Nov 15 (Reuters) - The National Transportation Safety Board said on Thursday that utility company NiSource Inc failed to adequately draft and oversee natural gas pipeline work orders and those lapses led to deadly blasts in three Massachusetts communities in September.
The federal regulator said in a review of how Columbia Gas Co of Massachusetts, a subsidiary of NiSource, handled pipeline repair work that better construction orders could have prevented the disaster.
Explosions and fires that killed one person, injured 21 and damaged 131 buildings erupted as Columbia Gas was replacing cast-iron pipe with plastic lines.
Utilities have told state regulators that thousands of miles of natural gas pipelines in Massachusetts are leak-prone and need repairs.
The National Transportation Safety Board said that a field engineer who developed the work orders told investigators that he did not recognize the critical role of pressure sensors in the work and did not document the location of the regulator-sensing lines that, when disconnected, flooded the system with high-pressure gas.
The agency recommended that NiSource revise its review process, update its records and documentation and be able to immediately shut down gas pipeline systems during repairs.
It said Massachusetts should require professional engineers to sign off on utility company work orders, which is not currently required.
The review expanded on a preliminary study into the explosions and fires in Lawrence, North Andover and Andover, Massachusetts.
NiSource, based in Merrillville, Indiana, said in a statement that it would adopt the agency's safety recommendations at all of its utility companies, and spend $150 million to install devices that would "slam shut" gas lines when they sense pressure reaching risky levels.
The company said in a regulatory filing this month that the U.S. Attorney’s Office in Massachusetts was conducting a criminal probe of the company as a result of the disaster.
It was the largest U.S. natural gas pipeline accident since 2010 in terms of structures involved.
Eight years ago, an interstate gas transmission line operated by Pacific Gas and Electric Co ruptured in San Bruno, California, killing eight people, destroying 38 buildings and damaging 70 others, according to the National Transportation Safety Board. (Reporting by Collin Eaton)