Upgrading the fire resistance of floors and doors in heritage buildings

Heritage fire protection – some considerations• A property fire risk assessment shouldbe made before any upgrading ofstructural fire precautions.• Consider importance and value ofitems at risk – structure, furnishings,contents.• Consider importance of site as arevenue earner• Have all plausible fire /smoke routesbeen identified?• Can fire detection be improved – e.g.can aspirated smoke detection bejustified?• Can in-house staff get to incipient firesin time to extinguish them–what aboutfires in cavities and fires at high level?• What fire suppression devices areavailable for immediate use• Can fire safety management beimproved – e.g. can 24 hoursurveillance be afforded?• What is attendance time of fire serviceappliances?• Has fire plan been considered insufficient detail. Staff may not be ableto remove important items to a place ofsafety and fight incipient fire at thesame time• What benefits will structural fireprecautions bring?• Improving fire compartmentation byupgrading the fire resistance of doorsand floors (the subject of thispresentation) is an important, but smallpart, of the overall fire safety strategy

• All attempts should be made toleave the fabric and structure of thebuilding in its original form• Structural improvements should beinvisible if possible. This issometimes possible, and exampleswill be shown to demonstrate howto do this for floors and doors

Step 1Employer starts to assess fire safety inworkplaceEmployer appoints person to carry out assessmentPlan and prepare for carrying out assessmentIdentify fire hazards- sources of ignition- sources of fuel- work processesHSE fire risk assessment planSource: Home Office et al, Fire Safety. Anemployer’s guide, HSE Books, London, UK,1999Step 2Step 3Identify location of people at significant riskin case of fireEvaluate the risksAre existing fire safety measures adequate?-control of ignition sources/sources of fuel- fire detection/warning- means of escape- means of fighting fire- maintenance and testing of fire precautions-fire safety training of employeesCarry out any improvements neededThis plan is concerned with life safety.Similar approach needed for determiningprecautions against loss of property (loss ofbuilding structure and fabric and buildingcontents e.g. furniture and paintings) and lossof business continuity and, of course, loss ofcultural heritage.Step 4Record findings and action takenPrepare emergency planInform, instruct and train employees in fireprecautionsStep 5Keep assessment under reviewRevise if situation changes

Stopping firespread throughfloor and ceilingcavities

Fire spread routes above ceiling at doorpositionUnderside of floorFloorLight fittingPossible fire pathsto be preventedCavity barriernecessary hereOverdoor panel shouldbe fire resistingDoor frameFire doorCeiling• Resistance to all fire spread routesshould be considered• Fire resistance of over door panelshould not be forgotten• Cavity barrier above ceiling isnecessary and should line up withdoor position• Light fittings and other fittings inceiling may be points of weakness

Flexible ceiling cavity fire barrier using rockwoolUnderside of floor or roof• Cavity barrier needed to preventhorizontal fire spread.System willacceptmovementDirection of flow ofsmoke and hot gasesCavity barrierboard materialRock wool skirt (possiblyweighted down to preventuplift due to pressure variations,as at flashover )CeilingCeiling in fire• Barrier should be flexible toaccommodate relativemovements of structure• Flexible rock wool skirt can beused to follow movement

Ceiling cavity barrier using spray materialSystem willacceptmovementDirection of flow ofsmoke and hot gasesUnderside of floor or roofCavity barrierboard materialRock wool skirt (possiblyweighted down to preventuplift due to pressure variations,as at flashover )CeilingCeiling in fire• Expanded metal mesh is placed in acurved shape in the cavity andfixed to floor and ceiling• Lightweight fire protecting spray isapplied at sufficiently low densityto provide some flexibility• Has the advantage that it fills allthe gaps.Disadvantage is that it is awet trade and can be messy, andmay involve fibres.

Increasing thefire resistance offloors

Fire resistance test criteriaFurnace enclosure3mInstabilityor collapseLoss ofintegrityExcessivetemperaturerise

Floor which needs no upgrading• Fan vaulted brickwork is idealshape to carry load. Brickwork incompression behaves well in fireprovided perimeter restraint exists• Cast iron columns are fire protectedwith intumescent spray. Basic formstill seen, retaining aesthetics.

