Risk assessment of fire accidents in chemical and hydrocarbon processing industry

Fire disasters are among the most dangerous accidents in the chemical and hydrocarbon processing industry. Fires have been the source of major accidents such as the Piper Alpha disaster (1976), the BP Texas City disaster (2005), the Buncefield oil depot fire (2005), Puerto Rico’s fire accident (2009), and the Jaipur fire accident (2009). The catastrophic impact of fire accidents necessitates a detailed understanding of the mechanisms of their occurrence and evolution in a complex engineering system. Detailed understanding will help develop fire prevention and control strategies. This thesis aims to provide a detailed understanding of fire risk in the hydrocarbon production and processing industry. In order to realize this objective, the work presented in the thesis includes three parts: i) Developing a procedure to study potential fire accident scenarios in an offshore facility with different ignition source locations. This procedure helps to design safety measures. The effectiveness of safety measures is verified using a computational fluid dynamics (CFD) code. This work emphasizes that an FLNG layout must be considered with the utmost care since it is the most effective measure in limiting a potential LNG release and subsequent dispersion effect, and directly influences the fire dynamics and thus limits the potential damage. ii) An integrated probabilistic model for fire accident analysis considering the time-dependent nature of the fire is developed. The developed model captures the dynamics of fire evolution using three distinct techniques Bayesian networks, Petri Nets, and a CFD model. The Bayesian network captures the logical dependence of fire causation factors. The Petri Net captures the time-dependent evolution of a fire scenario. The CFD model captures the dimension and impact of the fire accident scenario. The results in this work show that a time-dependent probability analysis model is necessary for fire accidents. iii) Whether fire alone can cause a domino effect is demystified in the last work. A solid-flame model is used in a CFD framework to calculate the escalation vector for a domino effect; escalation probability is assessed using a probit model. The results demonstrate that a pool fire alone sometimes may not cause a domino effect in the current industry. It is other factors, such as explosion and hydrocarbon leakage, work together with a pool fire to escalate into a domino event, for example, the results shown in the case study of the Jaipur fire accident

QRA with respect to domino effects and property damage

In 1996 the European Union adopted the Seveso II Directive. The Directive stated actions to be taken in the process industry in order to prevent and limit the impact of serious chemical accidents. In the Directive it is clearly stated that domino effects shall be considered, but the level of detail required is not specified. Due to that fact and the high degree of complexity linked to domino effects, these aspects are mostly dealt with in a qualitative manner. Such approach leads to subjective assessments and is highly dependent on simplified assumptions, leading to results that may be questionable. Thus, it would be beneficial to develop a method that incorporates the risk of domino effects in a quantitative risk analysis (QRA), which has been the aim of this thesis. The method was developed based on a literature review of existing research. Focus was on integrating domino effects as a natural part of a QRA without compromising the timeframe associated to a QRA. The developed method has been applied in a case study of an oil refinery in order to evaluate how well it is applicable in practise. During the case study, the method has proven to enable the risk of property damage with regard to domino effects to be quantitatively analysed. The results from the case study, evidence the importance of taking domino effects into consideration in QRAs, as the risk may be underestimated if not

Calculation of the flame size from burning liquid pools

The calculation of the consequences associated with a pool fire consists in a stepwise procedure where a number of parameters must be characterized, which depend on the geometrical size and shape of the flame. A number of calculation models exists in the literature, characterized by different levels of accuracy and complexity. In the present work we will focus on the characterization of the geometrical configuration of the flame generated from a pool fire: some of the most commonly adopted models will be shortly recalled, and compared against experimental data taken from the literature. It is expected that this would provide useful information about the range of applicability and the level of accuracy of these models. Also, it will help improve the quality of the results, and reduce the time required for carrying out important applications such as consequence assessment and risk analysis, where a large number of calculations must be run

Computational fluid dynamics (CFD) based approach to consequence assessment of accidental release of hydrocarbon during storage and transportation

