7.1Premature failure of the structure can be prevented by provisions for loadbearing elements of structure to have a minimum standard of fire resistance, in terms of resistance to collapse or failure of loadbearing capacity. The purpose in providing the structure with fire resistance is threefold, namely:
- ato minimise the risk to the occupants, some of whom may have to remain in the building for some time while evacuation proceeds if the building is a large one;
- bto reduce the risk to firefighters, who may be engaged on search or rescue operations; and
- cto reduce the danger to people in the vicinity of the building, who might be hurt by falling debris or as a result of the impact of the collapsing structure on other buildings.
Fire resistance standard
7.2Elements of structure such as structural frames, beams, columns, loadbearing walls (internal and external), floor structures and gallery structures, should have at least the fire resistance given in Appendix A, Table A1.
Exclusions from the provisions for elements of structure
7.4The following are excluded from the definition of element of structure for the purposes of these provisions:
- aa structure that only supports a roof, unless:
- ithe roof performs the function of a floor, such as for parking vehicles, or as a means of escape (see Sections 2 to 4); or
- iithe structure is essential for the stability of an external wall which needs to have fire resistance;
- bthe lowest floor of the building;
- ca platform floor; and
- da loading gallery, fly gallery, stage grid, lighting bridge, or any gallery provided for similar purposes or for maintenance and repair (see definition of “Element of structure” in Appendix E).
Application of the fire resistance standards for loadbearing elements
7.3The measures set out in Appendix A include provisions to ensure that where one element of structure supports or gives stability to another element of structure, the supporting element has no less fire resistance than the other element (see notes to Table A2). The measures also provide for elements of structure that are common to more than one building or compartment, to be constructed to the standard of the greater of the relevant provisions. Special provisions about fire resistance of elements of structure in single storey buildings are also given and there are concessions in respect of fire resistance of elements of structure in basements where at least one side of the basement is open at ground level.
7.5Guidance in other sections of this Approved Document may also apply if a loadbearing wall is:
- aa compartment wall (this includes a wall common to two buildings), (see Section 8);
- ba wall enclosing a place of special fire hazard (see Section 8, paragraph 8.12);
- cprotecting a means of escape, (see Sections 2 to 5);
- dan external wall, (see Sections 12 and 13); or
- eenclosing a firefighting shaft, (see Section 17).
7.6If a floor is also a compartment floor, see Section 8.
Raised storage areas
7.7Raised free-standing floors (sometimes supported by racking) are frequently erected in single storey industrial and storage buildings. Whether the structure is considered as a gallery or is of sufficient size that it is considered as a floor forming an additional storey, the normal provisions for fire resistance of elements of structure may be onerous if applied to the raised storage area.
7.8A structure which does not have the appropriate fire resistance given in Appendix A, Table A1 is acceptable provided the following conditions are satisfied:
- athe structure has only one tier and is used for storage purposes only;
- bthe number of persons likely to be on the floor at any one time is low and does not include members of the public;
- cthe floor is not more than 10m in either width or length and does not exceed one half of the floor area of the space in which it is situated;
- dthe floor is open above and below to the room or space in which it is situated; and
- ethe means of escape from the floor meets the relevant provisions in Sections 3, 4 and 5.
Notes:Where the lower level is provided with an automatic detection and alarm system meeting the relevant recommendations of BS 5839-1:2002, then the floor size may be increased to not more than 20m in either width or length.
The maximum dimensions provided above have been set in order to limit the distance that a firefighter may need to travel over or under floor to effect a rescue. Where agreed locally it may be possible to vary these dimensions, however, the safety of firefighters who may be on or underneath these floors must be taken into account.
Where the building is fitted throughout with an automatic sprinkler system in accordance with paragraph 0.16, there are no limits on the size of the floor.
Conversion to flats
7.9Where an existing house or other building is converted into flats, there is a material change of use to which Part B of the regulations applies. Where the existing building has timber floors and these are to be retained, the relevant provisions for fire resistance may be difficult to meet.
7.10Provided that the means of escape conform to Section 3 and are adequately protected, a 30 minute standard of fire resistance could be accepted for the elements of structure in a building having not more than three storeys.
Where the altered building has four or more storeys the full standard of fire resistance given in Appendix A would normally be necessary.