NOVELTY - The detection method for enabling gas composition observation during fuel cell system start-up, comprises initiating a flow of hydrogen to the anode to pressurize the anode, opening an anode flow valve, determining if an anode pressure exceeds an anode pressure threshold of 140-200 kPa, enabling anode flow set point detection after a first predetermined time of 2 seconds if the anode pressure exceeds the anode pressure threshold, monitoring an anode flow set point using the anode flow set point detection, and determining if the anode flow set point exceeds an anode flow set point threshold.    USE - The method is useful to detect when to enable the gas composition observation during fuel cell system start-up.    ADVANTAGE - The method provides a more consistent and complete flush compared to the current control method and avoids false positives of gas composition detection by exercising the function and various different pressure set points thus optimizing front speed and emission requirements and performing starts at various off-time values, and ensures the ending of flush function if the gas composition detection malfunctions thus avoiding emissions problems.    DETAILED DESCRIPTION - The detection method for enabling gas composition observation during fuel cell system start-up, comprises initiating a flow of hydrogen to the anode to pressurize the anode, opening an anode flow valve, determining if an anode pressure exceeds an anode pressure threshold of 140-200 kPa, enabling anode flow set point detection after a first predetermined time of 2 seconds if the anode pressure exceeds the anode pressure threshold, monitoring an anode flow set point using the anode flow set point detection, determining if the anode flow set point exceeds an anode flow set point threshold of 0.1-0.3 mol/s, and closing the anode flow valve after a second predetermined time of 1 seconds if the anode flow set point exceeds the anode flow set point threshold. The anode flow valve is closed when a boundary condition is exceeded if the anode pressure does not exceed the anode pressure threshold and if the anode flow set point does not exceed the anode flow set point threshold. The boundary condition comprises a third predetermined time of 2 seconds and an anode volume of 0-10.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic view of a fuel cell system.    Anode flow shifting stacks (12, 14)    Compressor (16)    Cathode input line (18)    Cathode input valve (20)    Cathode exhaust gas line. (24)