Is modern façade design a ‘Frankenstein’s monster’?

 

Aatif Ali Khan, Shaorun Lin, Xinyan Huang

Dept. of Building Services Engineering, Hong Kong Polytechnic University

 

    Modern façade systems effectively improve the performances of tall buildings and have been applied to thousands of buildings. Particularly, the façade helps reduce the building (HVAC) energy consumption, fitting the concepts of green and sustainability. However, such systems have created a route for the vertical fire spread over the building exterior, which has been responsible for many fire injuries and causalities.

    Today, façade fires in high-rise buildings are occurring more than once a month, and famous examples include the Shanghai apartment fire in 2010 (58 deaths), Beijing TVCC Tower fire in 2011 (1 death), Dubai Address Hotel fire in 2016, and the London Grenfell Tower fire in 2017 (72 deaths). Therefore, it raises a paramount concern, Does modern façade design prove to be a ‘Frankenstein’s monster’, and how could we create and promote these “monsters” all around the world without fully understanding its fire hazards?

    The tragic Grenfell Tower fire in London raised the profile of façade fire hazard, and its inquiry is still on-going. The exterior of a façade system generally includes aluminium composite panels (ACP) or aluminium composite material (ACM), where a core material is sandwiched between thin aluminium layers [1]. Due to the presence of polyethene (PE) and other flammable core materials in the façade, such systems have become a shortcut for fire spread along the building exterior. The burning of core materials, including PE and other polymers can generate a ‘cocktail of smoke’, which traps occupant and limits the egress time.

Picture2.png

    There have been many standard façade fire tests. The testing criteria and sample sizes in these standard methods vary from country to country, such as EN 13501-1 and BS 8414. The core materials are categorized based on the combustibility, smoke production, and droplets tests. In the market, A2- and B-grade cores (by EU standards) have been widely used in building facades and considered as “non-combustible” and “limited combustible”, respectively, although the concept of “non-combustible” itself is questionable. Unfortunately, in practice, the ACPs with these core materials are inappropriately used as such (‘non-combustible’ or ‘limited combustible’), which makes them the primary culprit for deteriorating fire accidents.

    Recent bench-scale fire experiments were conducted at The Hong Kong Polytechnic University to re-assess the fire hazard of ACPs with A2 and B-grade core materials under well-controlled external irradiation. It was found that these materials can still be ignited and burn when exposed to a fire, after the front aluminium layer peeled off. Due to the complexity, the fire hazard associated with the façade system is not only controlled by the core material but also affected by the structural failures at the system level. Under lower irradiation, even without ignition, the long-term heating can still cause severe deformation to lower its fire performance. This latest work has been published in Fire Technology [1].

Picture2.gif
Picture3.png

    The severe structural failures, including the peel-off of aluminium layer and core, bending, softening, and cracking, not only reduce the stability of façade system but also increased its fire hazard. It is worth noting that these structural failures would be affected by the size of the panel and fire, as well as how these panels are fixed in the facade. If properly fixed, aluminium layers may not fall off, but the core may get charred or cracked. This is the time to consider these kinds of structural changes in standard tests of façade systems!

 

    In summary, over the last few decades, the use of ACPs and ACMs in the façade system increased enormously due to their lightweight, formability and cost-effectiveness. However, its fire performance is still poorly examined and controversial. It is necessary to examine not only the core materials but also the whole ACP facade as a unit for its proper performance. Serious consideration is required from both fire and structural communities to capture or stop the “monster” that are created by careless ourselves.

Picture1.gif

[1] Khan AA, Lin S, Huang X, Usmani A (2021) Facade Fire Hazards of Bench-Scale Aluminum Composite Panel with Flame-Retardant Core. Fire Technology. doi:10.1007/s10694-020-01089-4.