All three workers had to be taken to the hospital, one in critical condition, after falling 20 feet.
Video and pictures taken by fellow construction workers moments after the collapse of a rebar show the injured men on the ground.
Coworkers worked tirelessly to remove the steel structure that fell on top of the men.
"From the weight of those individuals on that tower, the tower itself collapsed, which is approximately 1,000 pounds of rebar," said Battalion Chief Youngsma with the Fremont Fire Dept.
One worker was transported in critical condition, the others suffered moderate injuries.
After the accident, developer Queens Land closed off the construction site and sent workers home. Cal/OSHA inspectors arrived to determine the cause of the accident.
"We'll look into what occurred and how the incident took place and if there were any violations of those regulations on safe work practices," said Frank Polizzi, Cal/OSHA spokesman.
This is the second worksite injury Queens Land is being investigated for. Cal/OSHA says a worker fell from the second floor at a different Fremont site over the summer. That investigation is still ongoing.
The focus now is to determine if this latest accident could have been prevented.
"They were actually clipped in, per safety rules," said Youngsma. "They're supposed to be clipped in, anytime you're elevated and they were clipped into that rebar."
UPDATE: 2 of the 3 construction workers injured in #Fremont have been released from hospital, according to employer Queens Land. Third man sustained broken ribs from fall and is in stable condition. Cal/OSHA is investigating accident. https://t.co/IykWD2dinw@abc7newsbayarea pic.twitter.com/WAsyesVNV4— Carlos Saucedo (@Carlos_Saucedo) October 17, 2018
Queens Land, based in San Mateo, is the general contractor for project site. They tell me accident involving 3 workers is the first major accident of this kind at #Fremont construction site. Groundbreaking of 60K sq ft retail space began May of 2017. @abc7newsbayarea #abc7now pic.twitter.com/VwILlq8fIP— Carlos Saucedo (@Carlos_Saucedo) October 17, 2018
20ft rebar tower weighing 1k pounds fell on 3 construction workers as they were climbing it. 1 sustained critical injuries, 2 others moderate injuries. #CalOsha in route to investigate. @abc7newsbayarea #abc7news pic.twitter.com/r3Z3MmcxTM— Carlos Saucedo (@Carlos_Saucedo) October 17, 2018