final report, issued Monday, NTSB officials determined that the pipe failed because of "severe wall thinning caused by external corrosion." The pipeline was corroded at least partly because the rocky material used to fill in around the line prevented the anti-corrosion system used by the gas company from working properly.The agency also concluded that the alert system in Columbia Gas Transmission's control center wasn't configured in such a way to let controllers know there was a problem, and that the lack of the automatic shutoff or remote control valves made it harder to isolate the pipeline that had exploded, and let the fire after the explosion burn for longer than necessary.The explosion occurred near W.Va. 21 and Derricks Creek Road, about 100 feet away from Interstate 77, at about 12:40 p.m. on Dec. 11, 2012, destroying three homes and sparking a massive fire that closed the interstate for nearly a day.The NTSB report said the explosion blew out a 20-foot section of pipe installed in 1967, sending the pipe flying about 40 feet from its original location."The National Transportation Safety Board determines that the probable cause of the pipeline rupture was (1) external corrosion of the pipe wall due to deteriorated coating and ineffective cathodic protection and (2) the failure to detect the corrosion because the pipeline was not inspected or tested after 1988," NTSB investigators concluded in their report."Contributing to the delay in the controller's recognition of the rupture was Columbia Gas Transmission Corporation management's inadequate configuration of the alerts in the supervisory control and data acquisition system," the NTSB inspectors wrote. "Contributing to the delay in isolating the rupture was the lack of automatic shutoff or remote control valves."NTSB officials also recommended that federal pipeline safety officials require regular inspections of lines that run near major highways, regardless of how many people live in the area.The pipeline that exploded was called SM-80. Two other, larger pipelines in the area -- SM-86 and SM-86 Loop -- were required to be inspected under federal law because they were deemed to run through "high consequence areas," or HCAs.Under rules written by the federal Pipeline and Hazardous Materials Safety Administration in 2004, pipeline operators determine if an area is an HCA by considering the "potential impact radius" of an explosion, taking into account a line's size and pressure, and counting the buildings in that area where people live.Mandatory inspections of SM-86 and SM-86 Loop in 2009 revealed significant corrosion of both pipelines, such that Columbia Gas Transmission decided to replace some sections of damaged pipe. Had Columbia Gas Transmission been required to inspect SM-80, as well, NTSB inspectors concluded, they might have found the corrosion and replaced the pipe before it ruptured and caught fire.NTSB investigators noted that when the Pipeline and Hazardous Materials Safety Administration considered which lines should be regularly inspected, some people argued that lines near infrastructure like "interstate interchanges, bridges, certain railway facilities, electric transmission substations, and drinking water plants" should be included.However, the PHMSA decided that explosions near such infrastructure "would not likely include death or serious injury."In their report, NTSB investigators noted that, "had the [Sissonville] accident occurred during commuting hours, when traffic would have been significant, severe or fatal injuries could have occurred." They noted a December 2007 gas pipeline explosion that killed a driver and injured a passenger on Interstate 20 in Louisiana, and two people who were injured when a gas line burst in May 2009 between Interstate 95 and the Florida Turnpike.According to the PHMSA, natural gas pipelines cross divided highways or interstates in 7,105 locations around the country. Nearly 3,000 of those pipelines are too small to fall under the current mandatory inspection guidelines.The final NTSB report, like the preliminary report on the explosion, issued last year, also noted that there were no automatic or remote shutoff valves on the 29-mile section of pipeline that exploded. It took until 1:45 p.m., more than an hour after the explosion, to manually turn off the gas.Despite numerous pressure fluctuations on the line for more than 12 minutes after the explosion and fire, NTSB officials found that Columbia Gas Transmission controllers didn't notice that anything was wrong with the pipe until they got a call from a Cabot Oil and Gas controller at about 12:53 p.m. Cabot Oil and Gas found out about the explosion from a field technician who was near the scene of the accident and heard the initial explosion."The Columbia Gas Transmission Corporation supervisory control and data acquisition system alerts did not provide useful, meaningful information to the controller to assist him in determining the operating condition of the pipeline," the report noted.NTSB inspectors noted that the controller keeping an eye on the three Sissonville pipelines the day of the explosion got alerts that there were pressure drops on the system, but there was no simple way to compare the alerts and figure out what they meant. The controller also couldn't tell which of the three pipelines in the area was affected, so mechanics had to shut down all three.Columbia Gas Transmission also had not provided a plan for what to do when pressure drops were noted. NTSB officials recommended changing the alert system so controllers could compare data over time and have a plan in place for what to do if there's a problem.Shawn Patterson, president of parent company Columbia Pipeline Group, said the company has made changes as a result of the explosion."The report issued today confirms that the comprehensive response program Columbia has already initiated is on the right track, and will improve safety practices, not only at our company, but across the pipeline industry," Patterson said. "While Columbia was in full compliance with all federal and state pipeline safety regulatory requirements for the pipeline, the report identifies areas for continuous improvement opportunities, many of which are already underway."We take a proactive approach to safety and we look to apply lessons learned from incidents like this," he said. "We also look to better obtain, interpret and apply information on our systems to ensure safe and reliable operation."Sen. Jay Rockefeller, D-W.Va., issued a statement Monday evening, calling the lax inspection history for the pipeline "unacceptable.""The NTSB report should be a wake-up call for the pipeline industry," the senator's statement reads. "It is unacceptable that the Sissonville pipeline was not tested or inspected since 1988, and alarming that the company's systems were not better prepared to detect or respond to this emergency."While, fortunately, there were no fatalities in the Sissonville pipeline explosion, there was substantial damage, which calls into question how much industry has been doing to secure pipelines running through our communities."This is why I held a field hearing last year in Sissonville to examine pipeline safety, and why I will be following up with Columbia Gas on their plans to implement the recommendations provided by the NTSB."West Virginians deserve to know that everything is being done to prevent disasters like this from happening again."Reach Rusty Marks at firstname.lastname@example.org or 304-348-1215.