This thesis investigated the risk of accidental release of hydrocarbons during transportation and storage. Transportation of hydrocarbons from an offshore platform to processing units through subsea pipelines involves risk of release due to pipeline leakage resulting from corrosion, plastic deformation caused by seabed shakedown or damaged by contact with drifting iceberg. The environmental impacts of hydrocarbon dispersion can be severe. Overall safety and economic concerns of pipeline leakage at subsea environment are immense. A large leak can be detected by employing conventional technology such as, radar, intelligent pigging or chemical tracer but in a remote location like subsea or arctic, a small chronic leak may be undetected for a period of time. In case of storage, an accidental release of hydrocarbon from the storage tank could lead pool fire; further it could escalate to domino effects. This chain of accidents may lead to extremely severe consequences. Analyzing past accident scenarios it is observed that more than half of the industrial domino accidents involved fire as a primary event, and some other factors for instance, wind speed and direction, fuel type and engulfment of the compound. In this thesis, a computational fluid dynamics (CFD) approach is taken to model the subsea pipeline leak and the pool fire from a storage tank. A commercial software package ANSYS FLUENT Workbench 15 is used to model the subsea pipeline leakage. The CFD simulation results of four different types of fluids showed that the static pressure and pressure gradient along the axial length of the pipeline have a sharp signature variation near the leak orifice at steady state condition. Transient simulation is performed to obtain the acoustic signature of the pipe near leak orifice. The power spectral density (PSD) of acoustic signal is strong near the leak orifice and it dissipates as the distance and orientation from the leak orifice increase. The high-pressure fluid flow generates more noise than the low-pressure fluid flow. In order to model the pool fire from the storage tank, ANSYS CFX Workbench 14 is used. The CFD results show that the wind speed has significant contribution on the behavior of pool fire and its domino effects. The radiation contours are also obtained from CFD post processing, which can be applied for risk analysis. The outcome of this study will be helpful for better understanding of the domino effects of pool fire in complex geometrical settings of process industries. The attempt to reduce and prevent risks is discussed based on the results obtained from the numerical simulations of the numerical models

Modelling an integrated impact of fire, explosion and combustion products during transitional events caused by an accidental release of LNG

In a complex processing facility, there is likelihood of occurrence of cascading scenarios, i.e. hydrocarbon release, fire, explosion and dispersion of combustion products. The consequence of such scenarios, when combined, can be more severe than their individual impact. Hence, actual impact can be only representedby integration of above mentioned events. A novel methodology is proposed to model an evolving accident scenario during an incidental release of LNG in a complex processing facility. The methodology is applied to a case study considering transitional scenarios namely spill, pool formation and evaporation of LNG, dispersion of natural gas, and the consequent fire, explosion and dispersion of combustion products using Computational Fluid Dynamics (CFD). Probit functions are employed to analyze individual impacts and a ranking method is used to combine various impacts to identify risk during the transitional events.The results confirmed that in a large and complex facility, an LNG fire can transit to a vapor cloud explosion ifthe necessary conditions are met, i.e.the flammable range, ignition source with enough energy and congestion/confinement level. Therefore, the integrated consequences are more severe than those associated with the individual ones, and need to be properly assessed. This study would provide an insight for an effective analysis of potential consequences of an LNG spill in any LNG processing facility and it can be useful for the safety measured design of process facilities

Sustainability and risk management of LNG as a fuel for marine transportation

The use of liquefied natural gas (LNG) as an alternative ship fuel marks a fundamental step towards the reduction of emissions linked to maritime transportation of goods and passengers. Despite the positive safety record of the LNG shipping industry, natural gas is a hazardous substance and safety concerns for its use onboard passenger ships demand a thorough evaluation. This study aims at a comprehensive safety and sustainability assessment of marine LNG technologies, focusing on small-scale applications, seeking to fill the current knowledge gap in this field. An in-depth evaluation of the safety of existing technologies for LNG bunkering and onboard fuel gas supply systems is performed, providing key information about the credible accident scenarios and their expected consequences. The safety criticalities are identified based on the application of specifically developed models for the evaluation of the inherent safety performance of LNG bunkering and propulsion technologies. Another part of the work is dedicated to the development of a computational fluid dynamic (CFD) setup to model the behaviour of cryogenic tanks exposed to accidental hydrocarbon fires, overcoming the limitations of the previous modelling approaches, and providing precise data for further analysis of the tank structural integrity under extreme conditions. Furthermore, a preliminary CFD modelling of LNG fire scenario consequences occurring inside the fuel preparation room of gas-fuelled ships is carried out to evaluate the heat flux received by the ship structure. The obtained results represent a first step towards a wider approach aimed at enhancing the safety of the entire LNG supply for maritime propulsion. Furthermore, these results can make a valuable contribution to support the decision-making process for shipowners and port authorities in the design and safety assessment of such systems, both in port areas and onboard ships, also providing guidance for emergency responders

Accidental release of Liquefied Natural Gas in a processing facility: Effect of equipment congestion level on dispersion behaviour of the flammable vapour

