The leakage and diffusion characteristics of natural gas were investigated in the condition of the leakage of liquefied natural gas (LNG) in the storage tank. Fluent was adopted to simulate the process in a series of three-dimension unsteady state calculations. The effects of different heights of the cofferdam (1.0 m

2.0 m and 3.0 m)

wind directions

ambient temperature

leakage location

leakage volume on the diffusion process of natural gas were investigated. The diffusion characteristics of the natural gas clouds over cofferdam were found. Under windless condition

when the gas clouds met

the gas clouds rose due to the collision

which made them easier to cross the cofferdam and spread out. The higher the ambient temperature was

the higher the gas concentration around the cofferdam was

and the smaller the gas concentration difference was. When the leakage occurred

the higher cofferdam was more beneficial to delay the outward diffusion of gas clouds. However

when the leakage stopped

the higher cofferdam went against the dissipation of gas clouds. Under windy condition

the time to form stable leakage flow field was faster than that of windless

and the lower cofferdam further reduced this time. Therefore

considering the effect of barrier and dissipation

it was suggested that the rational height of cofferdam should be designed in the range of 1.0 m to 2.0 m. In case of emergency

the leakage of gas should be deduced reasonably by combining the measurement of gas concentration with the rolling of gas clouds. When windless

the leakage area should be entered between the overflows of gas clouds.