ISO 21927-4:2019

ISO 21927-4:2019 pdf free.Smoke and heat control systems一Natural smoke and heat exhaust ventilators一Design, requirements and installation.
5 Design principles
5.1 General
The design of natural smoke and heat exhaust ventilation systems (see Figure 1) depends, inter alia, on: — the rate of energy release; — the theoretical fire area ofa building or the resulting design group; — the target height of the clear layer; — and the height of the relevant space.The values to be used to determine the parameters above are auxiliary design values and only apply to designs in accordance with this document.
5.2 Height of space
The height, h, of the space to be protected shall be the clear height in the case of horizontal roofs/ floors and the mean clear height in the case of pitched roofs or sloping floors. In both cases. it shall be measured from the floor to the lower surface of the roof/floor. Floors with smoke outlets are not regarded as floors in this context.
In the case of sawtooth roofs, the height of the space to be used for design purposes is the mean height of the NSHEV above the floor.
5.3 Target height of the clear layer, height of smoke barrier
The clear layer is defined as the distance between the surface of the floor assumed for design purposes and the lower surface of the smoke layer.
Clear layers enable, inter alia: — the occupants of a building to escape to safety; — the emergency services to rescue people, animals and property; — fires to be fought effectively; and — damage due to fire gases and products of thermal decomposition to be reduced. The target height of the clear area, d, shall be not less than 2,50 m.Design should be based on higher values of d if required by the purpose for which the space is to be used (e.g. spaces containing objects sensitive to smoke or flammable warehouse stock). The distance between the objects to be protected and the smoke layer should be not less than 0,5 m. For clear layers with a height d≤4 m, the height of the smoke barrier shall protrude at least 0,5 m into the clear layer. For clear layers with a heightd > 4 m the smoke barrier shall at least equal to the height of the smoke layer, z, but not less than 1,0 m in all cases.
5.4 Area of smoke reservoir
To enable NSHEVs to be designed according to this document, spaces shall either have a maximum area of 1 600 m2 or be divided into smoke reservoirs with a maximum area, AR, of 1 600 m2 by means of smoke barriers. The maximum distance between smoke barriers or between wall and smoke barrier shall not exceed 60 m. Any further subdivisions (e.g. closed joists) within the smoke reservoir shall not affect the design.
NOTE Smoke reservoirs are created by placing separating elements around the perimeter of a space or, at the minimum, by placing continuous smoke barriers around the open inner sides of a space. A “space” is defined as an area enclosed by separating elements on all sides.
5.5 Air inlets
An adequate number of air inlets, with an area, A1, is always required in the lower part of external walls to act as air replacement openings near floor level.
The required area of the air inlets shall be based on the area of the largest smoke reservoir. This area shall be taken into account when designing the external walls of a space. The air inlets should be located on at least two sides of the building and should be evenly distributed.
The following are considered as air inlets:
— separate supply air devices;
— doors or windows provided they are labelled as “air inlets for NSHEVs” on the inside and outside and can be opened from outside without being destroyed in the process (e.g. it shall not be necessary to smash window panes or break down walls or doors). This does not apply in cases in which a works fire service is able to create the necessary air inlets.ISO 21927-4 pdf download.

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