Firefighters responded following a report of an explosion at the Irving Oil refinery in Saint John, N.B., just before noon, fire platoon Chief Brian Wilson said.
Wilson said the explosion involved an 1,100-barrel tank of potassium hydroxide, which is a caustic substance, but there was no fire. He said the injured man was blown to the ground and suffered some scrapes and bruises.
"He was knocked down by the explosion," Wilson said in an interview. "There was just the road rash and him contacting the ground that scraped him up."
Irving Oil issued a statement saying the tank was undergoing scheduled maintenance work at the time when it became "over-pressurized."
"An employee suffered minor injuries and was taken to hospital as a precaution," Irving Oil said.
Wilson said the potassium hydroxide did not escape from the tank during the explosion.
"There's no environmental risk because the container was not compromised," he said.
"The liquid was contained, and should it be released it goes down through their drains and their treatment systems and can be confined."
The company said there was no other damage and normal operations at the refinery resumed about 50 minutes later. It did not immediately return messages seeking comment.
Wilson said Irving Oil crews were cleaning up the scene and WorkSafeNB is investigating what happened.
It's not the first time an explosion has occurred at the refinery.
In March 2002, three workers were hospitalized suffering from burns following an explosion during routine maintenance.
And in June 1998, one employee was killed and two others injured when an explosion rocked the facility.
The refinery is the largest in Canada, producing more than 300,000 barrels of petroleum products per day. It opened in 1960.