Safety evaluation on LNG bunkering : to enhance practical establishment of safety zone

This paper is to evaluate the LNG bunkering safety for a 50,000 dead weight tonnage bulk carrier renowned as the world first LNG fuelled bulk carrier. To establish a proper level of the safety zone against the potential risk of gas release from the LNG bunkering systems encompassing from truck to ship, it introduces an enhanced quantitative risk assessment process with two key ideas: firstly, the integration of the population-independent analysis with the population-dependent analysis, and secondly, the combination between the probabilistic analysis and CFD simulation for gas dispersion. Research results reveal that the appropriate levels of the safe zone can be set at 28.8 m in 1E-4 /year criterion that concerns the individual risk of a fatality at the given distance to the risk source of 1 in 10,000 years, whereas at 46.6 m (in 1E-5 /year criterion) and at 213.3 m (in 1E-6 / year criterion) when the area within 5 % and higher gas concentration in air is regarded the critical zone. On the other hand, in case of the critical area considered to be within 2.5 % and higher gas concentration in air, the safety zone will much expand to 34.9 m (in 1E-4 /year criterion), 80.4 m (in 1E-5 /year criterion) and 541.8 m (in 1E-6 /year criterion). These dissimilarities suggest that LNG bunkering ports pay attention to selecting appropriate safety criteria which would considerably change the range of safety zones. The case study also demonstrates the effectiveness of the proposed approach that can remedy the shortcomings/shortfalls of existing technical and regulatory guidance on establishing the zones. It is, therefore, believed that the risk assessment approach proposed in this paper can contribute to determining the appropriate level of safety zones whereas providing practical insight into port authorities and flag states

A study on factors affecting the safety zone in ship-to-ship LNG bunkering

The objective of this paper is to examine the characteristics of leaked-gas dispersion in ship-to-ship liquefied natural gas (LNG) bunkering, thereby providing an insight towards determining the appropriate level of safety zones. For this purpose, parametric studies are undertaken in various operational and environmental conditions, with varying geometry of the ships, gas leak rate, wind speed and wind direction. The study applies computational fluid dynamics (CFD) simulations for case-specific scenarios where a hypothetical LNG bunkering ship with a capacity of 5100 m3 in tank space is considered to refuel two typical types of large ocean-going vessels: an 18,000 TEU container ship and a 319,000 DWT very large crude oil carrier. It is found that wind speed, wind direction, ship geometry and loading condition are important parameters affecting the extent of safety zones in addition to gas leak rate and leak duration. Details of the computations and discussions are presented

Potential risk of vapour cloud explosion in FLNG liquefaction modules

Floating Production Storage and Offloading vessels have been in operation for four decades and there are now well over 250 vessels in existence, but their gas equivalent floating liquid natural gas plants kwon as FLNGs are still very new. Consequently designs and arrangement of top-side process units are still evolving and their safety has yet to be fully and objectively evaluated. This paper explores the probability of occurrence of accidents leading to vapour cloud explosion at one of the topside liquefaction modules of an FLNG. The worst possible scenario with the maximum tolerable probability is identified and the impact of the corresponding vapour cloud explosion is estimated. The strength of the structures supporting the neighbouring modules was examined using finite element analysis to determine if the accident has a potential of escalating to neighbouring modules. It is found that the current levels of safety gaps between the liquefaction modules may be insufficient for the structural arrangement in place. It is thought that a new structural design using circular pipes as the structural elements instead of the I-beams may enhance the integrity of the top-side supporting structures against the impact of potential vapour cloud explosion. The effectiveness of the new structure is demonstrated by comparing it to the conventional supporting structure using I-beam members. This also implies that, by using pipe elements, the safety gaps can be reduced, thus making it possible to optimise the topside arrangement more easily

Extent of damage analysis of naval ships subject to internal explosions

A well-balanced naval ship design to enhance the survivability from the initial design stage in parallel with other designs focusing on the major function and its inherent mission is considered as a desirable design trend in ROK navy since Cheonan sinking accident. Because it is difficult to estimate a hit location of a given threat for survivability evaluation, a statistical approach based on multiple-hit scenarios is frequently addressed, and it is necessary to accomplish rapid analyzes considering the tight design schedule. In addition, accurately estimating the extent of damage caused by the given threat is also an important matter to secure the reliability of evaluation. In particular, the empirical formula-based damage extent estimation method, which is frequently used for initial rapid vulnerability analysis, has limitations in not faithfully reflecting the latest technology advances such as hull design changes and diversification of threats, so researches on this have been continuously accomplished. In this study, a method for analyzing the extent of damage was developed considering the structural response of a ship to damage under a blast load. The proposed method quickly and easily calculates the extent of damage using physical design parameters together with the accurate analysis results and is also very effective at the initial design stage of the naval ship (e.g., in evaluating various design candidates for structural configurations). To show the effectiveness of suggested method, FLACS, a well-known commercial program for explosion analysis, is used for the analysis of nine representative scenarios together with the stepwise validations of the suggested procedure; the analysis results are observed the same in most cases with the developed program based on the proposed procedure, with a difference of approximately 15% for one scenario