Residents in parts of the city's southend may have noticed a sulphur-like odour Tuesday morning.
There was an operating issue at one of the processing units at Imperial's Sarnia facility.
Imperial spokesperson Jon Harding says personnel began responding to an odour around 7:30am. He says air quality monitoring was conducted on and off site and determined no health related issues.
"There was an odour present and it was probably related to our operating issue, we need to investigate that, but there was an odour present and we apologize to anybody in the community who was inconvenienced by this," says Harding.
As a result of the operating issue, Imperial restarted its coker unit early Tuesday afternoon. Imperial says the plume from the site’s main boiler stack may occasionally be darker than normal during this process.
Personnel are taking steps to minimize emissions during the restart process. Imperial does not expect emissions during restart to exceed government guidelines.
The Ministry of Environment and Climate Change and city officials were notified.
The all clear was issued by Imperial to the Chemical Valley Emergency Co-ordinating Organization (CVECO) sounded shortly after 10am.