STRUCTURAL FIRE PRECAUTIONS

3.1 GENERAL

3.1.1 The purpose of this chapter of the Code is to stipulate requirements to minimise the risk of spread of fire between adjoining buildings by separation, prevent the untimely collapse of buildings in the event of fire by the provision of a stable and durable form of construction and prevent the spread of fire between specified parts of the buildings by the division of such buildings into compartments.

Structural fire precautions relate to the integrity and stability of building elements during fire for a required period of time. “Structural” does not only apply to the structural elements of buildings but other building components, e.g. doors, shafts, walls/ceiling finishes.

The objectives of structural fire precautions are :

(a) To unload the spread of fire between adjoining buildings by adequate separation;

(b) To prevent the untimely collapse of building, including walls and floors of each unit in the event of a fire

(c) To prevent spread of fire from one unit to another within the building envelope by compartmentalising each unit with walls, floors and doors having the requisite fire resistance rating.

3.2.4. (d) Single household dwelling

Buildings may consist of more than 3 floors if they are occupied as a single household dwelling.

4 storeys or levels form one compartment
                                                                                                                     Diagram 3.2.4(d)

Building having 4 stories or levels under Purpose Group I are permitted. The above relaxation was introduced in 13 June 1996 to take into consideration of proliferation of 4-level purpose group I buildings due to the sudden surge in the public demand for two storey conventional houses with and attic and basement.

FSSD reviewded the above matter and issued a circular on 14 Dec 1999 to allow buildings under purpose group I to have more than 3 storeys or floors if they are occupied as a single household dwelling without the need to provide automatic fire system or external staircase.

3.2.5 Other cases requiring compartment wall & compartment floors The following situations shall require compartmentation by provision of compartment walls and/or compartment floors.

(c) Any floor immediately over a basement storey if such storey –

(i) forms part of a building which has five or more storeys
(including the basement storey)

Diagram 3.2.5 – (c)

Floor over a basement

Any floor immediately over a basement storey if such storey forms part of a building of purpose group I which has five or more storey (including the basement storey), shall be constructed as a compartment floor, ie horizontally separating the upper storeys from the basement. The exit staircase serving the basement shall be made to discharge into the exterior at grade level.

3.2.5 (m) Coldroom
(ii) Provision of the fire resisting outer layer enclosure, including the fire door, to the coldroom would not be required if :

* The coldroom is located in a building under purpose group I.
(No illustration)

3.3.1 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 to
have fire resistance for not less than the relevant period specified in Table 3.3A having regard to the purpose group of the building of
which it forms a part and the dimensions specified in that Table, provided that –

(a) Any separating wall shall have fire resistance of not less than 1-hour, and to take diagrams and explanatory notes from hand book

Single storey residential building as provided for under Table 3.3A needs to have minimum half-hour fire resistance rating for all elements of structure irrespective of the floor area. All elements of structure shall be constructed of non-combustible materials
unless otherwise permitted as in the construction of attic.

Houses not more than 3-storey

Table 3.3A Part 1 provides for residential building. Residential buildings having not more than 3 storeys or levels, including basement or attic, shall be provided with minimum period of fire resistance rating of half-hour for all elements of structure forming the ground or upper storey and 1-hour for the basement storey. If the basement storey has a floor area not exceeding 50m2 , the period of fire resistance rating for the elements of structure can be reduced to half-hour.

 

 

 

 

 

 

 

 

                                                    

Fire resistance to colums, beams, floors and external wall

Diagram 3.3.1

Footnote(a) to Table 3.3A allows the period to be half an hour for elements forming part of a basement storey which has an area not exceeding 50 sq.m to houses having not more three storey.

Houses having 4 storeys

For buildings in which each storey does not exceed 250m2, the minimum period of fire resistance rating for elements of structure forming part of:

a. a ground storey or upper storey – 1 hour (this period can be reduced to halfhour for floor which is not a compartment floor, except the beams which support the floor or any part of the floor which contribute to the structural support of the building as a whole).

b. basement storey – 1 hour.

 

Where the floor of each storey in the building exceeds 250m², all the elements of structure for basement and above ground shall have min. 11/2 hour and 1 hour fire resistance rating respectively.

Diagram 3.3.1 – (b)

3.3.3 Exemption for single storey buildings

In the case of a single storey building or a building consisting of a first storey and one or more basement storeys, nothing in Cl. 3.3.1 shall apply to any element of structure which forms part of the first storey and consists of :

(a) A structural frame or a 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 of it 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 may, in accordance with Cl. 3.5 be an unprotected area.

