By Karl Wallasch, Foivos Giorgallidis. The construction output in the United Kingdom is more than £110 billion per annum and contributes to 7% of gross domestic product (GDP) and approximately 60% of construction output in the UK is new build, whilst 40% is refurbishment and maintenance . In London, due to its history and present city structure, as well as the amount of existing building stocks and existence of listed building system, refurbishment and change of use developments are common. Design teams can face unique constraints and challenges in the design and construction process of refurbishments including change of use, extensions, and restrictions due to listing of buildings or building parts.
These changes to an existing building can create significant implications and changes to the existing fire safety strategy. In addition, the application of current fire safety standard guidance can be difficult – if not impossible – to apply. However, in these situations, the use of modern fire engineering techniques can assist the design team and client to develop safe and robust fire safety strategies meeting the regulator’s requirements while still considering the unique constraints of an existing building. Furthermore, the use of fire engineering an provide designers and end-users with a better and more detailed understanding of the level of fire safety as well as future flexibility for the building.
This article outlines how modern and innovative fire engineering techniques have been applied to the change of use and extension of an existing building into a modern office in London: The Department Store in Brixton, the new headquarter for architectural practice Squire and Partners. This article will outline the history of the building, the client’s design aspiration and the key fire engineering solutions that have been applied where compliance with standard guidance could not be met. The article also makes reference to relevant regulations in the UK in relation to the fire safety, and also describes how the fire safety strategy principles have been implemented into the client’s Fire Risk Assessment and management plan.
The article was published in FeuerTRUTZ International, issue 1.2018 (January 2018).
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The Department Store
The Bon Marche department store was built in 1876 by James Smith and was the first steel framed building in the UK. The original owner was inspired by the original Bon Marche (France) and wanted to establish Brixton as a shopping destination. It was used as a retail building for five decades after which it was sold in 1955 and converted into offices. The Bon Marche was used by a variety of occupiers until 2012 when the site fell vacant and subject to squatters . In 2015 architectural practice Squire and Partners made the decision to purchase the property and convert the building into a modern office building .
The client’s aspiration
The Department Store in South London has been restored, refurbished and extended to accommodate a new office, a members club on a new top floor level, flexible exhibition/conference space, several individual retail units as well as housing an independent restaurant.
The office comprises 4,767m2 of design studio including a new social rooftop space expressed as a series of pavilions, a staff café, gallery/seminar space, model shop and facilities for staff including cycle storage, showers and a landscaped garden courtyard. Also a bar/restaurant is located on the new fourth floor. The office demise is served by three existing means of escape stairs: i.e. one internal and two external. The premises comprises of four levels above ground (three existing and one new floor level), ground floor and a single basement level.
As well as the escape stairs, the existing building included compartment floors and sprinkle protection. The new concept was based on adding a new floor level, removing sprinkler protection, removing compartment floors and introducing voids throughout all office levels to create connections from basement level up to upper floor levels.
Fire safety regulations in the UK
In the UK any building work which is intended to be conducted requires a Building Regulation  application to be submitted. The key building work includes an erection or extension of a building, material alteration, the insertion of insulating material into the cavity wall of a building etc. The Department Store included the erection of an additional floor and a material alteration and as a result a fire safety strategy was required to support a Building Regulations submission and a consultation with the Approving Authorities (Approved Inspector and local Fire Brigade).
The building was subject to the requirements of the Building Regulations 2010 and was necessary to meet the requirements of Schedule 1 of the Regulations relating to the following:
- B1 (Means of warning and escape)
- B2 (Internal fire spread – linings)
- B3 (Internal fire spread – structure)
- B4 (External fire spread)
- B5 (Access and facilities for fire service).
The fire safety strategy concept has been developed in close working relation with the architects, engineers and the Approved Inspector JMP Partnership. The fire safety concept developed included the use of fire engineering principles to allow a deviation from standard building guidance (Approved Document B – ADB ) as follows:
- Develop a fire safety strategy for a building which was originally used as a department store i.e. change of use.
- Meet the client’s design aspiration of an open office by keeping significant design features of the historical building.
- Develop a unique means of escape strategy (escape passing voids, use of existing external fire escape stairs) and considering future flexibility.
- Allow increased occupancy load in each office floor and the member’s club on top floor level.
- Use of evacuation modelling to understand overall evacuation time.
- Omitting of compartment floors and introduction of voids (implications on internal and external fire spread).
- Removal of existing sprinkler system.
- Overall fire alarm and detection; and evacuation strategy for all individual users on the entire site.
Generally, in England and Wales Approved Documents are available, providing recommendations for engineers to design the so called “code compliant building” . By following those recommendations the design will meet the functional requirements as outlined in the Building Regulations and therefore the building should gain compliance certification.
However, the Approved Documents are intended to provide guidance for some of the more common building situations, and the regulators recognise that there are also alternative ways of achieving compliance.
