The collapse of the twin towers at the World Trade Center on September 11, 2001 has provoked several recommendations for the improvement of high rise fire protection.

The exact causes of the collapses are highly controversial, but one theory holds that the twin towers collapsed for three reasons. First, the structures were weakened by the high impact collision with a speeding airliner. One of the results of that impact could have been the jarring loose of the fire retardant applied to the steel in the buildings. Second, the intense heat generated by the burning jet fuel weakened structural components of the building and ultimately allowed them to buckle. Finally, the collapse of one floor onto another created a pancaking effect in which two floors fell onto a third, and so on with increasing velocity.

Engineers are still sorting out the effect of the collapse of the towers on building fire protection. One change may be an upgrading of the fire resistance materials and the methods by which they were applied to building steel supports. In 1995 a fireretardant rehabilitation program was commenced, but failed to make rapid progress before 2001.