Case study: Chapelfield Inner City Retail and Residential Regeneration
The Chapelfield development, by BDP Architects, is a major enclosed shopping centre within the city of Norwich, with surrounding residential units.
The design team adopted a fire-engineered approach to the shopping centre from the start. Quick-response sprinklers, automatic fire detection (including aspirating smoke detection - in malls and car park), voice alarm, and smoke control in malls, ensure flexibility in both the use of the mall and for tenant fit-out. As the design developed, it became apparent that fire engineering offered solutions to some areas of detailed design.
The mall is a mix of single-, two- and three-storey spaces, and each section required a different solution for smoke control. The preferred option was for natural vents, as these offer a number of benefits, including: simplicity, reliability, reduced weight for roof load, no noise to interfere with voice alarm, natural ventilation in summer, and reduced ongoing maintenance. All areas of the mall (other than the single-storey section) have been designed with natural smoke vents, with inlet air provided from adjacent smoke reservoirs.
The geometry of one area of the mall lent itself to the formation of a single smoke reservoir, rather than the two that would be required if following standard guidance.
A preliminary analysis suggested that the extra length and greater area of the reservoir would not compromise the smoke control.
A CFD study, conducted to demonstrate the feasibility of the design, showed that a single smoke reservoir would work, with minimal alterations to the fire-safety provisions already proposed. The results also allowed for a cost saving by using a reduced number of vents and omission of a smoke reservoir screen, as well as enabling the architect to realise its aspirations for the glazed roof.
Jeremy Gardner Associates used the results of research into human behaviour to develop a fire-engineered solution to the means of escape, which places emphasis on familiar exits rather than dedicated escape corridors.
This required detailed analysis of published research, and was supported by the results of a number of studies of occupant numbers in existing shopping centres. In one area of the mall, the design made use of escalators as part of the escape strategy. The escalators would continue running in a fire, as they form the familiar route from that area of the centre.
In back-of-house and servicing areas, the need for lobbies to protect lifts were reviewed. An investigation into alternative methods and products led to the provision of fire curtains across some lift doors, rather than lobbies.
The development includes a two-storey basement car park, which is also intended to function as a public car park, with the expectation that it will serve the adjacent Theatre Royal. A detailed study of real and experimental car fires from worldwide studies showed that sprinklers were not needed to ensure an acceptable level of safety. Smoke control and compartmentation from the rest of the development, with fire-fighting shafts to serve the deep basements, would provide adequate protection within the car park. Each level is 100 x 150m and, to achieve the necessary level of fume venting, about 120m 3 per second of smoke extract would be provided.
The large dimensions of the car park also challenged the recommendations for travel distances within it.
The car park has a 'welcome hall' that leads up to the shop levels. In recognition of the fact that this would be the most obvious route from the car park, it was integrated into the means of escape to deal with extended travel distances and shortfalls in the exit capacity in the dedicated escape stairs.