A holistic approach to fire safety helped with design freedom and cost efficiency at a striking new set of university buildings. Adam Monaghan and Simon Goodhead outline the approach that won them the fire engineering category of the FSE Design Award.
The university of manchester is currently in the process of redeveloping large areas of its estate. Project SCAN is a development that consists of a single stair, high-rise student halls of residence, and teaching blocks which include the School of Nursing, a teaching centre and a large, auditorium. With a site surrounded by other university buildings and main roads into Manchester city centre, combined with the need to be sensitive to the budget, Arup Fire was appointed early in the design phase to provide fire engineering advice to maximise value to the client.
Due to architectural aspirations the design options explored in the initial phases went outside the approach prescribed in Approved Document B. Through a complex cost-benefit analysis, the final outcome of the design included a combination of sprinklers, horizontal evacuation, smoke management, reduced periods of fire protection, sprinkler protected glazing and reduced exit widths.
Although sprinkler protection could have been avoided under Approved Document B and appeared to be an expensive approach, a cost benefit analysis demonstrated the overall value of having them. They formed part of a package of fire engineering principles to allow for value, design innovation and flexibility, so maintaining the individualism of the university’s scheme.
The development consists of a residential building for students and a series of teaching blocks. The teaching blocks comprise the School of Nursing, a series of small lecture theatres and a 1000-seat auditorium. The 15-storey residential building consists of four individual flats per storey, accessed from a single stair enclosure. The teaching blocks, located to the west of the residential building, are separate buildings connected at ground floor level, and range from four to six storeys. The potential for fire spread between each block required consideration to achieve both Building Regulation and client requirements.
A light well is provided in each of the two teaching blocks (Blocks 2 and 3) and pass from the first floor and ground floor respectively. The ground floor of Block 2 is provided with a refectory which will seat up to 430 people. The ground floor area of Block 1 is designed as a reception area for the auditorium, so will also have a maximum occupancy of 1000 people. Block 1 is provided with an open escape stair which serves as a means of escape for the auditorium and as an alternative escape from Block 2. Early consultation with the approved inspector; Greater Manchester Fire Service and the university’s fire safety office ensured the expedient progress of the fire safety design approval process.
Means of escape
For the residential building, the principles outlined in the code of practice for the design and construction of residential buildings, BS 5588: Part 1, were adopted, namely increased levels of compartmentation, common area ventilation together with enhanced detection and alarm capabilities. This enables the evacuation of the whole floor and remaining areas of the building, should the circumstances be appropriate.
In the initial stages of evacuation, only the flat where the detection occurs would evacuate; only at the second stage would the whole floor be evacuated. Evacuation after that would depend on the university’s management. This approach minimises the risk of false alarms for the rest of the building. False alarm reduction also limits the risk of complacency when an alarm does go off, and therefore increased levels of safety are achieved. This enhanced system within each individual student apartment resulted in a permitted extension to the prescriptive travel distance.
The nature of the teaching blocks will result in high occupancy levels. If the whole development were to be evacuated in a single stage, it would have required a significant increase in the number of staircases provided. So each block evacuates independently to limit the impact on evacuation width, while adjacent blocks are provided with a voice activated pre-warning. The use of L1 detection and alarm, combined with a suitable warning matrix, has enabled the minimal impact of a fire in one location on the remaining areas. The facility for full evacuation exists, should the university’s management team deem it necessary. Floor plenum detection was dispensed with due to the high levels of sub-division above comprising a range of offices and rooms with detection in all areas. A number of means of escape principles are used within the teaching blocks which are not outlined in ADB. These include:
– horizontal escape to adjacent compartments
– reduced escape widths (increased evacuation times)
– open plan escape stair cores
The use of the adjacent block as a means of escape route substantially reduces the widths of the escape stairs i
Block 2. The use of compartmentation between the blocks ensures the route is available if required. Should this route be compromised from Block 1, then the escape requirements of Block 2 are not time dependant as they are in a place of comparative safety. This maximised the nett usable area and reduced construction costs.
Fire spread
Due to the floor areas being marginally over 2000m2, additional compartmentation would have been required under prescriptive guidance. Arup Fire carried out a quantified cost benefit analysis in collaboration with the architects and established a best value route forward for the design. This concluded that sprinklers would be the most cost efficient approach and have minimal impact on the aesthetics. Value was shown to be delivered in a number of key areas including: the period of fire resistance; external fire spread issues; glazed compartment walls; and smoke control measures. These benefits are outlined further in the sprinkler section below. The reduced level of compartmentation also rationalised the need for active service penetration protection such as fire dampers. Smoke control measures were provided for smoke clearance in Block 2. Due to the open plan nature of the escape corridors and firefighting shaft lobby discharge point, a full smoke management system is being installed for Block 3. Smoke curtains will be used to increase the smoke reservoir size, though they will only need integrity performance because the low smoke temperatures anticipated from sprinkler protection has shown that insulation against radiated heat would not be necessary.
Sprinklers
The sprinkler system was designed to the life safety requirements of BS 5306: Part 2 and provided the following major benefits:
– The period of fire resistance to all structural elements was reduced from 90 minutes to 60 allowing a more efficient structural design.
– Reduced fire size assumptions allowed a reduced smoke production rate. The smoke ventilation then needed lower ventilation levels to achieve the required performance.
– Toughened glazing was used along the compartment line between the refectory and Block 1 areas at ground floor. This is a well researched area and compartmentation was maintained through the use of window wetting sprinklers
– Reduced fire size assumption outlined in BR187 permitted a significant increase in the permitted unprotected areas between each block. This is further detailed below.
Due to the provision of sprinklers and using a temperature control system, it was demonstrated that although a fire could break into the atrium, it could not break back into the upper floor levels when using toughened glazing. The use of toughened glazing as opposed to fire rated glazing provides value to the client, not only in terms of the cost of the glazing itself, but also the framing system and specialist contractors which would have been needed for installation. In addition to the cost savings, flexibility was also provided to the architect in terms of the framing system they were able to use.
Full external fire spread calculations were carried out between the residential building and surrounding buildings, from the teaching blocks to adjacent sites, and, due to the use of the teaching blocks, between the blocks themselves. Due to the close proximity of the teaching blocks, the provision of sprinklers aided substantially in the requirements for any fire rated facades being rationalised. If sprinklers were not provided, fire rated glazing would have been required between blocks.
The close communication between the university and the design team has enabled a comprehensive strategy to be maintained, in line with that currently operated within other university buildings. The key areas discussed with the university included:
– Maintenance of equipment and systems to ensure the university was fully aware of its responsibility. Significant ‘buy in’ was required from all parties.
– Management of evacuation procedures is key to the ongoing performance of the fire strategy. Again the university agreed that sufficient staff and procedures were in place to manage it effectively. The fire safety risk assessment required under the RRO was given due consideration in how this would be carried out and maintained.
Conclusions
The use of sprinklers, where alterations to the scheme would have enabled them to be designed out, actually created a number of opportunities for fire engineered value and aesthetic improvement. This was recognised early in the design process. Creative use of compartmentation to enable horizontal escape and reduced width and numbers of stair cores, helped to ensure the viability of the scheme. Close contact with the client enabled a better understanding of the university’s management procedures and achieved significant ‘buy in’ throughout the design process. The implications of each area where fire engineered approaches have been used are complementary of others and so, a full building understanding is required to fully appreciate that no one element can be viewed in it’s own right.
Adam Monaghan is an associate and Simon Goodhead is a fire engineer at Arup Fire
