A number of employees and contractors, who were in the vicinity of the release, were assessed by Suncor and Alberta Health Services personnel, company spokeswoman Erin Rees said.
A handful of the workers were transported to hospitals for further assessment and have since been released, Rees said, adding the affected unit was stable and refinery production was not impacted.
The refinery processes 142,000 barrels per day of crude oil from oil sands projects, according to Suncor's website.
(Reporting by Apeksha Nair in Bengaluru; Editing by Christian Schmollinger and Sherry Jacob-Phillips)
