Professional engineering oversight lacking in CNRL Horizon tank collapse

The Association of Professional Engineers and Geoscientists of Alberta (APEGA) has reopened its inquiries into a fatal accident that occurred in the oil sands in 2007.

The association’s director of communications told the Edmonton Journal that they had only recently received a final copy of the Alberta Occupational Health and Safety Incident report into what caused the collapse of a large tank under construction at the Canadian Natural Resources Ltd. Horizon oil sands site.

“Even though it’s been a long time between the time the event occurred and the time that report was done, we felt obliged to take a closer look at that new information,” said Mulder.

The collapse of the tank roof structure occurred during windy conditions on April 24, 2007. The large tank was one of 11 being constructed by SSEC Canada, a Chinese company, on the east tank farm on the CNRL Horizon site, 70 kilometres north of Fort McMurray.

The tank was to be a circular steel high-cone roof tank, 56.5 metres in diameter and 19.8 metres high. At the time of the accident the tank’s roof support structure was only partially complete and the roof was suspended by cables. A team of temporary workers from China were inside the tank working on the structure when it started to collapse inwards. Some of the workers managed to escape through holes in the tank’s wall, but an “electrical consultant” who was standing on top of a welding machine was struck by falling steel and thrown onto scaffolding. He was pronounced dead at the scene. A scaffolder who was on the tank floor was also crushed by the falling steel and died on the way to hospital in Fort McMurray. Two other workers in the tank were seriously injured.

APEGA says it is now investigating because the health and safety report indicates that a professional engineer was not involved as was required.

Indeed, the analysis in the health and safety report includes several indications that professional oversight was lacking and labour rules were being ignored:

For example, at 8.1.2: “Tenth Construction Company of Sinopec (TCC) [a Chinese construction company ] did not take reasonable practical measures to protect the health and safety of the Electrical Cosultant. The tank roof support structure that collapsed onto the worker was a skeleton structure. The erection procedures for erecting the roof support structures had not been prepared and certified by a Professional Engineer. The Electrical Consultant did not have a work permit as a temporary foreign worker and thus should not have been working at this work site.”

The report makes it clear that the structural design of the tank was inadequate:

At 7.2.6: “The roof support structure was a completely bolted structure using ASTM A-307 Grade B bolts without the use of wedges or washes. The bolted roof support structure, which was required to be flexible, did not have the necessary restraints to resist the lateral forces generated by the wind.

And, at 7.27. “The number and size of guy wires that were supporting the roof support structure in tanks 72-TK-1A and 72-TK-1B, was not designed for the static and dynamic loads imposed by the 33 to 45 km/h wind that occurred on the day of the incident, let alone for the maximum expected wind speed of 83 km/h as determined by the Alberta Building Code, or 190 km/h recommended by the American Petroleum Institute.”

Alberta Workplace Health and Safety Compliance contracted Anderson Associates Consulting Engineers to examine the circumstances of the roof collapse and summarize the causes.

To read the  health and safety report, click here.