3.11 CONCEALED SPACES
3.11.1 General provision
R Rationale - Clause 3.11.1Concealed spaces or cavities in station provide a ready route or flue for smoke and flame to spread undetected, thus increasing the risk to life safety of occupants in the station. This is particularly so in the case of void spaces above a suspended ceiling or in a roof space or in a raised floor system. The cavity barriers shall be constructed of non-combustible materials and of at least ½-hr fire resistance rating so as to provide adequate protection.
Concealed spaces in a station shall be interrupted by construction of cavity barriers to restrict the spread of smoke and flames.
3.11.2 Closing the edges of cavities
Cavity barriers shall be used to close the edges of cavities, edges around openings through a wall, floor and any other part of the construction which contains a cavity and to separate any cavity in a wall, floor, or any other part of the construction from any other such cavity.
3.11.3 Interrupting cavities
Cavities shall be interrupted by cavity barriers where a wall, floor, ceiling, roof or other part of the construction about the cavity, if there is provision for the element of structure to form a fire resisting barrier. Such cavity barriers shall be of fire resisting construction at least equal to the provision for that required for the fire resisting barrier.
3.11.4 Sub-division of extensive cavities
R Rationale - Clause 3.11.4The reason for limiting the dimension of cavities is to minimise fire or smoke within concealed space.
Cavities, unless otherwise permitted, shall be sub-divided so that the maximum distance between cavity barriers in any direction shall not exceed 20m.
3.11.5 Fire resistance and fixing of cavity barriers
R Rationale - Clause 3.11.5Compartment walls shall be extended to the full height of the storey i.e. from the floor to the soffit of the ceiling slab. This will ensure a complete compartment of each unit and prevent smoke and fire spread that may occur via the concealed ceiling space.
Cavity barriers shall be:
a. constructed to provide at least ½ hour fire resistance, and .
b. tightly fitted to rigid construction, or the junctions shall be fire stopped to comply with the requirements of Cl.3.12.
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3.11.6 Openings in cavity barriers
A cavity barrier shall have no opening in it except for:
a. a door which has at least ½ hour fire resistance and shall be kept closed all the time, or
b. a pipe which complies with the provision under Cl.3.9.3, or
c. a cable or conduit containing one or more cables, or
d. an opening fitted with suitably mounted automatic fire damper, or
e. a duct which is fitted with a suitably mounted automatic fire damper where it passes through the cavity barrier.
3.11.7 Raised floors with or without accessible panels
The construction of raised floors with or without accessible panels shall comply with the following requirements:
a. The supporting structure shall be constructed of non-combustible materials having a melting point of at least 750°C.
b. The concealed space between the structural floor and raised floor shall not be used for storage purpose.
c. No services or installation shall be permitted within the concealed space other than;
(1) Electrical wiring in metal conduit and metal trunking in compliance with the requirements of SS 638;
(2) Communication cables for computer equipment; and
(3) Fire protection installations serving the area.
d. Where the raised floor is used as a plenum, requirements in Chapter 7 shall be satisfied.
e. Decking of the raised floor shall be constructed of non-combustible material or where combustible material is used as core material, if allowed in the case of sprinkler protected areas/ compartment, the top, bottom, all sides and cut edges shall be covered with material with surface property complying with Class 0 (excluding materials for floor finishes).
f. In the case of raised floors with accessible panels, access sections or panels shall be provided such that all concealed spaces between the structural floor and raised floor are easily accessible.
g. Openings in the raised floor for entry of electrical cables shall be effectively closed to prevent entry of debris or other combustible material into the concealed spaces.
h. All sides shall be properly sealed.
i. The concealed space shall be sub-divided by cavity barriers such that the maximum unobstructed area within the concealed space do not exceed 930m2.
j. Where the concealed space is fitted with an automatic sprinkler system which complies with the requirements in Chapter 6, cavity barriers are not required.
k. The height of concealed space measured between the top of the structural floor and underside of the raised floor decking shall not exceed 400mm and shall be fitted with automatic detection system complying with requirements of SS 645; and in the case of sprinkler protected compartment, the height of concealed space can exceed 400mm if the space is fitted throughout with an automatic sprinkler system which complies with the requirements in Chapter 6.
3.11.8 Suspended ceiling over protected areas
The concealed spaces of suspended ceiling over an exit passageway, smoke-free/ fire lift lobby, exit staircase, firefighting staircase, or other designated means of escape facilities, shall comply with the following:
a. The ceiling supporting elements and the ceiling shall be constructed of non-combustible materials; and
b. The exposed surfaces within the concealed space shall be of Class 0 surface flame spread.
3.11.9 Exemption of cavity barriers
Provision of cavity barriers within the concealed spaces of suspended ceiling is exempted if the following requirements are complied with:
a. The concealed space are not used for storage purpose.
b. The supporting elements shall be constructed of non-combustible material.
c. The exposed surfaces within the concealed space is of Class 0 flame spread, (excluding surfaces of any pipe, cable, conduit or insulation of any pipe).
d. If the concealed space does not exceed 800mm in depth or if the concealed space is fitted with:
(1) detectors which comply with the SS 645, or
(2) an automatic sprinkler system complies with SS CP 52.