Buy CEN/TR SMOKE AND HEAT CONTROL SYSTEMS – PART 5 : GUIDELINES ON FUNCTIONAL RECOMMENDATIONS AND CALCULATION. exhaust ventilation systems (published as CR ). Part 6: Specification for pressure differential systems — Kits. Part 7: Smoke control. Design approaches for smoke control. in atrium buildings. G 0 Hansell*, BSc, PhD, CEng, MCIBSE, AlFireE H P Morgan, BSc, CPhys, MlnstP, AlFireE.
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Please help us to share our service with your friends. I11 Page iv Chapter 7 Atrium smoke layer temperature 44 Chapter 8 Additional design factors Atrium roof-mounted sprinkler systems Smoke detection systems in the atrium Pressurisation of stairwells and lobbies Air-conditioned atria Channelling screens and hybrid systems Wind-sensing devices and natural depressurisation 46 46 46 46 46 46 47 Appendix A Case history 48 Appendix B Users guide to BRE spill plume calculations Introduction Scenarios and assumptions Outline of procedure Detailed procedure 49 49 49 50 50 Nomenclature used in Appendix B 54 Acknowledgements 55 References 55 I 1!.
This Report is the culmination of a long-running collaborative project between the Fire Research Station of the Building Research Establishment and Colt International Limited on aspects of smoke movement and its control in atrium buildings.
It is based on both the latest scientific knowledge and practical experience of smoke movement and control systems, and has been prepared under the overall supervision of the Fire Research Station.
T h e present Report is intended to serve the designers of smoke control systems for atrium buildings in the same way that the earlier Building Research Establishment Report, Design principles f o r smoke ventilation in enclosed shopping centres, has served designers of smoke ventilation systems in shopping malls.
As such, those graphs and tables it contains which are relevant to a particular design of building can be applied directly to that building; or the formulae cited can be used to apply the work to a broader range of circumstances.
The Report does not exclude the options of using alternative methods where they are appropriate, or of using new techniques such as computational fluid dynamics as they are developed and validated. The list of nomenclature used in Appendix B is given on page V VI “wind W WB X Y P A ADB e B 01 P PO Volumetric flow rate of gases m3s-1 Volumetric flow rate of gases from a reservoir m3s-I Design wind velocity ms-‘ Width of vertical opening m Width of balcony distance from vertical opening to front edge of balcony m Height from the base of the smoke layer to the neutral pressure plane m Height from the base of the fire to the smoke layer immediately above m Coefficient in critical exhaust rate equation kgrnp3 Empirical height of virtual source below a balcony edge m Additional smoke depth due to local deepening m Temperature rise above ambient of smoky gases “C Temperature rise above ambient of smoky gases under a balcony “C Temperature rise above ambient of smoky gases in a reservoir “C Temperature rise above ambient of smoky gases in a vertical opening “C Density of gases kgm-3 Density of ambient air kgmW3 vii.
Introduction This Report is intended to assist designers of smoke ventilation systems in atrium buildings. Most of the methods advocated are the outcome of research into smoke movement and control at the Fire Research Station FRSbut also take into account experience gained and ideas developed whilst the authors and their colleagues have discussed many proposed schemes with interested parties. The primary purpose of the Report is to summarise in a readily usable form the design advice available from FRS at the time of its preparation.
As such, it does. However, the majority of these deaths occur in domestic premises. This implies that the life-safety measures required by legislation for most public and commercial buildings have been effective on the whole. Fire safety in buildings must in the UK conform to the relevant regulations guidance for England and Wales is given in Approved Document B2.
The principal objective of these regulations is to safeguard life by: Means of escape in case of fire was first introduced to the Building Regulations for England and Wales in The design of structural compartmentation and separation has been largely empirical, and the concepts gradually refined and enhanced in such a way that the Building Regulations now cover primarily life safety and the protection of means of escape.
It is necessary to consider four major aspects of buildings – purpose, size, separation and resistance to fire – to promote safe design. Social and technical changes have led to changes in building environments which incorporate new or revived building forms and the use of innovative construction techniques and new synthetic materials.
