The rush to build ever higher skyscrapers is accompanied by the need to more effectively deal with fire hazards in these super-tall structures.
A report from the US National Institute of Standards and Technology (NIST) into the collapse of the Twin Towers in September 2001, which were just over 400 metres tall, found that “the towers withstood the impacts and would have remained standing were it not for the dislodged insulation (fireproofing) and the subsequent multi-floor fires.”
In many modern cities where land prices are extremely high, the logic of building upwards is inescapable – as long as the design lessons of the past are properly heeded.
The biggest lesson came over one hundred years ago from the Triangle Shirtwaist Factory in New York, when a catastrophic fire killed 146 garment workers in 1911 and led to new legislation on fire safety in tall buildings. Aside from the 9/11 terrorist attack, the worst recorded tall building fire was in Sao Paulo, Brazil in a 1974 blaze that killed 179.
For the new generation of super-buildings, fire safety takes on a whole new dimension, because – beyond sprinkler systems – it can be extremely difficult to tackle a fire a kilometre up in the sky.
There have also been several notable cases where a sprinkler system has made things worse, with cold water coming into contact with non-fire rated glass and causing the glass to break, thereby allowing more oxygen to reach the seat of the fire. The same is true of tempered glass which has a limited fire-rating.
Tim Kempster, MD of Wrightstyle, the fire and blast resistant systems supplier, is concerned that in the headlong rush to build faster and higher, issues of fire safety in some countries may not be adequately addressed or, just as bad, that components in that building may not have proper fire-safety characteristics.
For example, in Grozny, Russia last year, fire destroyed the tallest skyscraper in the North Caucus region, a 145-metre tall structure with 40 storeys. Within two hours, fire had engulfed three sides of the building. It spread so quickly because, it was reported, combustible building materials were used in the building's construction.
“We have publicly raised concerns about how fire regulations were being applied across parts of the Middle East, and changed our certification processes , so that a fire certification on one of our glazing systems could not be unilaterally applied on another project,” Kempster said.
Statistically, a significant proportion of fire fatalities and injuries occur while occupants are attempting to get out of a building, generally within paths of travel to the exit. When it comes to evacuating a tall building, events like the World Trade Centre have had an impact on the design for fire, although not always deliberate. The question that arises is: do you really need to get people out?
The most effective way of dealing with fire at high altitude is by means of fire compartmentation: keeping the fire contained in one protected area and preventing it from spreading. A contained fire can be dealt with - an uncontrolled fire can’t.
“A rule of thumb for fire safety in supertall buildings is that any fire should be able to burn itself out, without external intervention, and without building collapse,” explained Kempster. “That allows for a limited evacuation of people on the affected floor and on floors immediately above and below the fire.”
Everyone else he says should be “defended in place” – a realistic strategy when you might have elderly or disabled occupants stranded 200 storeys up.
“Options to evacuate or defend in place are essential for tall buildings,” agreed Denny Verghese, Leader – Fire Engineering at Meinhardt. “Depending on the type of building and the nature of the occupants, these options can aid in providing a sound basis for the performance of a building in the event of a fire.
“Modern tall buildings can be significantly different from historical building stock, which form the basis of most building codes. Building codes around the world have prescribed requirements generally based on thresholds on building height, size and occupancy type."
In terms of fire protection systems, research demonstrates that a combination of a sprinkler system and non-fire rated glass is not a good safety solution. An “active” sprinkler system needs good maintenance and activation sequences to work properly, whereas “passive” fire-rated glazing systems are guaranteed to work – if the right systems have been specified.
Sprinkler systems can also be compromised by low water pressure - a major consideration in very high buildings, and PVC water supply pipes can be damaged by fire and rendered inoperable.
A report published last year on fire safety design in tall buildings was presented to a major Asia-Oceanic symposium. It concluded that “only once we understand fires in modern compartments can we truly assess the critical components of the fire safety strategy and begin to provide relevant, refined, innovative fire safety that truly reflects the nature of tall buildings.”