Grenfell Fire: Why Cladding Burns

“The blaze started on one side of the tower block, before rushing up and around the outside of the building and engulfing it in flames from the second to the top floor.”

 

This was the account given by witnesses of the Grenfell Tower fire, but it could just as easily have applied to the fires at Dubai’s The Address in 2015, Marina Torch in 2013, and Tamweel Tower in 2012 and Beijing’s BTC Center in 2009. These four Asian conflagrations were fueled by their respective buildings’ exterior cladding. Technical details remain unclear about Grenfell Tower’s cladding, but it appears to be of similar composition: a polyethylene core sandwiched between aluminium sheets. This cladding appears desirable for the insulation provided by the plastic core and the waterproofing and clean appearance provided by the aluminium, and its lightweight qualities- each panel is less than a centimeter thick- allow easy support and installation. However, after these recent events, it is apparent that this material is entirely unsuitable for high rises.

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Left to right: Grenfell, The Address, Tamweel fires

This type of cladding is never the root cause of a fire, spontaneously combusting, but when a foreign spark reaches it- a short-circuiting refrigerator at Grenfell, a firework in Beijing- broad fronts of flame swiftly expand across it. A misconception among observers is that the aluminium itself is catching fire; this is not exactly true, as even at the high temperatures of fires the metal is inflammable. Instead, the sheets melt and thus deform and delaminate, shedding like a snakeskin and exposing the plastic beneath, which is flammable. The thinness of the plastic facilitates fast ignition and spread in all directions. As it burns it melts, and molten globs drip down, endangering the structure below.

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Cladding can be seen peeling off Grenfell Tower

Cladding does not have to be such a tinderbox in its composition. Steel facing has a higher melting point than aluminium and will not delaminate as easily. There are many insulation materials that are less risky to use than polyethylene. The plastic foams polyurethane and polyisocyanurate, both commonly used, are combustible but swiftly form a char layer, containing the burning region. Phenolic foam is another plastic used which both chars and is extremely difficult to ignite. The best material to use is mineral fibre, which is entirely noncombustible. However, steel and these insulators are heavier and more expensive than aluminium and polyethylene.

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Grenfell Tower mid-refurbishment. The gap between the cladding and structure can be seen.

At Grenfell, the flammability of the cladding may not have been its only issue; it was installed as a giant sheath of a curtain wall around the tower, leaving a small gap between it and the main walls of the building. Eyewitness testimony seems to indicate that this gap acted as a chimney, allowing flames to shoot up at a rapid rate to higher floors. Again, this sort of spread is easily preventable with firebreaks of a material such as concrete, which would have compartmentalized the gap and contained the blaze to smaller areas. However, like the safer cladding, such firebreaks are expensive, as well as difficult to add to an existing structure.

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Diagram of Grenfell Tower’s facade

Without a doubt, building regulations need to be be in place which prevent developers from choosing the cheap and easy but dangerous option. In London, a question that needs to be asked is whether or not Grenfell Tower’s cladding violated fire codes. This is not necessarily simple to answer; polyethylene insulation is a relatively recent development, and may not be directly covered by codes. Additionally, in many countries, building laws are strict in regards to the surface of cladding and lax for the interior. Manufacturers take advantage of this; Alumco, the producer of the panels that burnt at The Address, advertises them by praising the fireproof qualities of the aluminium, conveniently glossing over the combustibility of polyethylene. 

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Cladding installation on The Address

The cladding of Grenfell Tower has come under rightful scrutiny and at this point appears to be a major factor in the tragedy; it should by all means be subject to investigation, and fire codes and its installers should come under the microscope. However, it is too simplistic to simply blame the building’s skin for the scale of the disaster. In the fires in Dubai and China, the blaze remained confined mostly to the outside of the building, and there were no casualties. The Grenfell investigators need to figure out how the fire devastated the tower block’s interiors, and whether measures such as extra exits, sprinklers, or structural firebreaks should have been installed. In the meantime, swift steps should be taken to identify other buildings with at-risk cladding and refit them. Fortunately, this appears to be an immediate priority of the government, who have identified a number of such tower blocks and will likely take fast action to render them safe for habitation.

Update: June 27th

Cladding company Arconic has released a statement stating that one of its products, Reynobond PE, was “a component” of Grenfell’s cladding, and that it will no longer be selling this product to high rise construction firms. Reynobond PE was, indeed, aluminium and polyethylene sandwich cladding. Arconic do not indicate awareness of whether or not it was compliant with fire codes, claiming that responsibility lies with the installer: “while we provided general parameters for potential usage universally, we sold our products with the expectation that they would be used in compliance with the various and different local building codes and regulations.”

Though, as mentioned earlier, fire codes may not be specific in regards to polyethylene cladding, British law stipulates that a cladding must undergo a flammability test in order to be approved for use. It is hard to imagine polyethylene surviving this sort of procedure; one wonders if it was not approved but used anyway, or ineffectively tested. This is yet another missing piece in the puzzle.

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