BS 7346-5-2005 Components for smoke and heat control systems - Functional recommendations and calculation methods for smoke and heat exhaust ventilation systems employing time-depe.pdf

1、BRITISH STANDARD BS 7346-5:2005 Components for smoke and heat control systems Part 5: Functional recommendations and calculation methods for smoke and heat exhaust ventilation systems, employing time-dependent design fires Code of practice ICS 13.220; 91.140.30 BS 7346-5:2005 This British Standard w

2、as published under the authority of the Standards Policy and Strategy Committee on 31 March 2005 BSI 31 March 2005 The following BSI references relate to the work on this British Standard: Committee reference FSH/25 Draft for comment 03/117591DC ISBN 0 580 45520 3 Committees responsible for this Bri

3、tish Standard The preparation of this British Standard was entrusted by Technical Committee FSH/25, Smoke, heat control systems and components, upon which the following bodies were represented: Association of Fire Consultants Association of Roof Light Manufacturer British Blind and Shutter Associati

4、on Building Research Establishment (BRE) Building Services Research and Information Association (BSRIA) Fire Resistant Glass and Glazing Federation HEVAC Association Institution of Fire Engineers (IFE) London Fan Company London Fire and Emergency Planning Authority Office of the Deputy Prime Ministe

5、r (ODPM) Smoke Vent Association Steel Window Association Co-opted members Amendments issued since publication Amd No. Date CommentsBS 7346-5:2005 BSI 31 March 2005 i Contents Committees responsible Inside front cover Foreword ii Introduction 1 1S c o p e 4 2 Normative references 4 3 Terms, definitio

6、ns, symbols and units 5 4 General recommendations 10 5 Recommended calculation procedure 15 6 Further acceptability criteria 22 7 Interaction with other fire protection systems and other building systems 26 Annex A (normative) Supporting documentation 28 Annex B (informative) Example of an iterative

7、 calculation procedure 28 Annex C (informative) Plugholing 30 Annex D (informative) Factors influencing the choice of time-dependent design fires 34 Bibliography 36 Figure 1 Effect of smoke ventilation on smoke layer depth 16 Figure 2 Examples of fire development curves 18 Figure 3 Fire growth rates

8、 19 Figure 4 Smoke barrier depth margin (with barrier in deflected position) 23 Figure 5 Smoke transfer duct 24 Figure 6 Effective layer depth 24 Figure 7 Example of excess gap caused by deflection of smoke barrier mounted adjacent to a column 26 Figure C.1a) Plugholing at a supercritical ventilator

9、 opening 31 Figure C.1b) Onset of plugholing at a critical ventilator opening 32 Figure C.1c) Absence of plugholing at a subcritical ventilator opening 32 Figure C.2 Qualitative examples of time-based layer deepening 33 Table 1 Various t 2fire growth rates 19 Table 2 Minimum clear height above floor

10、 level on escape routes 21BS 7346-5:2005 ii BSI 31 March 2005 Foreword This part of BS 7346 was prepared under the direction of Technical Committee FSH/25. The other parts that comprise BS 7346 are as follows: Part 1: Specification for natural smoke and heat exhaust ventilators; Part 2: Specificatio

11、n for powered smoke and heat exhaust ventilators; Part 3: Specification for smoke curtains; Part 4: Functional recommendations and calculation methods for smoke and heat exhaust ventilation systems, employing steady-state design fires Code of practice; Part 6: Specification for cable systems. Parts

12、1, 2 and 3 of BS 7346 will eventually be replaced by the equivalent parts of BS EN 12101. The parts of BS EN 12101, Smoke and heat control systems, relevant to BS 7346-5 will include: Part 1: Specification for smoke barriers Requirements and test methods; Part 2: Specification for natural smoke and

13、heat exhaust ventilators; Part 3: Specification for powered smoke and heat exhaust ventilators; Part 7: Smoke control ducts 1) ; Part 8: Specification for smoke control dampers 1) ; Part 9: Control panels and emergency control panels 1) ; Part 10: Power supplies 1) . This British Standard gives reco

14、mmendations for the design of smoke and heat exhaust ventilation systems. It is assumed in the drafting of a standard that the execution of its provisions is entrusted to appropriately qualified and competent people. As a code of practice, this British Standard takes the form of guidance and recomme