With respect to building works in an existing building, Regulation 4 Paragraph (3) of the Building Regulations states that that building work shall be carried out so that it complies with the applicable requirements of Schedule 1 or, where it did not comply with any such requirement, is no more unsatisfactory in relation to that requirement than before the work was carried out. It simply states that if the additional works are not worsening the existing arrangements then no addition fire measures are required. Regulation 4 is not applicable when a change of use is proposed.
Although, it is recognized that ADB is intended to provide guidance for more common buildings, it should be pointed out that ADB acknowledges that the guidance documents intended specifically for assessing fire safety in existing buildings will often include provisions which are less onerous than those set out on ADB which is more applicable to new buildings (paragraph 0.21 Alternative Approaches). As such ADB is unlikely to be appropriate for use, where building work is proposed.
Alternative solutions are acceptable, provided that compliance with the functional requirements of the Building Regulations can be demonstrated. For complex buildings it is a common practice to deviate from the standard guidance documents when adopting a fire engineering design as modern buildings often cannot follow the standard guidance.
ADB makes reference to BS7974  (paragraph 0.31 Fire Safety Engineering in ADB), a standard related to the fire safety engineering in buildings and supporting published documents which provides a framework and guidance on the design and assessment of fire safety measures in buildings. BS 7974 allows fire engineers to develop a fire safety strategy based on first principles of fire engineering deviating from the “code compliant design” allowing an innovative design.
Key fire safety features
From the very start it was clear that the scheme would provide significant challenges to the fire engineers due to it being an existing building and because of the proposed innovative architectural design. Hoare Lea was appointed at an early start to assist the architectural design team to overcome those challenges by using modern fire engineering techniques deviating from standard building regulations to achieve a robust and safe design without restraining the freedom and flexibility of the architectural design.
Developing a fire safety strategy for existing buildings is considered to be challenging due to the physical constrains and restrictions of the building geometry and materials. Available solutions can be limited and the fire engineers need to work closely with the design team to achieve the optimum design.
There was no document outlining the fire safety strategy for the existing building, the fire safety principles (e.g. compartmentation, means of escape strategy) or fire safety system (fire detection, sprinkler system etc.). The Department store was designed over a century ago and during its lifetime has undergone some building works and changes. At the same time, fire safety regulations have been developed and changed. As such, to fully understand how the existing building would behave in the event of a fire a site visit was arranged to understand the active and passive fire safety measures by conducting a visual site survey.
Means of escape
In mixed use schemes with multiple tenants the type of evacuation strategy needs to be considered. A simultaneous evacuation was proposed for the office demise, the bar on fourth floor and the adjacent restaurant at ground floor. This was due to the shared means of escape routes among the aforementioned areas. The remaining units were designed to adopt a “stay put” strategy based on the high degree of compartmentation with the office demise and individual evacuation strategy.
A key fire safety parameter was to define the maximum permitted occupancy of the building and different areas. In new buildings, it is a common practice to size the stairs based on the proposed design occupancy while in existing buildings the stairs with fixed widths and exit doors can define the maximum population of the building.
The permitted maximum population should be based on evenly distributed population. This is because as the stair capacity values recommendation in ADB are applicable to an evenly distributed population. In the Department Store, a detailed evacuation assessment was carried out analyzing various scenarios: for example during daytime, and during the evening when events take place in the bar on the fourth floor and/or at basement level etc. Figure 6 outlines the ground floor level and highlights means of escape stairs and exit provisions.
Following the standard guidance, external stairs are generally recommended for occupants who are awake and familiar with the premises. However, the new top floor of the Department Store includes a bar (that serves alcohol) open to members of the public. Therefore the occupancy is likely to be unfamiliar. External escape stairs are not recommended for members of public and, therefore, the bar was licensed to members only who can accompany three members of the public.
One reason why external stairs are not recommended is due to the adverse weather conditions. Therefore a trace heating system was proposed in order to protect at least one of the external stairs from weather conditions.
Under the guidance of ADB means of escape via external escape stairs in recommended only if there is at least one internal escape stair. Any part of the external envelope of the building within 1800 mm should be fire rated.
Disable refuge points
In accordance with ADB every stair core should be provided with a disabled refuge point to assist the evacuation of mobility impaired persons at each storey exit with minimum dimension of 900 mm by 1400 mm. It proved to be a design challenge to provide a protected lobby to each stair. One disabled refuge point was provided within the internal stair core at each floor level. Rather than providing a protected lobby in front of each external stair core, the meeting room adjacent to the stair was provided with fire resting. This meant it could function as a refuge point and, in case of not being available, a second refuge point was provided within the office floor plate near the second external stair core.
External fire spread
The proposed building works (involving removing the existing sprinkler system and creating open voids to link various levels) worsened the situation in terms of external fire spread. A sprinkler system has the ability to limit the fire size and radiation and therefore reduces the risk of internal and external fire spread. Buildings provided with compartment floors have the benefit that only one floor is affected by a fire and therefore radiation and risk of fire spread to adjacent buildings is lower.
