A propane leak at the Cenovus oil refinery in Superior, Wis., set off an emergency response Wednesday morning.

The Superior Fire Department was called to the refinery, still building up to full operations after a 2018 explosion rocked the city, around 8 a.m. The company's own emergency response crews were already quelling the propane leak with water fog streams, the Fire Department said.

Crews stopped the release of propane from a process unit around 9:30 a.m. The Fire Department continued to monitor the air inside and outside the facility and said the public isn't in danger.

Nonessential Cenovus workers were temporarily evacuated and have already returned to work, a company spokesperson said in an email.

No one was injured in the incident. The refinery's emergency procedures involved shutting down several units, which caused flaring, or the burning of natural gas.

At the time of the 2018 explosion, the refinery, owned then by Husky Energy, was shutting down its fluid catalytic cracking unit for planned maintenance. The unit is a common piece of equipment at oil refineries used to refine crude oil into higher octane fuels.

A worn valve inside the unit allowed air to mix with hydrocarbons, leading to the explosion of two outdated vessels, spraying metal fragments up to 1,200 feet and puncturing a nearby asphalt storage tank. About 17,000 barrels of hot asphalt spilled and ignited, causing multiple fires. In a final report, the U.S. Chemical Safety and Hazard Investigation Board laid out several safety recommendations for the new plant.

The $1.2 billion rebuild came with new safety measures, including tanks built to change color in the event of a leak, along with other leak detectors, and remote control water cannons built to address hydrogen fluoride vapors.