Welcome to the club! I have the same thing -- that's vintage 1950s era fireblock right there (at least in my part of the country).
In my house they used, bricks, rocks, and sand -- and covered it in each bay with a piece of wood to hold it all back. It makes it impossible to run any new wiring from the basement directly to the first floor as one normally would.
It also makes sealing the rim joist impossible. The best I can do is seal the blocking piece of wood. Thus, there is cold air leaking up from the rim joist to the outer wall baseboards on the first floor. If you haven't sealed your first floor baseboards, you probably have the same issue.
I have cast iron piping running up the some of the bays, and in my case, the bricks were either removed or are not present -- I imagine to not block the passage and allow the piping to be run. Unless your bricks are too hot to touch, I don't imagine there would be an issue there, but others can chime in on that regard.
In my house they used, bricks, rocks, and sand -- and covered it in each bay with a piece of wood to hold it all back. It makes it impossible to run any new wiring from the basement directly to the first floor as one normally would.
It also makes sealing the rim joist impossible. The best I can do is seal the blocking piece of wood. Thus, there is cold air leaking up from the rim joist to the outer wall baseboards on the first floor. If you haven't sealed your first floor baseboards, you probably have the same issue.
I have cast iron piping running up the some of the bays, and in my case, the bricks were either removed or are not present -- I imagine to not block the passage and allow the piping to be run. Unless your bricks are too hot to touch, I don't imagine there would be an issue there, but others can chime in on that regard.