Eye witnesses reported several explosions which would suggest something being stored in the warehouse may have detonated. You just never know what is being stored in any building be it domestic or industrial. Don't think it would have been a roof collapse as Standard operational guidelines would not have an Incident Commander committing a BA team to a building that was already engulfed (unless there was savable life without taking an unacceptable risk) Those RSJs will warp between 500 and 700 degrees a temperature that would be easily achieved and surpassed in a fire like this. Firefighters are taught to " take some risk to save saveable life, take little risk to save saveable property, take no risk at all to save lives or property that are already lost" That is the world over.
An Awful Tragedy, May both firefighters and the Civilian who also perished Rest In eternal Peace. Thoughts and prayers with the injured Firefighters and the families of all involved.