Items where Subject is "B3: Internal fire spread (structure)"
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- B3: Internal fire spread (structure) (105)
B3.(1) The building shall be designed and constructed so that, in the event of fire, its stability will be maintained for a reasonable period
(2) A wall common to two or more buildings shall be designed and constructed so that it adequately resists the spread of fire between those buildings.
For the purposes of this sub-paragraph a house in a terrace and a semi-detached house are each to be treated as a separate building.
(3) Where reasonably necessary to inhibit the spread of fire within the building, measures shall be taken, to an extent appropriate to the size and intended use of the building, comprising either or both of the following—
(a) sub-division of the building with fire-resisting construction;
(b) installation of suitable automatic fire suppression systems.
(4) The building shall be designed and constructed so that the unseen spread of fire and smoke within concealed spaces in its structure and fabric is inhibited.
Requirement B3(3) does not apply to material alterations to any prison provided under section 33 of the Prison Act 1952.
In the Secretary of State’s view, requirement B3 is met by achieving all of the following.
a. For defined periods, loadbearing elements of structure withstand the effects of fire without
loss of stability.
b. Compartmentation of buildings by fire resisting construction elements.
c. Automatic fire suppression is provided where it is necessary.
d. Protection of openings in fire-separating elements to maintain continuity of the fire separation.
e. Inhibition of the unseen spread of fire and smoke in cavities, in order to reduce the risk of
structural failure and spread of fire and smoke, where they pose a threat to the safety of people
in and around the building.
The extent to which any of these measures are necessary is dependent on the use of the building
and, in some cases, its size, and on the location of the elements of construction.
Fire doors between the garage and dwellinghouse to have a minimum fire resistance of E30 Sa and be fitted with a self-closing device
Wall and any floor between the garage and dwellinghouse to have a minimum fire resistance of REI 30 from the garage side
The door opening threshold should be a minimum of 100mm above garage floor or
Floor to fall away from door to the outside
See paras 5.6 and 5.7
Adjoining buildings should only be separated by walls, not floors. Compartment walls common to two or more buildings should comply with both of the following.
a. Run the full height of the building in a continuous vertical plane.
b. Be continued through any roof space to the underside of the roof (see Diagram 5.2).
A compartment wall should achieve both of the following.
a. Meet the underside of the roof covering or deck, with fire-stopping to maintain the continuity of fire resistance.
b. Be continued across any eaves.
To reduce the risk of fire spreading over the roof from one compartment to another, a 1500mm wide zone of the roof, either side of the wall, should have a covering classified as BROOF(t4), on a substrate or deck of a material rated class A2-s3, d2 or better, as set out in Diagram 5.2a.
Thermoplastic rooflights that, because of paragraph 12.7, are regarded as having a BROOF(t4) classification are not suitable for use in that zone.
Materials achieving class B-s3, d2 or worse used as a substrate to the roof covering and any timber tiling battens, fully bedded in mortar or other suitable material for the width of the wall (Diagram 5.2b), may extend over the compartment wall in buildings that are a maximum of 15m high.
Double-skinned insulated roof sheeting should incorporate a band of material rated class A2-s3, d2 or better, a minimum of 300mm in width, centred over the wall.
As an alternative to the provisions of paragraphs 5.12 to 5.14, the compartment wall may extend through the roof for a minimum of either of the following (see Diagram 5.2c).
a. Where the height difference between the two roofs is less than 375mm, 375mm above the top surface of the adjoining roof covering.
b. 200mm above the top surface of the adjoining roof covering where either of the following applies.
i. The height difference between the two roofs is 375mm or more.
ii. The roof coverings either side of the wall are of a material classified as BROOF(t4).
Cavities in the construction of a building provide a ready route for the spread of smoke and flame, which can present a greater danger as any spread is concealed. For the purpose of this document, a cavity is considered to be any concealed space.
To reduce the potential for fire spread, cavity barriers should be provided for both of the following.
a. To divide cavities.
b. To close the edges of cavities.
Cavity barriers should not be confused with fire-stopping details (Section 9).
Cavity barriers should be provided at all of the following locations.
a. At the edges of cavities, including around openings (such as windows, doors and exit/entry points for services).
b. At the junction between an external cavity wall and every compartment floor and compartment wall.
c. At the junction between an internal cavity wall and every compartment floor, compartment wall or other wall or door assembly forming a fire resisting barrier.
