A flash fire was quickly extinguished at Imperial Oil's Sarnia manufacturing site's refinery Thursday afternoon.
Plant sirens sounded around 1:35pm.
Company spokesperson Jon Harding says there were no reports of injuries.
He says air quality at the site's fence-line was being monitored, but no indications of impacts to the air quality had been detected.
The cause is being investigated.
The Ministry of Environment and Climate Change has been notified.
This is Imperial Oil's third fire in under three weeks.