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Victoria Square is a large new shopping development in the centre of Belfast which is due to be opened in early 2008. As it is not a sealed environment, conventional fire safety codes were not appropriate, so a fire engineered approach was adopted, writes Jon Pagan.
The Victoria Square, belfast shopping development is different from conventional shopping centres in that it is not a sealed, environmentally conditioned environment. The malls are covered by an over-sailing roof which is not sealed, and is primarily intended to keep out rain and to reduce wind. As such, the development is not a typical shopping centre and so conventional fire safety design codes for such premises would not have been appropriate.
A fire strategy for the site was therefore developed, based on functional fire safety objectives. Belfast Building Control and the Northern Ireland Fire and Rescue Service were involved throughout the design, and were very supportive in this innovative approach to fire safety.
The development contains a wide variety of different areas, including:
– a two-storey shopping mall on the lower and upper ground floors
– two additional floors housing a food court on the 1st and 2nd floor levels
– an eight screen cinema on the 2nd floor level
– a ‘feature’ dome with viewing platforms
– a two-storey basement car park and
– two residential developments.
A detailed fire strategy was developed in order to describe the fire safety design for the site. The most complex area of the strategy was the behaviour of smoke within the main mall areas, so extensive smoke modelling was carried out to ensure that smoke did not compromise safety.
In addition, fire safety engineering techniques were used in the following areas:
– structural fire protection analysis of the exposed steel structure within the feature dome
– structural fire protection analysis of the external balconies for the residential apartments
– radiation analysis of the risk of external fire spread from various locations; and
– evacuation analysis from all areas.
Sprinklers were provided throughout the development.
Smoke flow
One of the fundamental aspects of the development was in relation to the behaviour of smoke within the mall areas. In a conventional shopping centre, these are fully enclosed and a smoke ventilation system is provided at a high level. This would be impossible to achieve at Victoria Square project as the roof is primarily a rain screen. But under standard guidance (i.e. BS 5588: Part 10) by providing a roof at all it would mean the entire development should be designed as a conventional shopping centre!
So an alternative approach – based on extensive CFD smoke flow analysis within the centre – was taken. The smoke modelling investigated the effect of fires in a variety of locations, allowing smoke to flow out of the shop units into the malls. Fires from ‘kiosks’ within the malls were also modelled.
The effect of various wind conditions were included. At an early stage, wind tunnel testing had been carried out for environmental purposes. Though such testing was not in itself suitable for smoke flow modelling, the outputs of the wind tunnel tests, as well as meteorological data for the area, were included as inputs for the CFD analysis.
The analysis showed that the conditions within the public areas were always tenable in any environmental conditions, for a very long period of time. As such, the malls could effectively be treated as a place of safety. The exceptions to this are the high level viewing platforms within the glazed dome.
Dome truths
The dome – 35m in diameter and 45m high – is an essential architectural feature of the development and there are platforms inside it at various levels, including one viewing platform at high level. This top platform is accessed by a single open spiral staircase and a lift as shown in in the picture above.
The smoke models demonstrated that if a fire occurred inside the dome, the smoke would flow to a high level in that area. Because of the height of the rise of the smoke, it would be relatively thin and diffuse and would not form a defined smoke layer. Anyone on the top platform would therefore find that the smoke would gradually increase in density within that area.
Automatic smoke ventilation was provided at high level within the dome to reduce the rate of smoke build-up. The rate of increase of smoke density was compared with an evacuation analysis of the top platform. The analysis included evacuation of able-bodied occupants using the stair and mobility-impaired people via the lift. This showed that there would be more than sufficient time to evacuate the top platform before the conditions became untenable. This was therefore sufficient to demonstrate that the proposed design was safe.
Structural fire engineering
Structural fire protection analyses were carried out in two parts of the development: at the dome platforms structure and at the residential access balconies.
The dome viewing platforms are supported by a tripod structure, consisting of three inclined columns and the adjacent lift structure. As most of the structure is remote from any major fire load, it should need less fire protection than other structures. So a structural fire protection analysis was carried out using BS 7974 and Eurocodes. This analysis:
– predicted the ‘worst case’ fire that could occur adjacent to the structure
– predicted the size and temperature of the flames that could impact on the structure
– predicted the maximum temperature reached by the steel and hence the residual strength that the steel would retain and
– determined from discussions with the structural engineers whether the remaining strength was sufficient to maintain the stability of the structure.
