If rush hour in the Bay Area wasn’t bad enough already, commuters encountered a novel obstacle on their way homes Friday: a truck spilled 300 gallons of acid on a major freeway, stalling traffic and igniting a fire in surrounding vegetation.

The truck was carrying a blend of phosphoric and nitric acid when the chemicals spilled onto Interstate 880 near the city of Hayward in the East Bay. The corridor is a major thoroughfare used by people working in Silicon Valley and commuting to homes north of the tech hub.

While the cause of the acid spill was unknown, the incident led to a toxic vapor plume that led authorities in Hayward to urge nearby residents to shelter in place. The San Francisco Chronicle said that the spill also caused a vegetation fire, prompting the California Highway Patrol to shut down traffic on I-880 on both directions.

Late Friday afternoon, hazmat crews managed to stop the acid leak and was working to clean up the spill, the Chronicle said.

The summer of 2018 has been a hard one for California residents, with a number of wildfires raging in both the northern and southern portions of the state. Firefighters have battled blazes near recreational areas and homes in Northern California, notably the Mendocino Complex Fire that has become the largest wildfire in the state’s history.