The refinery was shut in early April for repairs after a deadly fire that killed seven workers. It was the most destructive accident at a U.S. refinery in 5 years.
According to the Skagit Valley Herald, company officials told community leaders in a private meeting this week that an initial report indicated "some sort of chemical reaction" caused the flash fire.
The blast was an isolated event at a heat exchanger at a naphtha hydrotreater and caused a flash fire. Physical inspections of the damaged site has been completed but state and federal investigations are ongoing. The damaged unit is being evaluated by an independent lab and repairs are taking place at the refinery.
After speaking to a Tesoro engineer Thursday, Mark Asmundson, executive director of the Northwest Clean Air Agency, the agency responsible for monitoring air quality in the state, said the goal was to begin the restart in September after completing repairs, according to a report by Down Jones news service.