I think you're talking about Cor-Ten steel. This steel is alloyed a little bit to make a rust stain that is supposed to be protective. However, this stuff hasn't always worked as well as planned. In some places, the local atmosphere is too aggressive for the steel, and the film isn't protective. Instead, the steel just keeps making a fine rust that falls from every surface and covers everyone and everything underneath.
Bill
Maybe you should inform US Steel (Now USX) about it. People in Pittsburgh, PA should be warned that the USX Corporate Headquarters skyscraper, downtown, is an enviornmental hazard since it is primarily constructed of the stuf.. :)