San Francisco Blackout: What You Need to Know and Prepare

What you need to know about the San Francisco blackout is that a major December 20–22, 2025 outage affected a significant portion of San Francisco, impacting about 30% of the city at its peak. A fire and arc-flash event at PG&E’s Mission Substation disrupted electricity, traffic signals, BART, Muni, internet service, businesses, and autonomous vehicles.

Power was restored to most customers by December 22, but the event highlighted the need for food-safety habits, emergency lighting, and reliable backup power. This guide covers the outage’s timeline and causes, as well as practical backup-power options for future emergencies.

San Francisco Blackout Facts and Timeline

San Francisco’s power outage began on Saturday morning and expanded across large parts of the city. The disruption was especially severe because it occurred during the holiday shopping season, when stores, restaurants, transit systems, and delivery services were operating at high capacity.

These are the key dates and figures associated with the event:

• Around 9:45 a.m. on December 20: Initial blackout reports began appearing.
• Around 2:16 p.m.: The San Francisco Fire Department received a report of a fire at the Mission Substation near Eighth and Mission Streets.
• December 20: The outage reached approximately 120,000 to 130,000 PG&E customers.
• From December 20 to 21: Electricity began returning to many neighborhoods, but major sections of northwestern San Francisco remained without service.
• December 21: About 17,000 customers were still without power, primarily in the Presidio and Richmond areas.
• December 22: PG&E expected to restore power to remaining customers affected by the substation incident by approximately 2 p.m.

PG&E established a temporary resource center at the Richmond Recreation Center, 251 18th Avenue. It offered device charging, Wi-Fi, bottled water, snacks, ice, restrooms, and updates from utility representatives.

What Caused the San Francisco Power Outage?

A 77-page investigation prepared by Exponent for PG&E identified an arc-flash event and fire at the Mission Substation as the immediate trigger. The report pointed to moisture and surface contamination as the most likely factors behind the equipment failure.

Arc-Flash Event and Substation Fire

An arc flash is a sudden electrical discharge that can create intense heat, light, pressure, and fire. At the Mission Substation, the event damaged critical equipment used to distribute electricity throughout San Francisco.

Firefighters contained the blaze, and reports indicated that there were no injuries or structural damage. However, the substation’s electrical damage required extensive inspection and repairs before power could be safely restored.

Because substations connect multiple parts of the electric grid, damage to one important facility can affect customers far beyond the immediate neighborhood. That helped turn a localized fire into a citywide service disruption.

Moisture and Surface Contamination

The Exponent report said moisture and surface contamination most likely caused a piece of electrical equipment to fail. Contamination can reduce the insulating ability of electrical surfaces, while moisture can increase the risk of tracking, short circuits, and flashovers.

PG&E damp conditions make moisture control particularly important in enclosed electrical facilities. The report recommended additional humidity monitoring, evaluation of water-intrusion pathways, HVAC improvements, and further protection against surface contamination.

Equipment Damage and Ventilation Concerns

The investigation found that PG&E observed damage to an insulating board during a November inspection. PG&E said it took corrective action after that inspection, but the later failure prompted further scrutiny.

The report also described concerns about elevated humidity and moisture inside the building. Ventilation-system filters were reportedly degraded or water-saturated and were not effectively filtering outside air entering the switchgear room.

These findings do not necessarily establish that one maintenance issue alone caused the outage. They do show why regular inspections, moisture monitoring, effective filtration, and timely equipment replacement are essential for grid reliability.

Affected Neighborhoods, Transportation, and Essential Services

The blackout was not uniform across the city. Some areas regained power relatively quickly, while portions of the northwest remained disconnected into the second day. Transportation and communications were affected alongside homes and businesses.

Neighborhoods With Major Power Disruptions

The Sunset and Richmond districts, Golden Gate Park, the Presidio, and parts of the Inner Sunset and Outer Richmond experienced major disruptions. Additional outages were reported in the East Bay, although they were less widespread than the main San Francisco event. Oakland, the city of Richmond, and South San Francisco were not affected by the same large-scale outage.

Residents should check PG&E’s current outage map or official alerts rather than assume that a nearby neighborhood has the same status. Restoration can vary by block, building, and circuit.

BART and Muni Service Changes

BART closed or bypassed several stations, including Powell Street and Civic Center, during the disruption. SFMTA also suspended portions of Muni Metro service when stations, tunnels, and related systems lost power.

Muni trains on the J and N lines turned back at Church/Duboce, while K, L, and M trains turned back at Castro. Stations between Embarcadero and Van Ness were closed for part of the outage. The Central Subway later reopened.

Transit conditions can change quickly during a blackout. Check BART and SFMTA alerts before leaving, and allow extra time if a trip requires transfers or walking through areas with dark signals.

Traffic Signals and Road Safety

Power loss at intersections created dangerous conditions for drivers, cyclists, and pedestrians. Treat every dark intersection as an uncontrolled crossing: slow down, look in every direction, and yield cautiously.

Avoid unnecessary travel during a widespread outage. Downed lines, disabled signals, stalled vehicles, emergency response activity, and poor visibility can combine to make ordinary routes hazardous.

Waymo and Other Autonomous Vehicles

Waymo temporarily paused its Bay Area ride-hailing service after vehicles encountered dark traffic signals and blocked roads. Some autonomous vehicles stopped in the streets, adding to congestion and complicating emergency access. Service resumed after conditions improved.

The incident showed how transportation systems depend on more than the vehicle itself. Autonomous cars also rely on functioning signals, communications networks, mapped road conditions, and clear routes. Claims about other robotaxi systems should be checked against official operating updates rather than social media posts.

