The aim of the present work is to identify and characterize the type of combustion of hydrogen-air mixtures near the flammability limits for different initial temperatures (from 298 to 423 K) and pressures (100 and 250 kPa) relevant to pressurized water reactor conditions. This experimental study has been carried out using a spherical vessel equipped with a pressure transducer to monitor the pressure increase subsequent to the combustion and with two optical windows to record the flame propagation. From the schlieren images, different regimes of flame propagation have been identified depending on the temperature and pressure. The maximum pressure obtained experimentally has been compared to the theoretical maximum pressure for adiabatic combustion at constant volume. The flammability limits have been determined for different temperatures and pressures and are compared to the literature.