A blast and an acid spill at a Rolls-Royce plant near Indianapolis has injured nine workers, emergency officials said. Eight of those injured were treated at two hospitals for acid exposure, while the ninth was treated at the scene, a Fire Department spokesman said. The spokesman said nitric acid was being moved from a 250-gallon tank when the blast created a giant chemical cloud at the luxury car maker's aviation and marine production plant in Wayne Township, Ind., around 1 p.m. ET. The cause of the blast hadn't yet been determined, pending an investigation, and it wasn't clear how full the tank was when it blew up, the spokesman said. Nitric acid, which is explosive and highly corrosive, can cause severe burns and, if inhaled, respiratory problems.