After the initial knock down - look at the charring & burn-through of the engineered lamb beams (which were supporting the #1 floor). There was no real fire load within the space & the beams were brought to failure. AS A SUGGESTION: Companies operating on the floors above need to be aware of fire conditions & fire location, as well as building construction features. A proper 360 will often provide vital information for command strategies & tactical operations.
***Even though there was no structural collapse, dynamic loading of firefighters operating on the floor above (Primary searches or fire attack), could have been sufficient to cause such collapse injuring or killing firefighters.***
