Extensive damage

The long delay between detection and fire brigade intervention played an important role in allowing the unsprinklered fire to grow out of control. In addition the rapid spread of the fire above the 21st Floor appears to be due to failure of the compartmentation measures between the facade detail and the floor which is intended to prevent vertical fire spread.

Fire safety design in many countries relies heavily on sprinkler protection to prevent fire growth and thereby limit possibilities for fire spread via the facade. The lack of sprinklers, along with the failure of compartmentation, appears to be an important factor in this case.

Although there is a requirement to fire stop the gap between the slab edge and the inside of the curtain wall, most codes do not address the tie-back connection of the curtain wall to the structure. Therefore a light facade structural element can heat up quickly and the resulting expansion can produce an outward bulging away from the slab edge, which can create internal flues if it happens before the facade glazing breaks. In other words by not considering the thermo-mechanical response of the system, there are no provisions to prevent such damage in Building Codes worldwide.

An added complication in the case of Edificio Windsor was that the curtain wall facade had recently been replaced and it appears that a new support structure had been fixed onto the outside of the original mullion and transom arrangement. This means that there would have been a double-layered gap that needed to be fire stopped, complicating this detail still further.