Hydrogen have the potential that can replace fossil fuels which is the primary source of environmental pollution. Hydrogen should be stored in high pressure reservoirs for any practical purpose. In this work hydrogen leak from a high pressure vessel by means of a 2mm tube length and 4.8mm diameter of pipe in atmospheric air is simulated using FLUENT 13. A strong shock wave is formed during the flow of high pressure hydrogen in a tube filled with atmospheric air which leads to heating of hydrogen behind the shock wave. This is mainly because of compression effect and which leads to an auto ignition. The simulated results are not in agreement with the results obtained by Yamada Eisuke et al. (2010).