This does not apply where a wall meets the conditions of Diagram 5.3.
It is not appropriate to complete a line of compartment walls by fitting cavity barriers above them. The compartment wall should be extended to the underside of the floor or roof above.
If one element of structure supports or stabilises another, as a minimum the supporting element should have the same fire resistance as the other element.
a. ANY BUILDING OR COMPARTMENT
Roof covering over this distance to be designated BROOF(t4) rated on deck of material of class A2-s3, d2 or better. Roof covering and deck could be composite structure, e.g. profiled steel cladding.
Fire-stopping to be carried up to underside of roof covering, boarding or slab.
Roof covering to be designated BROOF(t4) rated for at least 1500mm either side of wall.
b. RESIDENTIAL (DWELLINGS) AND RESIDENTIAL (OTHER) A MAXIMUM OF 15M HIGH
Boarding (used as a substrate) or timber tiling battens may be carried over the wall provided that they are fully bedded in mortar (or other no less suitable material) where over the wall.
Thermoplastic insulation materials should not be carried over the wall.
Double-skinned insulated roof sheeting with a thermoplastic core should incorporate a band of material of class A2-s3, d2 at least 300mm wide centred over the wall.
Sarking felt may also be carried over the wall.
If roof support members pass through the wall, fire protection to these members for a distance of 1500mm on either side of the wall may be needed to delay distortion at the junction (see paragraph 5.9).
Double-skinned insulated roof sheeting should incorporate a band of material rated class A2-s3, d2 or better, a minimum of 300mm in width, centred over the wall.
If roof support members pass through the wall, fire protection to these members for a distance of 1500mm on either side of the wall may be needed to delay distortion at the junction (see paragraph 5.9).
Fire-stopping to be carried up to underside of roof covering, e.g. roof tiles.
Section X–X
Roof covering to be designated BROOF(t4) rated for at least this distance.
Roofing battens and sarking felt may be carried over the wall.
Fire-stopping to be carried up to underside of roof covering above and below sarking felt.
NOTES:
1. Fire-stopping should be carried over the full thickness of the wall.
2. Fire-stopping should be extended into any eaves.
3. The compartment wall does not necessarily need to be constructed of masonry.
c. ANY BUILDING OR COMPARTMENT
The wall should be extended up through the roof for a height of at least 375mm above the top surface of the adjoining roof covering.
Where there is a height difference of at least 375mm between two roofs or where the roof coverings on either side of the wall are BROOF(t4) rated, the height of the upstand/parapet wall above the highest roof may be reduced to 200mm.
See paras 5.12 to 5.15
Cavity barriers, tested from each side separately, should provide a minimum of both of the following:
a. 30 minutes’ integrity (E 30)
b. 15 minutes’ insulation (I 15).
They may be formed by a construction provided for another purpose if it achieves the same performance.
Cavity barriers in a stud wall or partition, or provided around openings, may be formed of any of the following.
a. Steel, a minimum of 0.5mm thick.
b. Timber, a minimum of 38mm thick.
c. Polythene-sleeved mineral wool, or mineral wool slab, under compression when installed in the cavity.
d. Calcium silicate, cement-based or gypsum-based boards, a minimum of 12mm thick.
These do not necessarily achieve the performance specified in paragraph 5.20.
NOTE: Cavity barriers provided around openings may be formed by the window or door frame, if the frame is constructed of steel or timber of the minimum thickness in (a) or (b), as appropriate.
Cavity barriers should be tightly fitted to a rigid construction and mechanically fixed in position. If this is not possible (e.g. where a cavity barrier joins to slates, tiles, corrugated sheeting or similar materials) the junction should be fire-stopped.
Cavity barriers should be fixed so their performance is unlikely to be made ineffective by any of the following.
a. Movement of the building due to subsidence, shrinkage or temperature change, and movement of the external envelope due to wind.
b. During a fire, collapse of services penetrating the cavity barriers, either by the failure of the supporting system or through degradation of the service itself (e.g. by melting or burning).
c. During a fire, failure of the cavity barrier fixings. (In roof spaces, where cavity barriers are fixed to roof members, there is no expectation of fire resistance from roof members provided for the purpose of support.)
d. During a fire, failure of any material or construction to which cavity barriers abut. (For example, a suspended ceiling that continues over a fire resisting wall or partition collapses, and the cavity barrier fails prematurely because the ceiling was not designed to provide a minimum fire resistance of EI 30.)
