Raised Floors

[Mark Matlock]

   The discussion on raised floors in data centers reminded me of an interesting past experience. My company had installed its first supervisory process control system in an enzyme plant. The plant had been around for quite some time and the process control system was part of a retrofit of the facility. Part of that retrofit was remodeling a room for the PDP-11/44 and the related racks of industrial controllers. There were hundreds of cables carrying various analog and digital signals and control signals under the raised floor that they installed. 

   The only bad thing about the location of the data center was that it was directly under some tanks that were installed on the roof. One tank was for concentrated sulfuric acid which was used to adjust pH in the fermenters. That acid tank was filled from tanker trucks that would come from time to time. One day a trucker who was filling the tank was not paying attention and over filled the roof tank and acid overflowed over onto the roof which should have held the overflow, but it was a flat roof designed to protect from rain not concentrated sulfuric acid. Down in the data center the operator noticed that liquid was flowing down the walls of the room and past the raised floor tiles into the space below. It was easy to confirm it was acid since it was attacking the paint on the wall. The acid pooled under the floor with the cables.

     That was when they called the research chemists next door. We came in and determined that there were some drains under the floor (it had been a factory room before it was converted) and we suggested that they flush the space under the floor with water to dilute the acid to get as much of it out as possible. Then they used fans to try to dry out the room and the space under the floor.

     After all this, miraculously everything seemed ok, but about once every 6 weeks or so that PDP-11/44 would develop some issue and the DEC field service guy (it was under contract) would come out and swap a board or two, marveling at how he had never seen boards that were so corroded. In retrospect I’m amazed that 11/44 survived as well as it did.

Mark