Using this technique, it was possible to demonstrate that certain parts of the structure would need 30 minutes’ fire protection, but that other areas would not need any fire protection. The residential blocks are accessed from external walkways located against the facade and are supported by a steel frame structure. Because the structure is external, it would be affected by a fire to a much lesser extent than the internal structure. A structural fire protection analysis was conducted, based on flames projecting from apartment openings and engulfing part of the structure. This demonstrated significant reductions in the amount of fire protection required, while also guaranteeing the safety of occupants and of firefighters.
Radiation analysis
In a number of locations there are glazed elevations that face onto other adjacent buildings, either within the development or on an adjacent site. Some of the buildings within the site have large open compartments spread over several levels. Conventional techniques such as the ‘enclosing rectangles method’ would have resulted in either extensive fire rating of the facades or significant compartmentation within the units, which would have compromised the tenants’ flexibility.
Detailed radiation analyses of the elevations were therefore carried out, which demonstrated that there were no major problems and the risk of external fire spread was extremely low. This demonstrated that it was unnecessary to provide extensive sub-compartmentation or fire rating of the external walls.
Because of the large size of the development and the complexity of the design, as well as the interactions between occupancies, an evacuation analysis was carried out. The analysis included the development of a detailed evacuation ’cause and effect’ matrix based on the overall fire strategy that had been developed, in terms of compartmentation, space separation and the results of the CFD smoke modelling. The matrix was used to determine which areas of the design were to be evacuated together, and which could continue to operate, depending on the location of the fire.
Analyses were also carried out to determine the number and width of escape routes, especially from the levels that do not have direct access to the mall areas.
Summary
The Victoria Square development is a new type of retail development. The decision was made at an early stage to design the development using a functional fire engineering approach. This resulted in an extremely safe design which meet the needs of the client and tenants, as well as achieving major cost savings in a wide variety of areas.
Jon Pagan is a director at bodycote warrington. More on the Victoria Square development can be found www.victoriasquare.com
[
Victoria Square is a large new shopping development in the centre of Belfast which is due to be opened in early 2008. As it is not a sealed environment, conventional fire safety codes were not appropriate, so a fire engineered approach was adopted, writes Jon Pagan.
The Victoria Square, belfast shopping development is different from conventional shopping centres in that it is not a sealed, environmentally conditioned environment. The malls are covered by an over-sailing roof which is not sealed, and is primarily intended to keep out rain and to reduce wind. As such, the development is not a typical shopping centre and so conventional fire safety design codes for such premises would not have been appropriate.
A fire strategy for the site was therefore developed, based on functional fire safety objectives. Belfast Building Control and the Northern Ireland Fire and Rescue Service were involved throughout the design, and were very supportive in this innovative approach to fire safety.
The development contains a wide variety of different areas, including:
• a two-storey shopping mall on the lower and upper ground floors
• two additional floors housing a food court on the 1st and 2nd floor levels
• an eight screen cinema on the 2nd floor level
• a ‘feature’ dome with viewing platforms
• a two-storey basement car park and
• two residential developments.
A detailed fire strategy was developed in order to describe the fire safety design for the site. The most complex area of the strategy was the behaviour of smoke within the main mall areas, so extensive smoke modelling was carried out to ensure that smoke did not compromise safety.
In addition, fire safety engineering techniques were used in the following areas:
• structural fire protection analysis of the exposed steel structure within the feature dome
• structural fire protection analysis of the external balconies for the residential apartments
• radiation analysis of the risk of external fire spread from various locations; and
• evacuation analysis from all areas.
Sprinklers were provided throughout the development.
Smoke flow
One of the fundamental aspects of the development was in relation to the behaviour of smoke within the mall areas. In a conventional shopping centre, these are fully enclosed and a smoke ventilation system is provided at a high level. This would be impossible to achieve at Victoria Square project as the roof is primarily a rain screen. But under standard guidance (i.e. BS 5588: Part 10) by providing a roof at all it would mean the entire development should be designed as a conventional shopping centre!
