From any point of view the renowned "Gherkin", originally the new headquarters for Swiss Re's UK operations at 30 St Mary Axe in the City of London is a remarkable building.
Rising to 180m the 40-storey building, thrusting skywards, strikes a dramatic pose in the heart of the City and reflects the vibrancy of one of the world's great commercial centres. Revolutionary in shape and function, the "Gherkin" incorporates many advanced methods of planning, design and construction. One unique design feature is the six light wells on every floor spiralling at 5-degree angles from the floor above down the building. Created by offset, triangular cut out areas at the outer perimeter of the floors, the light wells are intersected by transverse, major structural floor plates in series of between two and six storeys throughout the height of the building.
The deepest (‘six pack') light well voids extend to approximately 25 metres in depth. As the light wells provide ventilation throughout the structure it was imperative that an early form of smoke detection was applied to these areas because smoke would most certainly travel through these areas in the event of a fire. Hilson Moran Partnership (HMP), the Building Services Consulting Engineer, was charged with the responsibility to find the most efficient fire detection system to protect these areas.
The use of systems involving conventional smoke detectors such as beam detectors or aspirated smoke detection systems were all considered and discounted for different reasons. Also, the Architect wanted to keep the areas as "clutter free" as possible so as to retain the aesthetic features of the light wells.
An engineer at Hilson Moran, who had seen the new concept of CCTV Video Smoke Detection (VSD) explained on BBC's "Tomorrow's World" proposed further investigation. Their enquiries led HMP to D-Tec (an AD Group company), the inventors and developers of the CCTV VSD technology. Demonstrations of the technology were arranged so that the Client, Swiss Re, the architects, the District Surveyor and the main contractor could evaluate the system and make a decision as to whether it would give the desired level of protection. The demonstration was carried out in the new Swiss Re Tower where a 30 second burn smoke pellet was ignited on the fourth floor and a camera set up on the ninth floor. Upon ignition the system picked up the smoke within thirty seconds. Several tests were made and all gave similar detection rates. One of the key issues was identified during testing; the smoke did not follow the same flow patterns as the testing progressed. As the VSD System does not rely on smoke reaching a specific point it can detect the smoke no matter what the airflow direction. This made the decision making process somewhat easier as it soon became apparent that no other system could offer this level of protection.
The instruction to install a six-camera system to protect the light wells was issued. It was also agreed that the same technology would be utilised in the main lobby where the existing security cameras would be used also for fire protection. The lobby height was 6.5 m and again the architects specified the minimum of services' clutter. By running D-Tec software on 6 of the security cameras, smoke detection was achieved with the minimum of disruption.
|The CCTV Video Smoke Detection (VSD) technology was developed and invented by D-Tec|
The installation was carried out in phases so as to fit in with the main construction schedule. In essence the system was integrated with the security CCTV System, the main Fire Panel and the Building Management System. All components of the system were completed on schedule and a date was set for the demonstration to the District Surveyor and Swiss Re representatives.
The lobby area was tested first. A portable smoke generator was brought in so that no residual material would linger in the brand new lobby. The system detected the smoke within thirty seconds and the sounders and voice annunciation system were initiated. Then the light wells were tested where there was far more integration with other systems in place. Again, a portable smoke generator was used and again the system detected the smoke within 30 seconds. The detection initiates a number of building functions to operate. Firstly the Fire alarm sounders begin and the voice annunciation system advises people within the 4th to 9th floors to evacuate. Also the automatic diamond-shaped windows on the floors 4 - 7 close and the windows on floors 8 and 9 open. At the same time smoke curtains drop down around each triangular light well 2 meters on floors 4 to 7 and on levels 8 & 9 the curtains drop down to the floor. This provides a spiral chimney effect to vent the smoke out of the building.
The District Surveyor was very impressed with the technology and believes that many other buildings will benefit from using the VSD Technology, especially when large atriums are becoming more popular with designers. The fact that the same CCTV security cameras can be used as fire detectors means that the system becomes a cost effective viable solution.
It is likely that the D-Tec system will be utilised for the light wells between the major floor plates on other floors, as they are completed and let in the building.