The first article does specify rail grinding, so that's my guess. Looks scary enough in pictures, can only imagine driving alongside that.
But what kind of rail grinding? Track welders do various repairs which include a lot of grinding. Or was it a grinding train? The latter usually comes with automated spraying plus tank cars and active human spotters supposedly to prevent such fires.
Further update published about 3 PM CST states that the MOW crew was using "heavy" grinding equipment. http://www.heraldguide.com/details.php?id=16622 The last photo in the WWL-TV post (#3) shows a dozen or more bents on fire heavily.