Method 3.- Protection using Fire ResistingDuctworkThe ductwork itself forms a protected shaft. Thefire resistance may be achieved by the ductworkmaterial itself or through the application of a pro­tective material provided that the ductwork hasbeen tested and/or assessed to BS476 Part 24 witha fire resistance, when tested from either side thatshould not be less than the fire resistance requiredfor the elements of construction in the areathrough which it passes. It should also be notedthat the fire resisting ductwork must be supportedwith suitably sized and designed hangers, whichreflect the reduction in tensile strength of steel ina fire condition .i.e:Fire resisting ductwork rated at 60 minutes(945°C), reduces the tensile strength from 430Nzrnm' to 15 Nzrnm'.Fire resisting ductwork rated at 120 minutes(1,049°C) tensile strength reduced to -10Nzmm-,Fire resisting ductwork rated at 240 minutes(1,153°C) tensilestrength reduced to 6 Nzmm'.Where the fire resisting ductwork passes througha fire compartment wall or floor. a penetrationseal must be provided which has been testedand/or assessed with the ductwork to BS476 Part24, to the same fire rating as the compartmentwall through which the fire resisting ductworkpasses. It should also be noted that where the fireresisting ductwork passes through the fire com­partment wall or floor, the ductwork itself must bestiffened to prevent deformation of the duct in afire to:a) maintain the cross-sectional area of the ductb) ensure .that the fire rated penetration seal

around the duct is not compromised.

D.2.2 - Main areas within building whereDuctworkshould be fire protectedThe following notes are for guidance only, and itshould be noted that authority rests with theBuilding Control Officer and/or the Fire Officerresponsible for the building. Reference on thefolowing systems should also be made to the cur­rent Building Regulations.a. Smoke Extract Systems:

If the ductwork incorporated in a smokeextract system is wholly contained within thefire compartment, it must be capable of resist­ing the anticipated temperatures generatedthrough the development of a fire. BS 476Part 24 also requires ductwork, which isintended as a smoke extract, must retain atleast 75% of its cross-sectional area within thefire compartment. If the ductwork penetrates afire resisting barrier, it must alsobe capable ofproviding the same period of fire resistance.

b. Escape Routes covering Stairways, Lob­bies and CorridorsAll escape routes must be designed so ~at. thebuilding occupants can evacuate the building

D.l Fire and smoke containmentlhazards arefactors which influence the design and installationof ductwork systems.Information. concerning fire protection systems islaid down in BS 5588, Fire Precautions in thedesign. and construction of Building Part 9 (1989)Code of Practice for Ventilation and Air Condi­tioning Ductwork and tested in accordance withBS 476Part 20(1987) and BS 476 Part 22 (1987)forFire and Smoke Dampers and British Standard476 Part 24 (1987) - ISO 6944 - (1985) for FireRated Ductwork.D.2 Building Regulations in the Umted Kingdomrequire that new buildings be divided into firecompartments in. order that the spread of smokeand fire in the building is inhibited, and to stop thespread of smoke and fire from one compartmentto another, for given periods of time as specifiedby the Building Regulations 1991 (ApprovedDocument B).D.2.1 There are three methods of fire protection,related to ductwork systems as given in BS 5~88Part 9 (1989).

Method 1 - Protection using Fire DampersThe fire is isolated in the compartment of originby the automatic or manual actuation of closureswithin the system. Fire dampers should, therefore.be sited at the point of penetration of acompartment .wall or floor, or at the point ofpenetration of the enclosure of a protected escaperoute.Fire dampers should be framed in such away as toallow for thermal. expansion in the event of fire,and the design must provide for the protection ofany packing material included.Standard types of fire dampers and frames aredescribed in Section 22 of this specification.For further information refer to the impendingHVCA publication DWfTM3, 'Guide to GoodPractice for the Design for the Installation of Fireand Smoke Dampers'.Method 2 - Protection using Fire ResistingEnclosuresWhere a building services shaft is providedthrough which the ventilation ductwork passesand if the shaft is constructed to the highest stan­dard of fire resistance of the structure which itpenetrates, it forms a compartment known as aprotected shaft. This allows a complicated multi­plicity of services to be transferred togetherthrough a shaft transversing a number of compart­ments andreaching remote parts of the building,without requiring further internal divisions alongits length ..The provision of fire dampers is thenrequired only at points where the ventilation ductleaves the confines of the protected shaft.However, if there "isonly one ventilation duct andthere are no other services within the protectedshaft, between the fire compartment and the out­side of the building, no fire dampers will berequired.

