is also stopped and the remaining catholyte is discharged the cathode gap can also be flushed with dilute aqueous alkali metal hydroxide solution the concentration of the alkali metal hydroxide solution used for flushing is 2 to 10 mol l preferably 4 9 mol l in a further embodiment the lower third of the catholyte space is flushed this can be done for example by conducting alkali metal hydroxide solution into the cathode space from the bottom and then releasing it again small residual amounts of aqueous alkali metal hydroxide solution remain in the cathode gap the oxygen supply can be adjusted when the electrolysis voltage is switched off the oxygen supply is preferably adjusted after the cathode space has been emptied and the oxygen supply can be adjusted before during or after flushing of the cathode space with alkali metal hydroxide solution the positive pressure in the cathode space of approx 10 100 mbar relative to the anode space is maintained during the running down operation after emptying anode space and cathode space the electrolysis cell with the moist membrane can be kept ready for a further startup in the installed state over a prolonged period without impairing the performance of the electrolysis cell in the case of shutdown periods extending over several weeks it is appropriate for stabilization to flush the anode space with dilute aqueous alkali metal chloride solution and the cathode space with dilute aqueous alkali metal hydroxide solution at regular intervals in another embodiment of the process which includes particular conditions for the shutdown of the electrolysis cell after shutdown and emptying of the electrolysis cell the anode space is flushed repeatedly every 1 to 12 weeks preferably 4.