This is a hollow sidewalk supported at points by wooden floor joists. A small hole in the sidewalk received a cigarette butt.
The joists caught fire. Firefighters used their sledge hammer to open up the sidewalk to get at the fire and extinguish it
No injuries. Some smoke in the basement. Public Works called to bring steel plate to cover hole for now.
So now we know why you can't park on a hollow sidewalk: You might fall through into a bottomless abyss.