APPENDIX D - DUCTWORK SYSTEMS AND FIRE HAZARDSI

This appendix incorporates information given in the A.S.EP publication 'Fire Rated and Smoke OutletDuctw?rk: An ~d~stry Guide to Design and Installation' available from Association for Specialist FireProtection, ASSOCIatIonHouse, 235 Ash Road, Aldershot, Hampshire GU12 4DD (Telephone: 01252 21322Fax: 01252 333901) .

compartment). Basements with natural venti­lation should have permanent openings, .notless than 2.5% of the floor area andbe arranged to provide a through draft withseparate fire ducts for ea~h compartment.

f. Pressurisation SystemsPressurisation is a method of restricting thepenetration of smoke into certain critical areasof a building by maintaining theair at higherpressures than those in adjacent areas. Itapplies particularly to protect stairways, lob­bies, corridors and fire fighting shafts servingdeep basements as smoke penetration to theseareas would inhibit escape.As the air supply creating the pressurisationmust be maintained for the duration of a fire,fire dampers cannot be used within the duct­work to prevent the spread of fire. Any duct­work penetrating fire resisting barriers mustbe capable of providing the same period offire resistance.

g. Hazardous AreasThere are other areas within the buildingwhere the Building Control Officer or the FireOfficer could state a requirement for fireresisting ductwork, ego areas of high risk,Boiler Houses, Plantrooms, TransformerRooms etc.

D.2.3 Cautionary note to all DuctworkDesigners! Manufacturers:Ductwork constructed to DW/144 Standard hasno tested fire resistance. General purpose ventila­tion/air conditioning ductwork and its ancillaryitems do not have a fire rating and cannot be eitherutilised as or converted into a fire rated ductworksystem unless the construction materials of thewhole system including supports and penetration­seals are proven by test and assessment in accor­dance with BS 476 Part 24.In the case where galvanised sheet steel ductworkis clad by the application of a protective material,the ductwork construction must be as type testedand comply with the protective material manufac­turers recommendations, ego gauge of ductwork,frequency of stiffeners and non-use of low melt­ing point fasteners or rivets. Sealants, gaskets andflexible joints should be as tested and certificatedin accordance with BS 476 Part 24 and complywith the manufacturers recommendations.Careful consideration must also be given to themaximum certificated size tested to BS 476 Part24 and the manufacturers recommendationsshould always be followed.

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safely in. the case of fire. Ductwork whichpasses through a protected escape route musthave a fire resistance at least equal to the firecompartment through which the ductworkpasses, either by the use of fire dampers orfire resisting ductwork.

c. Non Domestic Kitchen Extract SystemsWhere there is no immediate discharge toatmosphere, i.e. the ductwork passes toatmosphere via another fire compartment, fireresistant ductwork must be used. Kitchenextract ductwork presents a particular hazardas combustible deposits such as grease arelikely to accumulate on internal surfaces,therefore, all internal surfaces of the ductworkmust be smooth. A fire in an adjacent com­partment, through which the ductwork passes,could lead to ignition of the grease deposits,which may. continue. through the. ductworksystem, possibly prejudicing the safety of thekitchen occupants. For this reason considera­tion must be given to the stability, integrityand insulation performance of the kitchenextract duct which should be specificallytestedto BS 476 Part 24 for a kitchen extract rating.• Access doors for cleaning must be pro­

vided at distances not exceeding 3 metres.• Fire dampers must not be used.~ Use of volume control dampers and turn-

ing vanes are not recommended.Further information on kitchen extract systemswill be found in the HVCA publication DW1171Specification for Kitchen Ventilation Systems.d. Enclosed Car Parks - which are

mechanically ventilatedCar Parks must have separate and indepen­dent. extract systems, because of the pollutednature of the extract air. Due to the fire riskassociated with car parks, these systemsshould be treated as smoke extract systemsand therefore maintain a minimum of 75%cross-sectional area under fire conditions inaccordance with BS 476 Part 24. Fire dampersmust not be installed in extract ductwork serv­ing car parks.

e. Basements - Ductwork from Basementsmust be Fire RatedIf basements are compartmented, each sepa­rate compartment must have a separate outletand have access to ventilation without havingto gain access (i.e. open a door to another