Example of historic ceiling• Clearly unacceptable to apply structuralfire protection to underside of thisceiling• May be possible to increase the fireresistance from above the floor• Any fire precautions should considersmoke damage as well as a fullydeveloped fire.• Cavity barriers within floors may beneeded.• Best option is early fire detection (byaspiration) and rapid fire suppressionby trained staff.• In small rooms automatic water spraymight be appropriate as fire suppression

• Impossible to upgrade the fireresistance of this ceiling frombelow without destroyingaesthetic• Cost of closing the building(which houses an importantcollection of paintings andfurniture) unacceptable.• Is upgrading necessary?• Could floor be upgraded fromabove?

Upgrading by adding new ceiling belowPlain edge timber boardingExisting ceiling in poor conditionTimber joistAdditional timberprotectionExisting ceilingChicken wireTimber battensAdditional boardedceiling• Existing floor boards and ceilingare in poor condition. Access to topand bottom available. Aestheticsnot important• New ceiling can be added usingfire protecting ceiling boards andtimber battens• Old ceiling kept in place forthermal protection using chickenwire mesh• Fixings important• BRE Digest 208 guides

Charring rate of timber versus radiationintensity4Charring rate, cm/s x 101000500100501013.4 mm/min1.7 mm/min0.6Radiation in real firesUSA charring rate dataUK charring rates (nuclear test simulation)1 5 10 50 100 500Radiation intensity, W/cm2• Charring rate depends markedly onradiation intensity• For ISO 834 fire exposure, timbercharring rate is in the approximaterange 0.6 to 0.9 mm/min accordingto DD ENV -1-2 and BS PD 7974-3, 2003• Source: Butcher E G, Do we knowhow fast it burns? Fire Surveyor,Dec 1976 and FRS FR Note 896,Note on charring rates in wood,Nov 1971

Upgrading timber floor using inset ceilingTimber battens addedTRT = RExisting floor boardsof poor integrityLarge sectiontimber floor beamAdditional timberprotectionNew ceiling boardChar line• Existing floor of poor integrity. Largebeams.• Inset ceiling considered aestheticallyacceptable• Inset ceiling can be fire protectingboard or plaster (or expanded metalmesh if adequately supported mid-span• Residual section of floor beamcalculated to be structurally acceptable.Residual section assumed to have roomtemperature strength. Neutral axis ofsection has moved.• Ceiling fastener (e.g. woodscrew) needsto allow for charring of batten aroundfastener• Additional timber protection (sheeting)gives integrity against cold and hotsmoke• Radius of char = char thickness

Upgrading a timber floor by adding plaster ormineral fibre from the topAccess to cavity by raising floor boardsMineral fibreinfillExisting ceilingof good integritySteel wire meshnailed to timber joistPlaster infillDamp proof sheetingExisting ceilingof poor integrity• Floor boards are in poor condition withsquare edges. Historic moulded ceiling alsoin poor condition – typically plaster on timberlath loosely held with corroded nails.• Access only from the upper face. Upgradingprocess: temporarily remove some floorboards, place damp proof sheet, fix expandedmetal to sides of joists, pour in lightweightplaster, replace floor boards, apply timbersheeting to improve integrity and resistanceto smoke flow if necessary.• Added ceiling of plaster and metal lath mustremain in place after historic ceiling fallsaway. Damp proof sheet must be pushedtightly into corners so that new plasterprotects faces of joists• Can floor carry additional weight? Canceiling carry wet mass of plaster ? (OK whendry and rigid)

Upgraded floor using poured plaster• Example of m

Kenwood library ceiling by Robert Adam• Early fire detection andsuppression essential• Major risk is of firestarting above ceiling inroof space. Aspirationcould deal with detectionin roof space and at highlevel under ceiling.• How deal with fire aboveceiling? Fire fighting aproblem?

Increasing thefire resistance oftimber doors

Historic door and ceiling.• Fire risk assessment essential.Objective should be early firedetection and immediate firesuppression – this is question forfire safety management. Why isstructural fire protection necessary?• Necessary structural fire protectionmust be unseen.• Can intumescent be used forimproving fire integrity at dooredges and at thin areas of doorface? Can door be dismantled toallow hidden improvements to bemade?

