Agilent Technologies has reopened the two-story building shaken by an explosion that critically injured an employee Tuesday morning.

The move followed a review of chemical residue tests performed by company safety teams overnight and early Wednesday morning.

"We have reopened the building, both floors," said spokesman Jeff Weber. "This was after we determined that it obviously was safe for employees to reenter the building."

The building was reopened around 11 a.m., Weber said, about 24 hours after a chemical explosion rocked a laboratory on the first floor of Building 1 at the Fountaingrove campus.

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

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

Twenty others underwent decontamination after complaining of respiratory problems, and more than 80 people were put under observation in the wake of the flash, which spewed smoke with a chemical odor, officials 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, spokesman Jeff Weber 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.

Colbus was exposed to a combination of chemical substances that burned his face, head and torso, fire officials said.

He was taken to Santa Rosa Memorial Hospital and then flown to the UC Davis burn unit, where a nursing supervisor said Wednesday he was still critical.

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

More than 100 employees work in Building 1. They were told to remain home until notified that building would reopen, and Weber said some had already returned to work by late morning. He expected more to return to work over the course of the day.

"At least there is a feeling of return to a semblance of normalcy with the reopening of the building," Weber said.