A method of operating a process a combustion analyzer having a measurement cell is provided. The method includes exposing the measurement cell to exhaust of a combustion process where fuel and oxygen are combined in a burner to produce a flame. The measurement cell is heated to a temperature above a flashpoint of the fuel. When a condition is detected, such as a fault or abnormal situation, gas is directed to the measurement cell to form a gaseous barrier between the measurement cell and unburned fuel while the detected condition exists. Once the condition abates, the gas flow is disengaged and process combustion gas measurements are provided.