Diagram 3.3.3

Single storey building with or without basement

Exemption for Single Storey Buildings
Irrespective of floor area, the minimum period of fire resistance rating for elements of structures is half-hour. However, clause 3.3.3 of the Fire Code 2002 provides exemption for single storey buildings which need not comply with half-hour fire resistance rating for the structural frame or beam or column subject to:

a. the beams or columns are not supporting a wall or gallery;
b. the beams or columns are not forming part of the separating wall between houses;
c. the external walls including the supporting beams or columns which are not supporting a gallery or in accordance with cl.3.5 be an unprotected area.

3.3.4 The interpretation and application of Cl. 3.3 shall be as follows:

(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. (With the exception of fire protecting suspended ceilings, surface materials for walls and ceilings and floor finishes may be combustible, if they are not relied on to contribute to the fire resistance of the wall or floor).

 

Diagram 3.3.4(d) – 1

The above diagram shows the construction of a non-load bearing fire rated compartment wall. If the C-channels or horizontal channel supports are replaced with timber members, the construction would not meet the requirement of the above subclause, as timber members are combustible. However, combustible finish if added to the surface of the wall would be considered as acceptable, provided it complies with Cl.3.13.

Diagram 3.3.4(d) – 2

The above diagram shows the addition of timber floor finish to the R.C floor. The combustible floor finish is not to be considered as contributing to the fire resistance of the floor.

For fire protection to suspended ceilings see cl. 3.3.6. The above clause is also not applicable to buildings under preservation or conservation where structural timber members are required to be retained. See also cl. 3.4.3.

3.3.6 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 and the construction complies with the requirements under
Table 3.3B for Limitations on Fire Protecting Suspended Ceilings.

Diagram 3.3.6-1

Diagram 3.3.6-2

The suspended ceiling is to be treated as the soffit as the floor system or assembly consists of the timber boarding, joists and the suspended ceiling to achieve the necessary fire resistance rating.

Therefore the concealed space in the floor system or assembly is to be treated differently from concealed spaces mentioned under Cl.3.11. The main different is that concealed spaces in floor system or assembly are not permitted to have services such as air-con ducts, cables, pipes etc; even if these services are housed in fire rated enclosures.

3.3.7 Fire rated board

(i) Material shall be non-combustible (BS476 Pt 4 or Pt 11); and

(ii) It shall have fire resistance for not less than the relevant period specified in Table 3.3A having regard to the purpose group of the building of which it forms a part and the dimensions specified in that Table; and

(iii) It shall meet the criteria, in terms of water absorption and bending strength performance, when subject to test of BS1230 Pt 1 (for gypsum plaster board) or ISO 1896 (for calcium silicate or cement board); and

(iv) 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

(vi) 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.

Note : Fire rated boards should not be used to protect structural steel in areas which may be subject to explosion risks as the boards may be displaced by the force of the blast (No illustration)

3.4 Test for Fire resistance

3.4.1 Performance for the fire resistance of elements of structure, doors and other forms of construction shall be determined by reference to the methods specified in BS 476:Part 20 to 23, which specify tests for stability, integrity and insulation.

Specific requirements for each element in terms of the three performance criteria of stability, integrity and insulation are given in
Table 3.4A.

In conjunction with Part 20, methods of test are provided for – Beams, columns, floors, flat roofs and walls(Part 21); Partitions, doorsets and vertical shutter assemblies, ceiling membranes and glazed elements(Part 22); and Suspended ceilings protecting steel beams and intumescent seals for use in conjunction with single acting latched timber fire-resisting door assemblies(Part 23).

Part 20 specifies standard heating conditions based on a temperature/time curve (Diagram 3.4.1) which furnaces are required to follow; the temperature at defined locations close to the exposed face of the specimen under test rising to 821°C after 30 minutes and 1133°C after four hours.

 

 

 

Standard temperature/time curve (BS 476: Part 20 )
The specimen to be tested should be either full size or, where the element exceeds the size that can be accommodated by the furnace, it must have the following minimum dimensions.

Non-separating elements:                                              Vertical 3m high
                                                                                    Horizontal 4m span

Separating elements:                                                     Vertical 3m high X 3m wide
                                                                                    Horizontal 4m high X 3m wide

Specimens are normally heated to simulate their exposure in a fire, eg walls from one side, floors from beneath and columns from all sides.

Elements of building construction are required to satisfy various criteria according to their designed function in the event of fire. These are:

“Stability” or          the ability of a loadbearing element to support its test load

“Loadbearing         without excessive deflection;
capacity”
“Integrity”              the ability of a separating element to resist collapse, the formation of holes, gaps or fissures through which flames
and/or hot gases could pass, and the occurrence of sustained flaming on the unexposed face (the side of the specimen remote from the furnace)

“Insulation”           the ability of a separating element to resist an excessive rise in temperature on its unexposed face.

