Looks like it was already in the process of collapsing when the video cut in.
Reports in the article about "...blocking stairwells with fabric from cramped garment workshops..." sound like a very dire situation. Combustible materials stored in a tall chimney...
There is no fire protection of structural steelwork in the third world ....
Every once in a while it is useful to have a disaster like this to remind us why we must spend a few dollars extra for a building that complies with western codes and standards.
To Jed's comment... the rules are there, and the building was made according to the rules. The tenants made stupid mods/storage decisions (like Tehran's stacking of bolts of cloth in the stairwell), but you have to look at the building design itself, not what the tenants do with it.