Suddenly, the wind, already whipping so much that Sullivan tweeted that it was "terrifying," surged as high as 51 mph.
The lift toppled over, crashing through a fence before coming to rest in a street just behind a goal post.
"Things started flying by me that had been stationary for all of practice - Gatorade containers, towels," Athletic Director Jack Swarbrick recalled Thursday. "I noticed the netting by the goal post start to bend dramatically, and I heard a crash."
Sullivan, a junior film student from the Chicago suburb of Long Grove, Ill., was taken to a hospital, but Swarbrick said he received a call from the ambulance before it arrived saying that the 20-year-old was not breathing. The young man was soon pronounced dead.
Most such lifts extend to about 40 feet, but Swarbrick said he did not know how high Sullivan was when the machine fell over, and it was unclear who authorized Sullivan to go up in it.
As a student worker, Sullivan reported to a video coordinator associated with the football team. Swarbrick said the decision to practice outdoors is left up to individual athletic programs.
A workplace safety expert said the lift should never have been used in such blustery conditions.
The university pledged to review its policy for using the lifts.
"We're going to look at how it was done this day," Swarbrick said, adding that at least one other student was in a lift at the same time as Sullivan.
Just before the practice began, Sullivan posted Twitter messages in which he said "Gusts of wind up to 60 mph today will be fun at work ... I guess I've lived long enough."
Less than an hour before the accident, he tweeted again, saying it was "terrifying" to be on the tower in the high winds.
Ellie Hall, another Notre Dame film student who had friends in common with Sullivan, told The Associated Press in an e-mail that she was "horrified" by the "eerily prophetic nature" of the tweets, which she captured in a screen shot and later described in a contribution to the Huffington Post.
Within hours of Sullivan's death, his family made his Facebook profile, and the messages, private, Hall said.
Swarbrick said he was aware of the tweets and promised to look into "all the dynamics" that preceded Sullivan's death.
A safety consultant with Workplace Group LLC, a Chapel Hill, N.C.-based consortium with expertise in occupational safety, said wind gusts of 50 mph are much too high for the safe outdoor use of any scissor lift.
Some manufacturers make lifts that can be used in winds up to 25 mph, but W. Jon Wallace said he would recommend against using a lift in winds above 10 mph because the higher the winds, the more unstable the equipment becomes.
"Having 50 mph winds with someone inside the scissor lift, it's just an accident waiting to happen in my professional opinion," he said.
Other schools said they are careful to follow safety instructions from the manufacturers of the hydraulic lifts.
Penn State and the University of Michigan said their lifts are grounded if wind gusts reach 28 mph. On Tuesday and Wednesday, when much of the Midwest was being swept by winds much higher than that, the Wolverines football team practiced with lifts at 15 to 20 feet.
Athletic officials at the University of Wyoming and the University of North Carolina said they would look at adopting specific policies for video lifts. Ohio State coach Jim Tressel said he checks wind conditions when preparing for practice, even though the school installed permanent video towers last year.
"You try to get as safe as you can," he said. "The wind is a scary thing when you're up there."
Texas Tech football spokesman Blayne Beal said students on the Lubbock campus do not use scissor lifts at all when winds reach 40 mph, and they are allowed to go up only 20 feet when wind speeds reach 20 mph. Each person on the lift has a hand-held wind monitor. "That gives us real-time data and they can make the instant decision to come down," Beal said.
At the University of Arizona, director of football operations Erick Harper said video staff must be certified to run and inspect the scissor lifts they rent. He said the certifications are done by the rental company.
"They have the authority to lower (the) lift as needed if they feel uncomfortable because many times the degree of wind 30-40 feet high can be different from on the ground," he wrote in an e-mail. "Our guys are harnessed in and ... if for some reason the camera stand lock breaks just let the camera fall."
Ole Miss has permanent towers, but video coordinator Andy Commer said he watches the weather just the same.
"There isn't a football drill or practice in the world that's important enough to get somebody hurt or, God forbid, killed," Commer said. "We agreed that we're never going to make that call to a parent. The question I always ask myself is: 'Would I put my kid up there?"'
The Indiana Occupational Safety and Health Administration sent an investigator to South Bend. Spokesman Marc Lotter said it was too early to say when the agency, which has the authority to levy fines, might release its findings.
The team planned to host Tulsa on Saturday as scheduled, Swarbrick said, but players planned to wear decals on their helmets to honor Sullivan.
Notre Dame was making grief counselors available for students and planned a special Mass in Sullivan's memory Thursday night. A long line of people waited to get in. The football coach, his staff and most of the team were there.
The fallen tower was hauled away on a flatbed truck Thursday night.
Sullivan's parents met with school officials Thursday, and the family had many questions about his death, his uncle Mike Miley told The Associated Press.
For now, the family wants to remember and celebrate the life of the 20-year-old Sullivan. "He always brought joy to people, and that's how we're remembering him," Miley said.
Matt Gamber, editor in chief of The Observer, the independent student newspaper for Notre Dame and Saint Mary's College, said Sullivan had written about arts and entertainment events for the newspaper over two years.
"He was an extremely enthusiastic and a really driven kid, and that really showed through for us in his writing," Gamber said.
Robert Beamer, assistant rector of Fisher Hall where Sullivan lived, said he was intelligent and a good student.
"Declan was always very, very joyful, just a great presence to be around," Beamer said.
The university president, the Rev. John Jenkins, said Sullivan "was a bright, energetic, dedicated young man, and we will miss him greatly."
Associated Press writers Ken Kusmer and Rick Callahan in Indianapolis; Bob Moen in Cheyenne, Wyo.; Betsy Blaney in Lubbock, Texas; David Brandt in Jackson, Miss.; Rusty Miller in Columbus, Ohio; Aaron Beard in Raleigh, N.C.; and John Marshall in Phoenix contributed to this report.