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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This creates a large surface area for entrainment on both sides of the plume along its spill width Figure 24 bfor which reason they are also known as double-sided plumes. 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. This Report will only provide guidance for the design of smoke control systems for a fuel-bed-controlled fire in an office, and a fully-involved fire in a hotel bedroom.
The pressure difference across any small opening on to the route must be large enough to offset adverse pressures caused by wind, building stack effect and fire buoyancy. The purpose of this Report is to provide guidance to assist designers of smoke control systems in atrium buildings in line with current knowledge.
Further research and statistical data are desirable in this area. Cellular room Early experiments with smoke flow in shopping malls29 and unpublished workI7 at FRS also N R Marshall, Fire Research Station; private communication, have shown that the smoke flowing from a room with a deep downstand and then under a balcony beyond the opening becomes turbulent with increasing mixing of air.
If the compartment is open to the atrium, then the gases flow out immediately they reach the opening. It is much simpler to assess the maximum size a fire can reasonably be expected to reach during the escape period, and to design the system to cope with that.
These can be simply defined as follows: Initially this mass flow rate of smoke will be controlled by the fuel-bed, as mentioned above.
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.
Even for this scenario therefore, the above value should err on the side of safety. A,VH This is the area of the opening into the atrium A,”, multiplied by the square root of its height H. The smoke spreads out radially underneath the ceiling and forms a layer which deepens as the compartment begins to fill.
Sprinkler systems vs smoke control: the EN approach – FMJ
A system using natural ventilators depends on the buoyancy of the hot gases to expel smoke through the Table 1 Volume em rate 112101-5 temperature of gases from a 1 MW fire including cooling within room of origin Mass flow rate Mass rate of extraction kgs-9 Temperature of gases above ambient.
Similar threats will occur if there is a serious fire in the atrium space itself. A fan-driven inlet air supply may be employed, but can give problems when mechanical extraction is used the building will usually be fairly well sealed in such circumstances.
This is sometimes known as ‘plugholing’. Should a designer wish to examine the effect of a plume emanating from an open window in a sprinklered hotel bedroom, it would not seem unreasonable to use a value of 6 m perimeter equivalent to a single bed with a convective heat output of around kW as the design fire.
Screens may be fixed or may descend upon smoke detection. It is suggested that either of the extreme values should be adopted in seeking a conservative design approach. This is similar to the procedure used in multi-storey shopping complexesI6.
It follows that, for efficient extraction, een number of extraction points must be chosen to ensure that no air is drawn up in this way. Ventilation of the fire room may be achieved by either a dedicated smoke exhaust system or by adapting and boosting an air-conditioning or ventilating system. 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 121101-5.
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I Figure 7 A fully-involved ventilation-controlled fire Smoke removed from these lower level reservoirs should usually be ducted to outside the building but can be ducted into the 12101–5 reservoir of the atrium Figure As such, it does.
If screens activated by smoke detectors or as permanent features are hung down from the balcony edges, the region below each balcony can be turned into a ceiling reservoir. This is because the warmed air taken out will have a greater volume than the inlet air.
The sn of smoky gases produced ie the mass flow rate of gases in and from the compartment, and een energy heat flux contained therein are different for both regimes. When, however, smoke is able to flow unrestricted under a horizontal projection, eg a balcony, it will flow forwards towards the balcony edge, and laterally sideways. A potentially valuable bonus of such a system in a sprinklered building is that the sprinklers which are normally required in the space above the false ceiling will cool the smoky gases before they reach the fan.
BS en 12101-5
For any given size of fire, an equilibrium can be reached where the quantity of gases being removed equals the quantity entering the layer in the fire plume – no significant mixing of air occurs upwards into the base of the buoyant smoke layer. Larger chambers should be subdivided by smoke screens extending the full height of the chamber and below the false ceiling to form a complete smoke reservoir below. This condition is known as the ‘fully-involved, large-opening fire'”.
This suggests that inflow airspeeds should not usually exceed 5 ms-I. 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.
Similarly, where smoke is collected within a balcony reservoir adjacent to sprinklered offices, operation of sprinklers under the balconies will lead to increased heat loss reducing the buoyancy of smoke, which in turn can contribute to a progressive loss of visibility under the smoky layer. In both tables the first number of each pair denotes extraction points wcll away from the walls, and thc second is for those close to the walls.
This option has frequently been used, but is widely regarded as being architecturally restrictive. Other screens can be U Exhaust from balcony reservoir Figure 19 An under-balcony smoke reservoir 13 0 alternative escape routes, 0 shorter escape paths along the balcony, and the installation of sprinklers to cool the gases further.
This is explained in more detail in Chapter 5.