ON MOST schemes, the architectural design of. Flexible strategy. Case study. The Forum

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1 Flexible strategy ON MOST schemes, the architectural design of a building is influenced by fire engineering strategy. This could be in the form of visual, physical elements such as fire doors, fire curtains, compartment walls and ventilation vents, and also hidden technical provision, such as sprinklers, smoke detection and smoke ventilation. Yet, fire engineering strategies resulting from performance-based design principles do not necessarily need to influence or disturb the architectural design by adding physical elements. Frequently, fire engineering techniques can The Forum Case study be applied which achieve compliance with the Building Regulations, but may not follow current statutory guidance documents, such as Approved Document B of the Building Regulations (ADB) 1. By considering the unique challenges of an individual building, a bespoke fire engineering approach can offer a higher degree of flexibility and the possibility of more than one design solution, to help support the architect s vision and achieve a more cost-efficient design solution. This is illustrated by the following in-depth case study of a building scheme designed for flexible use. Currently under construction, The Forum Southend-on-Sea (as it is known) is a new-build development undertaken for the University of Essex, South Essex College and Southend-on-Sea Borough Council. Due to open in summer 2013, the building comprises five levels (lower ground to third floor) and includes a café, lecture theatre, children s library, creative hub, library, reading area, academic hub, teaching and learning areas, stores and offices. The design team consisted of architects, civil and structural engineers, acoustic and lighting engineers, and fire engineers. The scheme has demonstrated that, for a fire engineered strategy to be successful, fire engineers must be part 38 April

2 Karl Wallasch shows how fire engineering solutions can ensure fire protection while supporting the unique aspirations of buildings to benefit architects, clients and end-users of the design team at an early stage in order to highlight potential life safety risk and areas where descriptive codes may unnecessarily detract from the architectural vision and, where instead, a fire engineering strategy may allow the unique aspirations for the building to be achieved. Initial advice The initial architectural concept allowed for four stair cores. From experience, the fire engineers, Hoare Lea Fire Engineering (HLFE), felt that the number of stairs and stair widths could be reduced, when taking into account the technical provisions planned for the building such as automatic fire detection and voice alarm. They demonstrated to the architect and clients that the Figure 1: 3D section showing internal open stair serving ground to third floor levels, and lecture theatre connecting lower ground and ground floor (ADP Architects) building could be designed in accordance with ADB, with reference to British Standard (BS) Based on initial means of escape calculations, the architect was advised that three stairs were sufficient, with at least two of them serving all levels and located at each end of the building. As the height of the building is greater than 7.5m, but less than 18m, firefighting shafts (which did not need to include firefighting lifts) were required. Due to the shape of the building, these were also located at either end. Client requirements The scheme is designed to accommodate three clients with different aspirations and needs, which presented some challenges regarding integration and management. Southend-on-Sea Borough Council intends to use the lower floor as a library and for presenting plays, films, live music and indoor sporting events, and there is a requirement also to serve hot food and drinks. The University of Essex wishes to use the building as an assembly recreational building for activities such as public lectures, conferences and exhibitions, and as an office space. South Essex College aims to use the building for similar educational and office purposes, including teaching rooms, open space and enclosed learning and meeting spaces. It is likely therefore, that The Forum Southend-on-Sea will be used by members of the public who are unfamiliar with the building. One aspect of the fire engineering strategy was to address the clients management strategies applicable when the entire building is occupied, as well as the strategies to be applied during times when only parts of the building such as the teaching rooms, gallery space, lecture theatre or cafe are in use. The architectural concept reflects this need for flexibility of use and the building is designed so that it can be divided into open and closed sections, or used as one large circulation space by different user groups. Design concepts Generally, architectural concepts consider circulation and movement of occupants within a building during normal use. Following the introduction of the Building Regulations, any building should be designed with the provision to allow for an early warning of fire and appropriate means of escape in case of fire, from the building to a place of safety. A fire engineering concept can allow for a safe means of escape by looking at the interaction between structural elements, such as protected escape corridors; technical fire precautions, for example automatic fire and smoke detection and ventilation; and management within a building. Forum fire precautions As a central atrium links all floor levels, it was stated at an early stage that, due to adjacent buildings, some degree of compartmentation was likely to be required to restrict external fire spread. April

