Abstract: A process and a device for quickly switching over from the premixing operation to the diffusion operation in combustion chambers of a gas turbine upon the extinction of the premixing flame or upon the occurrence of a disturbance that may lead to the extinction of the premixing flame. A pilot gas line, into which a pilot gas control valve is inserted, branches off from the fuel gas supply line before the fuel gas valve. The fuel gas supply line branches into fuel supply lines for both combustion chambers after the fuel gas control valve with displacement measurement. The fuel supply to the diffusion gas line and to the premixing gas line is controlled by installing a quick switch-over valve each with servo valves in the branching fuel supply lines. The combustion chambers are monitored in the area of the flame tube by pressure-measuring devices and by an optical flame-monitoring device.