Building Your Fire Wall

8/13/2019 Building Your Fire Wall

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O M P R T M E N T T I O

m odem buildings becom e m ore complex in design an d use ,re s m ore to consider w hen des ign ing and buildincf effective

Gordon Cooke guides us through the building blocks.

R E W A LL

Sandwich panels, such asthMe manufactured bySurobond. can be highlysuitable lor large intenial orexternal fire walls

NGS BECOME MORE COMPLEX THERE S A

inten ded to fill the gap and act as a check listign aspects to consider. Much of the

A fir wall may be used internally forng into fire compartm ents.

al or malicious), or tohazard by radiation to adjoining

limit foundation loads to an acceptable leveLSteel faced sandwich panels can be an

excellent ap plication for high fire walls sincethey are lightweight, can be rapidly erected,

have reasonable sound insulation, and canpossess a high level of fire resistance - up to

four hours if structural rock wool cores areused.

A fire safety strategy needs to consider theffect of a fire wall on life safety, pro per ty los

business contitiuity. environmen tal pollutioand preservation of heritage. Reference to th

BSI PD 7974 documents on fire safetyengineering may be helpful in developing a

safety strategy for the building as a whole.The fire wall should normally possess the

A fire safety en gine er may be able toadvise on less stringent levels of fire



required amount of fire resistance in terms of

stability, integrity and insulation whenexposed to the standard fire resistance

exposure test on one side, ie ISO 834 time-temperarure relation. The length of time

needed may be decided by reference toApproved Doc um ent B Fire Safety (ADB), by

the insurer, or by a professionally qualified fire

safety engineer who would need to beknowledgeable about the behaviour andseverity of fires in buildin gs. In the case of an

engineer, he or she may be able to advise onless stringent levels of fire resistance than tho se

recommended in ADB. For protection fromradiated fire from neighbouring buildings, for

example, hazards can be calculated usingconfiguration principles which underlie ADB

and are illustrated in BRE Rep ort 187.1 myself

have made several such calculations with somebased on idealised flame shape and emissivity.

P r o t e c t i o n z o n e

Depending on the strategic Importance of thefire wall, it may be necessary to in clude a zon eof fire protecting ex ternal wall and roofconstruction along either side, so that firecannot byp ass it The junction at the perimeterof the firewall needs good fire integrity toallow for any thermal deformation which canoccur in a fire. This is especially necessary if a crown -fire scenario (a fire that may start highup un der the roof of a building and thenspread laterally and downwards) is possible,such as in high rack storage facilities. It isaccepted that the zone of roof cladding in thefire compartment will eventually collapse in asevere fire, but the zone of roof cladding on theoth er side of the fire wall should resist collapseand remain acting as a radiation shield. Inaddition, the materials used in theconstruction of this zone of wall and roofshould not b e capable of generating m oltenflaming droplets, which could ignite thebuilding contents.

Tliis protecting zone concept is now

recommen dation in LPC design guidance,though the extent to wbich this is beingfollowed in practice is not k now n. Rarely isenougb attention paid to achieve effective firestopping at tbis junction and very often, thisprotecting zone is not present because it costs

too much or is inconvenient an d bas not beenallowed for in the contract ten der docum ents.As for ADB, tbe gu idan ce (para 8.29) is

1100

structural l ightweight core bonded to steel faces

0.5 to 0.7 thick flat sheet face with roll formed edge to giveinterlocking tongue and groove profile

Internal fire wall (subjectedto wind pressure whendoor/shutter is open)

Above: Cross sectionthrough a typicalsandwich panel

Right: protectionzone around eitherside of the fire wallmay he needed,especially in buildingssuch as high rackwarehouses

Large door or sh

essurised space

The materials used in the constructioof the zone of wall and roof should notbe capable of generating moltenflaming droplets, which could ignite thbuilding contents

fire wall above tbe roof is inadequ ate. But wemust remem ber tbat tbe ADB guidance isprincipally concerned witb tbe m inimumstandards for life safety, and tbat it isrecognised tbat better protection is needed forproperty loss reduction.

Sandwich panels witb tbermo plastic cores(for example, expanded poiystryrene foam)tbat over-sail the fire wall should incorporate

sandwich panels wbic b over-sail tbe fire wawould be an adequate fire stop at thisimportant position.

The fire wall must not b e seriously affecteby deformations of tbe roof structure underaction of variable live loads in normal use{snow and /or wind), and in tbe fire conditiowhere thermal distortions occur. In particuthe structural supp ort of the firewall must



C O M P R T M E N T T I O

de a smooth appearance for an sda superstore

The fire wall should not be susceptible toby the collapse of the adjoining roof

fically add ress this importan t issue. Very

ect of co llapse of higb storage racking

y constructed witb unprotected

value projects it may be necessary to designtbe fire wall as a free standing element i.e. as acantilever, structurally isolated from tbe roofso that collapse of tbe roof in a fire cannot dragdown the fire wall or other wise d amage it,

Squaring the security circleTbe need for security in and around tbebuilding may also bave implications for the

able to resist fire transfer when exposed tosevere fire on one side. In the photo, rockwocored panels manufactured by EurobondLaminates behaved very w ll in retaining panjoint integrity in tlie unexposed face, eventhough the exposed steel face expectantlydelatninated and buckled. Access for peopleworking in different fire compartments may

require security features as part of t he fire waBut these will need to fail safew ben a fire orother emergency occurs, so that people canescape from, and firefighters can enter tbe ficompartment. Again, this is the responsibilitof tbe building designer.

Construction of a firewall should ideally baccomplisbed witb minimum dirt and no wetrades, sometbing tbat is assured by usingsandwicb panels. It should be easily erected,with sandwicb panels being erected byspecialists witb appropriate lifting equipmenensuring minimum hazards to safety.

