The blast early Saturday morning could be felt 16 kilometres away and sparked a fire that burned for more than 14 hours.
No one was hurt, but nearby streets were closed for about seven hours and approximately 20 homeowners reported the explosion broke their windows.
The fire affected the refinery's isocracker unit, which processes about 25,000 barrels of crude per day.
Other parts of the refinery have been shut down as a precaution, but Husky is making plans to resume operations. The refinery can operate without the isocracker unit and customers will continue to be supplied with products while the refinery is down.
The Ohio Environmental Protection Agency said Sunday that no dangerous contaminants were released into the air by the explosion.
Testing was done by the U.S. EPA, Allen County and Husky Energy for a variety of contaminants, including benzene, carbon monoxide, sulphur dioxide, hydrogen cyanide, hydrogen sulphide and asbestos, Ohio EPA spokeswoman Heidi Griesmer said.
The results were all "non-detect," meaning no signs of the contaminants, Griesmer said.
The company, overseen by the Ohio EPA, will continue the monitoring this week, Griesmer said.
CIBC World Markets analyst Arthur Grayfer said the impacts of the explosion should be "immaterial" when it comes to estimates for Husky's cash flow this year.
The refinery churns out about 7.6 billion litres of refined petroleum products a year, including a quarter of the gasoline used in Ohio.
Elsewhere in the state, Husky has a 50 per cent interest in a refinery in Toledo alongside BP.
— with files from The Associated Press