Cracked "glass" shocks Willis Tower visitors

A protective coating on the glass of "The Ledge" in Chicago cracked Wednesday. (NBC Chicago photo)
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A California family got a huge scare Wednesday as they took a picture high above Chicago's skyline.

Alejandro Garibay tells NBC Chicago he was on "The Ledge" - a glass box that juts from the 103rd floor of Willis Tower - with his brother and two cousins when they heard a cracking sound. They looked down and thought they saw the glass below them cracking.

But officials say what cracked was a protective layer on the glass and there was no danger to visitors.

"This coating does not affect the structural integrity of The Ledge in any way. Occasionally, the coating will crack, as it is designed to in order to protect the surface of the glass," public relations spokesperson Brian Rehme said in a statement.

The cracked layer was reportedly covered with a carpet Thursday morning, NBC Chicago reported.

Engineers say the boxes are constructed of three layers of one-inch thick glass and can hold up to five tons of weight.