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
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