For someone with a fear of heights, having the glass floor of an observation box crack on the 103rd floor is the stuff of which nightmares are made. That is exactly what seemed to happen at Chicago’s Willis Tower – the reality of what happened, however, was much less exciting (as it so often is).
As it turned out the thing that actually cracked was not the glass, which is designed to withstand up to 10,000 pounds of weight, but the protective plastic shield, which protects said glass from the wear and tear of the endless pairs of tourist feet. So the good news seems to be that nobody was ever at risk of anything more than a heart attack.
In a somewhat related story, your author clearly remembers being on the observation deck of the Tokyo Tower, which also features a section of glass floor, when an M4 earthquake struck. Swaying back and forth at 850 feet above Tokyo is a great way to make you contemplate your own mortality.