3 Following a detailed external fire spread analysis based on the British Research Establishment s publication, External fire spread: building separation and boundary distances 3, it was suggested to the architects that it would be acceptable to link the ground and first floor, but that the second and third floor levels should be separated from the atrium via firerated glazing. Neither Approved Document B nor BS 9999 classifies the void as an atrium and therefore a dedicated smoke clearance system was not required. In addition, the means of escape strategy required a minimum distance of 4.5m from the edge of the void. Two means of escape stairs were proposed at either end of the building, and therefore at least one means of escape route was away from the void. A summer peak-time ventilation system in the atrium, linked to a firefighter s switch, allows the fire and rescue service to use the system to clear smoke. This assists the speed with which the building can return to normal operation and gives a higher degree of property protection. Lecture theatre The internal lecture theatre on the ground and lower-ground floors can accommodate 203 people. Means of escape is provided via two exits into the ground floor level area. An evacuation lift also serves the lower ground floor level up to ground floor level. At an initial meeting with building control officers and the clients fire officers, it was highlighted that occupants from the lecture theatre should be able to escape into a place of relative safety (the reception space at ground floor) and from there to a place of safety outside. A major concern was the means of escape of non-ambulant persons from the lower ground floor level of the lecture theatre. The following options were discussed: Option 1: Provision of at least one safe route from the lower-ground Figure 2: 3D geometry of The ForumSouthend-on-Sea used for the RSET analysis (HLFE) floor level of the lecture theatre to outside (via either protected corridor or protected stair). Option 2: Provision of an evacuation lift, serving the lower-ground to ground-floor level, and a higher degree of compartmentation in the main reception area at ground-floor level to create a protected route from the lecture theatre directly to the outside (eg provision of fire and smoke curtains). Option 3: The use of a fire engineered design solution, consisting of a comparison between the Required Safe Egress Time (RSET) and the Available Safe Egress Time (ASET). RSET is the time required by lecture theatre occupants to leave the building and escape to a place of safety, such as outside. ASET is the time available for occupants to escape before conditions within a building become untenable for escape due to fire and smoke spread. Typically, a successful fire engineered solution would demonstrate that RSET is less than ASET (RSET < ASET). Advanced (or evacuation) modelling was used to predict the time for an evacuation of the building (RSET); and a computational fluid dynamics (CFD) analysis was used to predict the time when conditions would become untenable (ASET). Evacuation model - RSET The RSET analysis consists of fire engineering calculations to determine the detection time, the time to activate alarm, premovement time and travel time required for escape. This is conducted in accordance with the British Standard document, PD : and CIBSE Guide E: Fire safety engineering, The RSET study for this development included all floors, interior walls, doors and stairs. The calculations for detection time, alarm time and pre-movement time were based on the following: clear ceiling height at ground floor level: 4m maximum distance between centre of fire and detector: 5m simultaneous evacuation for the entire building alarm time is based on automatic fire detection raised by a single-knock pre-movement time will vary between 30 seconds (for first few occupants) and 90 seconds (for last few occupants) all assumptions follow guidance of PD Evacuation scenario Different evacuation scenarios were developed, with different exits from the lecture theatre available, depending on the proposed fire location. Based on discussions with the clients and the building control officer, it was decided that one exit (exit 012) of the lecture theatre should not be used. Occupants therefore needed to escape via exit 013 into the open space at ground floor (see Figure 3). In the case of the proposed worst fire location, the main front exits 001 and 014 could be blocked, therefore these are not used within the evacuation model. All other exits and escape routes are available. The total occupant load has been assumed to be 2,235, including 203 occupants in the lecture theatre. 40 April

