Elsevier

Ocean Engineering

Volume 243, 1 January 2022, 110200
Ocean Engineering

A hybrid method for the safety zone design in truck-to-ship LNG bunkering

https://doi.org/10.1016/j.oceaneng.2021.110200Get rights and content

Highlights

  • A new method for designing the safety zones of LNG-fueled ships during truck-to-ship LNG bunkering.

  • A hybrid method as an alternative solution to the deterministic method based current industry practice.

  • Applied example for the safety zone layout of a truck-to-ship LNG bunkering.

  • Comparison between the deterministic method and the developed hybrid method.

  • Summary of insights and findings developed in the paper.

Abstract

This paper is a sequel to the authors’ earlier article, which addressed the safe layout design of liquified natural gas (LNG) fueled facilities for preventing LNG or natural gas (NG) leaks. This paper aims to develop a new method for designing the safety zone of LNG-fueled ships during truck-to-ship LNG bunkering. While the deterministic approach has limitations in practical application, a hybrid method is suggested as an advanced design solution. In this regard, this paper develops a hybrid method as an alternative solution to the deterministic approach based current industry practice. The applicability of the proposed solution is demonstrated with an illustrative example of the safety zone layout of a truck-to-ship LNG bunkering. The insights and findings of the paper are summarized in association with a new design method for the safety zone, contributing to the safety engineering of LNG bunkering.

Introduction

Currently, liquefied natural gas (LNG) is one of the leading alternative fuels for ships, and the increasing number of LNG-fueled ships is expanding the need for LNG fueling (bunkering). Due to the hazards associated with unwanted releases of LNG during bunkering, a set of safety measures are necessary to secure the safety of personnel, assets, and the surrounding environment. To address these concerns, the International Maritime Organization (IMO) and members of the International Association of Classification Societies (IACS) introduced safety guidelines for the design of LNG-fueled ships and bunkering operations (ABS, 2019; DNV, 2015; IACS, 2017; IMO, 2015; LR, 2019). Academic researches have also been made on the safety of LNG bunkering: Calderón et al. (2016), Kim et al. (2018), Kim et al. (2021) and Iannaccone et al. (2019a, 2019b, 2020) conducted a set of safety assessments of LNG bunkering in association with operation characteristics; Aneziris et al. (2020, 2021) and Peng et al. (2021) examined LNG safety relevant to the bunkering site; Fan et al. (2021) introduced a safety philosophy and a risk analysis method for LNG bunkering. Numerical computations for the safety associated with LNG-fueled ships and LNG bunkering were undertaken by many researchers (Seo et al., 2014; Sun et al., 2017; Lee et al., 2020; Nubli and Sohn, 2020; Sundaram and Karimi, 2020; Ursavas et al., 2020; Rudan et al., 2021; Wang and Ju, 2021). Meanwhile, the International Organization for Standardization (ISO) introduced the concept of a safe layout plan consisting of safety and security zones in LNG bunkering (ISO, 2015) in addition to the required specification for bunkering operation (ISO, 2017). This concept has been widely adopted in the LNG industry. The Society for Gas as a Marine Fuel (SGMF) extended concept was introduced by the ISO to prescribe a controlled zone consisting of five specific zones: a hazardous zone, as defined by the International Electro-technical Commission (IEC, 2015); safety zones and monitoring & security zones, as laid out by the ISO concept; a marine zone; and an external zone (SGMF, 2018). Table 1 provides detailed descriptions of the safety and security zones, and Fig. 1 shows a schematic representation of the zones with a focus on truck-to-ship bunkering.

The guidelines relevant to LNG bunkering commonly prescribe a safety zone established as a fundamental safety barrier. The safety zone aims to provide a safe condition in and outside the zone by limiting or controlling personnel access and working activities. An industry standard exists and is available for the design of the safety zone (ISO, 2015), where two methods, the deterministic and risk-based approaches, are introduced with their applicable bunkering conditions. The deterministic approach can be generally adopted under normal bunkering conditions, but the risk-based approach is highly recommended for exceptional circumstances such as simultaneous operations (SIMOPS) (DNV, 2015; ISO, 2015). Both approaches have pros and cons for their applications. The deterministic approach provides a concise procedure, but the resulting safety zone layout may be inaccurate due to deterministically defined LNG leak scenarios and LNG release simulations. The risk-based approach can provide a high-quality layout using qualitative risk assessment (QRA), which has been carefully established in the industry (CMPT, 1999; Paik, 2020; Vinnem and Røed, 2020). However, this method is cost- and time-intensive and may not be appropriate for practical engineering purposes.

Some limited research exists on the safe layout for LNG bunkering, but this is primarily related to the risk-based approach. Jeong et al. (2017, 2018, 2020) pointed out the absence of detailed guidelines for designing the safety layouts in LNG bunkering and suggested a practical application of the safety exclusion zone design using the probabilistic risk assessment method. Park et al. (2018) presented a computational fluid dynamics (CFD) simulation for designing safety zones with the quantitative risk assessment method. Tofalos et al. (2020) conducted a comparative study on the safety zone of marine fuels – LNG and liquefied hydrogen based on the probabilistic risk assessment. Park et al. (2020) called attention to a drawback of the risk-based approach and they offered a hybrid type method as an alternative design strategy for the safety and security zones of a LNG bunkering facility. Meanwhile, the deterministic approach is a general design method for the safety zone in LNG bunkering but research on its application is lacking. As a follow-up to our previous work (Park et al., 2020), we investigated the deterministic approach in this study and suggested an output. A limitation of the deterministic approach is discussed, and a strategy for improving its practical application is presented. Additionally, a hybrid method is introduced as an advanced solution. Its applicability is discussed with an illustrative example of a safety zone layout for a hypothetical truck-to-ship (TTS) bunkering scenario.

Section snippets

General

Fig. 2 presents a schematic for the deterministic approach, a generally applicable method for safety zone design in LNG bunkering. It can be applied to most bunkering operations that focus on fuel transfer from a supplying facility to a ship. This method designs the safety zone as the area within the distance to the specific level of lower flammable limit (LFL) concentration as determined by a recognized and validated dispersion model for the representative or maximum credible LNG release

General

Even when a safety zone is designed with a well-made scenario in the deterministic approach, it may not be generally acceptable. Due to the scenario unitarily and deterministically selected, the reliability of the resulting safety zone layout can be debatable, presenting an inherent limitation of the deterministic approach. We propose a new hybrid design method to overcome this limitation. The DNV (2015) introduced hybrid (or semi-quantitative) methods, combining deterministic and probabilistic

Applied example for truck-to-ship bunkering

A hypothetical LNG bunkering is conceived, and a safety zone is designed to provide an example using 1) the deterministic approach, providing an application of the current industry practice, and 2) the hybrid method, validating its applicability as an advanced solution. Truck-to-ship (TTS) bunkering, the most common and simplest energy transfer method, is considered as an ISO standard for bunkering and this is the target for application of the deterministic approach. Fig. 5 presents an

Concluding remarks

This study suggests a design solution for the safety zone in LNG bunkering. A hybrid method is developed as an alternative to the current industry practice, the deterministic approach. The summaries and conclusions of this study are below:

  • (1)

    A safety zone should be defined for LNG bunkering, and this can be done with two industrial design standards, namely, the deterministic and risk-based approaches. Both should be applied in a timely manner. This paper deals with the deterministic approach

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgement

This work was undertaken at the International Centre for Advanced Safety Studies (Lloyd's Register Foundation Research Centre of Excellence), Busan, South Korea.

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