FORT MCMURRAY, Alta. - Nexen Energy has pleaded not guilty to eight charges stemming from a fatal explosion at the company's oil sands site in northern Alberta.

Drew Foster, who was 52 and from Niagara Falls, Ont., died at the scene.

Thirty-year-old David Williams of Scotchtown, N.S., died several days later in hospital.

The men were doing maintenance inside a hydrogen compressor building at the company's Long Lake upgrader in January 2016 when the explosion occurred.

Alberta Occupational Health and Safety charged the Calgary-based energy company in December.

A trial date is to be set in a Fort McMurray, Alta., court on May 16.

Nexen Energy is a subsidiary of the Chinese state-owned firm China National Offshore Oil Corp., or CNOOC Ltd.

Some of the charges relate to whether a compressor at the site had been properly serviced and whether the workers in charge of the machine had read its operating manual and safety rules.