For fire protection design of building exterior wall sandwich panels, why is it insufficient to rely solely on the core’s flame retardancy rating?

In an actual fire, flames can enter the core through joints or damaged areas, creating a “chimney effect” – pyrolysis gases spread within the cavity between panels, causing flame propagation over several meters or entire floors. A typical example is the Grenfell Tower fire; although the core was B1 grade flame-retardant PU, the burning of the aluminum composite panel facings created a vertical fire spread. Therefore, advanced fire protection design must include: 1) Use non-combustible inorganic facings (e.g., magnesium oxide board); 2) Install horizontal fire stops at each floor (stone wool blocks); 3) Add expandable graphite strips between core and facing; 4) Apply fire-resistant sealant in joints. Ultimately, the system should achieve a total fire resistance rating of ≥1 hour.


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