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Concrete is not better than steel


It would be a mistake to suppose that concrete high rise structures perform any better than steel. Research by Sintef in Norway has shown that concrete spalling is very rapid when temperature rise is high as in hydrocarbon fires - something not seen in cellulosic fires used for the design of buildings to BS 476.

The problem is the rate of steam production versus the porosity of the concrete, versus out-of-plane tensile strength.

Spalling depth in the channel tunnel fire was 400mm due to compression and confinement - a factor one would also expect to see in high rise buildings.

Passive fire protection (PFP) and protection of it from falling debris would be a requirement for concrete structures, just as it is with steel. Unfortunatley, all spray type PFP systems for hydrocarbon fire protection give off poisonous fumes in less severe fires and so increase overall risk to health.

Rockwool and ceramic fibre with stainless steel cladding is used on offshore structures where people can be present, especially walls/decks exposed to blast before fire. However, it should be noted that ceramic fibre reverts to a blue asbestos characteristic after heat soaking above 800infinityC.

RW Brewerton (M), Natabelle Technology, Sevenoaks, Kent

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