Orica's Kooragang Island chemical plant released hexavalent chromium into the atmosphere on 8 August 2011. The known carcinogen was released between 6 and 6:30pm and the spill continued for approximately 20 minutes. An estimated of hexavalent chromium was discharged from the Orica plant, with another over the suburb of Stockton. Approximately 20 workers at the plant were exposed as well as 70 nearby homes in Stockton. Orica failed to notify government authorities until 16 hours after the incident and residents were not formally notified for three days. Under a Prevention Notice issued on 11 August 2011, the NSW Office of Environment and Heritage (OEH) closed the ammonia plant at Kooragang Island. The hexavalent chromium leak was the subject of a New South Wales Parliament Upper House inquiry that was concluded in February 2012.