The nation’s worst blackout began with three power line failures in Ohio and should have been contained by operators at FirstEnergy Corp., a three-month government investigation concluded Wednesday.

The report by a U.S.-Canadian task force said the FirstEnergy operators did not respond properly, allowing the Aug. 14 outage to cascade, eventually cutting off electricity to 50 million people in eight states and Canada.

The task force also cited outdated procedures and shortcomings at a regional grid monitoring center in Indiana that kept officials there from grasping the emerging danger and helping FirstEnergy deal with it.

“This blackout was largely preventable,” Energy Secretary Spencer Abraham said in remarks prepared for a news conference.

Among the faults found at FirstEnergy was a simple failure to keep trees around power lines trimmed.

FirstEnergy, based in Akron, Ohio, has maintained that its problems were but some of many in the Midwest power grid on the day of the blackout and that it should not be singled out.

The task force report cites the failure of a FirstEnergy line near Cleveland, follow by problems with two of its other lines, as the “initial events” of the blackout.

It said the company’s failure to adequately trim trees along the lines “was the common cause” for the lines tripping and said overall FirstEnergy “failed to ensure the security of its transmission system.”

Abraham and Canadian Natural Resources Minister Herb Dhaliwal released the findings in the 134-page report on the causes for the blackout that spread across eight states, from eastern Michigan to New York City and into Canada.

It was the worst blackout in the nation’s history, costing at least $6 billion in economic and other losses. It prompted new calls for upgrading the nation’s high-voltage electric transmission systems and giving the government power to enforce reliability standards.

The report raises questions about the monitoring of the power grid by the Midwest Independent System Operator (MISO), a group responsible for overseeing power flow across the upper Midwest.

The MISO operators, from a control center in Carmel, Ind., were using outdated information and didn’t have the means to identify significant transmission problems developing in the system, said the report. That prevented MISO operators from assisting FirstEnergy control operators, who themselves were hampered by a faulty computer and other mechanical glitches.

© 2012 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

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