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The principle of compartmentation does not necessarily mean following prescriptive guidance, says Andy Passington. Using progressive horizontal evacuation can lead to creative designs, while maintaining fire safety.
The use of compartments is a key element of the fire strategy for almost every building. Containing fire and smoke, protecting escape routes and enabling firefighters to access buildings are typical benefits of introducing compartment walls and floors into a design.
However, there have been many projects where the compartmentation recommended by prescriptive code guidance is at odds with the desire for architectural transparency and openness, and sometimes it also restricts the function of the building. There is therefore a balance to be achieved between the function and aesthetics of a building and its fire safety.
An approach which can meet all these needs is to use compartmentation as naturally as possible, and to open up areas of the building that would typically expect to be enclosed. By carefully integrating compartments with the ‘natural geometry’ of the building, it can be less intrusive and can allow the relaxation of enclosures in other parts of the building. This approach has its origins in healthcare design, but can be applied in all types of building.
An example of this approach is at the redevelopment of King’s Mill Hospital in Sutton-in-Ashfield, Nottinghamshire. The project includes both refurbishment and new build elements and is part of the Central Nottinghamshire modernisation of acute services. The existing facilities will be developed to create a single, unified hospital comprising 28 new wards, a new state-of-the-art diagnostic and treatment centre called the King’s Treatment Centre (KTC), a new emergency care and assessment centre with an out-of-hours GP service, and a dedicated women and children’s centre. Three T-shaped ward blocks, linked together over five floors, are located to the rear of the treatment centre and women and children’s centre. These two major new build elements are separated by a concourse approximately 200m in length.
The project architects are Swanke Hayden Connell, for the Skanska-Innisfree PFI Consortium. Arup Fire have been involved as fire engineers in the project since the early concept design at bidding stage, through to involvement in on-site issues as they have arisen. Continual consultation with the Trust and approval authorities has ensured that the unique design has been able to progress with minimal risk, despite containing major departures from code guidance.
Fresh thinking
This project has been the first major PFI healthcare project for the architects in the UK. From our perspective as fire engineers, it has been clear from the start that their approach to the design of the building – particularly the Kings Treatment Centre block – has been unhindered by the ‘healthcare design baggage’ which we sometimes encounter with designers who have been using the fire code guidance documents for many years. They have extensive experience of large commercial developments, and sought to combine this with the needs of a hospital. Their fresh approach to healthcare design, coupled with Skanska’s progressive construction approach, has challenged some of the fundamental concepts of the NHS Firecode.
This challenge to the basis of the NHS Firecode manifested itself most strongly in the design of the Kings Treatment Centre block at the front of the building. This block is spread over two storeys, increasing to three storeys as the site slopes down towards the south. The design aims to maximise the use of natural light by providing a series of ‘fingers’ of accommodation, each separated by a two or three storey void space. This form of building design presented the greatest challenges to the development of the fire strategy.
Guidance for the fire safety design of healthcare buildings is given in the NHS Firecode suite of Health Technical Memorandum documents. The treatment centre block was designed based on guidance given in HTM 81 Fire Precautions in New Hospitals, with fire engineered elements discussed and agreed as derogations from the code. Much of the guidance in this document is aimed at the design of large, acute healthcare facilities, and is mainly based around the movement of bed-ridden patients around the building, using progressive horizontal evacuation to move patients through lines of fire compartmentation away from the fire affected zone. This produces a policy of evacuating the compartment affected by the fire and then using a ‘defend in place’ approach to minimise the disruption to the operation of the hospital and reduce the necessity to evacuate patients vertically, either via evacuation lifts or by the stairs.
A key element of the ‘defend in place’ approach is to design the building so that each storey of the building forms a separate fire compartment, on the basis that it should only be necessary to evacuate a single storey of the building at any one time. The need for compartment floors was the central aspect of the HTM guidance that was challenged by the fire strategy, and underlying this challenge is an understanding of the nature of the building. By recognising that the operation and the type of occupants are very different to those at an acute healthcare facility, the applicability of some of the principles behind HTM 81 can be examined and questioned. As the building is a diagnostic and treatment centre, there are no bed-ridden patients nor wards, so the level of impairment to mobility is significantly lower than is assumed in the code. From this point of view, designing the building around the movement of beds is less vital than in the acute care areas of the hospital. While the strength of the guidance is that it is likely to produce a conservative solution, it does not particularly well address buildings such as the Kings Treatment Centre, where innovation is desired.
