Fire officials say an explosion involving a tank of nitric acid has injured nine workers at a Rolls-Royce plant near the Indianapolis International Airport. A 250-gallon tank of nitric acid exploded about 1:30pm, releasing a cloud of vapor that left nine workers suffering from acid burns and breathing problems. Eight of the workers were hospitalized, but none had life-threatening injuries. Nitric acid is corrosive. The National Institute for Occupational Safety and Health says the vapor or mist form can irritate the eyes, nose, throat, and skin. High concentrations of vapor can severely burn.