Design Fires for Fire Safety Engineering: A State-of-the-Art Review ABSTRACT 1 INTRODUCTION

Transcription

1 Design Fires for Fire Safey Engineering: A Sae-of-he-Ar Review by Alex Bwalya, 1 Mohamed Sulan and Noureddine Bénichou ABSTRACT In line wih he worldwide rend of moving owards performance-based codes, Canada and many oher counries are planning o inroduce performance/objecive-based codes in he near fuure. A performance-based approach allows for flexibiliy in design ha may lead o improved cos-effeciveness. The success of hese code sysems will depend, o a large exen, on he abiliy of he available compuaional ools, mos of which rely on suiably-defined design fires, o adequaely predic he impac of fires on buildings and heir occupans. I has always been recognized ha he specificaion of design fires, derived from appropriae design fire scenarios, is a possible source of uncerainy in conducing any fire safey engineering assessmen. This uncerainy sems from he difficuly in accuraely calculaing he combusion process (hea release rae, producion of smoke and oher gaseous species) based on he ype, quaniy, and arrangemen of combusibles, as well as he poin of igniion and subsequen fire spread o adjacen combusibles. This lieraure review was carried ou o deermine he range of mehods used o characerize design fires. The mehods currenly available were found o be largely empirical in naure and fairly unsophisicaed. The wo main quaniies used o describe design fires were found o be he hea release rae (pre-flashover scenario) and emperaure-ime profiles (pos-flashover). The mos widely-used pre-flashover design fires are fires, whereas a hos of empirical correlaions are available for pos-flashover design fires. 1 INTRODUCTION The use of analyic ools, paricularly compuer models, o address fire safey requiremens is se o increase wih he imminen inroducion of performance and objecive-based building codes in many counries around he world. Much has been published over he las several years regarding he benefis in cos, qualiy, design flexibiliy and fire safey ha can be realised hrough he use of performance and objecive-based code sysems. The success of hese code sysems will depend, o a large exen, on he abiliy of he available ools o adequaely predic he impac of fires on buildings and heir occupans. Many compuaional ools (compuer models) are now available, ranging from simplified wo-zone and single-zone models o sophisicaed compuaional fluid dynamics (CFD) models. A comprehensive web-based daabase of compuer models for fire and smoke is provided by Combusion Science and Engineering Inc [1] and a recen survey has been published by Olenick and Carpener []. An imporan sep in mos fire safey evaluaions, be hey experimenal or compuaional, is he selecion of a suiable simulaion fire, he design fire, for he comparmen under consideraion [3]. In fac, in he case of compuer models wihou a buil-in combusion model, he accuracy of he resuls of he simulaion is srongly influenced by he specified design fire. There is presenly a concered inernaional effor, coordinaed by he Inernaional Organizaion for Sandardizaion (ISO), Technical Commiee (TC) 9, Sub-Commiee (SC) 4, owards he developmen of echnical guidelines for design fires wih a view o sandardizaion. As a resul of his effor, a series of echnical repors [4-7] have been published, of which ISO Technical Repor (TR) [5] focuses on design fire scenarios and design fires. The Sociey of Fire Proecion Engineers (SFPE) has also made a significan conribuion o he emerging pool of informaion on design fires by dedicaing a chaper in one of heir engineering guides [8] o a discussion of design fire scenarios. In addiion, he SFPE currenly have a Task Group on Design Basis Fires (synonymous wih design fires) ha is developing an engineering guide on quanifying design basis fires. Furher informaion can be obained from he SFPE s websie [9]. A review of he ISO echnical repors [4-6] and he SFPE engineering guide [8] is a prerequisie sep for anyone underaking he ask of prescribing a design fire. I is recommended o perform a horough fire scenario analysis prior o characerizing a design fire. ISO/TR :1999(E) [5] and he SFPE engineering guide [8] conain comprehensive liss of iems o consider in idenifying design fire scenarios, such as: ype of fire, locaion of fire, poenial fire hazards, sysems impacing on he fire and probabiliy of occurrence. 1 Alex Bwalya, Noureddine Benichou and Mohamed Sulan are, respecively, research associae, research officer and senior research officer a he Naional Research Council of Canada (NRC), Insiue for Research in Consrucion, Fire Risk Managemen program, Oawa K1A 0R6, Onario, Canada.

