Workers went out on strike twice in one week after union claims that some workers' faces were burnt by a caustic substance that overflowed from faulty equipment.

Alcoa denied the claim and said only one worker received medical treatment for eye irritation.

The company said the strike caused some delays on a refinery expansion project but normal operations were not affected.

Mark Goldsworthy from the Manufacturing Workers Union said the union will meet with Alcoa executives to address the safety concerns.

"Our biggest concern is there's people being injured in the workforce," he said.