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The danger of combustible exteriors on tall buildings

London Grenfell Fire
Part of Grenfell Tower, after the tragic fire, as seen from near Notting Hill Methodist Church, London. June 16, 2017. Photo courtesy of ChiralJon via Wikimedia Commons.

On June 14, 2017, Grenfell Tower, a 24-story building located in West London, United Kingdom, experienced a tragic fire that resulted in 80 deaths. The fire reportedly started in a refrigerator of a fourth-floor unit. With no automatic sprinklers in the building, the fire spread to external openings. Once there, the highly combustible building cladding allowed the fire to sweep rapidly throughout the entire structure.

More high-rise fires

Within a 51-day period, the Grenfell Tower fire was followed by two more high-rise building fires. On July 14, 2017, the Marco Polo fire in Hawaii involved a 36-story, noncombustible building that wasn’t sprinklered. The fire only damaged two floors but resulted in three fatalities.

On August 3, 2017, the Torch Tower fire in Dubai burned an 86-story building with a highly combustible exterior, but the interior was protected by automatic sprinklers. The fire damaged 64 floors of the building; however, the interior damage was minimal, and no lives were lost. Most occupants returned to the building within one week.

These events point out an increasingly dangerous issue generating worldwide interest: the risk of using highly combustible panels for exteriors and cladding on tall buildings. The panels have a solid core of polyethylene between two sheets of aluminum. When ignited, they support fast vertical fire growth as the core burns rapidly, and the fire is supported by the vertical flue space between the inner and outer aluminum shell.

Verisk analysis of tower blocks across the UK

In the wake of the tragic fire at Grenfell Tower, the London Fire Brigade asked Verisk to perform an analysis on buildings in the UK that have similar characteristics to Grenfell Tower. Verisk analyzed all the tower blocks in London and validated the number of floors, construction date, and whether the structure had cladding. The following is a summary of the results from Verisk’s UKBuildings™ database as of June 19, 2017, and our subsequent analysis.

The database reported a total of 3,510 residential-only tower blocks (or point blocks) taller than six floors in height that covered all urban areas of the UK with a population greater than 10,000.

A total of 1,228 residential-only tower blocks (or point blocks) taller than six floors in height were found in London. Eighty-seven of them have some form of cladding. For London, the database shows 632 buildings at least six floors high that are primarily residential but classed as mixed-use (at least one floor of retail, office, or other use).

The world reacts to fire risk

The problem is growing throughout the world as ever-taller buildings are erected. A Wall Street Journal article, Buildings Across U.S. Are Wrapped in Same Panels That Fueled Deadly London Fire, highlighted the issue in the United States. An FM Global white paper, Grenfell: The Perfect Formula for Tragedy, discussed the worst-case scenario that enabled the blaze. And the National Fire Protection Association (NFPA) Fire Protection Research Foundation has initiated a project to develop a risk assessment methodology to assess the risks and prioritize inspection and remediation efforts for these high-rise buildings.

Fire protection experts call for restrictions

Fire protection experts are calling for restrictions on the use of these panels. Building code advisory groups around the world are reconsidering their approval of the panels for use on building exteriors. Recent flame-spread testing in the UK revealed that a great majority of these exterior panels fail flame-spread tests. In the past, the International Code Council (ICC) prohibited panels that failed flame-spread testing from use in buildings greater than 50 feet (15.2 meters) in height. But the ICC lifted that restriction in 2012, allowing use of the highly combustible panels in taller buildings.

Sprinklers proven to help

The rapid pace of fire spread facilitated by such panels is exacerbated when the building doesn’t have an automatic sprinkler system. The worst-case scenario presented by the Grenfell Tower fire was a tall building with combustible exterior cladding and no automatic sprinkler. As evidenced by the other two fires cited, when even one of those factors is present, outcomes are better. The Marco Polo fire had noncombustible exteriors that limited the damage. The Torch Tower fire had sprinklers that enabled residents to evacuate, resulting in no loss of life from the fire.

The FM Global white paper concluded that when using combustible exterior materials, fire spread in sprinkler-protected properties was limited to the exterior materials, internal property damage was limited, loss of life was lessened, and residents could return to the property more quickly. Buildings with damage-limiting construction, such as noncombustible buildings, still sustain extensive damage when sprinkler systems aren’t present. The white paper calls for local governments to review existing codes and make changes to prevent creating the worst-case conditions.

Worst-case scenarios for high-rise construction

It’s obvious that the combination of highly combustible exteriors and no automatic sprinkler systems is the worst case for high-rise construction. Even the presence of one of those factors can prevent a tragedy from becoming worse. The international fire service community is investigating ways to improve building codes and construction practices to mitigate this life-threatening and costly situation, but more needs to be done.

Seppe Cassettari

Seppe Cassettari is managing director of the GeoInformation Group, a Verisk Business.

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