Explosions are the main types of accidents causing casualties in underground mines. The high-speed flow caused by gas expansion and inertia is a main damage factor in gas explosion accidents, but the issue has not yet received considerable attentions. In this study, the propagation of pressure wave and combustion wave from methane-hydrogen premixed explosions were studied in a pipe with a close end and an open end. Analysis and comparison between pressure speeds and flame speeds were performed. On this basic, the hazard effects of dynamic pressure caused by high-speed flow were investigated. The results show that the addition of hydrogen can speed up propagation of pressure waves and combustion waves and that detonation is achieved at high hydrogen contents but not for low hydrogen contents. Additionally, the high-speed flow is a kind of high temperature airflow with a very high speed of dozens of meters even up to hundreds of meters per second. High-speed airflows can bring about high dynamic pressures, which are on the same order of magnitude as statistic pressures, even higher than statistics pressure at the pipe opening end. Compared with impacts of blast pressure, the damages of high-speed flow can last for a longer time. (c) 2013 American Institute of Chemical Engineers Process Saf Prog 33: 85-93, 2014