Agilent Technologies' Santa Rosa campus got back to business Wednesday, 24 hours after a chemical explosion critically injured an employee.

The high-tech company reopened the two-story building where the accident occurred after concluding it was free of contamination from the blast.

"We're confident it is safe again," said spokesman Jeff Weber. "At least there is a feeling of return to a semblance of normalcy with the reopening of the building."

A company engineer, Patrick Colbus, 45, was severely injured in the 10:30 a.m. blast and remained in critical condition on Wednesday at UC Davis Medical Center in Sacramento, a hospital nursing supervisor said.

Colbus, a Santa Rosa resident, was cleaning a piece of equipment used to produce coating for integrated circuits when the explosion happened, officials said.

It remained unclear if the explosion was caused by a mechanical process, or by chemical exposure or interaction related to the cleaning process, Santa Rosa Fire Battalion Chief Mark Basque said Wednesday.

Both Cal—OSHA investigators and Santa Rosa fire personnel are looking into the incident, Basque said.

More than 20 workers underwent decontamination after complaining of respiratory problems after the flash, which spewed smoke with a chemical odor, officials said.

They were checked out by Kaiser Permanente physicians, who reported no serious health issues, Weber said.

More than 100 people who work in the building on Fountaingrove Parkway remained at home Wednesday morning while inspectors determined whether they could return to work safely, Weber said.

They got the go-ahead after chemical residue tests performed overnight and early Wednesday came back clear, Weber said. Officials reopened most of Building 1 around 11 a.m.

The first floor laboratory that housed the machine involved in the flash explosion remained closed, Weber said.

The company denied press access to the building.

A contract employee leaving the campus Wednesday afternoon said most employees he had spoken with were concerned about the injured worker's health while trying to get back to work.

"Most people are just kind of getting on with their jobs," said the employee, who asked not to be identified.

Caution tape covered the doors of the first-floor entrance to Building 1. Shipping pallets, cardboard boxes and cleaning supplies were stacked nearby.

Agilent and Hewlett-Packard, the parent company from which Agilent was spun off in 1999, have good track records on worker safety, said Krisann Chasarik, a spokeswoman for the state Department of Industrial Relations.

Only a few work-related accidents have been reported at the Fountaingrove campus since it was opened in 1972, according to data from the state Division of Occupational Safety and Health.

A 1996 incident involved a worker whose arm was struck by a milling machine drill. And in 2003 a worker broke an ankle falling down a flight of stairs. The company wasn't fined in those incidents, Chasarik said.

"Nothing like this has ever occurred here," Weber said.