Partial waveform data representative of a waveform shape variation are extracted from supplied waveform data, and the extracted partial waveform data are stored along with time position information indicative of their respective time positions. The process includes passing the fresh feed and a process stream containing a first component selected from hydrogen, nitrogen and methane and a second component which is a monomer to a separator at a pressure of 0. Also provided is a method for assembling the fuel cell system.