Optical drives
I was once involved with an issue with a large Optical Drive based Jukebox. Entire platters gradually stopped working one by one. The Optical drives were replaced but they still could not read the platters. It turns out that there were printers in the same room as the jukebox and someone dropped an open carton of toner on the floor. They cleaned up the mess but did not tell anyone. The fans on the jukebox obviously sucked up some of the toner "dust" and gradually covered all the platters. An engineer went in and carefully cleaned them all and everything else they could clean and it all magically started working again.
The same customer also had some building work needed in the computer room over a few weekends so an engineer was sent in on a Friday to shut the sysytems down, cover them up with large pink plastic anti-static "condoms" and then come back on the Monday to unpack and restart it all having cleaned up under the floor as well. They were therefore aware that computers dont like dust! I think the printers got moved elsewhere after the toner accident.