Abstract: As the hydrogen properties make it an exciting gas, there are serious safety issues related to it. Hence, studying the behavior of hydrogen is essential to be able to use it on a large scale. This is feasible by performing detailed modeling of the risks using computational fluid dynamics (CFD). In using hydrogen as a fuel in the pipelines, leakage can occur. Extreme concentration around the pipe can cause flammability and explosion risk. Considering the leakage orifice as a choked converging nozzle, with three different leakage area sizes and four different wind velocities, twelve simulations were performed using Ansys Fluent. The hydrogen flammability zone (between 4 – 75% concentration) and explosion area (between 18.3 – 59% concentration) around the pipeline were found, considering the wind speed effect. The result shows that the orifice size changes the dangerous zone. Besides, the effect of wind speed on hydrogen dispersion and the air-hydrogen mixture is considerable. So, with increasing the wind speed, the hydrogen-air mixture is facilitated, while the mixture cloud was extended in the wind direction.