TECHNOLOGY FOCUS - INSTRUMENTATION AND TESTING - Preferred Components: The hydrogen generator comprises many contact members, each corresponding to one or a group of many segregated quantities of the exothermic mixture. In the hydrogen generator, an exothermic reaction in each one or group of the quantities of the exothermic mixture can be selectively initiated via the corresponding contact member. The initiator assembly comprises at least one heating element (18), each in thermal communication with at least one corresponding contact member such that the corresponding contact members conduct heat from one of the heating elements to the corresponding one or more quantities of the exothermic mixture. The initiator assembly conducts electrical energy through the contact members, each of which conducts electrical energy to corresponding quantities of the exothermic mixture. The fuel unit comprises the quantities of the exothermic mixture, each capable of providing heat for the release of hydrogen gas from a portion of the hydrogen containing material. The portions of the hydrogen containing material are segregated portions. The segregated portions of the hydrogen containing material are segregated by any one or a combination of a gap, a thermal insulator member and an electrical insulator member. The exothermic reaction in individual or groups of quantities of the exothermic mixture can be selectively initiated to selectively provide energy to the conductor members, each of which conducts energy to the quantities of the exothermic mixture. In the hydrogen generator, each of the contact members: is a heating element; has an elongated body; or has an end for contacting the fuel unit. The end is a tapered tip or can penetrate into the fuel unit. The energy is provided to the initiator assembly from an energy source. The compressible member includes hydrogen flow channels in its first surface. The access panel is moveable to provide access to the hydrogen generator for insertion and removal of the fuel unit. The fuel cell system includes a controller to selectively provide energy to the conductor members. The controller can selectively provide energy to the conductor members based at least one parameter of the fuel unit, the hydrogen generator and a hydrogen consuming device.