Yep, I had a front row seat to watch this from one of the tall buildings across the Charles. The wind was probably gusting at 45 mph right in line with the length of the building. Once some of the windows got broken there was a _lot_ of oxygen to fuel the fire. It must have been like a blast furnace in there.
When I first head about the fire it was 3 or 4 alarms, then I got distracted and heard it went to 7 alarms. By the time I found a scanner feed it had gone to 9. Even then they were calling for additional engines to get enough water pressure.
Based on the reports that the mayday was called just a few minutes after the to FFs entered the basement, I would imagine that was when the back windows blew out.