he California Public Utilities Commission has adopted an expanded set of rules aimed at clarifying when the state's big utilities can shut off power during times of high fire danger and what they need to do before they turn out your lights.
The power shutoffs — a practice the regulatory world calls de-energization — have been used sparingly in the past as a tool to reduce the risk of electrical equipment touching off fires during exceedingly windy, dry, hot weather. The shutdowns are a technique pioneered by San Diego Gas and Electric Co. after its power lines ignited 2007's Witch Fire, which killed two people and destroyed 1,100 homes.
Here are questions and answers on how the public safety power shutoffs work and what the CPUC's new guidelines will mean for utility customers.
Who makes the decision to shut off power?
The decision rests solely in the hands of California's three investor-owned utilities: PG&E, Southern California Edison and San Diego Gas and Electric. To assist in making the decision, each utility now maintains a special command center -- PG&E's is called a wildfire safety operations center -- to assess weather data and reports from field personnel and begin the process of deciding when and where a power shutoff might be necessary. The emergency operations centers typically include engineering, safety and communications personnel.
What conditions could prompt a public safety power shutoff?
There is no one standard for the three utilities that have been directed to develop shutoff plans. But the factors the utilities use involve an assessment of upcoming weather — a National Weather Service red-flag fire warning for hot, dry, windy weather, for instance — and conditions on the ground — such as topography and the moisture content of grass, brush and trees in areas the CPUC has identified as being at high risk for wildfires.
Below is one example: SDG&E's list of factors considered in shutting down power during a period of dangerous fire weather last November. Among them: a red-flag warning coupled with a warning of winds gusting up to 70 mph.