A fire and explosion on Tuesday at Syncrude's Mildred Lake oilsands upgrader that seriously injured one worker was caused by a mechanical failure, company officials say.

A line failure caused treated naphtha — a highly flammable hydrocarbon mixture —  to leak, triggering the explosion and fire, which continues to smoulder inside the facility, said company spokesperson Will Gibson.

"The fire remains isolated and under control as of this afternoon, and the remainder of the operation is in a safe and stable condition," Gibson said Wednesday. 

"While we're responding to this incident, flaring is occurring to ensure excess natural gas and hydrogen are safely managed. This flaring will also be used to consume excess hydrogen sulphide in a safe manner." 

Once the flames have been extinguished and the site is secured, the company will begin its own investigation and assess the damage, Gibson said.

"I won't have specifics on the investigation … but I can tell you it will be very thorough because someone was injured, and that's unacceptable." 

All plant personnel and contractors have been asked to report for their shifts as usual Wednesday, though the damaged part of the upgrader remains off limits.

"Our people are reporting to work as scheduled, but there are some modified issues around people who would normally work in the area that is affected by the fire," Gibson said.

"That area is being restricted to allow for investigation. Syncrude will be thoroughly investigating this incident and will be co-operating with other agencies that will be investigating it."

Gibson also said in a news release Wednesday evening that production has been affected by the fire and several upgrader units have been minimized or shutdown. Gibson could not say how many units have been affected.

Consequently, mining and extraction of oilsands bitumen at its Mildred Lake and Aurora sites are being paced to balance bitumen demand, he said.

'Facts will come when they can'

The fire broke out just before 2 p.m. Tuesday. One injured worker was transported to Fort McMurray's Northern Lights Regional Health Centre in serious but stable condition.

The employee is now being cared for in an Edmonton hospital and remains in stable condition, said a spokesperson for Occupational Health and Safety. 

Officials were not able to provide any details on the identity of the worker or the extent of the worker's injuries, but said the worker's family has been notified. 

Company crews fought the flames and workers were evacuated from the site. Wood Buffalo RCMP and other emergency services were dispatched to the scene as a plume of smoke appeared in the sky.

RAW: Fire burning at Syncrude plant north of Fort McMurray0:20

 

A spokesperson for the Alberta Energy Regulator said it has employees on site to ensure Syncrude is handling the situation properly. Whether the agency will formally investigate has not yet been determined. 

Occupational Health and Safety has indicated it will investigate, which is normal procedure when a worker is seriously injured or killed on the job.

As of Wednesday morning, investigators were still unable to access the site.

"We're very focused right now on making sure that the plant is stable, that people are looking at the damage," Gibson said. 

There's no confirmation on how many people were working at the site when the fire broke out. But Syncrude employs about 4,800 people in the region, including about 3,000 who work directly at the Mildred Lake site.

Another fire at the Mildred Lake site in August 2015 cut output from the facility by about 80 per cent. The fire damaged pipes, power and communication lines between two units of the upgrader. It returned to normal production the following October.

The Mildred Lake upgrader is located 40 kilometres north of Fort McMurray. 

With files from The Canadian Press