Toxicity threats
about the dangers and problems associated with smoke far more than fire itself (see Figure 2 on page opposite). Dame Judith has made it very clear that
industry should not wait for regulatory changes before driving transformation. It looks almost certain that sprinklers will become mandatory for buildings over 11m, although we wait to see how much MHCLG can reduce the scope of that requirement. However, sprinklers do not prevent smoke ingress from an external cladding fire. Fire Protection Association (FPA) research in measured the dangers of this
November 20181
for the first time, and the potential lethal effects of the toxicity of the external materials that can ingress via vents, poor seals or even an open window. In the context of B4, crucially it showed that fire ‘spread’ is not the only issue. Without even testing the most toxic of material combinations, measurements showed that lethal doses through a typical 100mm vent could be achieved in a 50m3
room within 30 minutes, possibly without the
fire reaching the vent itself (see Figure 1 on the opposite page and Figure 3 above right). It’s quite possible to modify the behaviour of a
material to limit the spread of fire, but still produce large quantities of smoke and gases. With multiple materials in a fully developed structure fire, the ease of ignition or ability to self extinguish may not be significant factors. A fire retardant material can still contain a large amount of fuel which may not burn quickly or spread, but which still has the capacity to produce large quantities of smoke and gas that can spread throughout a poorly compartmentalised structure.
Smoke production
The fire testing and certification framework that guides designers of higher risk buildings is likely to come in for significant criticism
Sample Cone calorimeter data
Peak HRR/ kW m-2
ACM_PE1 1364 ACM_PE2 1123 ACM_FR1 123 ACM_FR2 195 ACM_FR3 144 ACM_NC1 13.8 ACM_NC2 30.2 HPL_PF HPL_FR
530 263
Total heat release/MJ m-2
105.4 106.6 59.6 70.9
65.07 2.57 0.87
172.71 67.49
MCC data
Total heat release/MJ m-2
124 119 60 58 61 11 17
260 196
Figure 4: Potential heat release from each component of the facade system.
Figure 5: Heat release rates of ACM and HPL grades. Figure 3: FPA toxicity test project November 2018.
in the inquiry. Presently, there is very little to inform designers of the dangers of smoke production, or allow meaningful comparisons between different materials. EN 13501-1 does include a very simplistic classification of smoke production for construction materials, and the new combustible ban does require materials to be A2-s1, which is a sensible definition of non combustible in my view. However, BS 8414 large scale testing and its associated BR 135 classification contains no reference to smoke production – its primary objective is to classify the rate of spread of fire. This is despite the fact that the industry lacks a national standard for testing cavity barriers, which are one of the key products in the prevention of smoke spread. This creates a safety loophole whereby combustible materials can be developed with sufficient flame retardant to pass the BS 8414 test from a flame perspective, but in doing so create large amounts of smoke in the process. In July 2017, I wrote to the Department for Communities and Local Government to strongly urge the inclusion of high
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