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
