The garage was under construction at the time of its collapse.
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Federal investigators will take photos, interview workers, look at design plans, and more as they try to determine what went wrong.
The priority on Thursday morning was the search for two missing people.
Only a small corner of the planned garage, including a stairwell, had been built.
Philadelphia parking garage collapse: How OSHA will be involved
The project was underway to provide more employee parking for Children's Hospital of Philadelphia, designed to hold up to 1,000 parking spots when complete.
"Errors happen. It could be design-based, it could be construction-based, it could be material deficiency," said Dr. Abi Aghayere, Professor of Structural Engineering at Drexel University. "They take a look at the structural drawings and make sure that it is not a design error. They will interview the workers who were on the site."
Photos taken on March 27 show the progress over the last week and a half, from only two floors built without the full staircase, to now seven floors.
OSHA representatives will conduct interviews and a comprehensive review of the construction work.
"What OSHA is going to be looking at, and L&I is going to be looking at, is whether there were any issues with either pre-fabricated materials or the concrete pour of the steps themselves," said Aidan Carickhoff of law firm Saltz Mongeluzzi & Bendesky, which has represented victims of construction accidents.
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As of Wednesday, the firm had not been contacted by potential victims of this case.
Permits list HSC Builders and Construction as the general contractor. The national construction company develops large-scale projects, including museums and life science facilities.
Philadelphia Mayor Cherelle Parker said PreCast Services Incorporated, a subcontractor on the site, was installing precast concrete floor decking and roof segments, which were manufactured off-site and installed by the manufacturer.
The investigation will try to determine if the stairs were built to specifications by engineers and other professionals.
"They'll be digging back through all of the pour materials and all the construction information to make sure that that part of the job was done correctly," said Carickhoff.
Suppliers and subcontractor work will be reviewed, but for now, construction is on hold.
Mayor Parker said eight permits were required for this project and were properly issued, with all inspections up to date.
The OSHA investigation will likely take six months or more, the written report of which will then be made public.