On February 22, a fire swept through a 14-story apartment block in the Campanar neighborhood of Valencia, Spain. Ten people died in the blaze. Smartphone footage showed an awning on a seventh-floor balcony catching fire at around 5:30 pm CET, before the flames rushed upwards. Within 15 minutes, the entire building was engulfed, aided by 40-mph winds.
The inferno quickly drew comparisons to London’s Grenfell Tower fire, which killed 72 people in 2017. While what drove the blaze in Valencia is unclear, attention immediately turned to the building’s cladding—material added to the outside of high-rise blocks to improve insulation and aesthetics, and which helped the Grenfell fire spread so quickly. Until 2019, Spain, like many nations, permitted flammable materials to be included in cladding on new high-rises. While the law has changed, hundreds if not thousands of existing Spanish buildings are likely encased in non-flame-retardant panels.
The same danger lurks internationally. Many countries still allow highly flammable cladding to be used in construction. Others, despite banning dangerous materials on new buildings, still have older ones encased in layers of materials highly vulnerable to fire. “Valencia will not be the last one,” says Guillermo Rein, professor of fire science at the Department of Mechanical Engineering of Imperial College London. “Not in Spain, nor anywhere else.”
The world’s cladding crisis stems from another. In the 1970s, the oil crisis created a problem for architecture to solve: how to design more energy-efficient buildings in the face of soaring fuel prices. Facades were to be redrawn from the ground up. “They were once only made of stone, brick, or concrete and very simple,” says Rein. “But they play a complex role: the interface between inside and outside, sunlight and darkness, warmth and cold, noise and quiet.”
Integral to the design of new facades were synthetic polymers: materials made of chains of repeating subunits, and which are the main ingredient of household plastics. Versatile, lightweight, strong, and inexpensive, polymers became architects’ wonder material, offering improved insulation and faster construction time than concrete mixed on-site. It solved all their biggest problems, says Rein, except one. “All polymers are flammable.”
For more than five decades, a polymer core has typically been sandwiched between ultra-thin panels made from aluminum composite material (ACM) on the facade of modern high-rises. “Architects love what you can do with aluminum. You can curve the facade, add a shine, and make it visually appealing,” says Rein. “And it hides the ugly insulation beneath it.”
While commercial ACM manufacturers have always fire-tested these materials, before Grenfell, results would often be obfuscated from the building sector, says Rein. A typical test would see a blowtorch applied to the front of the ACM—the metal would sustain the flame long enough for the manufacturer to claim it was “fire resistant.” However, flammability comes from the polymer, not aluminum. And these tests didn’t necessarily engulf the material the way an actual fire would.
“If you turn the ACM 90 degrees, and attack the edge with the polymer exposed, the aluminum peels off in 20 seconds and a ball of fire rips, creating black smoke and big flames,” Rein says.