VIDEO EVIDENCE will be closely scanned by investigators into last weekend's Torre Windsor fire, experts said this week.
They will be looking for clues to how the flames spread both up and down the 32 storey structure and their conclusions are bound to influence the outcome of any legal action that might follow.
Fires can spread from floor to floor via a number of routes: stairwells, service ducts and lift shafts, for example. But where curtain walling is a feature as here, the flames can take a different path.
Full scale fire tests by the Loss Prevention Council (LPC) in 1999 showed that a fire on a typical fully fitted out office floor would break out via the curtain walling within minutes (NCE 24 June 1999).
'The ames will then flare up outside to the next storey level and beyond, ' said BRE Certification director of research Jeremy Hodge.
'Then heat from the flames will radiate back in through the glazing, ignite anything inflammable and start the whole cycle again.' Aluminium framed curtain walling will soften and distort when temperatures reach 200°C.
This can cause any firestopping between the floor slabs and glazing to fall out, creating an even faster route for the fire to spread. If significant gaps are created, debris from the burning floors can drop down and ignite floors below.
The LPC research indicated that an aluminium framed system could disintegrate completely within 30 minutes. A typical fire would have burnt itself out in this time, the LPC concluded, pointing to the fire in a 17 storey office block in Basingstoke in April 1991 (NCE 25 April 1991).
In this case glazing failure was the main contributor to rapid upward fire spread.
Hodge said that under older Spanish building regulations firestopping at floor/curtain walling interfaces was never mandatory. A major upgrade of local codes and regulations to bring them into line with European standards is under way.
Firestopping ill then become one way of satisfying the new requirements on control of fire spread. DP