Research into the size of safety exclusion zones (SEZs) around LNG bunkering stations for LNG-fuelled ships published in the IMarEST’s Journal of Marine Engineering & Technology produced some counterintuitive results.
While the potential benefits of implementing LNG as an emerging marine fuel have been extensively discussed, its establishment as a widely used fuel source has been constrained by a number of safety concerns and a lack of infrastructure. While the potential benefits of implementing LNG as an emerging marine fuel have been extensively discussed, its establishment as a widely used fuel source has been constrained by a number of safety concerns and a lack of infrastructure. LNG bunkering presents inherent risks, including the danger of large explosions resulting from rapid combustion of massive concentrations of LNG vapour gas and the risk of cryogenic burns to personnel. To minimise these risks, there is a global discussion on the introduction of safety exclusion zones (SEZs) – ‘safe’ areas restricting all non-essential personnel and activity within a given radius of the bunkering stations – to reduce ignition potential and the threat to human life. It is thought that establishment of SEZs would accommodate the safe refuelling of LNG powered ships and safe evacuation of LNG fuels from ships in an emergency situation. This would therefore be of paramount importance in reinforcing LNG bunkering as a commercially viable and acceptable undertaking. However, as yet there is no international consensus on an appropriate extent of the SEZ to ensure safe LNG bunkering and there is a pressing need for detailed studies to help inform industry guidelines. Current SEZ guidelines are based on previous studies that are too site specific in their approach to reliably inform a generalised set of guidelines. Several of these studies also ignored risks such as radiation exposure and blast pressure – instead focusing on flash fires as the primary consequence. Another concern has been the over-reliance on deterministic models, which overlook the probability of accidents and risks occurring, instead choosing to focus on a specific worst-case scenario of a bunkering incident. Furthermore, these deterministic models yield results that suggest SEZ sizes that are impractically large, regardless of their probability. As such, a rethink in SEZ guidelines is imperative deterministic models yield results that suggest SEZ sizes that are impractically large, regardless of their probability.
As such, a rethink in SEZ guidelines is imperative. A recent study by Jeong et al. (2017) aims to address these issues and attempts to identify key factors critical in determining an SEZ. The study was based on two different scenarios – a very large ore carrier requiring infrequent but larger refuelling events, and a smaller bulk carrier requiring more frequent but smaller refuelling events. A probabilistic risk assessment approach was used to determine SEZs and compared the results to those obtained by a deterministic approach. The models included a greater range of risks factors compared to previous studies, including: leak rate, explosions, LNG evaporation and flash fires. The study produced some intriguing results. In the probabilistic risk assessment model, bunkering frequency was a key factor in determining SEZ size. Yet, counterintuitively, it suggested that a 36m radius was appropriate for the smaller bulk ship while the ore carrier would only require a 6.4m radius exclusion zone. When compared to the deterministic model, the SEZ for the larger ship was many times larger, relatively speaking, while the projected SEZ size for the bulk carrier remained fairly consistent. This surprising result was due to the risk of catastrophe being more tightly coupled with bunkering frequency than vessel size.
This therefore explains the discrepancy in SEZ size recommendation between the probabilistic and deterministic models, given the exclusion of bunkering frequency in the deterministic model. However, it was noted that the results were influenced by the parameters used during analysis. Given LNG bunkering is a relatively new procedure, only factors involving equipment failure were included, with a distinct exclusion of other factors such as weather and human error – data for which either doesn’t exist or is not extensive enough to warrant inclusion. New procedure, only factors involving equipment failure were included, with a distinct exclusion of other factors such as weather and human error – data for which either doesn’t exist or is not extensive enough to warrant inclusion. While the study by Jeong et al (2017) did not result in an elegant formula for calculating an SEZ radius, it has shone a light on areas that merit further attention. Firstly, the identification of bunkering frequency being a key parameter for establishing risk level, and thus in the determination of SEZ size, highlights the need to adopt probabilistic models in future studies to drive a more comprehensive approach in advising SEZ guidelines.
This presents a case to make relevant rules and regulations more explicit and more stringent.to make relevant rules and regulations more explicit and more stringent. Secondly, the lack of data on a number of potential factors in LNG incident risk, such as human error and weather will need to be addressed. Until such factors can be included to ensure a comprehensive probabilistic model can be used to project recommended SEZ sizes, no reliable set of generalised guidelines will be able to be created. While the limitation of knowledge of LNG bunkering risk factors will be difficult to overcome in the near future, the study can still be used to contribute towards helping other IMO member states develop their own set of guidelines. Develop their own set of guidelines. If this summary has whetted your appetite, you can view the paper in full and related research by subscribing to the Journal of Marine Engineering & Technology (JMET). Visit www.imarest.org/resources/peer-reviewed-journals.
The editorial board of the Journal of Marine Engineering & Technology (JMET) is always on the lookout for new authors who can bring fresh perspectives on issues and technical challenges facing the industry today.
The research on LNG safety exclusion zones carried out and findings described left earned Byuong-ug Jeong at the University of Strathclyde’s Department of Naval Architecture, Ocean and Marine Engineering and his co-authors the prestigious Denny Medal. This special commendation is awarded once a year to a paper published in a complete issue or supplement in each of the Journal of Marine Engineering and Technology (JMET) and the Journal of Operational Oceanography (JOO), which is deemed to be an outstanding contribution to the advancement of our knowledge and understanding of the given subject area. It is awarded by the IMarEST Council following recommendation from the Editorial Boards and the Proceedings Supervisory Board, who consider the paper’s influence and impact, originality and innovation, completeness and consistency, and presentation and clarity of communication. Applications by joint authors are eligible with a maximum of three authors receiving a medal for any one paper. There is also an allowance for the lead author to support their attendance at the IMarEST Annual Dinner. To learn more, visit www.imarest.org/awards