A gas turbine for power plant application fed by pre-heated fuel gas; the gas turbine comprises: - a compressor configured for compressing incoming air; - a sequential combustor assembly configured for feeding at least a fuel in the compressed air and generating a hot gas flow; wherein the combustor assembly comprises in series a first combustion stage and a second combustion stage; - a turbine configured to be driven by the hot gas for performing work on a rotor; - a fuel source configured for suppling pre-heated fuel to a fuel gas distribution system comprising a first line for feeding the first combustion stage and a second line for feeding the second combustion stage; the second line comprising at least an upstream shot-off valve and at least a downstream control valve; the at least an upstream shot-off valve and the at least a downstream control valve are metal-seat valves; between the at least a downstream control valve and the second combustion stage a first duct being present where leakage fuel gas can accumulate; wherein the gas turbine moreover comprises a second duct configured for feeding cooled air into the first duct wherein the cooled air has a temperature lower than the auto ignition temperature of the fuel gas; wherein the second duct comprises at least a valve and the gas turbine moreover comprises: - a control unit configured for operating the gas turbine in a first stage only mode wherein the at least an upstream shot-off valve and the at least a downstream control valve of the second line are driven to be closed; the control unit being configured for feeding the cooling air in the second duct during the first-stage only mode operation by opening the valve of the second duct. - a compressor configured for compressing incoming air; - a sequential combustor assembly configured for feeding at least a fuel in the compressed air and generating a hot gas flow; wherein the combustor assembly comprises in series a first combustion stage and a second combustion stage; - a turbine configured to be driven by the hot gas for performing work on a rotor; - a fuel source configured for suppling pre-heated fuel to a fuel gas distribution system comprising a first line for feeding the first combustion stage and a second line for feeding the second combustion stage; the second line comprising at least an upstream shot-off valve and at least a downstream control valve; the at least an upstream shot-off valve and the at least a downstream control valve are metal-seat valves; between the at least a downstream control valve and the second combustion stage a first duct being present where leakage fuel gas can accumulate; wherein the gas turbine moreover comprises a second duct configured for feeding cooled air into the first duct wherein the cooled air has a temperature lower than the auto ignition temperature of the fuel gas; wherein the second duct comprises at least a valve and the gas turbine moreover comprises: - a control unit configured for operating the gas turbine in a first stage only mode wherein the at least an upstream shot-off valve and the at least a downstream control valve of the second line are driven to be closed; the control unit being configured for feeding the cooling air in the second duct during the first-stage only mode operation by opening the valve of the second duct. the second line comprising at least an upstream shot-off valve and at least a downstream control valve; the at least an upstream shot-off valve and the at least a downstream control valve are metal-seat valves; between the at least a downstream control valve and the second combustion stage a first duct being present where leakage fuel gas can accumulate; wherein the gas turbine moreover comprises a second duct configured for feeding cooled air into the first duct wherein the cooled air has a temperature lower than the auto ignition temperature of the fuel gas; wherein the second duct comprises at least a valve and the gas turbine moreover comprises: - a control unit configured for operating the gas turbine in a first stage only mode wherein the at least an upstream shot-off valve and the at least a downstream control valve of the second line are driven to be closed; the control unit being configured for feeding the cooling air in the second duct during the first-stage only mode operation by opening the valve of the second duct. - a control unit configured for operating the gas turbine in a first stage only mode wherein the at least an upstream shot-off valve and the at least a downstream control valve of the second line are driven to be closed; the control unit being configured for feeding the cooling air in the second duct during the first-stage only mode operation by opening the valve of the second duct.