Sarnia police say a Code 6 has been lifted following a chemical leak from Imperial Oil earlier Wednesday morning.
The company Tweeted Wednesday morning that its sirens were sounding as a result of a leak of light hydrocarbon.
As a result Vidal Street was closed and the emergency operations centre was activated for the company.
Police say a Code 6 was issued but that the incident was isolated and no shelter is in place order had to be given.
All barriers were removed and Vidal Street was reopened within a few hours.
This is the second incident since April at Imperial Oil. On April 3 high flaring was seen at the plant after a tower fell on site.
No one was injured in that incident.
A Code 6 was issued after the tower, which was not in use and was scheduled for maintenance, fell on the site. Sirens were sounded and local authorities were notified.
Vidal Street was also closed over the weekend as crews were on site on June 2 to clean up the tower.