Imperial Oil workers were forced to shelter in place Thursday afternoon, following a hydrogen sulfide (H2S) vapour release.
Sarnia police Constable Nelson Amaral says a Chemical Valley Emergency Coordinating Organization Alert was issued for an unknown vapour release and quickly confirmed to be H2S.
He says the Sarnia Police Service and Sarnia Fire and Rescue Services responded to the Vidal St. plant.
In an e-mail, the company says Imperial personnel responded to an "internal operating issue and onsite sulphur-like odour" and site alarms were activated in an "abundance of caution."
Imperial says the issue was noticed around 2:30pm as workers investigated and identified an issue with a rail car at the Sarnia Manufacturing Site.
The company says the issue has been resolved and Imperial undertook air quality monitoring at its fence-line and in the community and no offsite impact was identified.
An all clear sounded around 3:15pm according to Sarnia police.
No injuries were reported.