Over the course of two days in early November, Pacific Gas & Electric informed some 70,000 customers in parts of nine California counties that crews might need to turn off electric power to ensure public safety due to bad weather.

By the afternoon of November 8, weather conditions had improved to the point where the utility no longer saw a need to de-energize service.

But hours earlier, at around 6:15 that morning, the utility experienced an outage on the Caribou-Palermo 115 kilovolt transmission line in Butte County, one of the counties that the utility had been monitoring. Later that same day, aerial observers reported damage to a tower on that same transmission line, in the area of what had become a rapidly expanding fire that came to be called the Camp Fire.

Before it was brought under control in late November, that fire had consumed an area roughly the size of Chicago, killed more than 85 people, and caused as much as $10 billion in damage. The town of Paradise, California, was largely destroyed by flames.

Shut-off Authority

The utility's timeline of events as it monitored weather conditions on November 6-7 and weighed whether or not to shut off power to parts of its service territory came following a directive by state regulators. (Read the utility's report to state regulators.)

In July, the regulatory body adopted rules aimed at strengthening customer notification requirements before de-energization events and ordered utilities to work with local communities to develop de-energization programs.

According to the California Public Utilities Commission, PG&E, Southern California Edison and San Diego Gas & Electric have general authority to shut off electric power to protect public safety under California law, specifically California Public Utilities Code Sections 451 and 399.2(a). This process is called de-energization and allowable actions include shutting off power to prevent fires caused by strong winds.

Satellite images of the Camp Fire and the Hill and Woolsey fires in California, taken Nov. 9, 2018, by the Moderate Resolution Imaging Spectrometer on NASA's Terra satellite. Source: NASA Earth ObservatoryUnder state guidelines, utilities will de-energize electric facilities only during periods of "extreme fire hazard," and only if the utility reasonably believes that there is an "imminent and significant risk" that strong winds may topple power lines or cause major vegetation-related damage to power lines, leading to increased risk of fire.

In its late November compliance filing with state regulators, PG&E said that it activated its Emergency Operations Center (EOC) on November 6 in response to predicted extreme fire danger and high wind conditions expected on November 8.

Fire Danger

The EOC activation followed what the utility said was an extended period of dry fall weather, with only one rain event since May, and periods of dry north winds that caused the moisture content of live and dry fuels to remain low across high fire threat areas of PG&E’s service territory.

PG&E said that on Monday morning, November 5, weather models and fire danger models were generally forecasting dry and windy conditions that could lead to extreme fire danger from late Wednesday evening November 7, through Thursday morning, November 8.

At that time, forecasts did not indicate that conditions would escalate to the point where de-energization for safety was required, the utility said. On November 6, however, the forecast changed, and PG&E activated its EOC due to forecasted weather conditions with increasing fire risk, including forecasted high winds and extremely low humidity.

It said that teams from all Incident Command Structure (ICS) functions (Planning and Intelligence, Operations, Logistics, Public Information, Customer Strategy, Government Liaison, and others) were assembled to support the potential need for a service interruption. That same day, PG&E initiated what it said were outbound communications to around 70,000 customers across nine counties.

PG&E said that its customer communications plan included interactive voice response telephone messages, emails, texts, news releases, media interviews, social media and paid advertising. The utility said that it also alerted state agencies, local first responders and community leaders.

On November 7, PG&E reduced the forecasted impact down to 63,000 customers and eight counties (Butte, Lake, Napa, Nevada, Placer, Plumas, Sierra and Yuba). Weather conditions stayed consistent, the utility said, nearing but not reaching forecasted levels that would warrant temporarily turning off power for customer safety.

By around 1:00 pm Pacific Standard Time on November 8, winds were decreasing, and PG&E no longer anticipated a possible need to de-energize. PG&E said that it immediately informed all stakeholders of the change in conditions and that no lines would need to be proactively de-energized.

Earlier that morning, however, the utility reported the transmission outage in an area near what has been identified as the likely ignition point for the Camp Fire.

De-energizing Criteria

The utility said that it considers multiple factors when making the decision to de-energize lines. Those criteria, broadly speaking, include:

• A Red Flag Warning declared by the National Weather Service

• Low humidity levels, generally 20% and below

• Forecasted sustained winds above approximately 25 mph and wind gusts in excess of approximately 45 mph

• Site-specific conditions such as temperature, terrain and local climate

• Condition of dry fuel on the ground and live vegetation (moisture content)

• On-the-ground, real-time wildfire related information from its Wildfire Safety Operations Center and field observations from utility field crews

The exact cause of the Camp Fire remains under investigation.