Abstract: The invention is directed to a cell for an electrolytic apparatus which comprises a pressure vessel containing a self-contained electrode unit. The electrode unit has an inlet for the supply of electrolyte and an outlet for liberated ad-mixed hydrogen and oxygen gas. The electrode unit further having plurality of spaced-apart concentric cylindrical electrodes and a pair of internal end plates provided at each end of the concentric cylinders. At least one of the internal end plates includes the electrolyte inlet and/or gas outlet. The pressure vessel comprises a cylindrical outer shell having planar transverse end plates which are connected at or adjacent to the opposed ends of the cylindrical outer shell. The pressure vessel being capable of withstanding explosions of stored liberated gas.