FIRE RESISTANCE
(D2.1) (D3.2) (D7.2)
a. The requirements of D2.1 will be met by a steel portal frame having fixed column base connections or designed in accordance with the guide ‘The Behaviour of Steel Portal Frames in Boundary Conditions,’ second edition, (The Steel Construction Institute, 1990).
Where fire resistance is required for a steel portal frame member because it supports a separating wall or compartment wall or an external wall related to its distance from a boundary, such fire resistance shall apply only to that part of the member built into or directly supporting the wall up to the underside of the haunch or the underside of the rafter if there is no haunch, and shall not apply to any other part notwithstanding that it is part of the same portal frame.
In the case of a gable steel portal frame member which is required to be fire resisting because of the distance of the gable wall from a boundary, the entire portal frame shall be fire resisting.
b. The requirements of D2.1 (referred to in the tables), in the Notes to the table to D3.2,and in D7.2 for an appropriate fire control system will be met by adopting in the case of -
i. a sprinkler system, BS5306: Part 2 as amended in 1990;
ii. a carbon dioxide system, BS5306: Part 4: 1986;
iii. a low expansion foam system, BS5306: Part 6: Section 6.1: 1988;
iv. a medium and high expansion foam system, BS5306: Part 6: Section 6.2: 1989;
v. a powder system, BS5306: Part 7: 1988.
Note: Selection of system is discussed in BS5306: Part O: 1986.
c. In enclosed shopping centres the automatic fire control system must cover the entire shopping centre, except -
i. those parts of malls with a ceiling height in excess of 10m;
ii. stairway enclosures;
iii. car parks; and
iv. those areas where sprinklers would prove a hazard (e.g switchrooms).
In enclosed shopping centres the level of sprinkler protection must be appropriate to the occupancies within the shopping centre and must be determined on the basis of risk assessment, with Quick Response Sprinklers (with a response time index of less than 50m1/2s1/2); and comply with the Loss Prevention Council Rules for Automatic Sprinkler Installations (LPC, 1994) (including all additional life safety recommendations).
d. The requirements of D2.1 for a suitable pressurisation technique will be met by one complying with BS5588: Part 4: 1999.
e. In the case of a smoke control fire door as required in Table 2 to D2.1, unless pressurisation techniques are used complying with BS5588: Part 4: 1998 are used, the fire door should have a leakage rate not exceeding 3m3/m/hour, head and jambs only, when tested at 25Pa according to BS476: Section 31.1: 1983.
JUNCTIONS BETWEEN SEPARATING OR COMPARTMENT WALLS AND ROOFS
(D3.5) The requirements of D3.5 will be met where a separating wall or compartment wall projects through the roof to a distance at least 375mm above the top surface of the roof, except -
a separating wall or compartment wall may be taken to the underside of the roof substrate -
a. in the case of a non-combustible substrate, where the junction is fire-stopped and the roof covering is of designation AA, AB or AC (see BS476: Part 3: 1958) for a distance of at least 1.7m to each side of the centreline of the wall; or
b. in the case of a pitched roof covered by slates nailed directly to sarking and underlay, the junction between sarking and wall-head is fire-stopped; or
c. in the case of a pitched roof covered by slates or tiles fixed to tiling battens and any counter-battens, where only the tiling battens and underlay are carried over the wall and are fully bedded in mortar (or not less suitable material) at the wall-head.
Note: BRE Housing Defects Prevention Unit "Defect Action Sheet (Design)," DAS 8, (BRE, 1982) should be referred to in the case of c. above.
(D3.10) The requirements of D3.10 will be met in the case of a paint spray booth, or room where a cellulose or other flammable liquid spray, which is constructed in accordance with the Health and Safety Executive Guidance Note PM25
"Vehicle finishing units fire and explosion hazards" (HSE, 1981).
(D4.1) a. The requirement of D4.1 in addition to the requirements in Table 2 to D2.1 will be met where the cavity barrier -
i. is imperforate, except -
A. it may contain a fire door; or
B. it may be penetrated by a pipe, cable or duct, complying with D5.1; or
C. it may be penetrated by a duct enclosure constructed of mild steel at least 1.2mm thick (18swg) which is continuous throughout the cavity on both sides of the cavity barrier; or
ii. is imperforate and is in a timber stud wall or partition and formed of -
A. polythene sleeved mineral wool, or mineral wool slab, in either case under compression when installed in the cavity; or
B. calcium silicate, cement based or gypsum based board at least 12mm thick; or
C. steel at least 0.5mm thick; or
D. timber at least 38mm thick; and
iii. is tightly fitted to rigid construction, or where this is not possible (for example, in the case of a junction with slates, tiles, corrugated sheeting or similar materials) the junction is fire-stopped in accordance with (D5.2) and (D5.3); and
