Roughly a dozen workers had been in or near a break room on the ground floor near the path of the spewing white liquor. The hazardous conditions delayed rescue efforts for several days. In all, first responders spent five days retrieving the bodies of nine victims. Two others died at area hospitals.

Autopsies conducted by the Cowlitz County Coroner’s Office and the Multnomah County Medical Examiner’s Office later deemed severe chemical burns a significant factor in all 11 workers’ deaths.

The cause of the incident has not been determined. Investigations are underway by the Washington state Attorney General, the U.S. Chemical Safety and Hazard Investigation Board, Washington state Labor and Industries, and attorneys representing survivors and the families of the victims.

While the plant has been out of commission since the incident, Nippon officials notified state regulators on Monday they plan to install temporary storage tanks in order to restart work at the plant.