An investigation is now underway after five people were injured following an explosion at the Horizon Oil Sands facility located about 70 kilometres north of Fort McMurray. The incident now has critics charging the province isn't doing its job in making the industry safe for workers.

Canadian Natural Resources Limited says the fire was contained to the coker area. Occupational Health and Safety say the explosion and subsequent fire broke out in the primary upgrader, which had to be evacuated.

One worker, who asked not to be identified, captured home video footage of the fire.

"Must have been way over 100 feet," said the worker.

Canadian Natural Resources Limited says a total of five employees and contractors received injuries during the incident, with three being transported to hospital in Fort McMurray. Two have since been released from hospital and one has been moved to Edmonton for further care. Two others were treated on-site for minor injuries and released.

Officials say by 7:15 p.m. the fire had been extinguished. Oil production at the facility has been shut down, with no indication when it will resume.

This incident comes less than four years after another incident at the same site. Two people died and four were injured after a structure collapse.

The Alberta Federation of Labour say one in five workplace safety charges currently under prosecution involve Canadian Natural Resources Limited.

"This is a company that how shall we say is not at the top of the list when it comes to workplace health and safety," said Alberta Federation of Labour president Gil McGowan.

But Employment and Immigration Minister Thomas Lukaszuk says this particular site can't be isolated as a "more dangerous site to work."

"That simply cannot be substantiated," he told reporters Friday.

Critics believe the province isn't doing its job in making the industry safe for workers.

"Rather than investigating accidents after they occur what needs to be happening is that we are inspecting beforehand," said NDP MLA Rachel Notley.

The minister assures an investigation led by Occupational Health and Safety will find the answers many are now searching for.

"If we find that this incident occurred as a result of anyone's negligence, those parties will be brought before any form of repercussions that are available within the legislation," said Lukaszuk.

There is no timeline as to when the Occupational Health and Safety will be complete.

With files from Bill Fortier