Internet Providers and Local Businesses

Some internet services were also disrupted. Even if a home has battery backup, internet access may remain unavailable when neighborhood or provider-side network equipment loses power. Businesses faced lost sales, spoiled food, and interrupted payment systems. Grocery stores, markets, restaurants, and bakeries reported substantial losses from refrigerated and frozen inventory during one of the busiest retail weekends of the year.

What to Do During a San Francisco Power Outage

During a blackout, prioritize safety, food temperature, communication, and medical needs. Report the outage through PG&E’s official channels, follow city instructions, and avoid opening doors or using equipment unnecessarily.

Protect Refrigerated and Frozen Food

Keep refrigerator and freezer doors closed as much as possible. An unopened refrigerator generally keeps food cold for about four hours. A full freezer can stay cold for approximately 48 hours, although the actual time depends on room temperature, insulation, and how often it is opened.

Use a food thermometer when power returns. Perishable food that has been above 40°F for more than two hours should generally be discarded. When in doubt, throw it out rather than risk foodborne illness.

Unplug Sensitive Electronics

Unplug televisions, computers, gaming systems, microwaves, and other sensitive electronics during the outage. Power fluctuations or surges can occur when electricity returns, potentially damaging equipment.

Leave one low-wattage lamp switched on so you can tell when service has been restored. Once power is stable, reconnect essential devices gradually instead of turning everything on at once.

Use Flashlights and Battery Lanterns

Keep flashlights, battery-powered lanterns, and spare batteries somewhere accessible. Lanterns are useful for illuminating a room, while a flashlight is better for inspecting electrical panels or moving outdoors.

Avoid candles whenever possible. Open flames can ignite curtains, furniture, or other household materials, especially when people are navigating unfamiliar dark spaces.

Handle Garage Doors and Elevators Carefully

Learn how to use your automatic garage door’s manual release before an emergency occurs. This can help you open the door if the opener has no power, but follow the manufacturer’s instructions and avoid forcing the mechanism.

Do not use an elevator during a power outage unless emergency personnel confirm it is operating safely. If you become trapped, use the emergency button or phone and wait for assistance rather than attempting to force the doors open.

Support Vulnerable Neighbors

Check on elderly neighbors, people with mobility limitations, families with young children, and anyone living alone. They may need help with medication, food, heating, communication, or safe movement through dark hallways.

Keep visits brief and safe, but make sure vulnerable residents know where to find official updates and community resources. A charged phone, warm clothing, and a small amount of drinking water can make a long outage easier to manage.

Prepare for Medical Equipment and Refrigerated Medication

People who rely on oxygen concentrators, CPAP machines, powered mobility devices, refrigerated medication, or other essential equipment need a backup plan before an outage occurs.

Ask a healthcare provider or pharmacist how long medication can remain unrefrigerated. For life-support equipment, contact the medical provider and utility in advance to discuss emergency procedures. Do not wait until a battery is nearly empty to seek help.

Generator and Backup-Power Safety

Backup power can keep essential devices running, but the safest option depends on the equipment and where it will be used. Read the manual, calculate the expected load, and never improvise electrical connections.

Indoor Use of Portable Power Stations

Battery-powered Portable Power Stations do not produce exhaust and can generally be used indoors when operated according to the manufacturer’s instructions. They can charge phones, power lights, run routers, and support selected medical or household devices.

Models such as the Anker SOLIX S2000 may suit households that need more capacity for appliances and electronics. Despite its 2 kWh-class capacity, its compact and lightweight design makes it easier to move around the home when backup power is needed. Its UPS function can also help keep essential electronics running with minimal interruption when the power goes out.

Backup Power for Essential Appliances

Choose a power station that can handle your devices’ power needs and run them for long enough, while also checking its ports, surge capacity, and recharge time. A small unit may handle phones and lights, while larger systems can support a refrigerator, medical equipment, or a sump pump for longer.

For higher-demand home backup, the Anker SOLIX C2000 Gen 2 makes sense when a smaller power station may not be enough. Its capacity can be expanded up to 4 kWh, while six recharge options give you more flexibility when an outage lasts longer than expected. It also offers a compact design, making it a flexible option for extended outages.

Safe Placement of Portable Gas Generators

Operate portable gas generators outdoors only, far from windows, doors, vents, and attached garages. Carbon monoxide is an odorless, potentially fatal gas that can enter a home even when the generator appears to be outside.

Never run a generator in a basement, garage, shed, or covered porch. Refuel only after the generator has cooled, and use heavy-duty outdoor-rated extension cords designed for the required wattage.

Conclusion

What you need to know about the San Francisco blackout is more than a record of a past outage. The December 2025 event demonstrated how a substation failure can disrupt electricity, transportation, communications, businesses, and public safety across a dense city.

Residents can reduce the impact of the next outage by keeping food cold, using safe lighting, protecting electronics, planning for medical needs, and maintaining properly sized backup power. A few practical preparations can protect your household while utility crews work to restore service.

FAQ

What caused the San Francisco blackout?

The San Francisco blackout was triggered by an arc-flash event and fire at PG&E’s Mission Substation near Eighth and Mission Streets. An investigation identified moisture and surface contamination as the most likely factors behind the equipment failure. The report also raised concerns about previously observed insulating-board damage, elevated humidity, and degraded ventilation filters.

What should you get to prepare for a blackout?

To prepare for a blackout, keep a flashlight and spare batteries on hand so you can move around safely if the lights go out. A power bank or portable power station can help keep essential devices charged, while bottled water and shelf-stable food cover basic needs during a longer outage. It’s also worth having medications, a first-aid kit, and a battery-powered radio ready in case you need them.

What’s important to have during a long blackout?

During a long blackout, the most important supplies are safe drinking water, food that does not require cooking, prescription medication, lighting, communication tools, warm clothing, and backup power for essential equipment. A carbon monoxide alarm is also critical if fuel-burning appliances are present.