"Magellan's 8-inch, Line 501 Beatrice to Greenwood Nebraska, anhydrous ammonia pipeline leaked on July 23, 2010 during maintenance activities to dislodge cleaning pigs. The pigs were being used to remove the commodity (anhydrous ammonia) from the pipeline prior to conducting a planned hydrostatic test. Air had leaked past the pigs, resulting in a vapor lock which caused the pigs to become lodged in the pipeline upstream of Beatrice pump station. The air in the pipeline made it difficult to push the pigs without exceeding the maximum operating pressure (MOP). This occurred in Gage County, Nebraska near the town of Pickrell. At the time and location of the failure, Magellan personnel were working to install a 2 inch Thread-O-Ring (TOR) fitting at milepost 153.4, a high point in the pipeline. The TOR fitting was being installed to bleed air out of the pipeline and remove the vapor lock. [...] The total amount of anhydrous ammonia lost was reported by Magellan to be 0.48 barrels. As the release occurred, the anhydrous ammonia formed a white vapor cloud that damaged about 4 acres of crops before it dispersed in the wind. No unusual weather or geological components were determined to be a factor. The release did not ignite, and no one was killed or injured although 9 were evacuated. Air and water monitoring was performed at the site and no water impact was found. Minor soil contamination was found and remediated."
Pipeline and Hazardous Materials Safety Administration: http://phmsa.dot.gov/