Openings should be limited to the following.
a. Fire doorsets with a minimum E 30 rating, fitted in accordance with Appendix C.
b. The passage of pipes that follow the provisions in Section 9.
c. The passage of cables or conduits containing one or more cables.
d. Openings fitted with a suitably mounted and appropriate fire damper.
e. Ducts that are either of the following.
i. Fire resisting (minimum E 30).
ii. Fitted with a suitably mounted and appropriate fire damper where they pass through the cavity barrier.
NOTE: For further guidance on openings in cavity barriers see Section 9.
The following are excluded from the definition of ‘element of structure’.
a. A structure that supports only a roof, unless either of the following applies.
i. The roof performs the function of a floor, such as a roof terrace, or as a means of escape.
ii. The structure is essential for the stability of an external wall that needs to be fire resisting (e.g. to achieve compartmentation or for the purposes of preventing fire spread between buildings).
b. The lowest floor of the building.
c. External walls, such as curtain walls or other forms of cladding, which transmit only self weight and wind loads and do not transmit floor load.
NOTE: In some cases, structural members within a roof may be essential for the structural stability system of the building. In these cases, the structural members in the roof do not just support a roof and must demonstrate the relevant fire resistance for the building as required by paragraph 5.2 above.
NOTES:
1. Materials used to close the cavity in this arrangement do not need to achieve a specific performance in relation to fire resistance.
2. Domestic meter cupboards may be installed provided that the following conditions are met:
a. There are no more than two cupboards per dwelling
b. The openings in the outer wall leaf are not bigger than 800X500mm for each cupboard
c. The inner leaf is not penetrated except by a sleeve not more than 80X80mm, which is fire-stopped.
3. Materials achieving class B-s3, d2 or worse may be placed within the cavity.
See para 5.18
Where adding an additional storey to a two storey single family dwellinghouse, new floors should have a minimum REI 30 fire resistance. Any floor forming part of the enclosure to the circulation space between the loft conversion and the final exit should achieve a minimum rating of REI 30.
The existing first-storey construction should have a minimum rating of R 30. The fire performance may be reduced for integrity and insulation, when both of the following conditions are met.
a. Only one storey is added, containing a maximum of two habitable rooms.
b. The new storey has a maximum total area of 50m2.
Dwellinghouses that are semi-detached or in terraces should be considered as separate buildings. Every wall separating the dwellinghouses should be constructed as a compartment wall (see paragraphs 5.8 to 5.12).
If a garage is attached to or forms an integral part of a dwellinghouse, the garage should be separated from the rest of the dwellinghouse by fire resisting construction (minimum REI 30) (Diagram 5.1).
Where a door is provided between a dwellinghouse and the garage (see Diagram 5.1), it should meet one of the following conditions.
a. The garage floor should be laid such that it falls away from the door to the outside, to allow fuel spills to flow away.
b. The door opening should be a minimum of 100mm above the level of the garage floor.
All compartment walls and compartment floors should achieve both of the following.
a. Form a complete barrier to fire between the compartments they separate.
b. Have the appropriate fire resistance, as given in Appendix B, Table B3 and Table B4.
Timber beams, joists, purlins and rafters may be built into or carried through a masonry or concrete compartment wall if the openings for them are both of the following.
a. As small as practicable.
b. Fire-stopped.
If trussed rafters bridge the wall, failure of the truss due to a fire in one compartment should not cause failure of the truss in another compartment.
The following are excluded from the definition of ‘element of structure’.
a. A structure that supports only a roof, unless either of the following applies.
i. The roof performs the function of a floor, such as for parking vehicles, or as a means of escape.
ii. The structure is essential for the stability of an external wall that needs to be fire resisting (e.g. to achieve compartmentation or for the purposes of preventing fire spread between buildings).
b. The lowest floor of the building.
c. A platform floor.
d. External walls, such as curtain walls or other forms of cladding, which transmit only self weight and wind loads and do not transmit floor load.
