State safety investigators and Minneapolis-based Mortenson Construction are seeking to determine the cause of a worker fatality on the $1.1-billion U.S. Bank Stadium project, which was being monitored via an enhanced safety program with the Minnesota Occupational Safety and Health Administration.

At about 7:45 a.m. on Aug. 26, Jeramie Gruber, 35, a worker with Berwald Roofing Co., and a co-worker fell from the edge of the stadium’s roof. According to Mortenson officials, Gruber died when he fell an estimated 30 ft onto an intermediate structure. The unidentified co-worker’s fall was arrested by a safety barrier and resulted in only minor injuries.

Calling the incident “really devastating for everybody involved with this project,” John Wood, senior vice president with Mortenson, says roofing work is halted until the company completes its own investigation into the fatality’s “root cause.”

“We don’t have a time frame. It will take us as long as it takes us to do it absolutely completely and right,” Wood says. While “it is clear” what Gruber and the other worker were doing at the time, the company cannot divulge that information now, he adds.

According to the contractor, the fully enclosed stadium’s roof slopes to the north and south from a single ridge. Berland was contracted to build only the north side of the roof, which includes a conventional metal deck with insulation and a single-ply PVC roof material. A different contractor is handling the south section, which will be built mostly of ethylene tetrafluoroethylene (ETFE), a lightweight plastic material that can be transparent or translucent.

Over the past 18 months, Mortenson Construction has been working with Minnesota OSHA’s workplace-safety consultation program, as it had done on two previous sports projects, Target Field and TCF Bank Stadium. As part of this program, says OSHA, “state consultants periodically visited the stadium to conduct a walk-around site visit with representatives of safety professionals from the various on-site contractors.”

Those visits would have included inspections of Berwald Roofing’s activities, says OSHA spokesman James Honerman. While the agency could not reveal any details related to those visits, it noted that, in the past five years, 16 OSHA compliance inspections at Mortenson worksites did not result in any citations or penalties.

After the incident, Mortenson halted all work on the project for the rest of the day. Most construction activities resumed the next day, though roofing work will not restart until Mortenson completes its investigation, and, as Wood says, “we can ensure that any required modifications to their work plan or the equipment on the roof have been made.” He continued, “We want to be absolutely certain that there isn’t any repeat to this horrible incident.”