Completed in 2014, the 20 Fenchurch Street tower, designed by Architect Rafael Vinoly has become an iconic London landmark. The 160m tower, with a unique inclinatory façade, provides over 63,000 sq m of prime office space over 34 office floors, along with a public sky garden at the top of the building offering 360 degree views of the city.
As part of a multi-disciplinary service, we developed the fire strategy and engineering design for the building with systems which included an intelligent fire alarm system coordinated over 40 floors and an external annex building, 30,000m of fire protection pipework, four tanks installed at basement level holding in excess of 25,000 litres of water, along with two 800kg fire-fighting lifts.
Our scope also included developing the strategy and engineering systems for the Sky Garden – the highest public park in London.
To comply with the design guidance adopted for the project, which included BS9999 and Section 20 of the London Building Act (Amendment Act), our initial assessment indicated that the Sky Garden would need to be fitted with both on floor smoke extract and automatic fire sprinklers. However our fire engineering team reviewed this requirement and developed an alternative approach utilising the design principles of the space itself rather than imposing restrictions on the use of the garden and the installation of extensive mechanical systems.
The anticipated fire loading, height, available exits and natural ventilation of the space were all taken into account and the evacuation of the sky garden was also modelled to establish the time required for the population to reach a place of relative safety. The analysis demonstrated the need for a rapid response to a fire alarm: As such, directional voice messaging was incorporated at the Sky Garden levels.
In addition, to determine if the time to evacuate was sufficient before conditions became untenable in the event of a fire, we utilised computational fluid dynamics (CFD) to perform design size fire modelling, enabling us to demonstrate that occupants would be able to evacuate safely with a smoke layer well above their heads and no impact from undue heat.
Ultimately, this detailed analysis enabled us to demonstrate that, despite no major mechanical systems being installed in the main public space, the Sky Garden meets agreed criteria for fire protection and evacuation. All enclosed areas of the Sky Garden, however, are sprinkler protected.
