Thanks to a city largely still in shutdown mode from the coronavirus, a potential catastrophe was avoided Wednesday morning when a window on the top floor of the Penn Medicine Washington Square building at Eighth and Walnut Streets broke and fell in pieces to the sidewalk and street 20 stories below.

Glass shards covered a section of Eighth between Walnut and Locust Street, a typically busy patient drop-off area as well as an entrance to the multistory garage below the seven-year-old medical office building.

There were no reports of injuries, a far different scenario than what possibly might have been if Philadelphia was not in the limited “yellow” phase of the state’s reopening plan.

That was not lost on those still sweeping up glass hours after the window shattered about 9:30 a.m., about 10 minutes after the Fire Department blocked access.

“Literally when the firemen and myself were walking across the street is when the main part of it came down,” said Ken Huck, a maintenance tech with Geis Realty Group Inc., which handles building upkeep and repairs. “We were out here trying to keep people from walking around.”

What initially cracked the window was anyone’s guess early Wednesday afternoon. One theory was a bird. Later, a spokesperson for Penn Medicine attributed it to the heat, saying no damage was done inside or outside.

“Nobody saw it happen," Huck said as crews from Geis and the Center City District swept up glass within an area cordoned off with yellow police tape just after noon. “It was cracked and was finally going to come down, and it came down.”

When Huck realized that was a likelihood upon seeing the damaged window around 8:45 a.m., he said he called the Fire Department to get that portion of Eighth closed to vehicular and pedestrian traffic. He wasn’t sure the window was going to fall but wasn’t taking any chances.

“I’d rather be wrong making that decision, closing the street off, than the other way around with somebody getting hurt,” Huck said.

He noted the good fortune of a city not yet functioning at full capacity. “We could have had a lot of other pedestrians out here,” Huck said.

Last July, the University of Pennsylvania Health System bought the medical tower for $99.25 million from developer Liberty Property Trust. The garage and retail portions of the property were not part of the deal.

Staff writer Rob Tornoe contributed to this article.