(57) Fire extinguishing apparatus forducting incorporating an extractor fan, comprising a fire extinguisher arranged to discharge extinguishing medium into the duct upstream of the extractor fan at a predetermined temperature and a temperature sensing unit operatively connected to a circuit selector control for cutting-out the fan when the unit detects a preset temperature less than the operating temperature of the extin- guisherand including a by-pass circuit where by the fan can be restarted following discharge of the extinguisher. A visual and/or audible indication of the state of the selector control circuit is provided to assist manual setting of the by-pass circuit when required.