From “Cast Iron Buildings: Their Construction and Advantages” by "James Bogardus, Architect in Iron” (New York 1858):

 

Were a cast iron building “filled with combustible goods, such as cotton or resin” and were to burn entirely, "the building itself would remain firm and unimpaired.”

 

What would really happen - say to a corner sited CI building, 75 x 100, 5 stories high? 

 

Christopher