The pressure vessel in a chlorine separation system exploded after the corrosion of the steel process equipment allowed chlorine and hydrogen to mix and form a volatile mixture. The chlorine receiving tank ruptured violently into five pieces (three large ones and two smaller) causing considerable damage to nearby equipment. The appearance of the pieces confirmed that a the tank had failed by a rapid brittle fracture. The large size of the pieces and the degree of external damage implied a vapour-phase explosion rather than a more energetic liquid-explosion. No organic material traces were detected so that hydrogen became the only possible responsible of explosion. A possible source was found in the corrosion of the steel packing below the feed point of the distillation column. It was not possible to identify a credible ignition source as in most previous chlorine-hydrogen explosions.