4 Figure 3: Ground floor layout (as STEPS model) outlining evacuation scenario 1 (HLFE) Computer software The computer evacuation model used to demonstrate people movement within the lecture theatre was Simulation of Transient Evacuation and Pedestrian movements (STEPS), designed to predict pedestrian movement under normal and emergency conditions. Producing real-time 3D simulations in an easily understandable graphic form allows the results to be interpreted by both non-specialists and experts. This helps to identify natural bottlenecks and preferred exits, as well as testing evacuation routes and timings for different emergency scenarios. CFD modelling was used to determine the ASET, when occupants exposed to a fire are likely to be unable to evacuate due to the effects of exposure to smoke, radiant heat and toxic gases. Using the National Institute of Standards and Technology s (NIST s) computer modelling software Fire Dynamics Simulator (FDS) 6,7, the time to untenable conditions was calculated and presented in visual formats. Some basic assumptions were made for modelling purposes. Geometry HLFE included ground and first floors as well as the void above only. The CFD model did not include the second or third floor, as these will be separated by fire-rated construction (see Figure 4). Electrical Product Safety Conference 2013 Safety of electrical products - a approach 16 May 2013 Church House Westminster London Only 75 An Electrical Safety Council event bringing together professionals with an interest in electrical product safety and consumer protection. Keynote speech from Malcolm Harbour CBE, MEP For further information and to book: The agenda will cover: Communication of risk Product recall processes Traceability Safety in design April

5 Fire size The area within the open space in front of the lecture theatre is mainly used as circulation space. However, close to exit 001 there is a buggy store, and tables and chairs from the café store are located on both sides of the lecture theatre. Furthermore, the main reception area is also located at ground floor level. Following guidance of the CIBSE Guide E, a heat release rate of 290 kw/m 2 was used and a total fire area of 4.0m 2 (2m by 2m). Based on the use of the building a medium fire growth rate was implemented. Fire scenarios The three fire scenarios differ in terms of fire location. Scenarios 1 and 2 assume that one exit of the lecture theatre is blocked due to a fire. This assumes the worst case of evacuation time required to empty the entire lecture theatre. In scenario 1, the fire location also blocks the main exit the widest exit of the building - delaying the total evacuation time. In the third scenario the fire location was chosen to be located near the evacuation lift, which links lower ground and ground floor. RSET-ASET results The CFD software, FDS and Smokeview by the US National Institute of Standard and Technology (NIST) were used. The design criteria assessing tenability Figure 4: Proposed 3D Geometry via FDS/ Smokeview (HLFE) considered minimum visibility, maximum temperature and toxic gases, as outlined in PD : 2004 and the CIBSE Guide E, Results of the CFD modelling indicated that a maximum evacuation time of 4 minutes and 5 seconds is required (this includes evacuation of wheelchair users) and that conditions become untenable after 6 minutes. The results of the modelling also indicated that the provision of smoke curtains would stop smoke spread into the means of escape routes mainly used by non-ambulant persons. It was therefore suggested to the design team that the installation of smoke curtains would increase the level of safety, maintaining a safe route clear of smoke for more than 360 seconds, thereby demonstrating a safe means of escape for occupants from the entire building, including the lecture theatre. The results of the RSET-ASET study were presented to the design team, the clients fire officers and the statutory authorities (building control and fire Officer) in the form of a presentation of the CFD video files. A comprehensive CFD report that accompanied the main fire strategy report also included the full analysis. The statutory authorities agreed that the level of safety had been significantly enhanced by the provision of the smoke curtains. The fire engineered strategy resulted in design implications and benefits. The modelling techniques employed required intense discussions with all parties and the simulation techniques resulted in a time-intensive approval process. Clear benefits were achieved. The strategy fits the use and architectural design of the building, allowing for a higher degree of flexibility, a reduced number of stair cores and the outlining of options for means of escape strategy from the lecture theatre, while negating the need for smoke ventilation. In addition, the performance-based design has allowed for a reduction in the number of escape stairs within The Forum Southend-on- Sea, freeing up space and assisting in achieving a cost-efficient design Karl Wallasch is executive engineer at Hoare Lea Fire Engineering References 1. Approved Document B (Fire Safety) Volume 2: Buildings other than dwelling houses, BS 9999: Code of practice for fire safety in the design, management and use of buildings, October BR 187: External fire spread: Building separation and boundary distances, BRE, PD : The application of fire safety engineering principles to fire safety design of buildings: Part 6: Human factors. Life safety strategies. Occupant evacuation, behaviour and condition (Sub-system 6), BSI, CIBSE Guide E: Fire safety engineering, 3rd Edition, The Chartered Institution of Building Services Engineers, London, May Fire Dynamics Simulator (Version 5) User s Guide, NIST Special Publication , FDS Version 5.5, October Fire Dynamics Simulator (Version 5) Technical Reference Guide, NIST Special Publication , Volume 1: Mathematical Model, FDS Version 5.5, October April