Utility giant Pacific Gas & Electric on Friday released a long-awaited investigation into the December blackout that left 120,000 San Francisco residents without power, revealing that the multibillion-dollar company was aware of damage at the Mission substation responsible for the incident but left faulty equipment in place.
The 70-page inquiry (opens in new tab), conducted by the engineering firm Exponent, found that inclement weather before the Dec. 20 blackout spurred high humidity levels inside PG&E’s Mission substation and caused condensation buildup, resulting in a fire and the subsequent outage.
PG&E personnel in November found a piece of equipment known as an “incident insulating board” with “burned spots” and warping that was partially responsible for the blackout, but they failed to replace or inspect it thoroughly, according to the report. The November damage was logged by PG&E as water issues, but Exponent investigators said it had other causes…