NOVA Chemicals reported a hydrocarbon release at its Corunna plant Tuesday morning.
The company, through the Aamjiwnaang Notification System, said there was a leak in its cold site.
NOVA spokesperson Julia Iacovella said plant personnel responded and isolated the leak, and ongoing air monitoring had not shown off-site impact.
She said site alarms sounded as part of the emergency response.
The all-clear was issued before noon.