Welders lots of times use acetelene gas.
Q: How much acetelene does it take to blow out windows?
A: Not very much!
Q: How much acetelene does it take to blow out windows?
A: Not very much!
I wouldn't discount the possibility that it was an O2 tank, either. A full oxy tank that gets the valve knocked off could easily take out a load bearing wall if it gets a little room to run, and fill the room with explosive levels of oxygen in the process.