The blast sent up a huge column of black smoke, but emergency services said several air quality measuring stations in the area showed normal readings, easing concerns about toxic pollution. However, police evacuated buildings within a 500 meter (1,640 foot) radius of the scene. Emergency services ordered the evacuation of five schools in the area. Firefighters said three of the injured were in serious condition, two for burns and one with a fractured pelvis. One of the workers, a 37-year-old man, suffered burns on 30 percent of his body, while one of his colleagues, 42, was burned on 18 percent of his body. It took firefighters eight hours to bring the blaze under control.The authorities are investigating the cause of the blasts. This is the second time in less than four years that a fire has erupted at the plant.