Also, what’s an incinerator shaft? Like a trash chute that leads to an incinerator?

Pretty much. In my grandmother’s apartment building, you could hear it go off every so often. The heat was used to help keep the hot water hot and, during the winter, to heat the steam in the radiator pipes that warmed every apartment in the building. Actually, thinking about it, it’s October 1, the day when they switch on the heat, so I’m guessing that’s got something to do with it.

With environmental regulations, I’m pretty sure the furnaces have all been replaced with garbage bins or maybe compactors, but yeah, there was an incinerator in the basement back in the day.

Edit: Looking at work permits, it looks like they were doing work on the boilers in 2022-2023: sealing oil tanks in place (I guess they were leaking?), switching the boilers to gas, they brought in a temporary boiler for a while. Since they’re saying this was a gas explosion, I’d guess something was deficient with the work.

Totally pulling this out of my ass, but there have been garbage strikes in NY before. Imagine how quickly this could build up in a fifty-story residential building (even ten stories would put out a lot of trash). I could totally see large buildings adding incinerators as a solution.