I was quoted in a news article last week (12 January) on the serious fire at the timber-frame construction site in Colindale, north London. I think several statements in the story require clarification.
Steve Cracknell, the fire investigator for the London Fire Brigade, said tests had shown that the insulation used on the project would not support a fire. The insulation used on the building was foam plastic insulation, which is a combustible material. To quote the view of the British Rigid Urethane Foam Manufacturers’ Association: “Any combustible material will ignite if heated to a sufficiently high temperature in air, in the case of polyurethane (PUR) and polyisocyanurate (PIR) foams this would need to be above 450°C.”
The self-ignition temperature of PUR foam is 400-450ºC and that for PIR foam 470-520ºC. The intense fire that destroyed the four-storey block in less than 10 minutes would have rapidly generated temperatures of 900-1100ºC, so unless the laws of chemistry do not apply in Colindale, the insulation would have burned.
Mr Cracknell is also quoted as saying, “As far as I can tell, it didn’t contribute to the fire as it has a flame retardant applied to it”. A flame retardant is added to a polymer formulation to reduce or retard the tendency to burn. It does not stop it burning. If the insulation did not burn, why was it not visible and intact at the end of the fire?
The point I made to Building is that it is important not to ignore the contribution of the insulation with regard to the speed of the fire and intense black smoke. Look at available calorific values before the fire: wood typically has a calorific value of 16-17MJ/kg and PIR/PUR of 26-27MJ/kg. Many thousands of square meters of insulation would have been exposed to the fire.
Peter Jones, independent fire consultant
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