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A Proterra electric bus battery caught fire in a South Philly SEPTA depot

There have been several battery-related fires in electric buses and cars.

The Proterra Catalyst bus that caught fire Wednesday morning at SEPTA's Southern Depot.
The Proterra Catalyst bus that caught fire Wednesday morning at SEPTA's Southern Depot.Read moreGreg Masi

A battery power pack in a sidelined electric bus ignited Wednesday at SEPTA’s Southern Bus Depot, occupying city fire crews for hours and delivering another possible setback to efforts to build a low-emission fleet in Philadelphia.

No injuries were reported.

The transit agency bought 25 battery-electric buses from California manufacturer Proterra in 2016, but all have been parked at the depot since 2020 after discovery of cracks in bus frames and performance problems.

Kathy Matheson, a spokesperson for the Philadelphia Fire Department said crews rushed to the depot, at 19th and Johnston Streets, around 8:50 a.m. Wednesday after smoke was seen billowing from a garage bay.

She confirmed the fire’s origin was traced to lithium ion battery units inside the vehicle.

“Though some garage sprinklers had activated, firefighters worked to extinguish the flames using multiple hose lines,” she said in an email. “Hazmat teams disposed of hazardous debris from the fire, and other companies remained on scene for several hours to ensure the bus batteries did not reignite.”

The bus was towed from the garage and isolated in a nearby parking lot. The Fire Marshal’s Office is investigating.

Andrew Busch, a spokesperson for SEPTA, said the agency would do its own investigation and that Proterra representatives were there and looking into the fire as well. He said no SEPTA staff were operating the bus when the fire started.

“We’re fortunate and happy no one was injured,” he said.

Busch said it was too early to assess damage to the depot, but said a photo showed that the fire melted a hole in the side panel of the bus during the blaze.

“We are working closely with SEPTA to thoroughly investigate this very rare event and are directing field service technician support to assist at their facility,” Proterra spokesperson Shane Levy said in an email Thursday. “Our initial on-the-ground assessment indicates that only one of the vehicle’s four battery packs was involved and the battery’s safety systems limited the damage to the vehicle’s structure, interior, and other battery packs.”

Proterra, the largest electric bus maker in the country, has been subject to other inquiries involving bus fires.

In 2021, a California transit agency considered shelving its entire Proterra fleet after a blaze the company attributed to “third-party components.” In 2015, a mysterious fire broke out inside a Proterra factory, destroying a bus. The company said that incident involved technology that is no longer in use.

Lithium ion batteries are vulnerable to “thermal overload” and are notoriously difficult to extinguish. They have been linked to similar incidents in electric vehicles made by a variety of manufacturers, including Tesla and General Motors.

Although the buses cost about $1 million each, several times more than diesel or hybrid counterparts, they have been pitched as an alternative that requires less fixed infrastructure than traditional trolleys or trackless trolley buses.

The company has continued to attract government grants aimed at reducing carbon emissions. President Joe Biden took a “virtual tour” of a Proterra facility last year.

Even prior to discovery of the cracks, the buses drew complaints about limited battery range and sensitivity to cold temperatures. Some experts believed the cracking may have been caused by overloading the buses with additional batteries to increase longevity.

SEPTA has considered spending millions in infrastructure improvements designed to prepare for a battery-powered future, including upgrades at Midvale Depot.

Busch said the fire would likely factor into SEPTA’s ongoing negotiations to get Proterra to fix the earlier defects. He could not say when or if the buses would be returned to service.

“There’s still discussions with them about the fleet that are ongoing, separate from this incident,” he said. “There has been progress.”