A conventional code based approach would require each floor to form a separate fire compartment. But the open ‘fingers’ which bring natural light into the building, are very much at odds with conventional healthcare design and the prescriptive guidance. To achieve compartment floors in the block, each of the two- or three-storey voids would have had to be completely enclosed with fire rated glazing. In addition, as each of the ‘fingers’ creates a dead end, a fire escape stair would be required at the end of each one.
HTM 81 recommends that each compartment is no more than 2000m2 in area. The concept for our strategy is to take this compartment size limit and split it over two or three storeys, using vertical compartment lines rather than horizontal. In this way, the evacuation of a single compartment would not affect any greater area than a conventional code-compliant solution. This splits the building into a series of vertical compartments, allowing open floors linking the storeys and removing the need for compartmentation between the floors.
Walkways
To address the issue of the dead ends and stairs in each finger, walkways linking the ends of the fingers were introduced. This greatly enhances the horizontal evacuation, allowing options for moving into adjacent compartments from all areas of the block. By providing these additional options for horizontal egress, the number of stairs required could be reduced. By extending the logic of initial horizontal evacuation, it became possible to provide a single stair in each compartment. These were moved into the voids and are fully open, designed to appear as accommodation stairs. The protection to the stairs is provided by the lines of compartmentation in the building – occupants would not use the stairs to evacuate the fire affected compartment, the stairs would only be used once occupants had already passed into an adjacent compartment.
Under prescriptive code guidance, a void which breaches a compartment is classified as an atrium. As such, in addition to a fire rated enclosure, it would be expected to be provided with automatic smoke control, which would involve designing either natural or mechanical extract at the top of the atrium, and make up air routes at the base – all of which would need to automatically opened or be activated by smoke detectors. An additional benefit to the removal of the compartment floors was that the void spaces between the fingers no longer breach these floors. So the design of the roof and facade of these spaces is greatly simplified. The roof is constructed from a Ethylene Tetra Fluoro Ethylene fabric – similar to that found at the Eden Project in Cornwall and more recently at the Olympic aquatic centre in Beijing – so the inclusion of automatic smoke control would have involved additional openable elements being incorporated into the design.
As the compartment lines run along the edge of the fingers, the design needed to ensure that fire would not spread across the voids. The compartment walls are therefore constructed from fire rated materials, including fire rated glazing in the windows. The prescriptive recommendation is that this glazing would be specified to provide both integrity and insulation from fire. But by carrying out an analysis of the radiation from the window panels, it was shown that the reduction in radiation from providing integrity-only glazing would not result in fire spreading across the voids. This meant a more cost effective solution, with greater flexibility available for the design team in the detailing of the glazing.
By adopting a fire engineering approach to the design of the building, it was possible to allow open floors, increased natural light and greater flexibility in the use of the spaces, along with a cost effective solution both in terms of capital cost and ongoing operational and maintenance costs. Working closely with the design team, the Trust and the approval authorities was essential throughout this process, to ensure that the design progressed with minimal risk and approval was granted on time. The result is a unique healthcare facility, freed from the restrictions of the prescriptive code guidance.
Artistic licence
The approach of using compartments to allow open escape stairs has also proved useful for other projects. For the Quad arts centre in Derby, the useful area of a relatively small footprint building was able to be maximised. The building consists of three storeys, with three cinema screens on the upper floors and gallery spaces below. By taking advantage of the natural geometry of the building and the inherent fire resistance of the cinema enclosures, it was possible to provide the building with two stairs, only one of which is protected in a conventional manner. Using egress assessments based on a number of scenarios, it was shown that the open stair could be used for evacuation for fires involving cinemas enclosures. The cinemas would shield the protected stair from a fire affecting the open stair, which links all stories of the building from the ground floor cafe.
