Glass enclosure atop Chicago's Willis Tower shows cracks during tourist visit

CREATED May 29, 2014 - UPDATED: May 29, 2014

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  • CHICAGO - Visitors stand out on the Ledge, a new glass cube that juts out from the 103rd floor Skydeck of the Sears Tower, during a media preview July 1, 2009 in Chicago, Illinois. (Photo by Scott Olson/Getty Images)

CHICAGO -- A glass enclosure sticking out from the side of Chicago's Willis Tower Skydeck -- 103 floors above ground -- reportedly cracked around 9:50 p.m. Wednesday night.

According to NBC Chicago, one of the four glass enclosures appeared to show cracks while four visitors were standing on it. The visitor told the station while he and his family members were on "The Ledge," they heard cracking and alerted staffers.

building spokesman told the Chicago Sun-Times the cracking was in a scratch-resistant coating on the glass structure and it did not affect the structural integrity of the box. He added that it is the result of the protective coating doing what it’s designed to.

The encolsures are composed of three layers of glass about one half-inch thick.

The tourist attraction opened in 2009. At 1,353 feet in the air, the glass boxes extend out four feet from the Skydeck.

A similar attraction, “Tilt!”, just opened on the 94th floor of the John Hancock Center. Visitors stand in bays and hold onto metal railings as the platform they’re standing on, and the windows in front of them, pitch forward and then downward at a 30 degree angle.