RALEIGH, N.C. — Consultants hired by West Pharmaceutical Services Inc. to explore the cause of a fatal explosion at its Kinston plant will attempt to reconstruct what happened, the company's chief executive officer said.

Company representatives, allowed into the plant for the first time Tuesday, retrieved damaged hard drives from computers used in the rubber-making process in the part of the plant where the explosion originated.

"We're hoping we can retrieve the data that was on there," West CEO Don Morel said.

While investigators have yet to explain what caused the blast, they're likely to find it was something unusual, Morel said.

"I think most important here is that when we get to the root cause, it will be an anomaly," he said. "I think it will be some unique set of circumstances. What those are we don't know yet. We need to get all of the facts assembled and then draw the proper conclusions from those facts."

The company's investigation will be carried out while the U.S. Chemical Safety Board, or CSB, also attempts to pinpoint the accident's cause. The federal agency's probe could lead to changes in industry standards or government regulations.

A mix of dust and air fueled the Jan. 29 explosion at the medical fittings factory, killing four workers and sparking a fire that burned for days, federal investigators said. Nine burn victims remained in critical condition Tuesday.

Inspectors said they have not determined what kind of industrial dust fueled the explosion or what sparked it.

The explosion occurred near the end of the production line on the first floor of the plant's four-story, 40-foot-tall "mixing tower," where rubber is made into sheets. Besides rubber, materials that could have created combustible dust included sulfur, polymer powders and other organic processing agents, investigators said.

"Any organic dust is combustible if it's suspended in air and the particle sizes are small enough," said Charles W. "Wes" Jordan, a private workplace safety consultant. He said he remembers an explosion caused by Play-Doh dust at a toy factory.

A University of Michigan expert on combustion and fires said people would be surprised at what might cause an explosion.

"I remember going to a candy factory once where they were using powdered sugar," said Bill Kauffman, an aerospace engineering professor. "The floor was squeaky clean, but they had a suspended ceiling. And you look up in the suspended ceiling, and there's a half inch of powdered sugar up there."

It took days for firefighters to extinguish flames so that investigators could enter the factory, where synthetic rubber was produced in one area and shaped into syringe plungers and intravenous equipment parts in another.

Morel said despite the destruction, technical and production staffers who have been inside the building have left him optimistic that most of the machinery inside can be recovered and moved to other plants, at least temporarily.

Morel started visiting the company's other U.S. rubber-making plants to talk to employees about the blast and production schedules that will change to fulfill orders. He visited plants in Lititz and Jersey Shore, Pa., on Tuesday, he said.

Morel said he plans to meet with employees in Kinston and St. Petersburg, Fla., on Wednesday, then visit Kearney, Neb., on Thursday.