iv. is fixed so that its performance is unlikely to be made ineffective by -
A. movement of the building due to subsidence, shrinkage or thermal change, or
B. collapse in a fire of any services penetrating it, or
C. failure in a fire of its fixings, or
D. failure in a fire of any material or element of structure which it abuts.
b. Where a fire resisting ceiling is provided instead of a cavity barrier in accordance with D4.1f.iv. the requirements of this exception to D4.1 will be met where the ceiling -
i. is of imperforate and non-demountable construction with no openings other than -
A. those complying with D5.1 and D5.2; and
B. a hatch which maintains the fire resistance of the ceiling when closed; and
ii. has a classification for surface spread of flame on the side facing the cavity of at least Class 0, or if there is any thermal insulation which is supported by the ceiling, that insulation has a classification for surface spread of flame on the side facing the cavity of at least Class 0.
(D5.1) a. The requirements of D5.1 other than for a ventilating duct will be met where the building service -
i. has at least the fire resistance required for fire division wall or floor, or
ii. is protected by a construction which has at least the fire resistance required for the fire division wall or floor provided by -
A. a casing which has the required fire resistance from the outside; or
B. a casing which has at least half the required fire resistance from each side; or
iii. is provided with an automatic heat activated sealing device which in the event of fire will close the opening to maintain the fire resistance required for fire division wall or floor; or
iv. is a pipe, or in the case of A. below is a cable, which -
A. has a bore, or diameter, of not more than 40mm and, if there are not more than 4 such pipes or cables, they are at least 40mm apart and at least 100mm from any other pipe or cable, or, if there are more than 4 such pipes or cables they are at least 100mm apart; or
B. has a bore of not more than 160mm and is of iron, steel or copper, or of a material capable of withstanding 800°C without allowing flames or hot material to pass through the wall of the pipe; or
C. is a branch pipe of a bore of not more than 110mm to a vertical drainage or water service pipe, is of aluminium or aluminium alloy, or of uPVC to BS4514: 1983, passes through a wall and the vertical pipe is enclosed throughout in a construction which is fire resisting as specified in sub-paragraph ii. above, or, is protected in accordance with sub-paragraph iii. above.
b. Where a pipe is connected within 1m of a fire resisting wall or floor to another pipe to which a more onerous provision applies the pipe has to meet that more onerous provision.
c. The requirements of D5.1 for a ventilating duct will be met where it complies with the provisions of BS5588: Part 9: 1999: Section 3; or -
i. is provided, where the ventilating duct passes through an element of structure, with an automatic damper or shutter or other sealing device which, in the event of fire, will close to maintain the fire resistance required for the element of structure, and prevent the flow of air or hot gases, except -
an automatic damper or shutter or other sealing device is not required in the case of a ventilating duct passing through a cavity barrier where the duct is constructed of mild steel at least 1.2mm thick (18swg) which is continuous throughout the cavity on both sides of the cavity barrier; or
ii. is of a construction or within a construction which has at least the fire resistance for the element of structure and the duct is provided at each point where it or the construction enclosing the duct no longer has the same fire resistance as the element of structure with an automatic damper or shutter or other sealing device, which in the event of fire will close to maintain the fire resistance, for integrity only, required for any element of structure through which it passes; or
iii. passes through a compartment wall or compartment floor and has openings within only one compartment of the building and in any other compartment has at least the fire resistance required for the compartment wall or compartment floor through which it passes; or
iv. is a non-combustible duct for mechanical extraction which passes through a separating floor of a building of purpose group 1 and serves only sanitary accommodation, the vertical part of the duct having either at least the fire resistance, or being within a construction which has at least the fire resistance, required for a separating floor and the branches to the duct being shunt ducts which enter the main duct not less than 900mm above their inlets; and
v. in any case is provided with extract grilles with non-return shutters.
(D5.2) The requirements of D5.2 and D5.3 will be met in the case when minimum differential movement
(D5.3) is anticipated by the use of -
a. cement mortar;
b. gypsum based plaster;
c. cement or gypsum based vermiculite/perlite mixes;
d. glass, crushed rock, blast furnace slag or ceramic based products (with or without resin binders); or
when differential movement is anticipated by the use of -
e. elastomeric materials which have been shown by test with representative gaps, and similar services to maintain the fire resistance of the element of structure; or
f. intumescent mastics which have been shown by test with representative gaps, and similar services to maintain the fire resistance of the element of structure; or
g. a proprietary sealing system which has been shown by test with representative gaps, and similar services to maintain the fire resistance of the element of structure.
To prevent displacement, materials used for fire-stopping must be reinforced with, or supported by, non-combustible materials -
i. where the unsupported span is greater than 100mm; and
ii. where non-rigid materials are used, unless they have been shown by test within their field of application to be satisfactory.