An accidental leakage of Liquefied Natural Gas (LNG) can occur during processes of production, storage andtransportation. LNG has a complex dispersion characteristic after release into the atmosphere. This complexbehaviour demands a detailed description of the scientific phenomena involved in the dispersion of the releasedLNG. Moreover, a fugitive LNG leakage may remain undetected in complex geometry usually in semi-confined orconfined areas and is prone to fire and explosion events. To identify location of potential fire and/or explosionevents, resulting from accidental leakage and dispersion of LNG, a dispersion modelling of leakage is essential.This study proposes a methodology comprising of release scenarios, credible leak size, simulation, comparison ofcongestion level and mass of flammable vapour for modelling the dispersion of a small leakage of LNG and itsvapour in a typical layout using Computational Fluid Dynamics (CFD) approach. The methodology is applied to acase study considering a small leakage of LNG in three levels of equipment congestion. The potential fire and/orexplosion hazard of small leaks is assessed considering both time dependent concentration analysis and areabased model. Mass of flammable vapour is estimated in each case and effect of equipment congestion on sourceterms and dispersion characteristics are analysed. The result demonstrates that the small leak of LNG can createhazardous scenarios for a fire and/or explosion event. It is also revealed that higher degree of equipmentcongestion increases the retention time of vapour and intensifies the formation of pockets of isolated vapourcloud. This study would help in designing appropriate leak and dispersion detection systems, effective monitoring procedures and risk assessmen

Study of FSRU-LNGC System Based on a Quantitative Multi-cluster Risk Informed Model

PresentationThe offshore LNG terminal, referred to as LNG floating storage unit or floating storage and re- gasification unit (FSRU), performs well on both building process and operation process. The LNG FSRU is a cost-effective and time efficient solution for LNG transferring in the offshore area, and it brings minimal impacts to the surrounding environment as well. This paper proposed a systematic method to integrate chemical process safety with maritime safety analysis. The evaluation network was adopted to process a comparison study between two possible locations for LNG offshore FSRU. This research divided the whole process into three parts, beginning with the LNG Carrier navigating in the inbound channel, the berthing operation and ending with the completion of LNG transferring operation. The preferred location is determined by simultaneously evaluating navigation safety, berthing safety and LNG transferring safety objectives based on the quantitative multi-cluster network multi-attribute decision analysis (QMNMDA) method. The maritime safety analysis, including navigational process and berthing process, was simulated by LNG ship simulator and analyzed by statistical tools; evaluation scale for maritime safety analysis were determined by analyzing data from ninety experts. The chemical process safety simulation was employed to LNG transferring events such as connection hose rupture, flange failure by the consequence simulation tool. Two scenarios, i.e., worst case scenario and maximum credible scenario, were taken into consideration by inputting different data of evaluating parameters. The QMNMDA method transformed the evaluation criteria to one comparable unit, safety utility value, to evaluate the different alternatives. Based on the final value of the simulation, the preferred location can be determined, and the mitigation measures were presented accordingly

Modelling pressure tanks under fire exposure: past experience, current challenges and future perspectives

CFD and lumped parameter models are available in the literature for the analysis of pressure tanks under fire exposure. The first type of models allows for a detailed representation of the phenomena occurring in the tank, providing accurate results in terms of pressurization rate and temperature distribution. However, they are computationally expensive and are currently unable to simulate PRV opening. Lumped parameter models run in very short time, but may lead to not conservative results. The present contribution provides an overview of the strengths and limitations of both approaches, highlighting the new challenges posed by the development of models for the analysis of cryogenic tanks exposed to fire

