*This image copyright NASA*
Metal whiskers, also referred to as tin whiskers or zinc whiskers, are something that I've read about with some curiosity before. Science does not currently fully understand why many metals and alloys form these tiny whiskers over time. The phenomenon has been known since the early 20th century, but we still don't know much about why it happens or how to effectively stop it. It is still being studied today, and you can find metal whiskers in the news being blamed for things like fires aboard aircraft. Obviously, these whiskers can wreak havoc in an electronic system whose components are packed tightly together. These whiskers can grow out of the solder used to manufacture electronic equipment, and they can also grow out of other non-electrified pieces of metal like server rack rails and the metal parts of datacenter raised flooring tiles. These tiny little metal whiskers can then be shaken loose or scraped off by such actions as lifting the floor tile and sliding it across the surface of an adjacent tile, then blown into the air by the datacenter ventilation system, and then subsequently sucked into the power supplies of the computers housed within the datacenter. Resulting short-circuits can cause electronic component failure, and even fire.
This question was asked today by someone on ServerFault, which rekindled my interest in the subject. I also recommend reading the Wikipedia on it. And I highly recommend visiting this NASA page - an entire page devoted to the phenomenon of metal whiskers.
From that page, if you just watch or read one thing from it, I specifically recommend this video, which is specifically about the damage metal whiskers can do in a datacenter environment.