A detailed external fire spread assessment was carried out to assess whether a compartment floor or fire resistant glazing were required for the new design. Due to voids, the façade height radiating was considered to be too large. Therefore it was proposed that rather than providing fire resistant glazing, the new additional floor would be designed as a compartment floor as shown in Figure 8.
Large and open spaces are currently an architectural design trend in office buildings. Similarly, Squire and Partners’ aim was to provide a large open plan office with very limited internal subdivision or compartmentation.
In areas where compartmentation was required fire curtains were proposed to meet the client’s design aspiration.
Only one compartment floor is provided to separate the existing floor from the new floor level, however, this was required due to an external fire spread as outlined above.
Base build strategy for adjacent units
Another challenge was to design the base build fire strategy for the neighboring retail units. During the design stage the client was exploring various potential tenancy agreements. Thus the fire engineers assisted to meet the demands of potential future tenants and explore flexibility in terms of the tenant use, size, design population, single or double levels etc.
A step beyond the fire strategy
In England and Wales, Article 9 of the Regulatory Reform (Fire Safety) Order 2005 (the “Fire Safety Order”)  requires that the responsible person, on whom the Fire Safety Order imposes requirements, should provide a suitable and sufficient assessment of the risks to which relevant persons are exposed, for the purpose of identifying the general fire precautions to be taken to comply with the requirements and prohibitions imposed under the Fire Safety Order. For the purpose of the Fire Safety Order, “relevant persons” are any person who is, or may be, lawfully on the premises and also any person in the immediate vicinity of the premises who is at risk from a fire in the premises, other than fire-fighters at the time of a fire as described in Part 1 of the “Fire Safety Order”.
Normally a specialist fire risk assessor undertakes the risk assessment for a premises. Nevertheless, in this case the client decided to appoint the fire engineers who developed the strategy to undertake the fire risk assessment. The rationale behind this decision was that fact that the fire engineers who had been involved from the early stages of the project would be more suitable to undertake that task as they were fully aware of the fire engineered fire safety strategy and could avoid any misinterpretation of the fire safety defined. Due to the complexity of the means of escape arrangements and the fact that there are multiple users on site, the main finding of the risk assessment was that a robust management plan is required to be developed.
There are elements of the fire strategy which depend on the successful implementation of the management plan. The management plan includes regular fire drills, trained fire marshals, and informing new starters about the escape routes of the premises. For example on the top floor where occupants are likely to be unfamiliar with the premises and alcohol is served. Also, an automatic detection and alarm system was used as part of the mitigation measures providing early detection and alarm in the event of a fire.
The refurbishment of an existing building, changing the original use, extending and the application of current fire safety standard guidance to existing buildings can result in a challenge for fire engineers. Using the project example of the refurbishment of the Department Store, this article shows how fire engineering techniques are a suitable tool to develop a robust fire safety strategy for an existing building. In this case, although the building was built over a century ago and its use has changed during its lifetime, the new proposed use was allowed by using fire engineering where compliance with standard guidance was not possible.
The architectural vision of the owner was to create something unique combining the historic importance of this site along with a modern, vibrant office environment for an architectural practice and allow for future flexibility. This vision was achieved.
A key parameter for achieving this was the regular communication with both the design team and the approving authorities from the early stages of the design.
Karl Wallasch (Associate Director, Dipl.-Ing., CEng) is a Fire Engineer working in Hoare Lea’s Fire Engineering team in London. Karl studied structural engineering at the Bauhaus University in Weimar, Germany. He has working experience in the UK, Europe and further afield.
Foivos Giorgallidis (BSc, MSc, AlFireE) is a Fire Engineer working in Hoare Lea’s Engineering team in London since 2015. Foivos graduated from University of Cyprus obtaining a degree in Civil and Environmental Engineering in 2013. Foivos also holds a Master’s degree from University of Leeds in Fire and Explosion Engineering, graduating with Distinction.
 Government Construction Strategy, Cabinet Office, May 2011
 Website The Department Store: www.thedepartmentstore.com/history
 Website Squire and Partners: www.squireandpartners.com
 Her Majesty’s Stationery Office, The Building Regulations 2010, England and Wales. The Stationary Office.
 Department for Communities and Local Government (DCLG), Approved Document B: Fire Safety - Volume 2: Buildings Other Than Dwellinghouses, 2013 Edition, vol. 2. NBS, 2006.
 Website Approved Document B: https://www.gov.uk/government/publications/fire-safety-approved-document-b
 British Standards Institution (BSI), PD 7974-0: Application of fire safety engineering principles to the design of buildings - Part 0: Guide to design framework and fire safety engineering procedures. BSI Global, 2002.
 UK Government, Regulatory Reform (Fire Safety) Order 2005. 2005
The article was published in FeuerTRUTZ International, issue 1.2018 (January 2018).
More information about eMagazine FeuerTRUTZ International