Horizontal evacuation has also been extremely useful in recent education building projects. As enclosed stairs are acknowledged problem areas for bullying, designs which allow these to be open not only improve the natural lighting and aesthetics of the building, but also help prevent anti-social behaviour. Careful use of compartmentation and consideration of horizontal, scenario-based evacuation enabled the central stair in Stroud College to be used for egress while being fully open. Several schools have also been developed using this approach, including the Pathfinder School in Writhlington, which is currently being designed and is adopting horizontal evacuation and open stairs in each compartment.
These concepts are equally applicable to all types of buildings and we currently have designs using these ideas for sports training centres, museums and theatres. For these public buildings this approach has an additional, powerful benefit – that of providing a better alternative for the evacuation of people with impaired mobility. Such a person will require assistance to leave the upper storeys of a building, and will therefore need a protected refuge to wait for this assistance to arrive. The conventional approach is to provide a refuge within a protected escape stair enclosure. A single refuge in each stair may be appropriate for a building that may be expected to have a low number of disabled occupants, but it is arguable whether this is sufficient for larger public buildings. Progressive evacuation and compartmentation naturally provides much larger refuge spaces, and ones that feel less ‘tucked away’ and are more visible than a typical staircase refuge. For projects such as Derby Quad, the new Leicester Theatre, and a design for the new museum for the Mary Rose in Portsmouth, we are recognising that these buildings are likely to host groups of disabled occupant. In theatres and cinemas the screens and auditoria can act as refuges from fires in foyers, and vice versa. For museums such as the Mary Rose building, we are proposing that the compartments being provided to protect the irreplaceable contents of the building can also be used to protect evacuating occupants and provide large disabled refuges, hence allowing open stairs.
By recognising the benefits of compartmentation but using it to the advantage of the design, we can turn around the common perception that compartments ‘chop up’ buildings – instead we are using them to open up buildings, while maintaining safe environments for all occupants.
Andy Passingham is associate director at Arup Fire.
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The principle of compartmentation does not necessarily mean following prescriptive guidance, says Andy Passington. Using progressive horizontal evacuation can lead to creative designs, while maintaining fire safety.
The use of compartments is a key element of the fire strategy for almost every building. Containing fire and smoke, protecting escape routes and enabling firefighters to access buildings are typical benefits of introducing compartment walls and floors into a design.
However, there have been many projects where the compartmentation recommended by prescriptive code guidance is at odds with the desire for architectural transparency and openness, and sometimes it also restricts the function of the building. There is therefore a balance to be achieved between the function and aesthetics of a building and its fire safety.
An approach which can meet all these needs is to use compartmentation as naturally as possible, and to open up areas of the building that would typically expect to be enclosed. By carefully integrating compartments with the ‘natural geometry’ of the building, it can be less intrusive and can allow the relaxation of enclosures in other parts of the building. This approach has its origins in healthcare design, but can be applied in all types of building.
An example of this approach is at the redevelopment of King’s Mill Hospital in Sutton-in-Ashfield, Nottinghamshire. The project includes both refurbishment and new build elements and is part of the Central Nottinghamshire modernisation of acute services. The existing facilities will be developed to create a single, unified hospital comprising 28 new wards, a new state-of-the-art diagnostic and treatment centre called the King’s Treatment Centre (KTC), a new emergency care and assessment centre with an out-of-hours GP service, and a dedicated women and children’s centre. Three T-shaped ward blocks, linked together over five floors, are located to the rear of the treatment centre and women and children’s centre. These two major new build elements are separated by a concourse approximately 200m in length.
The project architects are Swanke Hayden Connell, for the Skanska-Innisfree PFI Consortium. Arup Fire have been involved as fire engineers in the project since the early concept design at bidding stage, through to involvement in on-site issues as they have arisen. Continual consultation with the Trust and approval authorities has ensured that the unique design has been able to progress with minimal risk, despite containing major departures from code guidance.
