It is planned to use hydrogen extensively as a source of clean energy in the next century. So we have been studied to establish a safety scheme to ensure that both existing hydrogen technologies and new technologies are implemented without endangering public safety. The studies are administrated through the New Energy and Industrial Technology Development Organization(NEDO) as a part of the International Clean Energy Network Using Hydrogen Conversion(WE-NET) Program with funding from the Agency of Industrial Science and Technology(AIST) in Ministry of International Trade and Industry(MITI) of Japan. First we must specify safety features and functions for each WE-NET system to meet the safety goal, and evaluate the consequence of the postulated accident of liquid-hydrogen. Since we have developed the multi-phase hydrodynamics analysis code, we applied the code to establish the safety standard for the total WE-NET system.