应风险后,站场单个设备的风险要明显增大。     

易燃易爆危险品道路运输火灾事故应急区域的确定方法

从消防监管的角度给出了道路运输易燃易爆危险品的火灾危险性分级标准,分析了典型泄漏事故后果场景和常见的泄漏规模类型.介绍了美国消防协会NFPA471、应急响应手册ERG2008危险品运输事故初期区域的确定方法,并提出了基于影响半径的危险品道路运输火灾事故现场应急区域和人员疏散范围的确定方法.提出对于易燃易爆危险品道路运输事故应急区域的确定,在初期可优先采用ERG 2008提供的初期隔离距离与防护距离进行先期处置,然后根据运输危险品的类型、运输量和影响区人员总数进行定量评估分析,以确定适当的应急区域范围.依据运输道路场所环境和事故场景特点,快速而合理的确定事故应急隔离区和疏散区,可较科学地应对突发性灾难事故,采取快速应急响应措施,优化消防警力配备.该文研究提出的方法和研究结论,可为危险品道路运输消防应急力量优化调度,现场指挥员采取有效措施开展抢险救援行动提供技术支持,有利于现场事故应急处置和人员快速安全疏散.     

极端海况下海洋石油结构的风险评估

根据中国海上石油工业缺乏独立的风险评价体系的现状 ,笔者对极端海况进行了环境荷载的联合概率分析 ,利用随机模拟技术 ,求解结构的失效概率 ,提出结构失效分析的新方法 ,并利用DNV提供的历史数据 ,对结构失效的后果做了适当分析。以埕北 12 C井组平台作为实例 ,对平台甲板高程 (AirGap)失效分析进行了实例计算。结果表明 ,使用多维联合极值分布理论及相应的求解方法 ,是离岸工程结构物风险评估的重要手段。     

Methodology for consequence analysis of LNG releases at deepwater port facilities

A methodology to perform consequence analysis associated with liquefied natural gas (LNG) for a deepwater port (DWP) facility has been presented. Analytical models used to describe the unconfined spill dynamics of LNG are discussed. How to determine the thermal hazard associated with a potential pool fire involving spilled LNG is also presented. Another hazard associated with potential releases of LNG is the dispersion of the LNG vapor. An approach using computational fluid dynamics tools (CFD) is presented. The CFD dispersion methodology is benchmarked against available test data. Using the proposed analysis approach provides estimates of hazard zones associated with newly proposed LNG deepwater ports and their potential impact to the public.     

Risk and mitigation of self-heating and spontaneous combustion in underground coal storage

While the self-heating and spontaneous combustion of coal is a known challenge at coal mines and storage sites, there are known methods for mitigating this challenge for typical open stockpile storage. However, closing the storage will reduce access for corrective action, and it is then important to manage the storage and its transport system with added attention without unduly adding cost or hindering availability. This paper aims to discuss the risk, prevention and extinguishing of fires in closed coal storage facilities, particularly in light of the experience with the Salmisaari underground rock storage facility in Finland. The observed autoignition events have indicated an array of contributing factors, some of which are unique to underground silo storage facilities. On the other hand, many features of the storage facilities can be compared with other extant closed storage systems. The factors affecting fire risk are described and the associated fault and event trees are outlined for autoignition at underground storage. Drawing upon the experiences with past events of self-heating and spontaneous combustion, recommendations are given on cost-effective preventive, corrective and other mitigating action for minimising fire risk and promoting storage availability.     

Risk indicators for major hazards on offshore installations

Major hazards risk indicators are proposed for offshore installations, based on what has been used by the Petroleum Safety Authority Norway for the Risk Level approach in the Norwegian offshore petroleum industry. Since 2002 also leading indicators are used, in the sense that indicators for barrier performance are included together with the lagging indicators. There are individual indicators for a number of barrier functions, including fire and gas detection, a number of safety valves, active fire protection and mustering of personnel. The performance of the leading indicators during several years of data collection as well as lessons learned from the project are discussed. This is followed by a review of how indicators may be used by individual companies, and how the lessons may be utilised by individual companies to develop risk indicators for individual installations as well as company wide indicators.     

A risk-based approach to design warning system for processing facilities

Alarm flooding is a major safety issue in today's processing facilities. Important recommendations are available for alarm management; however, they are often violated in practice, especially in the alarm systems implemented through the distributed control system. An effective process alarm prioritization and management system is desired for a safe and effective operation of a process facility.In present work, authors address two main issues related to an alarm system – the reliability and the prioritization of the alarms. The main objective is to deal with the alarm-flooding problem in process facilities. A multi alert voting system based on sensor redundancy approach is proposed to improve the reliability. A quantitative risk-based alarm management approach is proposed to address the flooding issue. In the risk-based approach, an integrated model consisting of the probability (P), the impact (I) of the potential hazards, and the process safety time is proposed to prioritize these raised alarms.The proposed approach is further explained by a reactor system with pressure and temperature variable monitoring and controls, where the hazards associated with two alerts caused by over high pressure and over high temperature are analyzed and integrated with response time for alarms generation and prioritization.     

Review on the emergency evacuation in chemicals-concentrated areas

For serious accidents such as toxic/flammable release, fire and explosion in chemicals-concentrated areas, one primary issue is to evacuate on-site workers from potential affected zones. In this paper, based on corresponding reports, photos and videos, some accidents involving emergency evacuation are firstly investigated to present important and interesting problems to be considered in practice. These problems are summarized into three kinds of aspects including the poor efficiency of emergency plans, the low accuracy and high time-consuming calculation for evacuation route planning, and the neglection of evacuee's behavior and decision-making. Two main factors influencing the behavior and decision-making of evacuees are concluded as potential risk and impact from hazard sources, and the visibility at different locations. Then, the literature with respect to the emergency evacuation under toxic gas leakage, fire and visibility-limited conditions are reviewed. The key problems are related to ignoring the time-consuming requirement in emergency activities and domino effects of accidents, and the oversimplification of corresponding models. At last, from the famous cellular automata (CA) for emergency evacuation and atmospheric dispersion, a new general research framework for evacuation in chemicals-concentrated areas is proposed. It relies strongly on the quantitative assessment of risk, the establishment of individual visibility field, the use of CA coupled with artificial neural networks, and the optimal route planning. This paper could be useful for realistic problems on emergency evacuation in chemicals-concentrated areas.     

Human error risk analysis in offshore emergencies

Human factors play an important role in the completion of emergency procedures. Human factors analysis is rooted in the concept that humans make errors, and the frequency and consequences of these errors are related to work environment, work culture, and procedures. This can be accounted for in the design of equipment, structures, processes, and procedures. As stress increases, the likelihood of human error also increases. Offshore installations are among the harshest and most stressful work environments in the world. The consequences of human error in an offshore emergency can be severe.A method has been developed to evaluate the risk of human error during offshore emergency musters. Obtaining empirical data was a difficult process, and often little information could be drawn from it. This was especially an issue in determining the consequences of failure to complete muster steps. Based on consequences from past incidents in the offshore industry and probabilities of human error, the level of risk and its tolerability are determined. Using the ARAMIS (accidental risk assessment methodology for industries) approach to safety barrier analysis, a protocol for choosing and evaluating safety measures to reduce and re-assess the risk was developed. The method is assessed using a case study, the Ocean Odyssey incident, to determine its effectiveness. The results of the methodology agree with the analysis of survivor experiences of the Ocean Odyssey incident.