Units first received reports of a toxic cloud coming from smoldering debris on the right shoulder of southbound Highway 101 near Sierra Point Parkway at around 9:30 p.m., CHP Officer Ralph Caggiano said.
A preliminary investigation determined that five 1-liter bottles labeled "thionyl chloride," possibly dumped on the shoulder by an unknown party, were leaking and causing a chemical cloud, Caggiano said. A Sig-alert closing the far right hand lane was issued at 10 p.m. so a California Department of Transportation hazardous materials team could respond.
At 11 p.m., a full closure of southbound lanes was issued, Caggiano said. Southbound traffic was diverted on to Interstate Highway 280 in San Francisco for more than three hours, and various onramps to Highway 101 were shut down, including those at Paul Street, Alemany Boulevard and Third Street.
At 2:15 a.m., the CHP announced the reopening of three left lanes to southbound traffic, Caggiano said, and at 4:35 a.m., the Sig-alert was cancelled and the roadway was declared clear.
The chemical spill remains under investigation.