Quantitative risk assessment of the performance of barriers controlling fire and explosion risk
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- Institutt for marin teknikk 
The growing population of the world places an enormous demand for energy in someform or the other. Essentially, this means that the struggle to hunt and retrieve fossil fuelshas to continue for the smooth functioning of the world. Since the early 1900’s when drillingfor oil and gas started moving away from shores to some remote locations that we are attoday, the size and complexity of machinery and the interconnected systems have grownexponentially. Despite investing enormous time, effort and money into implementing technicallyadvanced and innovative barrier systems to prevent Hydrocarbon (HC) leaks onoffshore installations in the Norwegian Continental Shelf (NCS), the statistics still standsfar from the target zero. Hence, the efforts towards minimizing the number of leaks cannever be ceased due to the catastrophic nature of its potential consequences to humans,environment, asset or the reputation of a firm. This master’s thesis features one such effort to visualize the effectiveness of somebarrier functions proposed in Modelling Instantaneous Risk for Major Accident Prevention(MIRMAP) report. Some of the most critical barrier systems are incorporated intothe chosen generic module, which is then subjected to numerous gas leak simulations usingthe latest version of the software, Kameleon FireEx - Risk and Barrier Management(KFX-RBM), a Computational Fluid Dynamics (CFD) based simulation tool. A base casescenario is a set-up using the chosen module with a 100% functional gas detection system,Emergency Shutdown (ESD) system, with no temporary weather cladding attached andclosed fire-proof doors. This set-up is subjected to simulation with six different leak rates,four different wind speeds and two different wind directions. The results of this being abase for comparison, simulations are carried out with partially isolated gas detection system,presuming on-going hot works in the near vicinity with a temporary weather claddingand with fireproof doors left in open position. The variations in the total ignition probabilityof the module compared to the base case would be the main objective of this thesis.As additional objectives, since the barrier systems could be directly or indirectly influencedby humans, an attempt is made by simulating the base case with a practicallyacceptable delay in manual activation of the shutdown. Furthermore, to reduce the simulationtime, numerous simulations are run to arrive at the optimal grid resolution and courantnumber with the quality of results remaining undiminished. The case with delayed shutdown due to manual activation of ESD depicted the highestinfluence to the complementary cumulative frequencies, followed by the case simulatedwith a temporary weather cladding erected on one of the open ends of the module, withsecond highest influence. The comparison of the two base case simulations with differentleak scenarios (direction and location), revealed that the release point and release directioncan significantly influence the probabilities of ignition, either positively or negatively. Thesimulations that were carried out to optimize the grid resolution resulted in a significantreduction of simulation time with a grid resolution of 125000, while the quality of the resultswas undiminished. Further analysis by extracting the highest and the least releaserates separately resulted in an insight that the grid resolution is a function of release rate.