A protective coating on a glass sightseeing box that extends from the 103rd floor of the Willis Tower in Chicago cracked Wednesday night, but officials said no one was ever in danger.

Tourist Alejandro Garibay and four of his family members were standing in one of the glass boxes that jut out from the side of the tower when they heard a strange, worrisome noise below them.

A Willis Tower spokesman Bill Utter clarified Thursday that it was a protective coating, not glass, that cracked -- as it sometimes does.

"At no time whatsoever was the integrity of the structure compromised," he said.

The ledges are designed to hold 5 tons, and the coating keeps the glass from being scratched.

"The protective layer did exactly what it was supposed to do," Utter said.

The four Skydeck ledges are a series of clear bays with glass floors that extend a little more than 4 feet from the building. Visitors can see the street 1,353 feet below their feet. According to the Skydeck website, each bay is made from three layers of half-inch thick glass.

Visitors who step into one of the boxes can see for 50 miles across four states.

Since 2009, 6 million people have ventured into the ledges, which retract into the tower when the windows need cleaning.

The ledges were closed for some time Thursday, but the Skydeck viewing area on the 103rd floor was open.

Around 7 p.m., Willis Tower's Facebook page indicated that "the new protective coating on Ledge 4 has been installed."

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