The Camden Yards escalator accident that injured more than 40 baseball fans Saturday was caused when a metal shaft broke, sending the moving staircase "freewheeling" downward at high speed, specialists close to the investigation say.
The tear in the shaft left the escalator's safety brakes ineffective, and the staircase continued its near free fall until several steps were mangled at the bottom. After the accident, a sneaker was left wedged in the jumble.
Michael T. Shiflet, a consultant hired by Forensic Technologies International of Annapolis, said the break occurred within a large assembly that moves the steps along and is supposed to stop the escalator when problems occur. The shaft holds the assembly together.
"The shaft sheared," said Mr. Shiflet, part of the FTI team hired by the Orioles to help investigate the accident.
"When that shearing happened, you don't have braking on the escalator. And, when that happens, it's just like falling downhill."
FTI, the Orioles, the Maryland Stadium Authority and state inspectors would not discuss the accident or the investigation.
At least 43 fans were injured in the accident, which occurred about half an hour before the Orioles played the Minnesota Twins. The right-field-side escalator, which stretches from the ground-level concourse to the stadium's upper deck, was loaded with fans when it slid downward. Scores of people tumbled atop one another at the bottom.
The probe into the accident is being spearheaded by Moline, Ill.-based Montgomery Elevator Co., a 102-year-old firm that installed the escalators in 1992 and maintains them. The firm is one of the nation's four largest producers of elevators and escalators.
State officials said yesterday that the escalator has been dismantled and that its parts were flown Wednesday to an undisclosed location. Earlier, they said the equipment would end up in the hands of Montgomery engineers for examination.
Reached at Montgomery's headquarters, President Daniel S. Blount said he had been away from his office and did not know details of the accident. He said he was unaware of any previous problems with broken shafts. He referred questions to another company official, who did not return phone calls.
Mr. Shiflet and other industry experts made aware of the investigation said the shaft broke in a section where it holds the "bullgear," a powerful component that turns a large chain, moving the steps along.
The shaft is 4 inches in diameter in the largest section and narrows to 2 3/4 inches in diameter at each end. The break occurred at a narrow part of the shaft.
The braking mechanism, which is attached to the assembly, was rendered ineffective by the shaft's damage.
Instead of holding the staircase in place, it allowed the escalator to slide backward -- so fast that one injured fan described the frightening experience as similar to an amusement park ride.
Bernard L. O'Neill, a private consultant who learned about the problem from investigators, also said the shaft broke, preventing the braking system from holding the escalator in place.
"After I saw some of the steps, I realized the brake didn't hold," said Mr. O'Neill, a retired chief elevator inspector for Maryland who is widely respected within the escalator and elevator industry.
He also questioned whether Montgomery should be allowed to take charge of the investigation.
"It's not good to let the fox guard the henhouse," he said. "If there's anything that could have been wrong to start with, you're not going to find out about it."
State inspectors photographed and marked the equipment before Montgomery moved the damaged parts, officials say.
James A. Morkosky, safety inspector administrator for the state Department of Licensing and Regulation's Division of Labor and Industry, said his agency will issue a report on the accident after compiling information from Montgomery, outside contractors involved with the investigation, the stadium authority and his team of 31 inspectors.
The escalators on the right-field side of Camden Yards have had other problems in the past.
In the ballpark's first two seasons, they were closed on several occasions, leaving fans to use ramps and elevators to reach their seats.
Stadium escalators received major repairs during the off-season, including improvements to structural supports.
But on May 17, another free-wheeling problem on an escalator -- not the one involved in Saturday's accident -- injured a number of people.
State inspectors have not submitted a report for that accident, Mr. Morkosky said.