A small explosion erupted Wednesday at Intel's Fab 22 plant, a semiconductor manufacturing facility located near Chandler, Ariz., injuring seven workers.

The blast occurred shortly after 2 p.m. local time, injuring four workers who were taken to local hospitals with injuries ranging from concussions to shrapnel wounds, said Chandler fire department battalion chief Brad Miller, as reported by Reuters. Three others were less seriously hurt and treated at the scene.

The Fab 22 plant has been undergoing upgrades to support production of 22-nanometer chip fabrication, which Intel is developing for its upcoming Tri-Gate transistors.

The blast occurred in a solvent treatment room, which Intel uses to carry out parts of its semiconductor manufacturing process. Toxic and flammable compounds that are used in semiconductor manufacturing include concentrated hydrochloric acid, sulfuric acid, hydrogen peroxide, and ammonium hydroxide.

It is believed that the workers were just starting to treat a batch of solvents when the explosion occurred. The plant and adjacent multi-story building were evacuated of several hundred employees and will remain closed indefinitely while the cause of the explosion is investigated.

"Until we identify everything involved, there's no way we can say when people will be back to work," said Miller, Reuters reported. He added that the 10 other buildings on the campus remained open.

It has not yet been determined what caused the explosion, but Intel is investigating the situation. "We're trying to ascertain what happened. All we know is that there was no damage or release of chemicals to the community," said Josh Walden, Intel's VP and general manager for fab sort manufacturing, in a statement.

Fire suppression measures at the plant worked as designed and limited the damage, Walden said. Intel has not assessed the damage to the plant and said, other than the temporary evacuation, there was no disruption to manufacturing.

"They're all back in the production facility and there was disruption to the process," Walden said.

The Chandler plant is heavily automated and the explosion reportedly had no effect on chip production in other parts of the plant, even though the factory was evacuated as a safety precaution. Intel employs more than 10,000 people at the 705-acre Ocotillo Campus in Chandler. The chipmaker spent billions upgrading and combining the Fab 22 and Fab 32 plants earlier this year to have them produce new Intel chips, like the Tri-Gate.

Intel announced in February it will build a $5 billion Fab 42 plant in Chandler that will be the highest-volume chip plant in the world. Construction is set to begin soon and be completed in 2013, reported the Phoenix Business Journal.

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