NOTE: In some cases, structural members within a roof may be essential for the structural stability system of the building. In these cases, the structural members in the roof do not just support a roof and must demonstrate the relevant fire resistance for the building as required by the note to paragraph 6.1 above.
If a floor is also a compartment floor, see Section 7.
Where an existing dwellinghouse or other building is converted into flats, a review of the existing construction should be carried out. Retained timber floors may make it difficult to meet the relevant provisions for fire resistance.
In a converted building with four or more storeys, the full standard of fire resistance given in Appendix B is necessary.
The diagram shows three common examples which illustrate the principles. The elements enclosing the shaft (unless formed by adjacent external walls) are compartment walls and floors.
The shaft structure (including any openings) should meet the relevant provisions for: compartment walls (see paragraphs 7.5 to7.19), external walls (see sections 10 and 11 and Diagram 3.10).
See para 7.23
Compartment walls not described in paragraphs 7.8 and 7.9 should run the full height of the storey in which they are situated.
Compartment walls in a top storey beneath a roof should be continued through the roof space.
At the junction with another compartment wall or an external wall, the fire resistance of the compartmentation should be maintained. Fire-stopping that meets the provisions in paragraphs 9.24 to 9.29 should be provided.
At the junction of a compartment floor and an external wall with no fire resistance, the external wall should be restrained at floor level. The restraint should reduce movement of the wall away from the floor if exposed to fire.
Compartment walls should be able to accommodate deflection of the floor, when exposed to fire, by either of the following means.
a. Between the wall and floor, provide a head detail that is capable of maintaining its integrity while deforming.
b. Design the wall so it maintains its integrity by resisting the additional vertical load from the floor above.
Where compartment walls are located within the middle half of a floor between vertical supports, the deflection may be assumed to be 40mm unless a smaller value can be justified by assessment. Outside this area, the limit can be reduced linearly to zero at the supports.
For steel beams that do not have the required fire resistance, reference should be made to SCI Publication P288.
The requirements are the same as for dwellinghouses, detailed in paragraphs 5.11 and 5.12.
Materials achieving class B-s3, d2 or worse used as a substrate to the roof covering and any timber tiling battens, fully bedded in mortar or other suitable material for the width of the wall (Diagram 5.2b), may extend over the compartment wall in buildings that are both of the following.
a. A maximum of 15m high.
b. In one of the following purpose groups.
i. All residential purpose groups (purpose groups 1 and 2) other than ‘residential (institutional)’ (purpose group 2(a)).
ii. ‘Office’ (purpose group 3).
iii. ‘Assembly and recreation’ (purpose group 5).
Double-skinned insulated roof sheeting with a thermoplastic core should incorporate a band of material rated class A2-s3, d2 or better, a minimum of 300mm in width, centred over the wall.
As an alternative to the provisions of paragraph 7.16 or 7.17, the compartment wall may extend through the roof for a minimum of either of the following (see Diagram 5.2c).
a. Where the height difference between the two roofs is less than 375mm, 375mm above the top surface of the adjoining roof covering.
b. 200mm above the top surface of the adjoining roof covering where either of the following applies.
i. The height difference between the two roofs is 375mm or more.
ii. The roof coverings either side of the wall are of a material classified as BROOF(t4).
Openings in a compartment wall common to two or more buildings should be limited to those for either of the following.
a. A fire doorset providing a means of escape, which has the same fire resistance as the wall and is fitted in accordance with the provisions in Appendix C.
b. The passage of a pipe that complies with the provisions in Section 9.
Fire resisting construction enclosing these places should achieve minimum REI 30. These walls and floors are not compartment walls and compartment floors.
Fire resistance to protected shaft to be a maximum of REI 60
Fire resistance of construction to be a minimum of REI 30 (including fire doorsets that are a minimum of E 30 Sa)
Fire resistance of glazing to be a minimum of RE 30(including fire doorsets that are a minimum of E 30 Sa)
a. WITH CORRIDOR
b. WITH LOBBY
See para 7.25
Openings should be limited to those for any of the following.
a. Fire doorsets of the appropriate fire resistance, fitted in accordance with the provisions in Appendix C.
b. Pipes, ventilation ducts, service cables, chimneys, appliance ventilation ducts or ducts encasing one or more flue pipes, complying with the provisions in Section 9.
c. Refuse chutes of class A1 construction.
d. Atria designed in accordance with Annexes B and C of BS 9999.
e. Protected shafts that conform to the provisions in the following paragraphs.