15、ndations. It should not be quoted as if it were a specification and particular care should be taken to ensure that claims of compliance are not misleading. This publication does not purport to include all the necessary provisions of a contract. Users are responsible for its correct application. Comp

16、liance with a British Standard does not of itself confer immunity from legal obligations. 1) In preparation. Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, pages 1 to 36, an inside back cover and a back cover. The BSI copyright notice displayed in this

17、 document indicates when the document was last issued.BS 7346-5:2005 BSI 31 March 2005 1 Introduction 0.1 General Smoke and heat exhaust ventilation systems (SHEVS) create a smoke-free layer above the floor by using the buoyancy of the smoke to form a layer beneath the ceiling above the smoke-free l

18、ayer, and by removing smoke from that buoyant layer, they allow the continuation of clear conditions. SHEVS are of value in: assisting in the evacuation of people and animals from buildings; preventing smoke logging by exhausting hot gases released by a fire in the developing stage; NOTE Ventilation

19、 systems for smoke exhaust serve simultaneously for heat exhaust. reducing roof temperatures; retarding the lateral spread of fire; reducing fire damage to property and thereby financial loss; facilitating fire-fighting, while the fire is still in its early stages. For these benefits to be obtained,

20、 it is essential that smoke and heat exhaust ventilators operate fully and reliably whenever called upon to do so during their installed life. A SHEVS is a scheme of safety equipment intended to perform a positive role in a fire emergency. Components for a SHEVS ought to be installed as part of a pr

21、operly designed smoke and heat exhaust system. Fire Safety Engineering (FSE) is the discipline whereby Fire Science is applied quantitatively to the design of buildings to ensure safety in the event of a fire. As such, the design procedures for a SHEVS can be seen as a subsidiary part of FSE, with F

22、SE encompassing a much broader range of techniques and concerns. BS 7974 serves to guide the fire safety engineer through this wider field of application. It is the purpose of this British Standard to cover the design process for SHEVS in greater detail than is possible in BS 7974, and with a focus

23、that is restricted to SHEVS. In brief summary, this British Standard is intended to be complementary to BS 7974 and is not to be regarded as an alternative to BS 7974. This British Standard focuses on the design of SHEVS based on time-dependent design fires. It therefore complements BS 7346-4, which

24、 focuses on the design of SHEVS based on steady-state fires and which therefore bears a similar complementary relationship to BS 7974. The flow of thermally buoyant smoky gases through a building depends on the properties of the gases and any influences imposed on the gases by the building through w

25、hich the smoky gases pass. These influences include: the internal shape of the building controlling the flow path of the gases through the building; the heat losses from the smoky gases to the building; the heat losses to fire suppression systems in the building, such as sprinklers; the external sha

26、pe and the situation of the building and the likely external pressure field. The external pressure field is dominated by the wind. It follows that if SHEVS are to meet the recommended levels of performance in the building, it is essential that the design of that system takes explicit account of the

27、shape of the building (external and internal) and of the external influences (e.g. wind). If the building roof design is uncomplicated and it is unlikely to be affected by high adjacent buildings, normal assessment methods will be appropriate. If this is not the case, the design process ought to emp

28、loy calculation procedures or directly measured data appropriate to the building concerned. Such data may come from studies of the existing building, from scale-model studies, or from generically similar building data. Natural SHEVS operate on the basis of the thermal buoyancy of the gases produced

29、by a fire. Powered SHEVS operate on the basis of removing fire gases using mechanical devices, usually fans.BS 7346-5:2005 2 BSI 31 March 2005 The performance of the installations depends for example on: the temperature of the smoke; the aerodynamic free area of the ventilators, or the volume of smo

30、ke exhausted by powered ventilators; the wind influence; size, geometry and location of the air inlets; size, geometry and location of smoke reservoirs; the time of actuation; the location and conditions of system (for example arrangements and dimensions of the building). Ideally, the design fire up

31、on which calculations are based shows the physical size and heat output of the fire changing with time in a realistic manner, allowing the growing threat to occupants, property and fire-fighters to be calculated as time progresses. Such time-based calculations of the time to danger usually have to b

32、e compared with separate assessments of the time recommended for safe evacuation of occupants of the structure and the time recommended for initiation of successful fire-fighting. These assessment procedures fall outside the scope of this British Standard, which only outlines procedures for calculat

