London has many tall buildings. A high number of them are solely for business use but more and more, especially the newer buildings and those at the planning stage are designed to be solely residential.
The highest solely residential building in London and the UK with 49 storeys and a height of 592 feet is The Tower, One St George Wharf, Nine Elms Lane, SW8 2BW. According to a publication entitled ‘London’s Growing Up’ published by New London Architecture in 2014 it is about to be joined by 230 towers, all over 20 storeys,in the Greater London Area.
Why? The profit from residential buildings is four to six times greater than that from office buildings.
How high is a building of 20 storeys? The Council on Tall Buildings and Urban Habitat have a chart with various formulae to determine the height of a building when only the number of storeys is known but a rule of thumb is that the distance from the floor of one apartment to the floor of another is 3 metres. The height of a 20 storey building is therefore more than 60 metres as the ground floor will probably be taller than the others and the top floor may be a double height penthouse.
Let’s settle for 60 metres or 197 feet.
Rescue from that height is not possible using a turntable ladder and remember that 20 storeys is less than half the height of The Tower at St George Wharf. The tallest turntable ladder with a height of 150 feet was built by Leyland in 1936 for Hull Police and Fire Brigade which was a single unit at the time. That machine is now in the hands of a collector.
What’s the answer?
Since AD60 when it was razed to the ground by the Iceni the City of London has suffered a series of fires of which the best known is The Great Fire of London of 1666. Following that fire The Rebuilding Act of 1667 improved fire safety in a number of ways including.
• Outlawing the practice of jettying or oversailing. That is where subsequent storeys overhang the one below.
• Dictating that buildings must be built of fireproof material.
• Limiting the height of buildings.
The principles in that Act, particularly the height limit, were enshrined in subsequent legislation including the London Building Act of 1894. When the first motorised telescopic ladders were introduced in 1905 they could only reach a height of 82 feet.
The height limit was only removed in 1956. London had a low rise skyline until that time. Buildings became progressively higher until 1980 when the National Westminster Tower now Tower 42 was completed with a height of 183 metres (600 feet).
Fire safety, particularly evacuation, was paramount in the mind of the architect Colonel Richard Seifert. So much so that the building is spatially ineffective. The offices, with narrow floorplates, are wrapped round a concrete core. The core contains two fire escapes with their own air systems. In case of fire air would be pumped in so fast that smoke would be driven out. The fire precautions, the most advanced in the world predate the proposals following 9/11 by thirty years.
By the time the first of the next set of tall buildings appeared in the City of London in 2004 in the form of 30 St Mary Axe (The Gherkin) new techniques and materials were available.
Many modern buildings are being built elsewhere in the world.
I recently attended a lecture by Sir Norman Foster where he said, ‘More buildings will be built in the first thirty years of this century than have ever been built before’.
Amazing. By the way we are now into the second half of that thirty year period.
This article is entitled ‘Fires in Tall Buildings’ and I would like to concentrate on one particular fire.
The one that occurred on New Year’s Eve, Thursday 31st December, 2015 at the Address Downtown, Dubai which is a 63 storey hotel and apartment complex.
I have no specific knowledge of the event and I am relying on television footage and reported facts which are available in the twenty four hours following the outbreak.
Apparently the fire started on the 20th floor when a curtain caught fire. The fire was reported as being confined to the cladding.
Cladding is the outer covering which makes a building weatherproof and can include glass. In some cases the cladding is only decorative and not responsible for weather proofing .
The fire engulfed the exterior of the building within 10 minutes.
It was reported that fire alarms and sprinklers didn’t work.
Nevertheless all the occupants were evacuated safely.
From the television footage it seemed that the flames at their lower level had penetrated the rooms and debris including what appeared to be windows was falling to the ground. At the upper levels the flames appeared to be confined largely to the balconies.
It’s time for the analysis.
Why did the curtain catch fire? Even with a substantial ignition source it should not have caught fire.
I know someone who imports carpets from America. He showed me a sample which looked and felt like an expensive thick pile wool carpet and explained that it was made from recycled plastic bottles! Bearing in mind what it was made of I asked how it could comply with fire proofing regulations. He explained that it had to pass the ‘hot metal test’ to confirm its fire resistance. (BS 4790) applies. The test involves dropping a metal nut which has been heated to 900C on to the material and then determining how much of the area around the nut has been affected.
The curtain appears to have ignited combustible material on the balcony above and each subsequent balcony. The flames seem to have had a plentiful supply of combustible material and I wondered whether there was a fuel or gas pipe in the cladding as there will a plant room or rooms above the 20th floor. I quickly discounted both theories. If a fuel pipe had been involved burning fuel would fall to the ground. That did not happen.
If a gas pipe had fractured then there would have been a flare of gas at or near the fracture.
The heat from the burning curtain would set off the fire alarm.
The security staff’s first priority is to save life and the 20th floor would be evacuated first, followed by the two floors above and one below. It is normal to have a controlled evacuation and an evacuation as described is exactly what would happen if there is a fire at The Gherkin.
Fire alarms would not necessarily sound on other floors although they would as further evacuation occurred especially from the floors above the seat of the fire.
Once evacuation has taken place standard practice is to confine the fire and allow it to burn itself out. The apartment should contain very little of a combustible nature.
High buildings are required to be fitted with sprinklers. A pressurised water system is usually concealed between a ceiling and the floor of the premises above. It is designed to come into operation before the heat of the fire becomes life threatening. The pressurised water is held back by a plug covered with a decorative cap. At 57 degrees Centigrade the decorative cap falls off and at 65 to 70 degrees a glass phial shatters unplugging the water which will continue to spray until shut off manually. This will tackle the fire and limit smoke.
It is important that windows should be made of fire proof glass. Fireproof glass is designed to withstand flames on one side and cold water on the other for a period of two hours. If the windows are not fireproof they will shatter when sprayed with cold water and will allow the ingress of oxygen in the form of a draught which will feed the fire.
From the television footage I watched there appeared to be windows falling. The reason for that has not been established yet.
On that building there was no system to spray water on the outside but there is at least one building in the City of London where that could happen. The building, completed in 1976, is Bush Lane House next to Cannon Street Station. As a result of physical constraints it was difficult to provide a simple conventional means of evacuation in case of fire. The answer was to provide it with an exoskeleton (a frame) which operates in much the same way as a sprinkler by spraying water on the cladding of the building.
Since writing this article I’m indebted to Andy Bartlett who has pointed out that the exoskeleton does not in fact spray water but acts much like a car radiator and will absorb heat in the case of fire. If the water boils it will escape as steam at roof level.
It appears on my guided walk, ‘Modern Architecture in the City’ which shows how architects overcome problems. The emphasis on this walk is on constructional detail.
My other walk ‘The Rise and Rise of London’ covers the development of buildings from Roman times to buildings which are not yet built. The emphasis of that walk is about high buildings but it also covers fire prevention. That walk is also available as an illustrated talk.