Bowing of timber door in fireHingeHingeBowing athinged edgeBowing atswinging edgeLatch• Bowing will be constrained byhinges and latch• Timber door will bow towards thefire due to shrinkage of fireexposedface. Extent of bowdepends on design, thickness andgrain direction• Failure of integrity will occur attop of door first because a) top ofdoor is in hottest environment, andb) outward flow of hot gases causescharring of door frameBowing at topof timber door

Fire behaviour of glazed doorPositiveCeilingHot gas emission• Radiation through glass should beconsidered (ignition of nearbysurfaces on unexposed side)PressureprofileFireRadiationGlazed panelApproximatelyspherical radiation• Top of door is in most severeenvironment• Intumescent seal at door edges willprevent emission of hot gases butnot cold smoke flowNegativeTimber doorAir inFloor• Cold smoke can extensivelydamage contents of heritagebuilding. Use smoke seals on dooredges if aesthetically acceptable

Timber panelled door• The thin edge of each panel is theline of fire integrity weakness,especially for the panels near thetop of the door.• This moulded panel door is in dailyuse in a London museum. A spareidentical door has been fixed to theface of the other door , but it looksbetter than a boarded door. Theresulting door is heavier andrequired new heavy hinges to befitted. Aesthetics were important.• UK BRE Digest 220 givesguidance on timber fire doors

Mahogany doors in Kenwood House• Doors have an area ofweak fire integrityaround panels• High quality of firesafety managementessential• Value of works of artinestimable.• Self portrait ofRembrandt valued at£5m several years ago

Mahogany panelled door

Failure of fire resistance of panels in panelleddoorMoulded door panelChar lineLoss of integrity and insulationFrame holding panelsFireRetaining bead• Panels near top of door most likelyto fail – environment most severe• Timber chars at approximately0.8mm/min in standard ISO 834fire resistance test• Panel edge can char away allowingpassage of fire, or• retaining bead can char away or itsfastening may fail allowing panelto fall out

Upgrading timber door with fire protectingboardFire protecting boardNo loss of integrity or insulation• Fire protecting board applied to firerisk side using nails or screws.• Greatly improves fire integrity andinsulation performance• Hides nice appearance of door.Cheap method.• Unacceptable in heritage buildings• Makes door heavy and mayrequire more or bigger hinges andrelocation of hinges

Upgrading timber door with fire resistingglassFire resisting glass panelLoss of insulation only• Adding panel(s) of wired glass ornon-wired glass of proven integrity(e.g. Pyran) to door will improveintegrity at panel edges.• Glass will have little effect onthermal transmission so insulationperformance of door may beinadequate (but this may beunimportant).• Method of fixing glass panelsneeds special consideration toallow for different thermalmovement of timber and glass

Upgrading timber door using intumescentsystemIntumescent paintIntumescent char• Intumescent paint or varnish canimprove fire resistance (and flamespread)• Intumescent must be compatiblewith existing coating (or existingcoating should be removed). Adoptmanufacturer’s instructions• May need notice saying the coatingshould not be removed orimproperly cleaned - fire safetymanagement important• Perhaps only thin portions of doorneed be so treated

Upgrading timber door panels with steel stripinsertsLoss of insulationSteel strip placed in slot• Fire integrity can be improved (butnot insulation) using this method• Door is dismantled (beadingsaround one face removed) , paneledges are slit (partly or fully), steelstrips are inserted, and doorassembled again.• Suitable for unpainted doors ofoutstanding appearance (e.g.varnished mahogany doors) whereno other upgrading method isadequate.

Use of dooredge seals

Intumescent door edge sealsFrameIntumescent strip requirementsFR 30/20 strips not essentialIntumescent strips(typically 10 x 3mm)Door• Existing door sets (i.e. door and itsframe) can be upgraded withintumescent strips by makinggroove in edge of door and/orframe and placing preformedintumescent strips• Door edge gap should preferablynot exceed 3mm• Seal positions in door and frameshould not be reversed (to allow fordoor bowing)FR 60/45 strips in door edge or frameFR 30/30 strips in door edge or frameFR 60/60 strips in door edge and frame

Heat and smoke seals for double swing doorsBEFORE FIREDURING FIRETimber door leafDouble swing timber doorTimber door leafAluminiumalloy holderIntumescentNeoprenesmoke sealFoamed intumescentfills gap• Extruded aluminium sectionincorporating intumescentmaterials and a neoprene smokeseal is fixed into a groove in dooredges along sides and top withmetal nails. Neoprene seal needs tobe checked occasionally to ensuregood condition and fit.• In a fire the aluminium soaks upthe heat and causes the intumescentto swell early, before the neoprenesmoke seal is damaged.Char layerFire

• Electrically operated doorhold-open device• Break glass call point

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