In the photo, slim columns frame a person standing beneath a broad, round ceiling. Light catches the ribs near its center, while the outer edge disappears into the dark. The room looks as if it was designed around that ceiling. In a sense, it was. The builders of the exhibition hall in Oberhausen, Germany, worked around a giant steel disc that the building already had. For decades, the space below it had been used to store industrial gas.
The disc is the part worth looking for. In operation it could rise almost the height of the tower. Since the conversion, it has stayed just a few metres above the bottom. A visitor can now stand under it, then climb a staircase and look out from the other side of the same piece of machinery.
A ceiling that used to move
Gas entered near the bottom of the holder and accumulated beneath the disc. As more gas came in, it pushed the disc up the inside of the building. As gas was drawn off, the disc came down. Think of a piston moving inside an enormous cylinder, with the weight of the piston bearing down on the gas. The outside walls could stay where they were while the volume inside changed.
The disc needed a seal where its moving edge met the wall. The venue's technical account describes a circulating oil and tar mixture that ran down the inside wall, then was collected, cleaned and pumped back up. The disc also carried concrete ballast to increase the pressure on the gas. At full capacity, the disc could reach a height of 95 metres. That gives some idea of how much of the tower was once reserved for the movement of a single component.
How the disc became a floor
The plant stopped using the gas holder in 1988. The industrial exhibition initiative known as IBA Emscher Park proposed finding a second use for it, and conversion followed in 1993 and 1994. The team fixed the old disc 4.5 metres above the bottom. That left a low, wide circular exhibition room below it, with more than 3,000 square metres of floor area. Staircases lead to the upper side, where a stage was installed. Some of the supporting structure became seating.
The two spaces tell you something about the building that a view from the street can miss. Downstairs, the underside of the disc gives the room a ceiling low enough for the columns and lighting to feel close. Upstairs, the disc is underfoot and the tower opens overhead. It is the difference between standing underneath a machine part and standing on it.
GuidoR took the interior photograph in 2008, well after the conversion. The lit displays around the perimeter give the room away as a gallery. Look back to the rings overhead and the scale starts to make sense. What appears to be a ceiling in the photograph spent its working life rising and falling inside that same shell. The conversion made the old dividing line between gas and open space into one that visitors can cross.