About 250 people, including children, have fallen sick and hundreds of residents have been evacuated from their homes after a toxic gas leak from a fertiliser unit in Bangladesh's port city of Chittagong...Di-ammonium phosphate...leaked from the DAP Fertiliser Company Limited on the bank of Karnaphuli river last night...The reason behind the leak could not be known immediately. Bangladesh Chemical Industries Corporation...which runs the unit, formed a 10-member committee to investigate the incident, while the district administration has formed a three-member panel to probe the leak...At the time of the incident, the amount of ammonia in the air was recorded at 600ppm (parts per million) whilst workers at the factory can tolerate conditions with ammonia gas up to 25ppm.