So an alternative approach – based on extensive CFD smoke flow analysis within the centre – was taken. The smoke modelling investigated the effect of fires in a variety of locations, allowing smoke to flow out of the shop units into the malls. Fires from ‘kiosks’ within the malls were also modelled.
The effect of various wind conditions were included. At an early stage, wind tunnel testing had been carried out for environmental purposes. Though such testing was not in itself suitable for smoke flow modelling, the outputs of the wind tunnel tests, as well as meteorological data for the area, were included as inputs for the CFD analysis.
The analysis showed that the conditions within the public areas were always tenable in any environmental conditions, for a very long period of time. As such, the malls could effectively be treated as a place of safety. The exceptions to this are the high level viewing platforms within the glazed dome.
Dome truths
The dome – 35m in diameter and 45m high – is an essential architectural feature of the development and there are platforms inside it at various levels, including one viewing platform at high level. This top platform is accessed by a single open spiral staircase and a lift as shown in in the picture above.
The smoke models demonstrated that if a fire occurred inside the dome, the smoke would flow to a high level in that area. Because of the height of the rise of the smoke, it would be relatively thin and diffuse and would not form a defined smoke layer. Anyone on the top platform would therefore find that the smoke would gradually increase in density within that area.
Automatic smoke ventilation was provided at high level within the dome to reduce the rate of smoke build-up. The rate of increase of smoke density was compared with an evacuation analysis of the top platform. The analysis included evacuation of able-bodied occupants using the stair and mobility-impaired people via the lift. This showed that there would be more than sufficient time to evacuate the top platform before the conditions became untenable. This was therefore sufficient to demonstrate that the proposed design was safe.
Structural fire engineering
Structural fire protection analyses were carried out in two parts of the development: at the dome platforms structure and at the residential access balconies.
The dome viewing platforms are supported by a tripod structure, consisting of three inclined columns and the adjacent lift structure. As most of the structure is remote from any major fire load, it should need less fire protection than other structures. So a structural fire protection analysis was carried out using BS 7974 and Eurocodes. This analysis:
• predicted the ‘worst case’ fire that could occur adjacent to the structure
• predicted the size and temperature of the flames that could impact on the structure
• predicted the maximum temperature reached by the steel and hence the residual strength that the steel would retain and
• determined from discussions with the structural engineers whether the remaining strength was sufficient to maintain the stability of the structure.
Using this technique, it was possible to demonstrate that certain parts of the structure would need 30 minutes’ fire protection, but that other areas would not need any fire protection. The residential blocks are accessed from external walkways located against the facade and are supported by a steel frame structure. Because the structure is external, it would be affected by a fire to a much lesser extent than the internal structure. A structural fire protection analysis was conducted, based on flames projecting from apartment openings and engulfing part of the structure. This demonstrated significant reductions in the amount of fire protection required, while also guaranteeing the safety of occupants and of firefighters.
Radiation analysis
In a number of locations there are glazed elevations that face onto other adjacent buildings, either within the development or on an adjacent site. Some of the buildings within the site have large open compartments spread over several levels. Conventional techniques such as the ‘enclosing rectangles method’ would have resulted in either extensive fire rating of the facades or significant compartmentation within the units, which would have compromised the tenants’ flexibility.
Detailed radiation analyses of the elevations were therefore carried out, which demonstrated that there were no major problems and the risk of external fire spread was extremely low. This demonstrated that it was unnecessary to provide extensive sub-compartmentation or fire rating of the external walls.
Because of the large size of the development and the complexity of the design, as well as the interactions between occupancies, an evacuation analysis was carried out. The analysis included the development of a detailed evacuation ‘cause and effect’ matrix based on the overall fire strategy that had been developed, in terms of compartmentation, space separation and the results of the CFD smoke modelling. The matrix was used to determine which areas of the design were to be evacuated together, and which could continue to operate, depending on the location of the fire.
Analyses were also carried out to determine the number and width of escape routes, especially from the levels that do not have direct access to the mall areas.
Summary
The Victoria Square development is a new type of retail development. The decision was made at an early stage to design the development using a functional fire engineering approach. This resulted in an extremely safe design which meet the needs of the client and tenants, as well as achieving major cost savings in a wide variety of areas.
Jon Pagan is a director at bodycote warrington. More on the Victoria Square development can be found www.victoriasquare.com