Oneperson is deadand two are still unaccounted for following aparking garage collapse in Grays Ferryon April 8.
Officials, including Philadelphia Mayor Cherelle L. Parker, said Wednesday evening that search and rescue operations would proceed after the structure was stabilized, though a timeline was not clear.
The missing had not been found as of early Thursday evening.
Here's what we know about how the structure collapsed.
How did the Grays Ferry parking garage collapse?
According to an incident report summary delivered by Parker Wednesday night, all seven levels of the structure's stair system failed on the 30th Street side stairwell.
Subcontractors were in the process of installing precast concrete floor decking and roof segments, when a precast roof segment failed, falling to the level below and "literally triggering a progressive collapse of connected sections across all seven levels," Parker said.
The precast sections had been manufactured off site and installed by the manufacturer, officials said.
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What is precast concrete?
Precast concrete is concrete that has already been molded and cured before being transported and assembled.
How tall is the Grays Ferry parking garage?
The under-construction garage is seven stories.
Officials confirmed that the project was a non-accessory parking garage with ground floor retail space.
Who owns the Grays Ferry parking garage that collapsed?
The structure is owned by the Children's Hospital of Philadelphia and was intended for use by roughly 1,000 hospital employees.
Who was building the Grays Ferry parking garage? Who contracted the Grays Ferry garage?
The project was under the operation of general contracting firm HSC Builders and Construction Managers.
The firm is based out of Exton, Pennsylvania and services areas of Pennsylvania, New Jersey and Delaware.
Kaitlyn McCormick is a Philadelphia-based reporter writing all things trending, breaking and city-related for USA TODAY's Philadelphia Metro Connect Team.
This article originally appeared on USA TODAY:How did the Grays Ferry parking garage collapse? What happened