A man portable hydrogen source, the source comprising one or more hydrogen generating elements (2), an ignition control system (3) and a pressure vessel (1). Each hydrogen generating element comprises a pellet holder (7) provided with one or more recesses and a thermal insulation layer (9) to reduce heat transfer to adjacent hydrogen generating elements; wherein at least one recess contains a pellet (8) of a chemical mixture which on thermal decomposition evolves hydrogen gas; wherein the ignition control system comprises one or more ignitors (14), associated with an individual pellet (8), and activation means to activate the ignitors; and wherein the evolved hydrogen and hydrogen generating elements are contained within the pressure vessel.