Imperial reported its third hydrocarbon release this week at its Sarnia manufacturing site Friday morning.
Plant sirens sounded at around 8am.
Company spokesperson Kristina Zimmer says they identified an "impacted pipeline" located on their property and no action was required on the part of the community.
A Chemical Valley alert was issued but cleared by mid-morning.
Zimmer says the substance was a heavy hydrocarbon diesel-like material, air monitoring was initiated and the company said readings were "non-detectable."
She says weather conditions ranging from extreme cold to freeze, thaw conditions are impacting operations.
"Analysis that we've done on our end is telling us that the releases that we've been experiencing very recently are related to the extreme cold weather patterns we're seeing," says Zimmer. "We do take all of these incidents very seriously and we'll be conducting a full investigation."
Imperial reported two other hydrocarbon releases last Monday morning.
In each case, on-site personnel sheltered in place as a precaution while monitoring and other response activities took place.
The Ministry of Environment and Climate Change was notified.