Fresh thinking
This project has been the first major PFI healthcare project for the architects in the UK. From our perspective as fire engineers, it has been clear from the start that their approach to the design of the building – particularly the Kings Treatment Centre block – has been unhindered by the ‘healthcare design baggage’ which we sometimes encounter with designers who have been using the fire code guidance documents for many years. They have extensive experience of large commercial developments, and sought to combine this with the needs of a hospital. Their fresh approach to healthcare design, coupled with Skanska’s progressive construction approach, has challenged some of the fundamental concepts of the NHS Firecode.
This challenge to the basis of the NHS Firecode manifested itself most strongly in the design of the Kings Treatment Centre block at the front of the building. This block is spread over two storeys, increasing to three storeys as the site slopes down towards the south. The design aims to maximise the use of natural light by providing a series of ‘fingers’ of accommodation, each separated by a two or three storey void space. This form of building design presented the greatest challenges to the development of the fire strategy.
Guidance for the fire safety design of healthcare buildings is given in the NHS Firecode suite of Health Technical Memorandum documents. The treatment centre block was designed based on guidance given in HTM 81 Fire Precautions in New Hospitals, with fire engineered elements discussed and agreed as derogations from the code. Much of the guidance in this document is aimed at the design of large, acute healthcare facilities, and is mainly based around the movement of bed-ridden patients around the building, using progressive horizontal evacuation to move patients through lines of fire compartmentation away from the fire affected zone. This produces a policy of evacuating the compartment affected by the fire and then using a ‘defend in place’ approach to minimise the disruption to the operation of the hospital and reduce the necessity to evacuate patients vertically, either via evacuation lifts or by the stairs.
A key element of the ‘defend in place’ approach is to design the building so that each storey of the building forms a separate fire compartment, on the basis that it should only be necessary to evacuate a single storey of the building at any one time. The need for compartment floors was the central aspect of the HTM guidance that was challenged by the fire strategy, and underlying this challenge is an understanding of the nature of the building. By recognising that the operation and the type of occupants are very different to those at an acute healthcare facility, the applicability of some of the principles behind HTM 81 can be examined and questioned. As the building is a diagnostic and treatment centre, there are no bed-ridden patients nor wards, so the level of impairment to mobility is significantly lower than is assumed in the code. From this point of view, designing the building around the movement of beds is less vital than in the acute care areas of the hospital. While the strength of the guidance is that it is likely to produce a conservative solution, it does not particularly well address buildings such as the Kings Treatment Centre, where innovation is desired.
A conventional code based approach would require each floor to form a separate fire compartment. But the open ‘fingers’ which bring natural light into the building, are very much at odds with conventional healthcare design and the prescriptive guidance. To achieve compartment floors in the block, each of the two- or three-storey voids would have had to be completely enclosed with fire rated glazing. In addition, as each of the ‘fingers’ creates a dead end, a fire escape stair would be required at the end of each one.
HTM 81 recommends that each compartment is no more than 2000m2 in area. The concept for our strategy is to take this compartment size limit and split it over two or three storeys, using vertical compartment lines rather than horizontal. In this way, the evacuation of a single compartment would not affect any greater area than a conventional code-compliant solution. This splits the building into a series of vertical compartments, allowing open floors linking the storeys and removing the need for compartmentation between the floors.
Walkways
To address the issue of the dead ends and stairs in each finger, walkways linking the ends of the fingers were introduced. This greatly enhances the horizontal evacuation, allowing options for moving into adjacent compartments from all areas of the block. By providing these additional options for horizontal egress, the number of stairs required could be reduced. By extending the logic of initial horizontal evacuation, it became possible to provide a single stair in each compartment. These were moved into the voids and are fully open, designed to appear as accommodation stairs. The protection to the stairs is provided by the lines of compartmentation in the building – occupants would not use the stairs to evacuate the fire affected compartment, the stairs would only be used once occupants had already passed into an adjacent compartment.