The criterion of “stability” or “loadbearing capacity” is applied only to loadbearing elements. For floors, flat roofs and beams, allowable vertical deflection is limited to 1/20 clear span.

Loss of “integrity” in the context of the formation of holes, gaps or fissures is judged by ignition of a cotton fibre pad. Where this test is not suitable, failure is deemed to have occurred if either a 25mm diameter gauge can penetrate into the furnace through a gap at any point, or a 6mm diameter gauge can penetrate into the furnace through an opening and can be moved for a distance of at least 150mm.

Loss of “insulation” occurs when the temperature on the unexposed face (the side of the specimen remote from the furnace) increases by more than 140°C (mean) or by more than 180°C at any point. Loss of “integrity” also constitutes loss of “insulation”.

Columns and beams have to satisfy only the criterion of “loadbearing capacity”; glazed elements are normally required to satisfy only “integrity”; and floors and walls have to satisfy all three criteria. It is pertinent to note that under Table 3.4A, doors are only required to satisfy “integrity”, leaving aside “insulation” as it is assumed unlikely that combustible materials would be stored against them. However, doors to protected lobbies, exit staircases and exit passageways should be provided with insulation against transmission of heat by radiation from the fire floor into the protected enclosures which occupants use for evacuation.

It is important to note that fire rated glass door shall not be used in fire lift shaft, exit staircases and exit passageways. In other areas such as protected lobbies, seperating and compartment walls, the use of fire rated glass is permitted, provided the building is sprinklered protected. Please see clause 3.15.13 for more details.

3.4.2 “Deem to satisfy” provisions
An element of structure, door or other part of a building shall be deemed to have the requisite fire resistance if –

(a)` It is constructed to the same specification as that of a specimen exposed to test by fire in accordance with the method and procedure under BS 476: Part 20 to 23, and satisfied the requirements of that test for the three performance criteria of stability, integrity and insulation for not less than the specified period , or

(b) In the case of a wall, beam, column, stanchion or floor to which Appendix A to Cl. 3.4 relates, it is constructed in accordance with one of the specification set out in that Appendix and the notional period of fire resistance given in that Appendix as being appropriate to that type of construction and other relevant factors is not less than the specified period.

(No illustration)

Sub-clause 3.4.2(b) provides the alternative to complying with the specification of tested prototype under BS476 Part 20 to 23. Specification set out in Appendix A to Cl.3.4 could be used and there is no need to obtain separate testing. However, on completion of the building works, the qualified person concerned is to forward to the RIs his/her certificate of supervision that the relevant specification listed in Appendix A to Cl. 3.4 had been complied with on site when applying for TFP or FSC.

3.4.3 Timber floors

The use of timber floors shall not be allowed, except:

(a) for an attic in buildings; and

(b) in buildings designated for conservation where the timber floors are required to be retained, but subject to compliance with the technical guidelines for ‘FIRE SAFETY REQUIREMENTS AFFECTING SHOPHOUSES UNDER CONSERVATION.’

(No illustration)

Under clause 1.1.2, the “Fire Safety Requirements Affecting Shophouses Under Conservation” shall also be applicable to old shophouses (build before 1969) not designated for conservation.

3.5 External wall

3.5.1 Requirements of External Walls shall be as follows :
(a) Any external wall of a building or a separated part of a building which constitutes or is situated within a distance of 1 m
from any point on the relevant boundary, or is a wall of a building or a separated part of a building which exceeds 15 m in height shall

(i) be constructed wholly of non-combustible materials apart from any external cladding which complies with Cl. 3.5.4 or any internal lining which complies with Cl.3.13.4, and

(ii) be so constructed as to attain the fire resistance required by this chapter, and

(b) Any beam or column forming part of an external wall and any structure carrying an external wall which is required to be constructed of non-combustible material, shall comply with the provisions of sub-cl. (a).

Buildings of any height situated at 1m or less from relevant boundary

Diagram 3.5.1 – (1)

Buildings of any height situated at 1m or less from relevant boundary

Diagram 3.5.1 – (2)

3.5.2 Exceptions
The requirements of Cl. 3.5.1(a)(i) for non- combustibility of external walls shall not apply to the external wall of a building or separated part of a building-

(b) if that wall is situated 1 m or more from the relevant boundary:
(i) of not more than three storeys.

Diagram 3.5.2(b)

a) External walls to building under purpose group I need not be constructed wholly of non-combustible materials if :

a. the building does not exceed 3 storey, and
b. the external wall is situated 1m or more from the relevant boundary

b) However, any beam or column forming part of an external wall and any structure carrying an external wall shall be constructed of non- combustible materials and have the necessary fire resistance rating as the elements of structure, apart from any external cladding which complies with Cl.3.5.4 or any internal lining which complies with Cl.3.13.4.

