The United States power grid is at risk of a major blackout that could last up to 18 months, according to a new report. Concerns are heightened as one U.S. city has been without power for more than a week.

Jon Wellinghoff, former chair of the Federal Energy Regulatory Commission (FERC), told The New York Times Magazine that America’s aging infrastructure is badly outdated and potentially vulnerable to a coordinated attack. He first raised the alarm in 2013 after gunmen shot up 17 transformers at an electrical substation near San Jose, California

Wellinghoff said the FERC did an analysis that determined the U.S. power grid could be seriously disrupted if similar incidents targeted the 10 most important substations in the country’s three sections: Western, Eastern and Texas Interconnections. Substations are where multiple high-volate lines meet, routing electricity between power plants, transmission lines, and local neighborhoods