Calling it a “tragic day” in the Vikings stadium project, a Mortenson Construction executive said it’s too early to pinpoint exactly what caused the Wednesday morning accident that killed one worker and seriously injured another on the project.

The victims, both employed by North St. Paul-based Berwald Roofing & Sheet Metal Co., were working on the roof on the north side of the building about 7:45 a.m. when the accident occurred, said John Wood, senior vice president of Golden Valley-based Mortenson Construction, which is building the $1.08 billion stadium in downtown Minneapolis.

“A man lost his life on this project today, and that simply should never happen,” Wood said.

Wood said the fatally injured worker fell about 50 feet from the edge of the roof into a snow gutter, which is below the main roof on the north side of the 1.75 million-square-foot stadium. The stadium is about 300 feet above the ground at its highest point.

The injured worker also fell, but didn’t fall off the roof, Wood said at an 11:30 a.m. press conference, across the street from the downtown Minneapolis site where the stadium is under construction. Other than that, Wood said, the circumstances that led to the injury aren’t clear. He said that will be reviewed as part of a thorough investigation.

Minnesota OSHA investigators were on the site Wednesday conducting interviews and trying to determine what “caused or contributed to the events,” said James Honerman, a spokesman for the Minnesota Department of Labor and Industry. There’s no timetable for how long the investigation will take, he said.

Since December 2010, Berwald Roofing has been cited nine times for serious violations, including workers’ failure to use fall protection equipment, according to Department of Labor and Industry records.

A representative of Berwald Roofing declined to comment about the fatality and injury when contacted by phone Wednesday.

Asked at the press conference whether the workers were wearing safety harnesses, Wood said he “can’t answer that question today. … Those will be essential questions for us to ask in the investigation, but we have not been in a position to conduct that investigation as of yet.”

Mortenson will cooperate fully in the investigation by Minnesota OSHA, he said.

“Mortenson holds as its highest priority the safety of the men and women that work so hard every day on this project, and we can’t express our sympathy any more strongly to the family and loved ones of these two individuals,” he said.

Both workers were taken to the nearby Hennepin County Medical Center. First responders told officials the fatally injured worker “was pronounced dead on arrival at the hospital,” Wood said.

The Star Tribune reported that Jeramie Gruber, 35, died in the accident. KSTP-TV also reported that the man’s family had identified the victim.

Gruber’s Facebook page indicates he attended Faribault High School and was a member of the Roofers Union. His home was listed as Northfield.

The other victim’s identity was not released.

Wood said Berwald has been working on the project for about six months. Berwald is “a wonderful” and “very experienced” company, he said, with a “great history of performance in the Twin Cities.”

About 1,200 people are working on the project, including about 25 Berwald Roofing workers. All workers were sent home Wednesday morning, and Wood said the tentative plan was to resume construction Thursday.

Wood said the entire workforce was gathered after the accident. “It was a very solemn gathering” with “a great deal of sadness and respect for the two men that were involved. … When something like this happens, it hits people very hard,” he said.

Counselors are available at the project site and will be there as long as they are needed, Wood said.

The extent of the surviving worker’s injuries was unclear other than he was in serious condition.

The Minneapolis Fire Department responded to the construction site for a “technical rescue,” according to the department’s Twitter feed. The department reported that one worker fell into a crevice and was trapped with injuries.

Fire department responders used a “rescue basket and ropes along with cables” to tie firefighters off to secure the rescue, the department said.

“Emergency responders were there within a matter of a few minutes,” Wood said Wednesday. “The proximity to this hospital obviously ensures that we get immediate response. And I think they did everything possible for both of the individuals.”

Michele Kelm-Helgen, chair of the Minnesota Sports Facilities Authority, which oversees the stadium project, issued this statement: “We join our partner, Mortenson Construction, to express our sincere condolences to the family of the worker we lost and the one who was injured in this tragic accident this morning. We humbly thank all involved in our project for their efforts each and every day.”

“Today is an extremely sad day for the Minnesota Vikings organization and the entire stadium team,” the team said in a statement. “Our sincere thoughts and prayers go out to the family and friends of the individual who passed away, the worker who remains hospitalized, and the more than 1,000 dedicated construction workers who are on the site every day and are also affected by this accident.”

Mark Conroy, apprenticeship coordinator for the Roofers & Waterproofers Local 96 in Blaine, said, “Our thoughts and prayers go out to the family. We will follow up with our protocols and go from there.”

The accident at the Vikings stadium site was the second fatality on a local stadium project in the last two years.

In September 2013, 61-year-old Johnny Valek was working on the demolition project to make way for the new St. Paul Saints stadium at Fifth and Broadway streets in St. Paul when a 30-foot-by-10-foot piece of concrete fell onto the cab of his backhoe, killing him instantly.

Minnesota OSHA says falls are a leading cause of death among construction workers. In 2013, 291 of the 828 construction deaths in the U.S. stemmed from falls, OSHA said.

Last year, the state OSHA investigated 17 workplace fatalities, of which 35 percent were in the construction industry. Five of the 17 happened as a result of falls, according to state records.

From 2010 through 2014, OSHA investigated 27 fatalities due to falls, according to the Minnesota DLI. “Fall protection” was the most frequently cited standard in the state’s construction industry, with 564 citations, the department said.

The U.S. Bank Stadium is set to open in time for the 2016 football season, but the project’s timeline wasn’t the foremost concern Wednesday.

“We are not thinking about the schedule right now,” Wood said at the press conference. “We are thinking about these two men and their families. We will get to deal with the impact on the construction schedule when it’s appropriate to do so.”

Below is a gallery of images by Staff Photographer Bill Klotz from the construction site after the accident: