【Economist】Fire safety: Death in the city

As the planet urbanises, life in tall buildings is becoming more common. It need not be dangerous

A LITTLE after midnight on June 14th, London’s fire brigade was called to a fire at Grenfell Tower, a 24-storey apartment block built in the 1970s. Before long, 250 firefighters were on the scene. But the blaze was too fierce; hours later it had spread to three sides and gutted much of the interior. The upper floors continued to burn into the afternoon. A week later, as The Economist went to press, the number confirmed dead, or missing and presumed dead, stood at 79.

Such a fast-spreading and lethal fire should have been impossible. Because escaping from tall buildings is inherently difficult, strict fire safety is supposed to be designed in. Even as investigators sought to work out what had failed so catastrophically, many wondered if other tower residents were at risk, in Britain and elsewhere. Sadiq Khan, London’s mayor, said the capital’s entire stock of 1960s- and 1970s-vintage tower blocks might have to be demolished. Commentators on news programmes wondered whether the fire marked “the end of high-rise living”.

That is unlikely, even in Britain, where less than 2% of the population lives in purpose-built blocks of at least six floors, and where poor planning and neglect have given high-rise living a bad reputation. In East Asia, eastern Europe and the Americas, it is common (see map). And it will only become more common elsewhere, as urbanisation and growing wealth mean apartment and office blocks spring up. The UN thinks that by 2050 two-thirds of people will be urbanites. Many will live and work in towers, which make the best use of scarce, expensive land.

Better than sorry

With proper precautions, says Daniel Nilsson of the University of Lund, in Sweden, tall buildings can be at least as safe as any other sort. In an average year Singapore, which has 5.6m inhabitants, most living in high-rises, has a handful of deaths; Norway, with a similar population, mostly living in low-rise buildings, has dozens.

Engineers and architects seek to make tall buildings safe in two ways. The first is suppression—stopping fires from taking hold, or limiting their spread if they do. The second is evacuation—ensuring that occupants can get out quickly and safely.

The most basic suppression tactic, used in almost all tall buildings, is compartmentation. The idea is to use thick walls and fire-resistant liners to divide a building into enclosed zones, so that even if a fire does start, it spreads slowly. In residential buildings each flat is a single compartment, and building regulations state how long the compartmentation should hold before a fire spreads to adjacent flats or adjacent floors (usually an hour). In office buildings, compartmentation is usually by floor.

Most of the time, compartmentation works. Of the hundreds of fires in London flats every year, few spread. Fires in American high-rise apartment buildings spread beyond the room they start in only 4% of the time, compared with 10% in other flats.

But when compartmentation fails, the result can be catastrophic. It can happen in several ways. Pipes for heating and water, ducting for power and the like must penetrate fire compartments, and those holes must be fire-proofed. Sloppy renovation can allow fire to pass. Older, much-altered buildings are at particular risk.

It is too early to be sure what caused the failure at Grenfell. But the chief suspect is external cladding made from blocks of flammable plastic encased in sheets of aluminium that was added in 2014. Fire-safety experts think it helped the fire to spread rapidly across the façade, entering via the windows and bypassing the compartmentation. Similar cladding has been implicated in devastating fires elsewhere. Some, like a pair in Dubai in 2015, and another in Melbourne in 2014, were casualty-free. But one in Shanghai in 2010 killed 58 people.

According to Edwin Galea, who runs the Fire Safety Engineering Group at the University of Greenwich, Britain’s fire-safety rules have, at least in the past, relied unusually heavily on compartmentation. Sprinkler systems are another common method of fire suppression. Many countries mandate their use, citing mounds of evidence that they can help extinguish fires while they are still small, or slow their progression until help can arrive. Regulations in most parts of Britain are laxer.

Faith in compartmentation is why many of Grenfell’s residents were advised to stay in their homes for some time after the fire started. This strategy, called “defend in place”, relies on the compartments holding, in which case staying put may well be safer than fleeing through smoke and heat. It also helps keep emergency stairs clear, meaning firefighters can reach a contained blaze more quickly. For this reason, says Dr Galea, many older British tower blocks were not constructed with building-wide fire alarms, or intercom systems that enable firefighters to broadcast instructions to residents.

In most other countries, such systems are common. Other places also put greater weight on the second aspect of fire-safety engineering: escape, usually by insisting that tall buildings have at least two staircases, placed far apart. (Grenfell, like many British tower blocks, had only one). That logic is obvious. But, as with compartmentation, the strategy can occasionally fail, with horrific results. Staircases are designed to be fireproof compartments in their own right, and to keep smoke out. But research published in 2013 by academics at the University of Edinburgh analysing data from 50 building fires around the world found that significant amounts of smoke very often made it into stairwells while people were still escaping by them. In 1980 a fire at the MGM Grand hotel in Las Vegas killed 85 people. Most died in the smoke-filled stairwell.

Evacuating large numbers of people from a tall building is unavoidably difficult. And the problem is getting worse, for the world is not only building more of them—it is building them higher, as well (see chart). As floors are added, it takes longer to evacuate everyone by the stairs. In the tallest buildings, it can take an hour or more, comparable to the amount of time the building can resist the spread of fire. A further complication is that the populations of many rich countries are becoming older, fatter and less fit. Disabled people often cannot use stairs at all.

So engineers are studying other ways to evacuate buildings. One idea is to abandon decades of safety dogma and encourage residents of tall towers to evacuate by the lifts. Studies suggest that could speed things up by as much as two-thirds. Engineers know how to build fire-resistant lifts. They must install smoke-proof shafts so that the piston action of the lift does not draw in smoke. They must provide backup power and lips at every floor, to stop water from sprinklers running in. A few tall buildings, including the 828-metre Burj Khalifa in Dubai, the world’s tallest, already have such lifts.

Psychology is as important as technology. Studies Dr Nilsson has conducted using virtual reality suggest that, even when they know they are in no real danger, people are willing to wait only a few minutes for a fire-escape lift to arrive. One advantage of such lifts is that they can be programmed to give priority to the floors nearest the fire. But that can leave people on other floors feeling stranded. Displaying information such as an estimated time to the lift’s arrival can help quell panic.

Refuge floors are another idea. These are essentially super-compartments—uninhabited floors designed to resist the spread of fire for much longer than normal. They are often open to the outside so that smoke cannot build up. Disabled or injured occupants, or those farthest from the fire, whose evacuation is less urgent, can shelter on them until congestion on the stairs eases or help comes. Many countries, including Hong Kong, India, Singapore and South Korea, already specify their inclusion in buildings over a certain height.

“Sky bridges” linking two or more tall towers are another option. These enable evacuees from above the bridge to cross into a safe building. The sky bridge linking the twin Petronas Towers in Kuala Lumpur forms part of their fire-escape plan. Such bridges can be retro-fitted to existing buildings, says Dr Nilsson; the Gothia Towers in Gothenburg are an example. Other places are considering more exotic ideas. India insists that the tallest towers have helipads on their roofs, though Dr Nilsson is unconvinced. “Helicopters are small and slow,” he says. “And it can be very difficult to land them in the face of all the hot air rising from a burning building.”

Giving engineers more options is valuable, says Dr Galea. But none can solve all problems. Sprinklers help, but the 2014 Melbourne fire started on a balcony and only spread inside once it was established, by which time the sprinklers could not stop it. Defend in place is usually a good strategy, but when it fails, the consequences can be deadly. More escape routes are good, provided they do not put panicked occupants in extra danger. The best approach, he says, is “defence in depth”: including several safety features, each compensating for another’s vulnerabilities.

But even the best fire-safety methods and regulations will be useless if, because of corner-cutting or lack of vigilance, they are not translated into reality. After the Shanghai fire in 2010 Han Zheng, Shanghai’s mayor at the time, blamed poor oversight of the city’s construction firms, implying that building work had been done improperly. Another fire in Beijing, at a building owned by China Central Television, is thought to have spread partly because a sprinkler system failed. Grenfell residents had complained often about poor maintenance, power surges from faulty wiring, and vehicles parked in areas meant to be kept clear for emergencies.

The saddest words

Other countries, including Germany and America, had banned the flammable cladding used on Grenfell; Britain’s building regulations say it should only be used on low-rise buildings. Preventing a fire is better than having to put it out. If the regulations had been properly enforced, Grenfell might not now be a charred shell.

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June 24th 2017 | International | 1687 words