In an office where I used to work, installers were working downstairs on the floor below our offices installing hangers into the cement ceiling above their heads which was also the floor beneath our feet. Which was thinner than they anticipated.
|That's an office chair just off camera|
It's interesting from an archaeology standpoint. I'm always fascinated by the history of old buildings so seeing all the layers of flooring was like a look back through strata. That debris is the result of a drill bit coming up almost underneath a coworker. The incident caused a lot of very important people to make very concerned faces while inspecting the area for damage. Like I said, this isn't the part of the day you want to be exciting.