Tenements are Class 3 Wood and Joist construction normal with Brick exterior walls under the NYC Building Code. Row frames are all wood including the exterior walls this is class
5 Construction. The danger is that all the structural elements of the building are wood and therefore burn. So, the structural components that hold the building up are subject to rapid failure and collapse. ANY building at the end of a row of buildings OR that has had an attached building, that had been
removed or destroyed is more likely to collapse, due to the loss of the strutting effect of the other building/s. The buildings help hold each other up, especially when burning, or compromised by other structural damage. Last Photo below is of a Collapse I worked at on W. 31 St, in Manhattan. The adjoining building had been removed, the brick side wall bulged and collapse when untrained workers tried to remove bricks from the (Now fully exposed side wall) and the entire brick mixed occupancy building collapsed killing the owner and some of the workers.
I was a Lieutenant in Tower Ladder 21 at the time. Captain Bob Rainey FDNY Engine 26