In a laboratory in a university building, a gas tap is accidentally opened at the end of the working day. The gas tap is connected to a bank of large acetylene cylinders. The gas tap is ejecting 0.15 cubic meters of gas per minute. The gas tap remains open for about 8 hours before the acetylene spreading through the building finds an ignition source and is ignited, meaning that 7.2 cubic meters of instrument-grade acetylene spreads through the large 1940's era naturally ventilated multi-story building before ignition.
When the acetylene ignites, there is about 250 cubic meters of acetylene/air mixture that is above the lower explosive limit of 2.5% Acetylene in a 1940's style naturally ventilated multistory concrete slab/brick veneer building with large glass windows.
My question is how large an explosion will occur? At what range is the explosion likely to break or crack windows?
Please do not dwell on the lack of safety implicit in this event being able to occur... I am well aware of it, and it is part of my story . Please focus solely on the damage that this event might inflict upon a university campus, including gardens, trees and other buildings, as well as the surrounding suburbs.
If these conditions will not cause an explosion, then please assume conditions in which an explosion will occur with this amount of acetylene, and provide a damage estimate from that starting point.