TECHNOLOGY FOCUS - INSTRUMENTATION AND TESTING - Preferred Device: The temperature sensitive element is configured to inhibit the flow of fluid reactant when the threshold temperature is reached or exceeded. It includes a thermo-mechanical actuator, where movement of the actuator in response to temperature acts to control the supply of reactant fluid to the reaction chamber. The thermo-mechanical actuator comprises a bimetallic strip. The temperature sensitive element is located such that it is in thermal contact with the reaction chamber. It includes a valve and the thermo-mechanical actuator is configured to actuate the valve. The valve is located between the fluid supply chamber and the reaction chamber. It is configured to open against the flow of fluid reactant, when in use. The valve includes a valve body arranged to be moved with respect to a valve seat by the thermo-mechanical actuator to control the supply of fluid reactant. It includes a sealing diaphragm and a sealing plate having an aperture in it, the sealing diaphragm adapted to lie against the sealing plate to close the aperture in a closed position and the sealing diaphragm adapted to be displaced from the sealing plate by the valve actuator in an open position. The valve includes a flexible conduit through which the fluid reactant is arranged to flow and a valve head, the valve head arranged to compress or pinch the flexible conduit to restrict the supply of fluid reactant. The cartridge includes a moveable part in the fluid supply chamber for driving the reactant fluid into the reaction chamber and the temperature sensitive element includes a movement inhibitor for preventing and allowing the movement of the moveable part in response to changes in temperature. The movement inhibitor is moveable to a position which prevents the movement of the moveable part when the threshold temperature is exceeded. The fuel cartridge includes a second temperature sensitive element adapted to control or inhibit the supply of fluid reactant to the reaction chamber, the second temperature sensitive element configured to reversibly restrict the supply when a second threshold temperature is exceeded. The temperature sensitive element comprises a first valve with an associated first temperature sensitive valve actuator, and the second temperature sensitive element comprises a second valve with an associated second temperature sensitive valve actuator, the first and second valves connected in series. The temperature sensitive element and second temperature sensitive element comprise first and second valve actuators respectively that act on the same valve. Valve actuators act to control the supply of fluid reactant at different rates in response to temperature changes. The temperature sensitive element includes two or more bimetallic strips, the bimetallic strips connected together and arranged to act together to control the supply of fluid reactant to the reaction chamber.