Report suggests possible causes of Muskrat Falls structure collapse

(Canadian OH&S News) — A new investigative report has identified poor design, inadequate wood material and insufficient risk assessment as factors that may have contributed to the collapse of a support structure at a construction site at Muskrat Falls, N.L. last May 29.

The accident occurred during Nalcor Energy’s ongoing construction of a hydroelectric generating facility in Labrador. That morning, a group of workers was nearly finished pouring concrete into a powerhouse draft tube when the framework collapsed, causing more than 500 cubic metres of concrete to spill. Seven workers fell into the concrete; one of them was completely submerged, but a co-worker helped him to extract himself, and there were no serious injuries.

On May 1, Nalcor released a report by aDB Structural Engineering, a Vancouver-based company that had investigated the incident. The report concluded that one or more of the following scenarios had occurred and caused the collapse:

— improper design of the shoring system;
— incorrect installation of the shoring system;
— inadequate fabrication of the shoring system; and/or
— the wood integrity of the formwork being compromised.

aDB also suggested inadequacies in the shoring tower’s design, in a tower leg’s lumber splices and in the framework installation that may have affected the shoring system’s load-carrying capability.

“The collapse was fast, indicating that each section of the shoring was at or near ultimate capacity,” the report read, “and when the ultimate capacity was reached in one area… the collapse started, followed by failure of the adjacent overloaded structures.”

The report also commented on the safety culture of the worksite, noting that the labour crew and supervisors had failed to assess and identify the risks involved. “The lack of action in this case indicates a lack of competency, a lack of safety leadership, a complacent workforce or a combination of the aforementioned.”

Nalcor did not respond to COHSN’s request for comment before press time, but a May 1 press release from the company stated that it had taken all appropriate corrective measures since the incident.

“Over the last year, this incident has had our full attention and the dedication of the Lower Churchill Project’s and Astaldi’s management teams in the investigation into the root cause,” Nalcor president and CEO Stan Marshall said in a media statement, referring to the general contractor and another contracted entity respectively.

“Nalcor’s number-one priority is the safety of workers and the public. We encourage all workers and contractors to report any safety issues or concerns to us. Nalcor remains committed to providing a worksite where everyone chooses to follow our safety protocols and live our values.”

Service N.L., the provincial government entity that covers occupational health and safety, has been investigating the incident as well. Media-relations manager Gina McArthur could not comment on the incident or the aDB report, as the investigation was still ongoing.

“Our investigation into that incident has not been completed, so there’s nothing more that we can say at this point,” she said. “It’s done when it’s done.”

Nalcor’s release also stated that the draft-tube framework at the worksite was intended only as a temporary structure for concrete installation. Now that the draft tubes have been completed, the company is in the process of removing the framework.

Nalcor began construction of the Muskrat Falls facility in 2013. The project also includes more than 1,600 kilometres of transmission lines across Newfoundland and Labrador and a power link with Nova Scotia, according to information from the company’s website.

The aDB report is available online at http://muskratfalls.nalcorenergy.com/wp-content/uploads/2017/05/aDB-Muskrat-Falls-Draft-tube-2-Investigation-Report_Report-Section.pdf.