Vigilancia tecnológica

SummaryFollowing the Grenfell Tower tragedy in London, the US requirements for fire safety of façades were revisited. The 2018 edition of the key US regulation, the IBC, had associated shortcomings, in spite of the fact that no US fire losses with fatalities have resulted from complying wall assemblies. This is contained in Chapter 14, Exterior Walls.The key fire test used for exterior assemblies (façades) in the US is a large?scale test, namely NFPA 285. The test evaluates the vertical and lateral flame?propagation potential of any exterior wall assembly system with combustible components, typically including insulation. The systems are evaluated as flat specimens containing neither corners nor projections. The “typical” fire scenario modeled corresponds to a fire in a room, venting through a window opening and exposing the exterior wall from both inside and outside. The fire test equipment is a two?story structure with a test room on each story and a window opening. Two burners expose the test specimen: one is placed inside the ground floor test room and the other one is placed outside, near the window opening. The fire test contains pass/fail criteria based on measuring the following phenomena:• Vertical and lateral flame propagation over the exterior,• Vertical and lateral flame propagation inside the combustible core,• Vertical flame penetration into the second story,• Temperature rise on the exterior and within any wall cavities.The IBC includes requirements for a variety of products and also detailed requirements for three specific assemblies: metal composite materials, high?pressure decorative exterior?grade compact laminates, and exterior insulation and finish systems (known in Europe as external thermal insulation composite systems). It also includes requirements for fire?retardant?treated wood, water?resistive barriers, and exterior wall coverings, such as siding and very detailed requirements for foam plastic insulation (as tested on its own and within the assemblies). This work shows multiple changes made when revising the 2018 IBC to the 2021 IBC.Concerns have been expressed regarding the applicability of NFPA 285 to fire scenarios associated with the twin effects of either (a) vertical (such as angled walls) or horizontal (such as balconies) projections or (b) wind. No changes to that effect were made for the 2021 IBC.Three concepts were discussed in detail but not adopted into the code using the “16 ft. parallel panel test” (from FM 4880), either as an alternate or as an additional test, incorporating the effect of wind during the NFPA 285 test and considering the effect of corners and/or projections from flat surface during a modified NFPA 285 test. Also a requirement was incorporated into the International Existing Building Code to conduct an NFPA 285 test when façades are added, replaced, or modified.In summary, this work provides a comprehensive overview of the requirements for façades (both materials and assemblies) in the USA in the presently applicable building code (IBC 2018) and in the next edition (2021) of the applicable building code.