In the past few years, CEA has been fully involved at both experimental and modeling levels in projects related to hydrogen safety in nuclear and chemical industries, and has carried out a test program using the experimental bench SSEXHY (Structure Submitted to an EXplosion of HYdrogen) in order to build a database of the deformations of simple structures following an internal hydrogen explosion. Different propagation regimes of explosions were studied, varying from detonations to slow deflagrations. During the experimental campaign, it was found that high-speed deflagrations, corresponding to relatively poor hydrogen-air mixtures, resulted in higher specimen deformation compared to those related to detonations of nearly stoichiometric mixtures. This paper explains this counter-intuitive result from qualitative and quantitative points of view. It is shown that the overpressure and impulse from head-on reflections of hydrogen flames corresponding to poor mixtures of specific concentrations could have very high values at the tube end.