Sirens sounded at about 3:15 p.m. Friday at Imperial's Sarnia manufacturing site.
Spokesperson Kristina Zimmer said a small fire in the plant was put out by on-site responders within a few minutes.
There were no injuries.
Zimmer said the site activated its emergency plan which includes mustering employees in safe havens as a precaution.
The impacted equipment was isolated and the cause was being investigated.
There was elevated flaring at the site and air monitoring was initiated as a precaution.
Imperial started a planned maintenance turnaround in late September that was expected to continue for about two months.
