3.3 FIRE RESISTANCE OF ELEMENTS OF STRUCTURE
3.3.1 Interpretation and application
The interpretation and application of Cl.3.3 shall be as follows:
a. Subject to the provisions of sub-clause b. and any other expressed provision to the contrary, any reference to a station of which an element of structure forms a part means the station or (if the station is divided into compartments) any compartment of the station of which the element forms a part;
b. Any reference to height means the height of a station, but if any part of the station is completely separated throughout its height both above and below ground from all other parts by a compartment wall or compartment walls in the same continuous vertical plane, any reference to height in relation to that part means the height solely of that part;
c. If any element of structure forms part of more than one station or compartment and the requirements of fire resistance specified in Cl.3.3.2 in respect of one station or compartment differ from those specified in respect of any other station or compartment of which the element forms part, such element shall be so constructed as to comply with the greater or greatest of the requirements specified; and
d. If any element of structure is required to be of non-combustible construction, the measure of fire resistance rating shall be determined by the part which is constructed wholly of non-combustible materials.
3.3.2 Minimum periods of fire resistance
Subject to any expressed provision to the contrary, any element of structure shall be constructed of non-combustible materials and is required to have fire resistance for at least the relevant period specified as follows:
a. The fire resistance of elements of structure for aboveground stations shall be not less than 2-hrs.
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b. The fire resistance of elements of structure for underground stations shall be as follows:.
(2) Load bearing wall or load bearing part of a wall – 4 hrs
(3) Floor – 4 hrs
(4) Separating wall – 2 hrs
(5) Compartment wall – 2 hrs
(6) Structure enclosing a protected shaft – 2 hrs
c. Where there are habitable floors directly above a trainway within an aboveground station, the fire resistance of elements of structure around the trainway within the station shall be not less than 4 hrs as shown in Diagram 3.3.2c..
3.3.3 Exemption for non-loadbearing external walls
The requirement on fire resistance in Cl.3.3.2 shall not apply to any part of any external wall which is non-loadbearing and can, in accordance with Cl.3.5 be an unprotected area.
3.3.4 Exemption for single storey structure
In the case of a station consisting of a first storey and one or more basement storeys, nothing in Cl.3.3.2 shall apply to any element of structure which forms part of the first storey and consists of:
a. A structural frame, beam, or column, provided that any beam or column (whether or not it forms part of a structural frame) which is within or forms part of a wall, and any column which gives support to a wall or gallery, shall have fire resistance of not less than the minimum period, if any, required by this Code for that wall or gallery, or
b. An internal loadbearing wall or a loadbearing part of a wall, unless that wall or part is, or forms, part of a compartment wall or a separating wall, or forms part of the structure enclosing a protected shaft or supports a gallery, or
c. Part of an external wall which does not support a gallery, and which can, in accordance with Cl.3.5 be an unprotected area.
3.3.5 Suspended ceiling
In determining the fire resistance of floors, no account shall be taken of any fire resistance attributable to any suspended ceiling unless the ceiling is constructed specifically as a fire protecting suspended ceiling.
3.3.6 Fire-rated board for steel structure
Fire-rated boards are permitted to be used for protection to structural steel beams, columns, and wall construction in station if all the following are complied with:
a. The fire-rated boards shall be non-combustible (BS 476: Part 4 or Part 11);
b. It shall have a fire resistance rating at least equal to that of elements of structure required under Table 3.4A;
c. It shall meet the criteria, in terms of water absorption and bending strength performance, when subject to test of BS EN 520 (for gypsum plaster board) or ISO 1896 (for calcium silicate or cement board); and
d. The fire-rated boards shall be constructed to be in contact with the steel column. If it is unavoidable, the void space between the fire-rated board and the steel column shall be adequately filled to a height of 1.2m, measured from finished floor level, with fire protective material such as concrete, gypsum or grout to prevent any possible denting of the boards; and
e. There shall be no services running in the space between the steel structure and fire-rated boards, unless these services are encased in concrete or run in steel conduits.