The buildings adopting these changes often have included within their design large spaces or voids, often integrated with many of the storeys.
These large spaces have been described as malls, atria, arcades and lightwells. The original atrium was an entrance hall in a Roman house and was one of the most important rooms in the building. The concept of this space has evolved architecturally over 12101-55 past few hundred years and now applies to structures much larger than the typical Roman house.
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Atria today are designed as undivided volumes within a structure, intending to create visually and spacially an ideal external environment -indoors6. In Roman times the control of any smoke and hot gases that may have issued from a fire in a room adjacent to the atrium was likely to have been a simple matter.
Modern atrium buildings tend to contain large quantities of combustible material and often have open-plan layouts which increase the risk of the spread of fire.
The populations within such buildings are also greater; hence there has been a substantial increase in the number of people to be protected and evacuated in an emergency. Modern atrium buildings are usually designed with the atrium as a feature which can be appreciated from within the adjacent rooms. In conventional multi-storey structures there is always the possibility of fire-spread up the outside of the building, with flames issuing from one room and affecting the floors above.
Recent examples of this mode of fire-spread have been an office block in Siio Paulo7 and the Villiers building in London. If the escape facilities from the various rooms are of a suitable standard and segregated from other compartments as required in the UKthere should not in theory be any serious hazard to life safety in this fire condition.
It is only when the means of escape are inadequate or the parameters dictating their design are violated, that the loss of life may occur.
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Hence there is an increased risk to other levels of the entry of smoke, toxic gases and possibljl flames from a fire. Recent experience of fires in atrium buildings in the has shown the problem of flame travel internally through the atrium to be minor in comparison to that of hot and toxic gases accumulating and building down in the atrium – spreading throughout the ej and affecting escape routes. Thus there appears to be a need for a properly designed smoke control system in atrium buildings.
The ideal option would be to prevent any smoke from a room fire entering the atrium at all. An easily understood way of achieving this is to ensure that the boundary between the room and the atrium is both imperforate and fire-resisting, and that the atrium base has only a very restricted use. This option has frequently been used, but is widely regarded as being architecturally restrictive. Consequently it is not often favoured by designers.
Where the boundary between the room and the atrium is open, it is sometimes feasible to provide a smoke ventilation system within the 121015, to maintain smoky fire gases above the opening to the atrium.
Unfortunately it is often very difficult, impracticable, or extremely expensive to fit a separate smoke extraction system to each and every room, however small.
Occasionally circumstances dictate 121101-5 smoke control dedicated to each room in this way is the most viable option for protecting the atrium this can occur, for example, when the room layout is of a large area, is predominantly open-plan and open-fronted. There have been several examples of this. Nevertheless it remains generally true that this option is rarely found to be appropriate for most atrium buildings.
Another possibility is that the atrium should be pressurised to prevent smoke moving into it from a room. This is not usually a viable option where the opening between the room and the atrium is large for example, an open-fronted room or a room whose glazing has fallen away in whole or in large part. This is because the air speed needed from the atrium into the room in order to prevent the movement of smoky gases the other way through the same opening, can vary between about 0.
All of this air must be continuously removed from within the fire room in order to maintain the flow. The quantities of airhandling plant required will exceed the size of smoke ventilation systems for many typical atrium room openings.
Note however, that pressurising the atrium may be a viable option where the atrium faqade has only relatively small leakage paths. Similar threats will occur if there is a serious fire in the atrium space itself. In either case, the threat to means of escape which are either within the atrium or in spaces open 1. In other words a smoke control system in the atrium is essential to make certain that escape is unhindered, by ensuring that any large quantities of thermally buoyant smoky gases can be kept separate from people who may still be using escape routes, or awaiting their turn for evacuation.
Therefore the role of a smoke control system is principally one of life safety. It should however also be remembered that firefighting becomes both difficult and dangerous in a smoke-logged building. It follows that to assist the fire services, the smoke control system should be capable of performing its design function for a period of time longer than that required for the public to escape, allowing a speedier attack on the fire to be made after the arrival of the fire service.
