Just before noon, the blast shook the 890-acre facility and surrounding areas in Saint John, the Canadian Broadcasting Corp. said.
One 60-year-old man who was thrown by the blast was taken to hospital for treatment of superficial injuries, company spokeswoman Carolyn Van der Veen said in a statement.
She said scheduled maintenance work was being done on a carbonate tank and it was over-pressurized.
Less than an hour later, the refinery was back in full production, as company and provincial health and labor officials arrived to examine the tank, the report said.
The refinery is the largest in Canada and can produce 300,000 barrels of petroleum products per day.
As recently as May 15, the company issued a release saying "for the first time since the Irving Oil Refinery began operations in 1960, it has achieved 365 days without a lost time injury."