NORTH ANDOVER — Hazardous materials and bomb technicians removed a volatile chemical on Friday from a Dow Chemical Co. laboratory where an explosion injured five people on Thursday. The dangerous operation took hours and was described as among the largest and most complex in recent time.
A container of trimethylaluminum that had been compromised in Thursday’s blast was buried in sand in the back of a dump truck and driven away from the Willow Street facility under police escort just before 4 p.m. Friday.
Authorities said the State Police bomb squad planned to take the container, which is about the size of a basketball, to a remote location where it would be rendered safe.
“This is one of the more complex and larger hazmat incidents that we have responded to in recent times,” state Fire Marshal Stephen D. Coan said.
He said the operation was complicated by the volatility of the chemical, which is used to make LED lights and electronics, its proximity to other dangerous materials in the facility, and the painstaking work necessary to recover it from the pile of debris left behind by the explosion.
The blast took place in a laboratory measuring 15 feet by 20 feet, located in the rear of the building. It was so powerful that it blew out a section of wall, North Andover Fire Chief Andy Melnikas said.
“This is a very successful outcome. It could have been a much more tragic incident,” Coan said. “This went well because of the professionalism and the training levels of the people involved.”
On Thursday, the fire marshal said the explosion was caused by the interaction of trimethylaluminum with water. The chemical is so explosive that employees use a fume hood to work with it, Melnikas said.
Once the chemical container was removed from the plant, investigators from Coan’s office and the North Andover Fire Department entered the building to start their inquiry into what happened, officials said.
“It’s so wide open here as to what the cause could be,” Melnikas said.
Coan said it was too early to rule out the possibility of criminal charges.
“There’s nothing that is leading us to think that this is something other than a very tragic industrial accident but again that’s at a very preliminary stage of the investigation,” he said.
The US Chemical Safety Board is considering whether to send personnel, Coan said.
The US Occupational Safety and Health Administration sent inspectors to the plant to examine whether any violations of federal safety and health standards contributed to the explosion, the agency said.
Two victims are at Massachusetts General Hospital and one is at Beth Israel Deaconess Medical Center in Boston. A fourth victim is at Lawrence General Hospital in Lawrence. Coan said a fifth victim who was standing outside the lab where the explosion occurred suffered minor injuries.
Investigators have not been able to speak yet with the four workers who were most seriously injured, Coan said. Officials did not name the employees.
The workers mostly suffered burns and some shrapnel wounds, Coan said.
“Let’s keep our fingers crossed and pray for recovery of these four seriously injured workers,” he said.
“It could have been, at this time, much worse, and let’s hope it doesn’t turn worse.”
The plant is known as the Rohm and Haas Electronic Materials LLC facility and employs about 60 staffers and contractors, a Dow spokeswoman said. Dow said the injured workers are experienced, longtime employees.
The company also said it was cooperating with investigators and that the community is not at risk.
Mike Bello of the Globe staff contributed to this report. Laura Crimaldi can be reached at email@example.com.