A bundle of giant steel beams weighing up to 35 tons fell nearly 400 feet at the World Trade Center construction site yesterday — but, miraculously, no one was badly hurt.
A crane atop 4 World Trade Center was hoisting three beams, each 50 to 70 feet long, from a flatbed truck up to nearly the 40th floor when the cable snapped, authorities said.
The beams plunged straight down to the 18-wheel flatbed truck that had delivered them to the site.
“It sounded like a bomb,” said Frank Pensabene, 25, an ironworker from Staten Island.
The truck’s bed was crushed, but the truck driver — who was still with the vehicle, parked on Cortlandt Street — escaped injury.
Meanwhile, atop the building’s 48th floor, the crane seemed to teeter as if about to fall, too.
“The whole crane looked like it was going to topple over . . . Everyone was screaming to get out of the way,” said a laborer who gave his name only as Mike.
Frightened hardhats raced to escape 4 WTC and nearby 3 WTC, which is also under construction.
“The workers looked really scared. No one knew what was happening,” said security worker Frank Arzberger, 61, of Brooklyn.
But the crane held in place, and a fleeing worker who slipped and fell was the only reported injury.
After the 10 a.m. incident, cops and inspectors from the city Buildings Department pored over the scene.
Investigators were checking at least two possible causes for the disaster.
One was a hydraulic failure on the crane.
“There was a lot of hydraulic fluid found near the crane,” said a source.
A failure in the hydraulic system could have caused the cable to suddenly unspool from the winches that control it.
As the cable and its load suddenly dropped, an emergency braking system would kick in. If the brakes are applied too abruptly, they can cause the cable to snap, said sources.
Another possibility was that as the crane was raised over the last few days, an engineer miscalculated the amount of play the cable would need. A cable can snap if it has too much or too little slack, said sources.
Authorities are open to other possibilities and say they need more time to know the accident’s cause. Buildings Department officials have temporarily stopped work on the site.
Additional reporting by Kevin Fasick and Bill Sanderson