Stairs and service shafts connecting compartments should be protected to restrict the spread of fire between the compartments. These are called protected shafts. Walls or floors surrounding a protected shaft are considered to be compartment walls or compartment floors.
Any stair or other shaft passing directly from one compartment to another should be enclosed in a protected shaft. Protected shafts should be used for the following only, but may also include sanitary accommodation and washrooms.
a. Stairs.
b. Lifts.
c. Escalators.
d. Chutes.
e. Ducts.
f. Pipes.
g. Additional provisions apply for both of the following.
i. Protected shafts that are protected stairways: Sections 2 to 4.
ii. Stairs that are also firefighting stairs: Section 15.
The construction enclosing a protected shaft (Diagram 7.1) should do all of the following.
a. Form a complete barrier to fire between the compartments connected by the shaft.
b. Have the appropriate fire resistance given in Appendix B, Table B3, except for uninsulated glazed screens that meet the provisions of paragraph 7.24.
c. Satisfy the provisions for ventilation and the treatment of openings in paragraphs 7.28 and 7.29.
An uninsulated glazed screen may be incorporated in the enclosure to a protected shaft between a stair and a lobby or corridor entered from the stair. The enclosure must conform to Diagram 7.2 and meet all of the following conditions.
a. The standard of fire resistance required for the protected stairway is not more than REI 60.
b. The glazed screen complies with the following.
i. It achieves a minimum rating of E 30.
ii. It complies with the guidance on limits on areas of uninsulated glazing in Appendix B, Table B5.
c. The lobby or corridor is enclosed with fire resisting construction achieving a minimum rating of REI 30.
Where the measures in Diagram 7.2 are not provided, then both of the following apply.
a. The enclosing walls should comply with Appendix B, Table B3.
b. The doors should comply with Appendix B, Table B5.
A protected shaft containing a protected stairway and/or a lift should not also contain either of the following.
a. A pipe that conveys oil, other than in the mechanism of a hydraulic lift.
b. A ventilating duct. Two exceptions are as follows.
i. A duct provided for pressurising the protected stairway to keep it smoke free.
ii. A duct provided only to ventilate the protected stairway.
A pipe that is completely separated from a protected shaft by fire resisting construction is not considered to be contained within that shaft.
In a protected shaft, any pipe carrying natural gas or LPG should be both of the following.
a. Of screwed steel or all-welded steel construction.
b. Installed in accordance with both of the following.
i. The Pipelines Safety Regulations 1996.
ii. The Gas Safety (Installation and Use) Regulations 1998.
A protected shaft conveying piped flammable gas should be ventilated direct to the outside air, by ventilation openings at high and low level in the shaft.
Any extension of the storey floor into the protected shaft should not compromise the free movement of air throughout the entire length of the shaft.
Guidance on shafts conveying piped flammable gas, including the size of ventilation openings, is given in BS 8313.
The external wall of a protected shaft does not normally need to have fire resistance. Situations where there are provisions are given in paragraph 3.63 (external walls of protected stairways, which may also be protected shafts) and paragraphs 15.8 to 15.11 (firefighting shafts).
Openings in other parts of the enclosure to a protected shaft should be limited to the following.
a. If a wall common to two or more buildings forms part of the enclosure, only the following openings should be made in that wall.
i. A fire doorset providing a means of escape, which has the same fire resistance as the wall and is fitted in accordance with the provisions in Appendix C.
ii. The passage of a pipe that meets the provisions in Section 9.
b. Other parts of the enclosure (other than an external wall) should only have openings for any of the following.
i. Fire doorsets of the appropriate fire resistance, fitted in accordance with the provisions in Appendix C.
ii. The passage of pipes which meet the provisions in Section 9.
iii. Inlets to, outlets from and openings for a ventilation duct (if the shaft contains or serves as a ventilating duct), meeting the provisions in Section 9.
iv. The passage of lift cables into a lift machine room (if the shaft contains a lift). If the machine room is at the bottom of the shaft, the openings should be as small as practicable.
Parts of a building occupied mainly for different purposes should be separated from one another by compartment walls and/or compartment floors. Compartmentation is not needed if one of the different purposes is ancillary to the other. See paragraphs 0.18 and 0.19.
