Investigators in Saint John are trying to determine the cause of an explosion at the Irving Oil Refinery.

The explosion happened Tuesday in an area known as the hydro cracker unit, where crude oil is superheated into diesel and furnace oil. The blast sent flames and a huge cloud of black smoke over the facility.

One worker was killed and two others were injured.

The refinery, Canada's largest, is on the Bay of Fundy. People who live nearby have raised concerns for years about safety and pollution.

The province is sending in several inspectors to monitor air quality over the next few days.

New Brunswick Environment Minister Gene Devereux says early data collected from the city's air quality monitoring system indicate that smoke from the fire didn't cause any problems.