Ontario’s Ministry of the Environment is investigating after a Sarnia-area plant failed to report a possible chemical leak as legally required, a spokesperson said Thursday.

Nova Chemicals in Corunna, south of Sarnia, evacuated staff to a “safe location” Wednesday after an internal alarm went off for hydrogen sulphide, the company said. Hydrogen sulphide, which has a rotten egg odour, can paralyze the human sense of smell and cause death at high enough concentrations.

The ministry spokesperson said staff are investigating why Nova didn’t immediately report the incident, as required by law.

“We are communicating to Nova that it is our expectation that in incidents like this they do notify us,” said the spokesperson.

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The ministry also said its staff contacted Nova shortly after the alarm sounded, and the company let it know about the situation. The company later notified the ministry that the incident was resolved by 5:45 p.m.

Last month, a joint investigation by the Star, Global News, National Observer, the Michener Awards Foundation and journalism schools at Ryerson and Concordia universities revealed a troubling pattern of secrecy and potentially toxic leaks in the Sarnia area. There are 57 polluters within 25 kilometres of the city registered with the Canadian and U.S. governments.

The investigation also raised questions about whether companies and the provincial government are properly warning residents of Sarnia and the nearby First Nations community of Aamjiwnaang when potentially toxic substances are leaked.

In a statement released to media, Nova said two incidents happened Wednesday at its Corunna site, which employs about 500 people.

The first happened at 1 a.m., when ethylene and methane, both flammable and explosive gases, spilled from an open valve, the Nova statement said. The company called an all-clear 45 minutes later.

The possible hydrogen sulphide leak happened at about 4:50 p.m. Nova called the all-clear about an hour later.

When plant staff arrived Wednesday morning, they received written instructions to wear respirator masks in certain areas. Nova didn’t answer questions about how high the exposure levels must reach before staff are asked to wear protection, but said the mask memo was unrelated to either incident.

Nova said the company’s air monitoring didn’t show any effects to the surrounding community.

“We reiterate that these two events were unrelated,” said the company statement. “Both are still under thorough investigation. Nova Chemicals has been in close contact with the Ontario Ministry of the Environment and Climate Change.”

Nova said it contacted the local fire department and Aamjiwnaang, which notified residents of the afternoon leak at about 5 p.m. The company said it also posted information on a phone line residents can call for information. The City of Sarnia didn’t send out an alert.

Meanwhile, the provincial government unveiled a policy proposal Thursday intended to toughen air pollution standards in Sarnia and Hamilton — two heavily industrialized areas. If approved, it would consider the combined effect of local pollution rather than focusing on individual plants’ emissions.

Sarnia-area residents have been asking for such a measure for at least eight years.

The policy would apply only to facilities that are new or expanding. It covers emissions of benzene in the Sarnia area and benzo[a]pyrene and benzene in the Hamilton area.

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Both chemicals are known to cause cancer. Levels of the contaminants frequently breach provincial air standards in the two regions, the proposal said.

The policy wouldn’t require action from industry currently in the Sarnia area — only periodic review from the ministry, the proposal reads.

With files from Carolyn Jarvis and Andrew Russell, Global News

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