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