There was a hydrogen sulfide leak Thursday morning at the Shell Canada refinery in Corunna.
Company spokesperson Randy Provencal says H2S alarms sounded at around 6:30am in one of the units.
The incident forced an emergency shutdown and Shell was working on a restart plan.
A Chemical Valley Emergency Coordinating Organization alert was issued, but the media was not notified to make any public announcements.
Provencal says the operations team was able to identify the source of the leak and the all clear was sounded in just over an hour.
"We had no injuries reported," says Provencal. "We monitored air quality both at the source and downwind from the actual source as a precaution and there was no source of H2S detected downwind."
Provencal says the Ministry of Environment and other regulatory agencies were notified of the incident.