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Cladding fires: a fatal warning of a bigger problem

Giorgio Marfella

The disastrous Grenfell Tower fire in London shocked the world; and raised many questions about the safety of contemporary, tall, residential buildings. British authorities are still unearthing evidence necessary to pin down the exact causes and dynamics of the incident. But the preliminary consensus among experts points to a well-known problem: fires in building cladding, spread by composite metal panels with polyethylene backing.

The problem is well known in Australia, where in November 2014 a cigarette butt in a plastic container was enough to ignite a façade of polyethylene-backed metal panels on an apartment building in Melbourne. Once just a small section of the aluminium-polyethylene facing on a balcony wall was lit, the fire spread quickly. It travelled up the side of the building in 11 minutes. Fortunately, casualties were prevented by the limited amount of panels involved, the prompt response of the Melbourne Metropolitan Fire Brigade (MMFB), and the timely activation of internal sprinklers.

Part of the Grenfell Tower following the blaze. Picture: ChiralJon/Flickr

The ensuing incident report sparked a media frenzy. The concerns raised by the MMFB were many. Several similar cladding fires in residential buildings had occurred recently around the world (in Dubai, Shanghai and Europe), taking many by surprise. But the big surprise and concern was that the polyethylene cladding involved had never been tested for flammability according to Australian standards, or equivalent international standards.

The technical information necessary to understand this issue is simple. Under severe fire conditions timber chars, concrete spalls, steel melts, glass breaks and plastics burn. But polyethylene, which is a plastic, behaves differently to most structural building materials. Polyethylene becomes fuel. It does not spall, break, fall or melt: it inflames and spreads fire. Tall building façades clad with panels where a thin veneer of aluminium is mounted on a polyethylene core (or “black core’), can potentially transfer a fire, very quickly from one floor to the next, with terrible consequences.

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The good news is that most modern building codes, standards and regulations have come to terms with this issue. Most have learnt from the past, and façades must now be constructed out of non-combustible material. Façades may burn shortly, spall, deform and break glass, but they cannot add fuel to a fire. It is as simple as that.

So are these incidents isolated cases of negligence? Is it sufficient for the public to seek and identify a handful of dodgy manufacturers, unscrupulous importers or contractors who import sub-standard materials in our progressive projects and smart construction sites? Unfortunately, it’s not that simple.

The big problem is that despite the industry being aware of the danger of flammability, polyethylene-backed composite metal panels with aluminium facing are already everywhere, indoors and outdoors. They have been used in thousands of projects worldwide from the 1970s to present times. Polyethylene-backed metal panels are all around us – in apartment buildings, office buildings, supermarkets, commercial centres and, possibly even in schools, hospitals and universities.

Shiny samples of the material still abound in the show rooms of architects and builders. It has been used for years in presentation boards prepared for the approval of clients, councillors and ministers. The material is still indicated on architectural and shop drawings worldwide, while quantity surveyors and design managers often select the metal-plastic composite option as the much more affordable alternative to costly metal cladding.

The interior of an apartment in Grenfell Tower showing the fire resistance of the concrete structure. Picture: UK Met Police

So how is this possible? Could disaster happen again?

This question is more pertinent than ever, and further research should look at the current proliferation in Australian cities like Melbourne of high-density, high-rise residential buildings. And it’s around this area of high-volume, low-cost residential construction that important questions need to be asked; particularly the associated socio-economic issues that are the hardest to dissect and respond to.

The technical problem is easy to fix. Polyethylene is combustible, and should never be used again in façades. Given its widespread use and misuse, architects could easily refuse to specify composite metal panels mounted on polyethylene from now on: everywhere, and not only in tall buildings. And manufacturers could stop the production of this backing material and concentrate efforts on their safer, inflammable alternatives.

A thin veneer of aluminium mounted on a polyethylene core (or “black core’). Picture: Lep Beljac/University of Melbourne

So how did we get to this point?

Since the mid-1980s, in the name of innovation and productivity, the construction regulations of several countries, including Australia, have become less rigorous and prescriptive. In simplified terms, today’s performance-based code would state: “a façade must not be combustible; how you do so in detail is not for the code to tell, so long as it is not combustible”.

By contrast, a prescriptive code, like those before the 1980s, would state: “a façade in a high-rise building, in order to prevent the vertical spread of fire, should have a 900mm deep concrete spandrel able to resist fire for at least three hours.”

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The performance-based approach leaves the field open to alternative solutions, and innovation. Recent research by the University of Melbourne has looked at the key role of designers, specialist consultants and contractors as the gatekeepers of quality and safety when it comes to the construction of facades. It is these experts who should collaborate, calculate risks and make arguments and proposals on a case-by-case basis for the approval of the relevant authorities.

The prescriptive rules of the past were far from being perfect, but the widespread use of composite metal panels with polyethylene core shows the vulnerability of the present approach, which in some cases, may have departed too far from best practice. Cladding fires of recent times indicate that wrong-assumptions about risk may have been made or that measures to verify the details of these measures were inadequate.

So let’s make no further mistakes.

If there is any significant lesson to learn from this tragedy it is that we need to be prepared to get to the core of the problem and not limit our inquiries on the rediscovery of the obvious: façades must not be combustible.

Banner: Fire engulfs Grenfell Tower/Getty Images