Tall firewalls sho uld be lightweight to avo

the use of piled foundations, so again sandwpanels a re ideal in this respect. Large fire walshould take account of wind pressure actingeither during installation or after completionthe building. Altbough the room temperaturedesign of tbe sandwicb panel firewall mayallow for tbe eflect ot wind pressure on theinternal firewall (acting through a largeopening sucb as a shutter in the external walthe forces imposed by wind during a fire neeto be considered. It bas to be remembered tbon e xposur e to fire one face delaminates fromibe core, so the faces then behave as catenarelements which cannot transtnit bendingmovem ents. Itiiplicit in this is a conside ration

of compounding probabilities: tbe probabilitof higb wind occurr ing at tbe same time as fitbe wind being in an unfavourable direction,and a large door or shutter being open at thetime of a fire. In a fire engineered approa ch,one solution might be to bave the door orshutter closed automatically on detection of

fire, so that one element in this scenario canavoided.

The fire wall sbould be robust in normal uand resist or be readily capable of repair afternorm al impacts, for example that by a fork litruck, so that its fire resistance is not im paireEqually, it should be reparable if damaged by

localised fire. This is not always easy witbsandwicb panels whicb have roll-formedtongue and groove joints.



O M P R T M E N T T I O N

procedures. For instance, it should be possibleto reposition door openings and service

penetrations during the life of the building,without reducing tbe fire resistance. Whereverpossible, ducts whicb penetrate the firewallshould be avoided so as to prevent fire transfershould a fire damper fail to operate. Conveyorscarrying goods whicb unavoidably penetratetbe firewall need very careful design to ensuretbe continuity of fire resistance in the plane ofthe fire wall, Tbis may require special firedetection and actuation devices toautomatically close ibe opening at a pointwhere goods are not obstructing the closure.

Large penetrations of tbe fire wall, forexample, by fire resisting fire doors/shutters,should be designed carefully to account forload redistribution around the openings wheresandwicb panels are cut. Tbis would, of course,apply to any ligbtweigbt construction, not justsandwicb panels. Support for fire doors andshutters should be designed so that tbe dooror sbutter is adequately supported afterdeiamination of tbe fire exposed steel face ofpanels occurs. Wbere a bigb measure of fireresistance is required , tbis may be achievedusing double fire doors spaced apart in a fireprotecting lobby and in tbis case, it is essentialthat large doors and sbutters are supported bysupplementary protected steel framing. Fixingof doors and sbutters to assemblies of

ligbtweigbt sandwich panels tbat delaminate infire needs special attention. Other points tonote are:

• The extrapolation of fire resistance testresults forlarger-tban-tested constructionssbould only be ma de by a suitably qualifiedfire safety engineer, and tbe calculationssbould have a rational basis and betransparent.

• If a sandwicb panel wall bas been tested forfire resistance witb the panels in thehorizontal orientation, great care is neededto assess the fire resistance when the panelsare in tbe vertical orie ntation, and vice versa.

• Ideally the fire wall sbould be cotifirmed as•fit for purpo se by tbe insurers.

Use can also be made of practical guidancealready freely available. Some references aregiven in the panel below. The listing ofperformance needs given here does not coverany resulting from tbe Regulatory Reform (FireSafety) Order 2005. as tbe Orde r only kicks inafter completion of a building wben it becomesoccupied. However, wben a fire risk assessmentis needed for a building under tbe R R O sucb alist will be useful.

Finally, it may not be possible to satisfyofficial prescriptive guidance on tbe design ofa

fire wall and a fire safety engineered approachmay then be appropriate. Guidance on firesafety enginee ring is available in national and

This large scale testing showed tha t Eurobond pa nels retained Joint integrity in the unexposed face

Arsonists may resort to settin g multipfires - a scenario not usually covered innational fire protection guidance - orblast exp losion s m ay be initiated

Bibliography• The Building Regulations 20 00 , Approved Document B. Fre Safety. Vol 2 , Buildings other than dw ellihgs.

(2006 edition) (CLG)

• LPC Design Guide for the Fire Protection of Buildings (Fire Protection Association)

• Cooke G M Er When are sandwich panels safe in fire? Part 1 An overview (Rre Engineers Journal, July 19 9

p p 3 7 - 4 1 )

• Cooke G M E: W hen are sandwich panels safe in fire? Part 2 Avo iding collapse (Fire Engineers Journal, Sep1 9 9 8 pp 25-33)

• Cooke G M E: When are sandw ich panels safe in fire? Part 3 Rre scenarios, fire tests and check list (Fire

Engineers Journal, January 1999, pp 18-25)

• Cooke G M E: The behaviour of sandwich panels exposed to fire (Building Engineer, July 199 7,p 14- 29)

• Code of practice for fire protection in the food and drink ind ustry (Loss Prevention Council 199 9)

• Guidelines for the design, specification, cons tnjction, m aintenance and fire managem ent o) insulated

envelopes for temperature controlled environments (International Association of Cold Storage Contractors

European Division, 1999)

• Cooke G M E: The fire safety design of tall lightweight steel framed fire walls (Proceedings of the Nordic St

Construction Conference June 1995, Volume 2, pp 677-683)

• Cooke G M E: Fire engineering of tall fire separating walls (Fire Surveyor, Parts 1 2, June August 19 87

pp 13-29 and pp 19-29 respectively)

• Lightweight sandwich construction (edited J M Davles) (Blackwe ll Science, Oxford, UK. 20 01 )

• Cooke G M E: Sandwich panels for external cladding - fire safety issues and implications for tl ie risk

assessment process. (Eurisol, November 2000, pp 60)

• Cooke G M E: Design fires for testing combustible-cored sandw ich panels (Interflam 2 0 0 1 . published



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Building Your Fire Wall