Canadian Natural Resources Ltd. has been fined $10,000 by Alberta's professional engineering society — the maximum allowed — following an investigation into an accident at an oilsands site that killed two and injured five.

The Association of Professional Engineers and Geoscientists of Alberta said Wednesday that it found the company engaged in unprofessional conduct by failing to make sure building plans were certified by an engineer and by contracting with a company without making sure it was competent to do the work.

The investigation looked into events on April 24, 2007, where workers were building a 20-metre high oil tank at the Horizon oilsands project north of Fort McMurray, Alta., when cables holding up a roof support structure snapped due to high winds.

Investigators took this picture of a second storage tank before it also collapsed. (Alberta Occupational Health and Safety) The falling steel structure broke apart, with steel debris striking an electrical consultant, killing him. A scaffolder was crushed and died on the way to the hospital.

Two other workers were seriously injured and three others suffered minor injuries.

The engineering association found that the steel cables supporting the roofing structure were inadequate and did not meet regulations, and that the person who designed the construction procedures was not a professional engineer in Alberta.

"It was an extremely significant and unfortunate event," said APEGA registrar Carol Moen. "This particular event is likely to be probably the most significant one from an impact and outcome perspective that APEGA has engaged in, in our history."

Moen said the association levied the maximum amount allowable against the company. But, she added, work is underway to increase the maximum allowable fine for companies to $500,000 per violation as part of the first review of the provincial legislation that governs the engineering profession in about 30 years.

In addition to the fine, the association said Canadian Natural Resources will have to pay, up to a maximum of $150,000, to help develop a new practice standard on outsourcing engineering and geoscience work in the province.

Canadian Natural Resources said in a statement that it is looking forward to developing the new standards and that a senior member of its leadership team will actively participate and work together with the association on the initiative.

CNRL says safety practices changed

The company also said that it had changed its safety practices following the tragedy and now requires contracting companies to provide evidence of qualifications before engineering work is done.

The roof of a storage tank under construction collapsed in April 2007 killing two workers. (CBC) "We take every incident seriously," said company spokeswoman Julie Woo in an email. "Following this incident, CNRL took steps to advance our processes to ensure health and safety standards are consistently met by all contractors."

Last February, Alberta Occupational Health and Safety released the results of its investigation into the accident and concluded that the company did not do enough to ensure that one of its contractors had construction plans certified by a professional engineer.

The Canadian subsidiary of Sinopec Shanghai Engineering Co. Ltd., the Chinese engineering firm that Canadian Natural Resources contracted out to, pled guilty in 2012 to three workplace safety charges and was ordered to pay $1.5 million in penalties.

Canadian Natural Resources faced 29 workplace safety charges but they were stayed in 2012.

Engineering association spokeswoman Gisela Hippolt-Squair said the association is reviewing provincial legislation for the first time in 30 years and plans to recommend increasing the maximum fine for permit holders to $500,000 per violation.