Pacific Gas and Electric Co. said up to 940,000 customers across 36 counties will have their power cut starting Saturday to reduce the risk of an electrical line or another piece of equipment sparking a damaging blaze amid dangerous fire weather.

Here’s what you need to know about the potential outages:

How long do power shut-offs last?

Power is restored in stages, location by location. During shut-offs earlier this month, PG&E said workers might need up to five days to restore power, but most homes and businesses were back up and running in two days. The company must inspect all lines for damage before restoring power.

Why did PG&E start doing preemptive power shut-offs?

PG&E instituted the precautionary outages to prevent its equipment from starting wildfires in October 2018, a year after some of its power lines were blamed for the devastating Wine Country wildfires. CEO Bill Johnson told state regulators this month that his company is working to make forced power outages unnecessary, but the goal could take a decade to accomplish.

How does PG&E decide whether to issue a shut-off?

PG&E considers whether red-flag fire danger warnings have been issued. Humidity levels must generally be below 20% and high winds above 25 mph, with gusts in excess of 45 mph. Officials also consider the amount of dry vegetation and use observations from PG&E field crews and meteorologists.

How should I prepare for a power outage?

Public safety and PG&E officials advise residents to prepare for life without electricity by:

• Keeping phones and other electronics charged while also having backup charging methods available.

• Building or replenishing emergency kits that include flashlights, spare batteries, a first-aid kit, emergency food and water, and cash.

• Learning how to manually open your garage door.

• Unplugging electrical appliances to avoid overloading circuits and preventing fire hazards when power is restored.

• Storing drinking water — 2 gallons per day per person and more for pets, as water delivery services could be affected by a shutdown.

Can solar panels spare me from a power shut-off?

Customers with solar systems are still connected to the PG&E power grid, so if PG&E cuts off the power for safety, their power gets shut off automatically. People who have a home battery paired with their solar system can avoid full outages.

Should I buy a generator?

Generators can be a helpful but expensive solution to a temporary problem. They can run anywhere from a couple of hundred dollars to as much as $14,000. Don’t try to install your own generator if you aren’t an expert. The do-it-yourself dangers outweigh the savings benefit.

Why doesn’t PG&E have underground power lines?

Putting power lines underground is expensive — $3 million per mile, according to a 2017 estimate from PG&E, versus up to $800,000 for overhead lines. That’s just for smaller, lower-voltage distribution lines; long-distance transmission lines are even costlier. Underground lines would also be harder to fix in an earthquake. But PG&E has put some lines underground; in May, the utility said it would put lines underground in Paradise, the Butte County city destroyed by the 2018 Camp Fire.

It’s not windy in my area. Why is my power still cut?

A long-distance power line that delivers electricity to you may pass through a location where it’s very windy, or forecast to become windy, according to PG&E, which is turning off some of these high-voltage lines, known as transmission lines.

Will my cell phone still work?

Cell phone carriers said service should still work during shut-offs. Most cell phone towers have backup generators.

What should I do with food in my refrigerator?

Meat, poultry, fish and eggs should always be stored in temperatures 40 degrees Fahrenheit or colder, and frozen goods should be 0 degrees or colder. Officials advise people to keep refrigerator and freezer doors closed as much as possible during outages. Refrigerators can safely store food — and keep items cold — for about four hours. Freezers can keep their temperature for about two days if unopened. Dry ice or blocks of regular ice can help store food.

How can I get updates if I’m not a PG&E account holder?

PG&E has an alert system that notifies non-account holders of power outages in a specific area. Company officials said they will try to alert people 48 hours, 24 hours and just before power outages. To sign up, go to pge.com/pspszipcodealerts.

Michael Cabanatuan, Alejandro Serrano and J.D. Morris are San Francisco Chronicle staff writers. Email: mcabanatuan@sfchronicle.com, alejandro.serrano@sfchronicle.com, jd.morris@sfchronicle.com Twitter: @ctuan @serrano_alej @thejdmorris