Validation of CFD codes for risk analysis of accidental hydrocarbon fires

Accidental releases of flammable hydrocarbons in chemical process industries can trigger severe hazards: explosions, fires, and dispersion of toxic vapour clouds. Explosions and toxic releases may injure people within large damage radius; however, fires are the most common accidental events that may lead to catastrophic consequences in terms of life and property losses. Within this framework, the prediction of the related-fire effects may significantly contribute to identify measures needed to eliminate or mitigate the consequences of accidents in processing environments. Semi-empirical methods can provide rapid estimations of the flame-geometry descriptors as well as estimations of the heat flux received at a given distance from the fire origin. Based on that information, active protection systems and inherent safer design measures (i.e. safety distances between equipment) can be determined to prevent major fire accidents. Nevertheless, these are based on empirical and statistical data, and do not cover the overall characteristics of the fire behaviour. Computational Fluid Dynamics (CFD) modelling can provide more detailed insights of the related fire effects considering additional complexity, such as different geometries and alternative boundary conditions, and representing different fire sizes: from small to large scale fires. Nevertheless, CFD requires detailed input data, expert knowledge on the phenomenon simulated and on the physical models implemented, and demands high computational resources. The use of CFD modelling for technological risk analysis is still incipient, so detailed validation exercises are needed before their use in real applications. This thesis is mainly aimed at assessing the predictive capabilities of different CFD codes (FDS, FLACS-Fire and FireFOAM) when predicting the hazardous effects of hydrocarbon pool fires and jet fires. Specifically, large-scale pool fires of diesel and gasoline (from 1.5 to 6 m-diameter), vertical sonic jet fires of propane (from 0.09 to 0.34 kg/s with orifice diameters of from 10 to 25.5 mm), vertical subsonic jet fires of methane in normal- and sub- atmospheric pressures (from 0.6 to 1 bar with an orifice diameter of 3 mm), and vertical and horizontal subsonic jet fires of propane (from 0.007 to 0.11 kg/s with orifice diameters of from 12.75 to 43.1 mm-diameter) have been modelled in different CFD codes. Prescribing burning rates provide accurate predictions of the pool fire effects with maximum cell sizes of 0.2 m. On the other hand, the cell sizes of sonic and subsonic jet fires should be determined by considering a fire characteristic diameter of 16 and 12, respectively. A minimum number of 400 solid angles is recommended to obtain accurate estimations of the thermal flux. Based on the numerous computational simulations performed, Best Practice Guidelines (BPG) are developed to determine a code as ‘valid’ or not, and to provide guidance on the most suitable modelling settings when performing CFD simulations of accidental hydrocarbon fires. The BPG usefulness is proved through a case study of an oil storage farm located in the Port of Barcelona. Large over-estimations of the heat flux values are found with semi-empirical correlations and thus, the safety measures required would be very conservative and costly. Therefore, CFD modelling is recommended method to perform detailed FHA in chemical and process industries.Les fuites accidentals d'hidrocarburs inflamables en indústries de processos químics poden desencadenar greus riscos: explosions, incendis i dispersions de núvols de vapor tòxics. Les explosions i les dispersions de gasos poden ferir a persones en un radi de danys més gran; tanmateix, els incendis són els esdeveniments accidentals més habituals que poden causar conseqüències catastròfiques en termes de pèrdues de vida i de propietats. En aquest marc, la predicció dels efectes dels incendis pot contribuir significativament a identificar les mesures necessàries per eliminar o mitigar les conseqüències dels accidents en entorns de processos. Els mètodes semi-empírics poden proporcionar estimacions ràpides de la geometria de la flama així com del flux de calor rebut a una distància determinada de l'origen de l'incendi. A partir d'aquesta informació, es poden implementar sistemes de protecció actius i mesures de disseny inherents (és a dir, distàncies de seguretat entre equips) per evitar grans accidents d'incendis. No obstant, aquestes es basen en dades empíriques i no cobreixen les característiques generals del desenvolupaments dels incendis. El modelatge de dinàmica de fluids computacionals (CFD) pot proporcionar una visió més detallada dels efectes dels incendis ja que tenen en compte la complexitat addicional dels escenaris, com ara geometries i condicions límits diferents, i poden representar diferents mides d'incendis: des de petita fins a gran escala. No obstant, les simulacions CFD requereixen dades d'entrada detallades, coneixements experts sobre el fenomen simulat i sobre els models físics implementats, i exigeixen elevats recursos computacionals. L'ús del modelat CFD per a l'anàlisi del risc tecnològic encara és incipient, i per tant, es necessiten exercicis de validació abans de fomentar la seva aplicació en casos reals. Aquesta tesi està dirigida principalment a avaluar les capacitats predictives de diferents codis CFD (FDS, FLACS-Fire i FireFOAM) alhora de predir els efectes perillosos dels incendis de bassa i de dolls de foc. Concretament, de bassa a gran escala amb dièsel i gasolina (d'1.5 fins a 6 m de diàmetre), dolls de foc verticals sònics amb propà (de 0.09 fins a 0.34 kg/s amb diàmetres d'orificis compresos entre 10 i 25.5 mm), dolls de foc verticals subsònics amb metà a diferents pressions atmosfèriques (des de 0.6 fins a 1 bar amb un diàmetre d'orifici de 3 mm), i dolls de foc verticals i horitzontals subsònics amb propà (de 0.007 fins a 0.11 kg/s amb diàmetres d'orifici compresos entre 12.75 i 43.1 mm) s¿han simulat amb les diferents eines CFD. La prescripció de la velocitat de combustió proporciona prediccions precises dels efectes dels incendis de bassal quan la mida de la cel·la és de 0.2 m com a màxim. D'altra banda, la mida de la cel·la per a simulacions de dolls de foc sònics i subsònics s'ha de determinar tenint en compte un diàmetre característic de l'incendi de 16 i 12, respectivament. Es recomana un número mínim de 400 angles sòlids per obtenir estimacions precises dels fluxos tèrmics. A partir de les nombroses simulacions computacionals realitzades es desenvolupament directrius de bones pràctiques (BPG) per determinar un codi com a 'vàlid' o no, i per proporcionar orientació sobre els paràmetres de modelatge més adequats quan es realitzen simulacions CFD d'incendis accidentals d'hidrocarburs. La utilitat del les BPG es demostra mitjançant un cas d'estudi d'una granja d'emmagatzematge d'hidrocarburs situada al Port de Barcelona. Es troben grans sobreestimacions dels valors del fluxos de calor mitjançant correlacions semi-empíriques. Per tant, es recomana la utilització d'eines CFD per realitzar FHA detallats en indústries químiques i de processos