Abstract: A process and a device for monitoring the imperviousness of a radiant tube fired by a gas burner is disclosed. From a burner control a burner signal is derived that may have at least the states BURNER OFF when the burner is switched off and BURNER ON when the burner is switched on. In addition, the exhaust gas flow of the burner is monitored and an exhaust gas signal is derived there from which may at least have the states EXHAUST GAS OFF when there is no sufficient volume flow of exhaust gas flowing out of the radiant tube, and EXHAUST GAS ON when there is a correctly flowing exhaust gas. The burner signal and the exhaust gas signal are linked with each other for outputting a failure signal in case the combination BURNER ON and EXHAUST GAS OFF results.