Blocks of flats with a top storey more than 11m above ground level (see Diagram D6) should be fitted with a sprinkler system throughout the building in accordance with Appendix E.
NOTE: Sprinklers should be provided within the individual flats, they do not need to be provided in the common areas such as stairs, corridors or landings when these areas are fire sterile.
All compartment walls and compartment floors should achieve both of the following.
a. Form a complete barrier to fire between the compartments they separate.
b. Have the appropriate fire resistance, as given in Appendix B, Tables B3 and B4.
Timber beams, joists, purlins and rafters may be built into or carried through a masonry or concrete compartment wall if the openings for them are both of the following.
a. As small as practicable.
b. Fire-stopped.
If trussed rafters bridge the wall, failure of the truss due to a fire in one compartment should not cause failure of the truss in another compartment.
Where services could provide a source of ignition, the risk of fire developing and spreading into adjacent compartments should be controlled.
Adjoining buildings should only be separated by walls, not floors. Compartment walls common to two or more buildings should comply with both of the following.
a. Run the full height of the building in a continuous vertical plane.
b. Be continued through any roof space to the underside of the roof (see Diagram 5.2).
Compartment walls forming a separated part of a building should run the full height of the building in a continuous vertical plane.
Separated parts can be assessed independently to determine the appropriate standard of fire resistance in each. The two separated parts can have different standards of fire resistance.
Cavities in the construction of a building provide a ready route for the spread of smoke and flame, which can present a greater danger as any spread is concealed. For the purpose of this document, a cavity is considered to be any concealed space.
Fire-stopping (same resistance as compartment)
Cavity barriers
NOTE:
1. See paragraph 8.5
See para 8.2
To reduce the potential for fire spread, cavity barriers should be provided for both of the following.
a. To divide cavities.
b. To close the edges of cavities.
See Diagram 8.1. Cavity barriers should not be confused with fire-stopping details (Section 9).
NOTES:
1. Materials used to close the cavity in this arrangement do not need to achieve a specific performance in relation to fire resistance.
2. Domestic meter cupboards may be installed provided that the following conditions are met:
a. There are no more than two cupboards per dwelling
b. The openings in the outer wall leaf are not bigger than 800X500mm for each cupboard
c. The inner leaf is not penetrated except by a sleeve not more than 80X80mm, which is fire-stopped.
3. Materials achieving class B-s3, d2 or worse may be placed within the cavity.
See para 8.3
NOTE:
The ceiling should meet the following conditions.
a. Provide a minimum fire resistance of EI 30.
b. Be imperforate, except for an opening described in paragraph 5.24.
c. Extend through out the building or compartment.
d. Not be easily demountable.
See para 8.5
The insulation should make contact with both skins of sheeting. See also Diagram 5.2a regarding the need for fire-stopping where such roofs pass over the top of a compartment wall.
See para 8.7
If the fire resisting construction of a protected escape route is either of the following.
a. Not carried to full storey height.
b. At the top storey, not carried to the underside of the roof covering.
Then the cavity above or below the fire resisting construction should be either of the following.
i. Fitted with cavity barriers on the line of the enclosure.
ii. For cavities above the fire resisting construction, enclosed on the lower side by a fire resisting ceiling (minimum EI 30) that extends throughout the building, compartment or separated part (see Diagram 8.3).
In divided corridors (paragraph 3.25 and following) with cavities, fire-stopping should be provided to prevent alternative escape routes being affected by fire and/or smoke.
Cavity barriers are not required between double-skinned corrugated or profiled insulated roof sheeting, if the sheeting complies with all of the following.
a. The sheeting is rated class A2-s3, d2 or better.
b. Both surfaces of the insulating layer are rated class C-s3, d2 or better.
c. Both surfaces of the insulating layer make contact with the inner and outer skins of cladding (Diagram 8.4).
Cavity barriers, tested from each side separately, should provide a minimum of both of the following:
a. 30 minutes’ integrity (E 30)
b. 15 minutes’ insulation (I 15).
They may be formed by a construction provided for another purpose if it achieves the same performance.
