No one was injured and a preliminary investigation indicated a burst pipe caused the explosion, the university said in a statement. Foul play was not suspected.
There was no fire but a pool of what was believed to be liquid freon was seen on the floor at the California NanoSystems Institute, the school and Fire Department spokesman Brian Humphrey said. Hazardous materials teams were on scene.
"The building does not appear to be damaged externally, the damage appears to be within this area in the equipment room," he said.
According to its Web site, the NanoSystems Institute develops and promotes nanotechnology, which is extremely small technology on the scale of atoms and molecules.