NOVA Chemicals issued a notice late Thursday, clarifying a pair of unrelated incidents at its Corunna site on November 8.
The company says the first incident happened around 1am when emergency alarms sounded as workers were re-introducing feedstock into the plant.
It was determined a small drain valve was open in the Olefins unit, resulting in the release of a mixture of ethane, ethylene and methane. The company says a CVECO Code 8 was issued, continuous air monitoring was conducted, and the valve was isolated and closed.
The all-clear was given around 1:45am, and the company says there was no off-site impact.
Then, around 4:50pm, personel responded to a fixed monitor inside the Olefins unit that indicated higher than normal hydrogen sulfide (H2S) readings.
As a result, evacuation alarms sounded and workers were moved to a safe location.
NOVA says it posted information to the CAER Industry Update Line around 5pm, and emailed employees, contractors, St. Clair Twp Fire, and Aamjiwnaang First Nation Safety and Emergency Response.
The company says the issue was isolated, and the all-clear sounded around 5:50pm.
NOVA says both incidents are still under investigation and they've been in close contact with the Ontario Ministry of Labour and Climate Change.
The NOVA Corunna site is still in the process of restarting the facility after a planned maintenance shutdown which began in August.
As the plant is brought back online, periods of elevated flaring and some increased noise are expected.