NOTES:
1. The enclosure should meet all of the following conditions.
a. Be bounded by a compartment wall or floor, an outside wall, an intermediate floor or a casing(see specification at 2 below).
b. Have internal surfaces (except framing members)of class B-s3, d2 or better.
Note: when a classification includes ‘s3, d2’, this means that there is no limit set for smoke production and/or flaming droplets/particles).
c. Not have an access panel which opens into a circulation space or bed room.
d. Be used only for drainage or water supply or vent pipes for a drainage system.
2.The casing should meet all the following conditions.
a. Be imperforate except for an opening for a pipe
or an access panel.
b. Not be of sheet metal.
c. Not have fire resistance less than E 30 (including any access panel).
3.The opening for a pipe, in either the element of structure or the casing, should be as small as possible and fire-stopped around the pipe.
See para 9.4 and Table 9.1
NOTES:
1. Any metal (such as cast iron, copper or steel) which, if exposed to a temperature of 800°C, will not soften or fracture to the extent that flame or hot gas will pass through the wall of the pipe.
2. uPVC pipes that comply with either BS 4514 or BS 5255.
3. These diameters are only in relation to pipes that form part of an above-ground drainage system and are enclosed as shown in Diagram 9.1. In other cases, the maximum diameters given for situation 5 apply.
In mixed use buildings, non-domestic kitchens, car parks and plant rooms should have separate and independent extraction systems. Extracted air should not be recirculated.
Under fire conditions, ventilation and air-conditioning systems should be compatible with smoke control systems and need to be considered in their respective design.
Further information on fire resisting ductwork is given in the ASFP Blue Book.
Where ducts pass between fire-separating elements to serve multiple flats or dwellings, fire dampers or fire and smoke dampers should be actuated by both of the following.
a. Smoke detector-controlled automatic release mechanisms.
b. Thermally actuated devices.
Methods 1 and 4 should not be used for extract ductwork serving kitchens. The likely build-up of grease within the duct can adversely affect dampers.
Method 1 should not be used for extract ductwork passing through the enclosures of protected escape routes (Diagrams 9.3 and 9.4), as large volumes of smoke can pass thermal devices without triggering them.
An ES classified fire and smoke damper which is activated by a suitable fire detection system (method 4) may also be used for protected escape routes.
Both fire dampers and fire and smoke dampers should be all of the following.
a. Sited within the thickness of the fire-separating elements.
b. Securely fixed.
c. Sited such that, in a fire, expansion of the ductwork would not push the fire damper through the structure.
Access to the fire damper and its actuating mechanism should be provided for inspection, testing and maintenance.
Pipes passing through a fire-separating element, unless in a protected shaft, should meet one of the alternatives A, B or C below.
NOTES:
1.Make the opening in the structure as small as possible and provide fire-stopping between pipe and structure.
2.See Table 9.1 for materials specification.
3. The sleeve should be class A1 rated.
See para 9.5
Fire dampers should meet both of the following conditions.
a. Conform to BS EN 15650.
b. Have a minimum E classification of 60 minutes or to match the integrity rating of the fire resisting elements, whichever is higher.
Fire and smoke dampers should meet both of the following conditions.
a. Conform to BS EN 15650.
b. Have a minimum ES classification of 60 minutes or to match the integrity rating of the fire resisting elements, whichever is higher.
Smoke detectors should be sited so as to prevent the spread of smoke as early as practicable by activating the fire and smoke dampers. Smoke detectors and automatic release mechanisms used to activate fire dampers and/or fire and smoke dampers should conform to BS EN 54-7 and BS 5839-3 respectively.
Further information on fire dampers and/or fire and smoke dampers is given in the ASFP Grey Book.
The wall of a flue, duct containing flues or appliance ventilation duct(s) should have a fire resistance (REI) that is at least half of any compartment wall or compartment floor it passes through or is built into (Diagram 9.5).
In addition to any other provisions in this section, both of the following conditions should be met.
a. Joints between fire-separating elements should be fire-stopped.
b. Openings through a fire resisting element for pipes, ducts, conduits or cable should be all of the following.
i. As few as possible.
ii. As small as practicable.
iii. Fire-stopped (allowing thermal movement in the case of a pipe or duct).
NOTE: The fire-stopping around fire dampers, fire resisting ducts, fire and smoke dampers and smoke control ducts should be in accordance with the manufacturer or supplier’s installation instructions.
