The confirmed death toll in the chemical tank explosion at a Washington state paper mill rose to eight on Thursday after crews recovered the remains of six workers, officials said.

Three more individuals remain missing and are presumed dead. Eight other people were injured, including a firefighter responding to the incident.

A tank containing more than 500,000 gallons of a chemical mixture used to break down wood for making paper collapsed on Tuesday morning at the Nippon Dynawave Packaging Co in Longview, a city along the Columbia River. The explosion released a flood of caustic liquid capable of causing severe burns and lung injuries.

The tragedy is one of the deadliest US workplace accidents in recent decades.

The collapse occurred during a shift change, and the six workers whose remains were recovered had been in an area where they would congregate in the morning as they awaited their assignments for the day, said Matt Amos, Longview fire battalion chief.

Among the victims were a grandfather who was always willing to help anyone and a young husband described as selfless and caring, according to friends who organized fundraisers for the victims’ families.

The recovery of the victims has been slow and deliberate, complicated by the dangers posed by the remaining chemicals and other industrial hazards, Amos said. Crews were steering clear of a zone closest to the tank, in case of further collapse. They have been working with engineers to determine whether damaged buildings around the tank are safe to enter.

Crews must decontaminate the remains of the victims before turning them over to the coroner’s office for identification. The searchers also must decontaminate themselves.

Authorities said the cause of the disaster was still under investigation. They have not released the names of the people who were killed, but friends and relatives had begun confirming their names and posting online fundraisers to support their families.

Gilbert Bernal, a grandfather who was an electrician at the plant, was the first confirmed death, said his friend Todd Cornwell.

“He was one of the most genuinely good people that you’ve ever met. He would give you the shirt off his back if you needed it. He was always there willing to help in whatever needed to be done,” Cornwell said.

CJ Doran, who was 26, was among those presumed dead, according to a GoFundMe post verified by the crowdfunding site.

He was a husband who was “the spiritual leader of their family, the joy of their home, and the family provider”, the post said.

Other victims included John Forsberg, a father to two young children; Jared Ammons, who had two children and another on the way; and Braydon Finkas, an electrician at the plant who, along with his longtime partner, Kaitlyn Kincaid, took in exchange students and others in need at their home in Cathlamet, according to their friend Rex Czuba.

Finkas was always willing to help someone cut hay or to buy a beer for a new face in their small town, he said.

“He was a really big part of the town,” Czuba said. “He really jumped in and became a part of the community so quickly.”