The glass used to sheath the outside of modern buildings is no where near 4" thick. All of the structural loads are carried by the building's steel frame. Each pane of glass has only to be strong enough to support it's own weight and the calculated wind loads plus a safety factor. Add to that the fact that most of the glass is ordinary annealed glass that shatters into large shards, not tempered or laminated (safety) glass. If you look of pictures of downtown New Orleans you will see that most of the glass was broken on the windward side of the buildings - either from the wind or from flying debris.

Watch out below!

JimJr