There has been no readily usable guidance available to designers of atrium smoke control systems within the UK. There have been a number of purely qualitative papers, as well as papers on work using relatively simple models of smoke movement within atria see for example References While this code is in many ways very comprehensive and broader in purpose than the present Report, some of the approaches used differ from alternatives with which UK designers are more familiar, or are more approximate than methods currently used by the Fire Research Station.
This particularly applies to smoke entering the atrium from adjacent rooms. The purpose of this Report is to provide guidance to assist designers of smoke control systems in atrium buildings in line with current knowledge. The guidance is based on results of research where possible, including as yet unpublislied results of experiments, but also on the cumulative experience of design features required for regulatory purposes of many individual smoke control proposals.
Many of these design features have been evolved over a number of years by consensus between regulatory authorities, developers and fire scientists, rather than by specific research.
Such advice has been included in this Report with the intention of giving the fullest picture possible. It is therefore likely that some of this guidance will need to be modified in the future, as the results of continued research become available.
The aim of this present Report is to provide guidance only on design principles of smoke control and it is hoped to support the code rather than to preempt it. The Report cannot cover all the infinite variations of atrium design. Instead it gives general principles for the design of efficient systems, with simplified design procedures for an ideal model of an atrium, and then further guidance on frequently encountered practical problems.
As the design procedures are of necessity simplified, it also gives their limitations so that, when necessary, a more detailed design by specialists can be carried out. It does this by avoiding resort as far as is currently possible to experimental correlations, and returning to first principles to solve the basic laws of physics for the fluid flow. As a consequence, with adequate validation, this type of modelling should have a wide applicability.
The use of a computer is necessary since the technique involves the solution of tens of thousands of mathematical equations for every step forward the simulation makes.
An atrium can be defined as any space penetrating more than one storey of a building where the space is fully or partially covered. Most atria within shopping centres may be considered as part of the shopping mall and treated accordingly.
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Where atria have mixed occupancies including shops then reference should be made to these documents, or specialist advice sought. These can be simply defined as follows: The atrium space generally has no functional use other than as a circulation area Figure 1. Figure 3 Partially open atrium b The closed atrium The atrium is separated from the remainder of the building by ordinary non fire-resisting glass.
The atrium space may well be functional cafeterias, restaurants, recreation, etc Figure 2. Figure 4 Fully open atrium 3 Fire growth and smoke production In most instances, a room compartment fire may be assumed to burn in either of two ways: The ‘normal’ fire condition found in most singlestorey buildings whilst the fire is still small enough for successful smoke control.
The smoke spreads out radially underneath the ceiling and forms a layer which deepens as the compartment begins to fill. If the compartment is open to the atrium, then the gases flow out immediately they reach the opening.
If the compartment is glazed or the opening is below a deep downstand then the smoke steadily deepens. As the layer gets deeper there is less height for the plume of smoke to rise before it reaches the smoke layer, hence less air is being entrained, wit’h the result that the temperature of the smoke layer increases with layer depth, even for a steady fire. Most fires will continue to grow larger as the layer deepens, reinforcing this effect.
In most practical compartments there is sufficient oxygen to support combustion in the first few minutes, and the fire growth and smoke production are controlled by the fuel, ie, fuel-bed control.
Thus once this temperature is passed, there is an increasing likelihood that the glass will fracture. If the compartment is sprinklered and the water spray hits the glass, the localised heating of the glass by radiation from the fire and by the gas layer, combined with sudden cooling due to the water spray will increase the likelihood of the glass breaking.
The smoke and hot gases will then flow externally to atmosphere, or enter the atrium, or both, depending upon the nature of the compartment and its relative position in the building, the size and position of the fire in the compartment, and the strength of differing glazing systems. If the fire can be accidentally or deliberately vented externally then the threat to other levels via the atrium is greatly reduced.
As the plume rises, air is entrained into it, increasing the volume of smoke and reducing its There will, however, be instances when a fire will vent all its effluent gas into the atrium, and this is generally the worst design scenario Figure 5.
The quantity of smoky gases produced ie the mass flow rate of gases in and from the compartment, and the energy heat flux contained therein are different for both regimes.
It is therefore important to identify the regime which applies.