Two maintenance workers who were not wearing safety harnesses slipped and fell from the roof area of towering Cowboys Stadium on Thursday morning, and at least one suffered serious injuries, authorities said.

The two were working on the top hatch of the retractable-roof venue around 7:20 a.m. when they slipped, Assistant Fire Chief Don Crowson said. They were not using "fall protection," he said.

The workers fell from an upper roof to a lower section, police spokeswoman Tiara Ellis Richard said.

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

Both workers were transported to hospitals. Crowson said one man was severely injured but he had no details.

Cowboys spokesman Rich Dalrymple said workers were on the roof for ongoing maintenance that will continue through the new year. Dalrymple did not know the extent of the injuries and said 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.

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.

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.