In August 2003, a blackout affected a large swath of the Northeastern US and parts of Ontario:
“Triggered by an unpruned tree branch in Ohio — coupled with a software glitch and human error — the chain-reaction outage snarled transportation systems, shut down stock exchanges and was blamed for contributing directly to 10 deaths as it spread through the Northeast’s population centers.”
It was the world’s second most widespread blackout in history and affected an estimated 55 million people in Canada and 8 US States. Studies show that an additional 90 deaths were indirectly related to the blackout, which left people without power anywhere from 6 hours to 2 days.
A smaller blackout event in 2011 in Arizona, California, and parts of Mexico that left 3 million without power for up to 12 hours was caused by a single downed power line.
These blackouts highlight the vulnerability of the US electrical grid system. In most cases, backup systems prevent such outages, but they sometimes fail, as these two events demonstrate. And having been designed for severe weather events, they don’t necessarily protect against potential terrorist attacks on the grid.
Former FERC chairman Jon Wellinghoff said that moving towards a series of independent microgrids could help mitigate such cascading power outages in the future.