Luxury skyscraper hotel completely engulfed by fire in Grozny, Chechnya (VIDEO, PHOTOS)

[Hassin Bin Sober]

33. If steel buildings can't collapse from fire then why is structural steel required to be ...

.... treated with fire retardant coating? All modern buildings require exposed (to potential fire) structural steel to be coated. Why is that? The steel itself isn't flammable so why spend millions of dollars to coat steel?

My partner asked me: "why are the steel I-beams in our condo building garage covered with that ugly popcorn looking foam?"

The answer: Structural steel can heat and lose 50% (IIRC) of its strength from a 500 degree fire.

The coatings applied are given "hour ratings" based on how long they will withstand fire before, hopefully, the fire is extinguished or, worse case, the building collapses AFTER the occupants escape.

An office building like the WTC is a glorified shell with fancy cosmetic coverings like drop ceilings and paper thin wall coverings that offer no fire protections to the structure. Unlike a residential structure, which relies on fire blocking and fire retardant drywall to protect its structure before occupants escape and/or the fire department arrives, the WTC's fire collapse protection relied on surface applied fire resistant insulation applied to the steel structure.

Between the blast of the jet crash and the inability to fight any of those fires due to sprinkler/water loss, the buildings were doomed. The insulation was either gone from the initial blast or was bound to exceed its fire "hour rating" due to lack of ability to extinguish.

Let ANY building burn long enough and it will collapse. Steel or no steel. Some, like WTC1 and 2, will collapse faster when their fire retardant system is compromised. And all, like WT7, will collapse if left to burn for several hours.