The Suncor Sarnia refinery says elevated sulfur dioxide (SO2) levels were detected after an operational issue occurred Tuesday morning.
The company issued a notice through the Sarnia-Lambton Alerts systems at 11:21 a.m., advising residents of increased flaring and noise due to a process issue in one of its units.
An incident response was later activated at 12:28 p.m.
Sarnia News Today reached out to Suncor for further details but did not receive a response.
An update was issued shortly before 3 p.m. through Sarnia-Lambton Alerts.
"In the process of restoring the unit to normal operating state, a visible plume and potential odour may have been detected beyond the refinery fence line," read Suncor's public notice. "Out of an abundance of caution, we sounded the site siren. Air monitoring data on the Clean Air Sarnia and Area website shows elevated levels of SO2, and the community has been notified."
The company said air monitoring -- both on and off-site -- is ongoing.
"We continue to work diligently to restart the affected units which will return the refinery to standard operations," read the notice.
Sarnia fire crews were called to the refinery to offer support.
Suncor said no injuries were reported and all employees have been accounted for.