Authorities resumed searching Thursday for nine workers feared dead at a Washington state paper mill where a chemical tank ruptured Tuesday, in one of the deadliest U.S. workplace accidents in recent decades.

The disaster at Nippon Dynawave Packaging Co. in Longview has left 11 people presumed dead, including two confirmed fatalities and nine missing workers. Authorities have said there is no hope of finding survivors from the tank rupture, which also injured eight people including a firefighter.

The partially collapsed tank spilled more than 500,000 gallons of white liquor, a highly corrosive chemical mix used to break down wood for paper products. Fire officials said recovery efforts would be slow and deliberate due to the dangers posed by the remaining chemicals. The cause of the disaster remains under investigation.

Among the confirmed dead was Gilbert Bernal, a grandfather and electrician at the plant. CJ Doran, 26, was among those presumed dead. Friends described both men as caring family members who were dedicated to helping others.

Authorities said the chemical spill has not contaminated air or drinking water in Longview, a city of about 40,000 people near the Oregon border with deep ties to the paper and lumber industries. Crews are working to flush contaminated water from ditches near the plant before pumping it into the Columbia River, though the EPA said some contamination that reached the river has had no noticeable effect.

Nippon Paper Group, the mill's Japanese parent company, expressed condolences to the bereaved families in a Wednesday statement. The disaster has deeply affected the community where many families have worked in local mills for generations.