BS 5588-4:1998
9.2.2.8 Pressurization of refuges and central control rooms It may be necessary to provide refuges and central control rooms in buildings where occupants need to await evacuation for some time after the inception of a fire. The refuge or central control room should be separated from the fire zone by fire-resisting construction and should be provided with a protected route to a storey exit. Guidance on refuges for disabled people is given in BS 5588-8. In many buildings the refuge room may form part of the protected escape route, for instance, when stairway and lobby are pressurized and the lobby is used as the refuge. In such cases the design should ensure that the lobbies are large enough for their purpose. Where a central control room needs to be staffed during the course of a fire, it is essential that a fire-resisting construction is used and a protected route to a storey exit provided. A net pressure differential of 25 Pa between the refuge or central control room and fire zone should be sufficient to overcome the effects of wind and buoyancy on the fire storey (see Figure 10). Stack effect need not be considered since the refuge or central control room does not connect directly to other storeys within the building [see Figure 10a) and Figure 10b)]. The pressurized space should also be a fire compartment. Where more than one system serves any storey, account should be taken of the total leakage paths via the unpressurized spaces with all the systems operating simultaneously. In many cases the normal HVAC system may be used as a means of supplying air to the pressurized space; in other cases a dedicated air supply system may be necessary. NOTE The “open-door� airflow recommendation (see Clause 5) applying to stairwells and lobbies does not apply to refuges or central control rooms which are not integral with a pressurized stairwell or a pressurized lobby.
A pressurized refuge or central control room should not be connected to an unpressurized stair and the pressure within the refuge or central control room should not be greater than that within the pressurized stair. 9.2.3 Implications of pressurization system for building design 9.2.3.1 Pressurized and unpressurized stairs in the same building Where pressurized and unpressurized stairs are present in the same building, the potential exists for the unpressurized stair to become smoke logged as a direct result of the airflow created by the pressure differential system. All stairs in a building should be pressurized unless it can be clearly demonstrated that smoke will not be forced into the unpressurized stairs as a result. The use of pressurized and unpressurized stairs serving the same storeys should only be considered if either of the following conditions is met. a) The unpressurized stair is separated from the pressurized stair by a large undivided space, and air can escape by an opening twice as large as the door through which it enters. b) A detailed design flow analysis has shown that operation of the pressure differential system would not increase the airflows on the fire storey into the unpressurized stair. NOTE In the case of item b), detailed evidence should be supplied by the designer to justify this approach in the circumstances of the design.
9.2.3.2 Pressurized escape routes and other pressurized spaces in the same building A building may contain several spaces, such as computer suites or medical facilities, that are pressurized for reasons other than fire, and therefore consideration should be given to protecting pressurized escape routes from the effects of fire in such pressurized spaces. Each pressurized escape route should have its own independent air supply. Where a pressurized escape route is directly connected to a pressurized space, the pressure in the escape route should be at least 10 Pa greater than that of the pressurized space. Suitable leakage arrangements should be provided in unpressurized spaces to allow the pressurizing air from all the pressurized spaces to escape to external air.
Š BSI 8 December 2004
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