Materials used for fire-stopping should be reinforced with (or supported by) materials rated class A2-s3, d2 or better to prevent displacement in both of the following cases.
a. Where the unsupported span is greater than 100mm.
b. Where non-rigid materials are used (unless subjected to appropriate fire resistance testing to show their suitability).
Proprietary, tested fire-stopping and sealing systems are available and may be used. Different materials suit different situations and not all are suitable in every situation.
Other fire-stopping materials include the following. a. Cement mortar. b. Gypsum-based plaster. c. Cement-based or gypsum-based vermiculite/perlite mixes. d. Glass fibre, crushed rock, blast furnace slag or ceramic-based products (with or without resin binders). e. Intumescent mastics. These may be used in situations appropriate to the particular material. Not all materials will be suitable in every situation.
Guidance on the design, installation and maintenance of measures to contain fires or slow their spread is given in Ensuring Best Practice for Passive Fire Protection in Buildings produced by the Association for Specialist Fire Protection (ASFP).
Further information on generic systems, their suitability for different applications and guidance on test methods, is given in the ASFP Red Book.
Provide a proprietary, tested sealing system that will maintain the fire resistance of the wall, floor or cavity barrier.
NOTE:
Ventilation ducts which serve other parts of the building should not supply or extract air directly to or from a protected escape route.
Ductwork enclosed in fire resisting construction classified EI X in accordance with BSEN13501-2 (fire exposure from the duct side), or fire resisting ductwork classified EIS X in accordance with BS EN 13501-3, where X is the fire resistance rating (in minutes) of the walls of the protected escape route
See para 9.16
Where a proprietary sealing system is not used, fire-stop around the pipe, keeping the opening for the pipe as small as possible. The nominal internal diameter of the pipe should not exceed the relevant dimension given in Table 9.1. The diameter given in Table 9.1 for pipes of specification (b) used in situation 2 or 3 assumes that the pipes are part of an above-ground drainage system and are enclosed as shown in Diagram 9.1. If they are not, the smaller diameter given for situation 5 should be used.
ES leakage rated fire and smoke damper conforming to BS EN 13501-3/BS EN 1366-2
Smoke detection system in accordance with BS 5839-1 to activate ES damper
Ductwork passing through protected escape routes–method 4
NOTE:
Ventilation ducts which serve other parts of the building should not supply or extract air directly to or from a protected escape route.
See para 9.16
A pipe with a maximum nominal internal diameter of 160mm may be used with a sleeve made out of a high melting point metal, as shown in Diagram 9.2, if the pipe is made of one of the following.
a. Lead.
b. Aluminium.
c. Aluminium alloy.
d. Fibre-cement.
e. uPVC (pipes should also comply with either BS 4514 or BS 5255).
A high melting point metal means any metal (such as cast iron, copper or steel) which, if exposed to a temperature of 800°C, will not soften or fracture to the extent that flame or hot gas will pass through the wall of the pipe.
a. Flue passing through compartment wall or floor
b. Flue built into compartment wall
Flue walls should have a fire resistance of at least one half of that required for the compartment wall or floor and be of class A1construction.
In each case flue walls should have a fire resistance of at least one half of that required for the compartment wall and be of class A1 construction.
See para 9.23
Ductwork should not help to transfer fire and smoke through the building. Terminals of exhaust points should be sited away from final exits, cladding or roofing materials achieving class B-s3, d2 or worse and openings into the building.
Ventilation ducts supplying or extracting air directly to or from a protected stairway should not also serve other areas. A separate ventilation system should be provided for each protected stairway.
A fire and smoke damper should be provided where ductwork enters or leaves each section of the protected escape route it serves. It should be operated by a smoke detector or suitable fire detection system. Fire and smoke dampers should close when smoke is detected. Alternatively, the methods set out in paragraphs 9.16 and 9.17 and Diagrams 9.3 and 9.4 may be followed.
In a system that recirculates air, smoke detectors should be fitted in the extract ductwork before both of the following.
a. The point where recirculated air is separated from air to be discharged to the outside.
b. Any filters or other air cleaning equipment.
When smoke is detected, detectors should do one of the following.
i. Cause the system to immediately shut down.
ii. Switch the ventilation system from recirculating mode to extraction to divert smoke to outside the building.