Abstract: Gas samples are extracted from a rotary cement kiln type furnace in the area of raw material input and exhaust gas discharge from and to, respectively, a cyclone heat exchanger. The intervening chamber is provided with a door covering a passageway into the chamber through which a gas probe, carried by a gas pick-up device, is extended and retracted. The pick-up device is movably mounted in a guide and is provided with a coolant and apparatus for directing a blast of air to clean the probe immediately prior to withdrawal from the furnace. Emergency controls are provided to sequentially clean the probe, withdraw the probe and close the door for the passageway in response to detection of an adverse condition in at least one operating parameter of the system.