The present work is concerned with numerical simulations of large scale hydrogen detonations. Euler equations have been solved along with a single step reaction for the chemistry. Total variation diminishing (TVD) numerical schemes are used for shock capturing. The equations are solved in parallel in a decomposed domain. Predictions were firstly conducted with a small domain to ensure that the reaction scheme has been properly tuned to capture the correct detonation pressure and velocity. On this basis, simulations were set up for the detonation tests carried out at the RUT tunnel facilities in Russia. This is one of the standard benchmark test cases selected for HYSAFE. Comparison is made between the predictions and measurements. Reasonably good agreement has been obtained on pressure decay and the propagation speed of detonation. Further simulations were then conducted for a hypothetical hydrogen-air cloud in the open to assess the impulse as well as overpressure. The effects of cloud height, width were investigated in the safety context.