Under prescriptive code guidance, a void which breaches a compartment is classified as an atrium. As such, in addition to a fire rated enclosure, it would be expected to be provided with automatic smoke control, which would involve designing either natural or mechanical extract at the top of the atrium, and make up air routes at the base – all of which would need to automatically opened or be activated by smoke detectors. An additional benefit to the removal of the compartment floors was that the void spaces between the fingers no longer breach these floors. So the design of the roof and facade of these spaces is greatly simplified. The roof is constructed from a Ethylene Tetra Fluoro Ethylene fabric – similar to that found at the Eden Project in Cornwall and more recently at the Olympic aquatic centre in Beijing – so the inclusion of automatic smoke control would have involved additional openable elements being incorporated into the design.
As the compartment lines run along the edge of the fingers, the design needed to ensure that fire would not spread across the voids. The compartment walls are therefore constructed from fire rated materials, including fire rated glazing in the windows. The prescriptive recommendation is that this glazing would be specified to provide both integrity and insulation from fire. But by carrying out an analysis of the radiation from the window panels, it was shown that the reduction in radiation from providing integrity-only glazing would not result in fire spreading across the voids. This meant a more cost effective solution, with greater flexibility available for the design team in the detailing of the glazing.
By adopting a fire engineering approach to the design of the building, it was possible to allow open floors, increased natural light and greater flexibility in the use of the spaces, along with a cost effective solution both in terms of capital cost and ongoing operational and maintenance costs. Working closely with the design team, the Trust and the approval authorities was essential throughout this process, to ensure that the design progressed with minimal risk and approval was granted on time. The result is a unique healthcare facility, freed from the restrictions of the prescriptive code guidance.
Artistic licence
The approach of using compartments to allow open escape stairs has also proved useful for other projects. For the Quad arts centre in Derby, the useful area of a relatively small footprint building was able to be maximised. The building consists of three storeys, with three cinema screens on the upper floors and gallery spaces below. By taking advantage of the natural geometry of the building and the inherent fire resistance of the cinema enclosures, it was possible to provide the building with two stairs, only one of which is protected in a conventional manner. Using egress assessments based on a number of scenarios, it was shown that the open stair could be used for evacuation for fires involving cinemas enclosures. The cinemas would shield the protected stair from a fire affecting the open stair, which links all stories of the building from the ground floor cafe.
Horizontal evacuation has also been extremely useful in recent education building projects. As enclosed stairs are acknowledged problem areas for bullying, designs which allow these to be open not only improve the natural lighting and aesthetics of the building, but also help prevent anti-social behaviour. Careful use of compartmentation and consideration of horizontal, scenario-based evacuation enabled the central stair in Stroud College to be used for egress while being fully open. Several schools have also been developed using this approach, including the Pathfinder School in Writhlington, which is currently being designed and is adopting horizontal evacuation and open stairs in each compartment.
These concepts are equally applicable to all types of buildings and we currently have designs using these ideas for sports training centres, museums and theatres. For these public buildings this approach has an additional, powerful benefit – that of providing a better alternative for the evacuation of people with impaired mobility. Such a person will require assistance to leave the upper storeys of a building, and will therefore need a protected refuge to wait for this assistance to arrive. The conventional approach is to provide a refuge within a protected escape stair enclosure. A single refuge in each stair may be appropriate for a building that may be expected to have a low number of disabled occupants, but it is arguable whether this is sufficient for larger public buildings. Progressive evacuation and compartmentation naturally provides much larger refuge spaces, and ones that feel less ‘tucked away’ and are more visible than a typical staircase refuge. For projects such as Derby Quad, the new Leicester Theatre, and a design for the new museum for the Mary Rose in Portsmouth, we are recognising that these buildings are likely to host groups of disabled occupant. In theatres and cinemas the screens and auditoria can act as refuges from fires in foyers, and vice versa. For museums such as the Mary Rose building, we are proposing that the compartments being provided to protect the irreplaceable contents of the building can also be used to protect evacuating occupants and provide large disabled refuges, hence allowing open stairs.
By recognising the benefits of compartmentation but using it to the advantage of the design, we can turn around the common perception that compartments ‘chop up’ buildings – instead we are using them to open up buildings, while maintaining safe environments for all occupants.
Andy Passingham is associate director at Arup Fire.