A part of Willis Tower's glass observation ledge in Chicago cracked while people were 103 storeys up inside, according to BBC news.
The glass boxes that form “The Ledge” on the Skydeck are made from three half-inch thick layers of glass laminated together.
While authorities at the Willis Tower temporarily closed all four glass enclosures, a building spokesman said the damage was to the protective coating, possibly from a sharp item dropped on it, and there were no structural concerns.
The Ledge has since been re-opened.
Willis, North America