Comparative analysis on vapor cloud dispersion between LNG/liquid NH3 leakage on the ship to ship bunkering for establishing safety zones

This study presents a comparative analysis of vapor cloud dispersion in the case of accidental fuel release from a bunkering hose to enable the establishment of a safety zone during the bunkering process. The pipeline can carry marine fuels such as liquefied natural gas (LNG) or liquid ammonia (NH3). The safety zone can be regarded as the 3-dimensional area wherein the leak event takes place and where, under certain circumstances, there is a recognized potential to endanger crew members or damage equipment. The primary objective of this research was to investigate the characteristics of leakage dispersion and determine the safety distance during ship-to-ship LNG or NH3 bunkering. Mathematical models discussing the dispersion process for LNG/NH3 leakage during ship-to-ship bunkering are presented. Numerical studies were conducted for 26 scenarios, considering diverse operational and environmental conditions, leak hole diameters, leak rates, wind speeds, and wind directions. Findings suggest that under equivalent operational conditions, NH3 exhibited a greater dispersion range for the vapor cloud compared to LNG. Consequently, NH3 demands a more extensive safety zone distance. The dispersion time of NH3 was longer than that of LNG. The parametric study revealed that the toxicity and flammability limit range were important parameters that affect the extent of safety zones. In addition, weather conditions (wind speed and wind direction) and leak characteristics (leak rate and leak duration) are critical parameters. The data and insights regarding the prediction of danger areas can serve as a vital reference for both qualitative and quantitative risk assessments concerning emergency management in ship-to-ship LNG/NH3 leakage incidents.