3.5.3 Except where otherwise provided, unprotected areas in any side of a building shall comply with the following:

(a) Unprotected areas in any side of a building Any relevant requirements relating to the permitted limits of unprotected areas specified in Appendix B unless the building is so situated that such side may in accordance with Appendix B consists entirely of any unprotected area, and

Relaxation on Calculations of Unprotected Openings/
Setback Requirement

The relaxation of the enclosing rectangular for individual room is only applicable to buildings under purpose group I. This is because every room is enclosed by walls and could be construed as a compartment for the calculations of unprotected openings and setback requirement.

3.5.4 Cladding on External Walls shall comply with the following:
(a) Cladding on external walls

If such cladding is situated less than 1 m from any point on the relevant boundary, it shall have surface complying with the
requirements for Class `0', and

(b) If such cladding is situated 1 m or more from the relevant boundary it shall have, if the building is more than 15 m in height,
a surface complying with the requirements specified for Class `0', except that any part of such cladding below a height of 15 m
from the ground may consist of timber of not less than 9 mm finished thickness or of a material having a surface which, when
tested in accordance with BS 476: Part 6 have an index of performance (I) not exceeding 20.

Diagram 3.5.4(a)

(a) If such cladding is situated less than 1m from the relevant boundary, it shall have surface complying with the requirements for Class '0'.

(b) If such cladding is situated 1m or more from the relevant boundary and the building is more than 15m,

(i) any part that is situated above 15m from the ground shall have a surface complying with the requirements for Class '0'.

(ii) any part that is situated below a height of 15m from the ground may consist of timber of finished thickness not less than 9mm or of a material having a surface which, when tested in accordance with BS 476 Pt 6 has an index of performance (I) not exceeding 20. The index of performance is derived from the fire propagation test which provides a comparative measure of the contribution a material will make to the heat build-up and thus to fire spread within a room or space.

Values range in descending order of merit from ‘0’ (non- combustible material) to ‘100’. For example, 18mm thick softwood has an index of performance (I) 42.5 as compared to 13mm thick plaster board which has a value of 9.9.

3.5.5 Reference to Part I -II of Appendix B

Any reference to Appendix B shall be construed as referring to the provisions of Part I of that Appendix together with the provisions of
Part II.

3.5.6 Buildings on land in common occupation

If two or more detached buildings are erected on land in common occupation, any external wall of any building so erected which faces
an external wall of such other building, the relevant boundary shallbe a notional boundary passing between those buildings and such
boundary must be capable of being situated in such a position as to enable the external walls of those buildings to comply with the
requirements of Cl. 3.5.3.

 

 

Diagram 3.5.4(a

(a) It is necessary to assume a notional boundary when two or more detached buildings are erected on land in common occupation.

(b) The notional boundary is taken to exist in space between the buildings and is positioned so that the external walls of building A and B facing the notional boundary comply with the separation distance requirement in accordance with Tables of Appendix B, based on the percentage of unprotected area and the purpose group of the compartment/floor.

(c) Unprotected openings shall be assessed for each building separately. The separation distance between the two buildings shall be not less than the sum of the distance each building would require to a relevant boundary ie. “a” is equal to or greater than the separation distance to the boundary for building A and “b” is equal to or greater than the separation distance to the relevant boundary
for building B.

(d) The notional boundary can be shifted next to external wall of building A or B, if the external wall has no unprotected areas and is constructed of noncombustible materials having the requisite period of fire resistance rating as the elements of structure of the storey compartment.

3.6 SEPARATING WALLS

3.6.1 Every separating wall shall:

(a) Form a complete barrier in the same continuous vertical plane through the full height between the buildings it separates, including roofs and basements and shall be imperforate except for provisions of openings permitted under Cl.3.6.2, and

(b) Have the appropriate fire resistance to comply with the requirements of Cl.3.3, and

(c) Be constructed of non-combustible materials, together with any beam and column which form part of the wall and any structure
which it carries.
(d) Not include glass fire resisting walls
(e) Exception

Subclause (a) need not be applied to wall between car porches of buildings under purpose group I. For terrace-housing situation,
this exception will not apply if the carporch is spanning from one side boundary to the other.

Diagram 3.6.1(a)

Separating wall is the common wall that separates one house from another, as in the case of semi-detached or terraced houses. It is to prevent the spread of fire from house to house. The separating wall shall have the appropriate fire resistance rating as the elements of structure of the adjoining house having the larger floor area or cubical extent as the case may be. It shall not include fire resisting glass.