The team from the U.S. Chemical Safety and Hazard Investigation Board plan to interview additional witnesses and develop an agreement governing site access to the Synthron Inc. facility and the handling of physical evidence.
Investigators believe that the blast, which caused massive damage to the plant itself and to nearby buildings and residences, was caused by a pressure increase and a release of flammable vapor from the reactor.
Most of the employees left the building before the explosion, but 14 workers were burned or injured when the blast occurred.
"This was a very serious explosion that caused loss of life and widespread damage," said CSB Chairman Carolyn Merritt. "We will therefore be conducting a full investigation to understand what happened and help protect communities from similar accidents in the future."
Curtis "Butch" Brackett was one of the two workers who was critically injured as a result of the blast. He died Sunday at Wake Forest University Baptist Medical Center in Winston-Salem. The other worker, Dick Edwardson, currently is in fair condition with head injuries in a Charlotte hospital.
Jim Lay, one of CSB's lead investigators currently onsite, said that gaining access will be important in unraveling the events that lead up to the explosion. The task is difficult as facility structures suffered catastrophic damage, and some off-site buildings also were impacted.
"We need to establish the exact configuration of the equipment, determine what kind of pressure relief system was in place and characterize the damage caused by the blast," he said.