DALLAS — Two workers doing maintenance on the roof of towering Cowboys Stadium slipped and tumbled at least 50 feet Thursday morning before coming to a stop atop a rain gutter that rings the structure, authorities said. Both suffered injuries believed to be non-life-threatening.

The two were working on the top hatch of the retractable-roof venue in suburban Arlington around 7:20 a.m. when they fell, Assistant Fire Chief Don Crowson said. They were not using safety harnesses as required, he said.

One worker lost consciousness after breaking a leg and suffering injuries to his head and chest, Dallas Cowboys spokesman Brett Daniels said. The worker was taken by helicopter to a hospital. The other worker suffered a back injury and was transported by ambulance.

Arlington police spokeswoman Tiara Ellis Richard said the workers fell from an upper part of the roof to a lower part. Daniels estimated they fell between 50 feet and 75 feet down to what he called a "parapet."

"It's bigger than your average rain gutter," Daniels said. "It's a pretty major channel there around the bottom of the roof."

There was no immediate word on the workers' conditions from area hospitals, whose officials declined to release information.

"They do not have any apparent life-threatening injuries," Ellis Richard said.

According to the Manhattan Construction Group, the stadium's general contractor, the workers are employed by Birdair Inc., an Amherst, N.Y.-based contractor that specializes in long-span structures. The company said on its Web site that it was the roofing subcontractor for the stadium, which features the "largest, longest and steepest retractable roof ever constructed."

A Birdair spokeswoman did not immediately return a phone message seeking comment.

Live TV coverage showed fire department crews on the roof of the nearly $1.2 billion stadium, where the NFL's Dallas Cowboys began playing this season. Crews used baskets, lines and ladders to lower the workers in a rescue that took about 90 minutes.

Cowboys spokesman Rich Dalrymple said the workers were on the roof for maintenance that will continue through the new year. He was unsure if cold weather was a factor in the fall.

The National Weather Service said temperatures were near freezing at the time of the accident.

The stadium has been the site of previous accidents, including the 2008 death of an electrician who came into contact with a high-voltage line.

The Cowboys' indoor practice facility in Irving collapsed in a wind storm May 2, paralyzing a member of the team's scouting department from the waist down and injuring 11 others less severely.

According to the team's Web site, the roof at Cowboys Stadium is one of the largest domed sports structures in the world, at 660,800 square feet. The support arches, soaring 292 feet above the playing field, bolster the retractable roof, described as the world's longest single-span roof structure.

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Associated Press writers Diana Heidgerd and Jamie Stengle contributed to this report.