A 45-year-old Santa Rosa man who suffered major burns following a chemical explosion at Agilent Technologies remained in critical condition Monday night at a Sacramento burn unit.

Patrick Colbus, an engineer for Agilent, has been at the U.C. Davis Medical Center unit since April 26 and his condition hasn't changed.

That morning he was cleaning a sophisticated piece of equipment at the Fountain Grove Parkway campus when a chemical flash explosion occurred.

The explosion rocked the building, causing major damage to the lab, and left Colbus with injuries including burns to his face and upper torso.

About 100 people were evacuated from the building for the day. About 20 of those underwent decontamination proceedings, including giving up their clothing and taking showers.

State and local investigators have started what is expected to be a lengthy investigation into what caused the blast.