A hydrogen generator including an initiator assembly having one or more contact members within a compressible member, and a removable fuel unit adjacent a surface of the compressible member. The fuel unit contains a hydrogen containing material that can release hydrogen gas when heated and an exothermic mixture that can react exothermically upon initiation by the initiator assembly. When no fuel unit is in the hydrogen generator, the compressible member is uncompressed and the contact members are at or below its surface, and when a fuel unit is disposed in the hydrogen generator, the compressible member is compressed so the contact members extend beyond the surface to make thermal contact with the fuel unit. Energy from the initiator assembly is conducted by the contact members to corresponding quantities of the exothermic mixture to initiate an exothermic reaction, providing heat for the release of hydrogen gas from the hydrogen containing material.