33、ing the times to the onset of danger. It is essential that the time required for safe evacuation, and for initiation of successful fire-fighting, is assessed as accurately as possible. Whilst fire brigade target arrival times are detailed within other documents (for example PD 7974-5), the set-up ti

34、me for the fire brigade will be specific to the building (and to some extent to the fire type and location). This set-up time is vital to bringing the fire under control and thus limiting smoke production. It is therefore necessary to agree with the appropriate fire authority both the SHEVS systems,

35、 and the effects of operational fire-fighting times. Wherever doubt exists about the accuracy of these latter times, the designer needs to calculate in a safety margin when comparing the time to danger against the time needed for success. It is essential that fire growth curves are selected which ar

36、e appropriate to the circumstances of the building occupancies, fuel arrangements, and sprinkler performance. It is the purpose of this British Standard to present recommendations and guidance for the design of smoke and heat exhaust ventilation based on time-dependent, or “growing” fires. Many of t

37、he detailed calculation procedures, and most of the danger criteria defining the boundary between success and failure, are the same for time-dependent design fires as for steady-state design fires, and it is essential that this British Standard be used in conjunction with BS 7346-4. 0.2 Smoke exhaus

38、t ventilation design philosophies steady-state and time-dependent designs The fundamental objectives as given in 0.3 are the same for time-dependent fire designs as for steady-state fire designs but it is the way in which these objectives are approached that differs. Where time-based calculations ar

39、e not feasible, it is possible to use a simpler procedure based on the largest size a fire is reasonably likely to reach in the circumstances. This time-independent or steady-state design fire is not to be confused with steady fires that achieve full size instantly and then burn steadily. Rather, th

40、e procedure assumes that a SHEVS that is able to cope with the largest fire assumed for design will also cope with the (usually earlier) smaller stages of the fire. Design procedures based on steady-state design fires are presented in BS 7346-4. The purpose of a steady-state designed SHEVS, as descr

41、ibed in BS 7346-4, is to ensure that the objective is achieved throughout the entire duration of the fire with the recognized exception of an acceptably small proportion of fires that can grow larger than assumed by the design. For example, although there is a finite mathematical probability of a me

42、teorite crashing into the building, the probability is regarded as being too small to consider during design. The purpose in a time-dependent designed SHEVS is to ensure that the time between ignition of the fire and the onset of a significant danger is acceptably longer than the time required to su

43、cceed in the design objective. Even in a successful design, an acceptably small proportion of design fires will grow faster and/or larger than assumed for the design. For example, the extreme of a fast-growing fire is an explosion, although the probability of an explosion in most buildings will usua

44、lly be too low to be worth considering in most SHEVS designs.BS 7346-5:2005 BSI 31 March 2005 3 0.3 Objectives for time-dependent design fire SHEVS designs 0.3.1 Protection of means of escape (life safety) The objective is to delay the onset of dangers on escape routes (which are in the same space a

45、s the fire) for a long enough time for people to evacuate safely, by creating by calculation a desired smoke-free height beneath a smoke layer, and exhausting smoke from that layer at a rate that will slow the downward filling of the space with smoke. If the clear height and smoke layer temperature

46、remain sufficient for safety until the fire is brought under control (or the fuel is exhausted), the time available can become effectively infinite in the same way as for a steady-state design. 0.3.2 Temperature control Where the height of clear air beneath the thermally buoyant smoke layer is not a

47、 critical design parameter, it is possible to use the same calculation procedures (formulae) as for 0.3.1 in a different way. The smoke exhaust can be designed to limit the temperature of the gases in the buoyant layer. This allows the use of materials that would otherwise be damaged by the hot gase

48、s. For example, where an atrium faade has glazing which is not fire resistant, but which is known to be able to survive gas temperatures up to a specified value. The use of a temperature control SHEVS in such a case could, for example, allow the adoption of a phased evacuation strategy from higher s

49、toreys separated from the atrium only by such glazing. Further guidance on the incorporation of atria into new and existing buildings is given in BS 5588-7. 0.3.3 Facilitating the fire-fighting operation In order for fire-fighters to successfully deal with a fire in a building, it is first necessary for them to drive their fire appliances to entrances giving them access to the interior of the building. They then need