2 Recognizing he imporance of design fires in fire safey engineering analysis, he objecive of his lieraure review was o deermine he sae of deerminisic compuaional echnology in he subjec of design fires. The lieraure review did no include iniial seps ha are usually underaken in a fire safey evaluaion before specifying design fires, such as esablishing fire safey objecives, and ools and mehods used o idenify possible fire scenarios. A summary of he fire safey engineering assessmen process oulined in ISO/TR [4], which he auhors believe bes illusraes where design fires fi in he process, is as follows: 1. Qualiaive review: This sage deals wih: a) definiion of fire safey objecives and accepance crieria, b) esablishmen of prescribed design parameers by reviewing he archiecural design and he proposed fire safey feaures, c) characerizaion of he building and is occupans, d) idenificaion of poenial fire hazards and heir possible consequences, c) selecion of fire scenarios which should form par of he quaniaive analysis, e) esablishmen of rial fire safey soluions, and f) indicaion of appropriae mehods of analysis.. Quaniaive analysis: A his sage, a emporal quaniaive analysis is carried ou using appropriae subsysems. Design fires and mahemaical models are examples of subsysems. 3. Assessmen of oucome of analysis agains safey crieria: The process is repeaed if he accepance crieria are no saisfied. 4. Reporing and presenaion of accepable resuls. Ineresed readers are referred o appropriae documens in he lieraure, such as he SFPE engineering guide [8] and ISO/TR and [4; 5], for furher informaion on seps 1, 3 and 4, and he impac hey may have on he choice of design fires. Anoher area ha his lieraure review does no cover is ha of design fires for exreme evens such as blass. These are clearly unusual siuaions ha canno be reasonably expeced o occur in he vas majoriy of residenial, public and commercial buildings wihou inheren explosive hazards. The focus here is on fires, which normally begin wih a single burning iem, in a room, before involving oher iems. DESIGN FIRES The definiions of erms commonly used in he discussion of design fires are given in Table 1. Table 1. Terminology relaed o design fires Term Design fire Design fire curve Design fire scenario Fire scenario Definiion by Source Reference ISO/TR [5] SFPE engineering guide [8] Design fire: A quaniaive emporal descripion of assumed fire characerisics based on appropriae fire scenarios. Variables used in he descripion include: hea release rae, fire size (including flame lengh), yield of producs of combusion, emperaures of ho gases, and ime o key evens such as flashover. A specific fire scenario on which and analysis will be conduced. I includes a descripion of he impac on he fire of building feaures, occupans, fire safey sysems and would ypically define he igniion source and process, he growh of he fire on he firs iem ignied, he spread of he fire, he ineracion of he fire wih he building occupans and he ineracion wih he feaures and fire safey sysems wihin he building. A qualiaive descripion of he course of a specific fire wih ime, idenifying key evens ha characerize he fire and differeniae i from oher possible fires. Design fire curve: An engineering descripion of a fire in erms of hea release rae versus ime (or in oher erms elaboraed in he saed reference) for use in a design fire scenario. A se of condiions ha defines or describes he criical facors deermining he oucomes of rial designs. A se of condiions ha defines he developmen of fire and he spread of combusion producs hroughou a building or par of a building. The process of developing a fire scenario is a combinaion of hazard analysis and risk analysis. Furher informaion can be found in NFPA 7 [10]

3 Anoher ineresing definiion of design fires given by one auhor [11] is ha hey are fires ha can be buil and insrumened in a es faciliy; ha hey should produce consisen resuls from one es o he nex in he same faciliy and in oher faciliies, and hey should show a consisency ha can be described and used in fire modelling. This illusraes ha some people perceive design fires differenly and, perhaps, here is a need o have a common definiion. The course of a fire is generally described by he growh period, peak hea release rae, seady-sae burning period, and decay period [1]. The hea release rae as a funcion of ime is an imporan quaniy ha conrols he main characerisics of he fire, such as flame heigh, ho gas emperaures, and he rae of descen of he ho gas layer [13]. There are hree disinc combusion regimes of enclosure fires ha are imporan in any fire safey evaluaion: he pre-flashover regime, he flashover sage, and he pos-flashover regime. Flashover is a perilous sage in he course of a fire during which exposed surfaces of mos of he combusibles wihin he comparmen suddenly ignie and he fire is no longer resriced o he firs iem ignied. A his sage, he hea release rae, emperaure, smoke producion and smoke oxiciy increase rapidly [8], usually unil a sage is reached a which here is no enough oxygen reaching he fire o suppor a furher increase in he hea release rae and he fire eners he venilaion-conrolled regime. The occurrence of flashover is generally believed o be promoed by ho-gas emperaures of beween 500 o C and 600 o C, and hea flux levels of abou 15 o 0 kw/m a he floor level of he comparmen [13]. Life safey of he occupans akes precedence during pre-flashover, whereas he srucural inegriy of he building and he safey of fire rescue personnel are he major concerns during he laer posflashover sage. Simple correlaions are available in he lieraure [14-16], which can be used o deermine he likelihood of flashover and wheher or no a fire will be venilaion-conrolled or fuel-conrolled, based on he knowledge of he hea release rae, size of he room, hermal properies of he maerials forming he comparmen boundaries, and he size and number of venilaion openings. The process of deermining a design fire usually begins wih he esablishmen of he objecives of he fire safey engineering asks [5], which could be, for example, o evaluae he smoke managemen sysems or smoke deecor response, provide life safey or proec propery. The design fire required for each of hese objecives could be differen. Once he objecives are esablished an appropriae fire load is seleced and he naure of he combusibles likely o be involved in he fire is idenified. The fire load is an imporan variable required o esimae he duraion of a fire. I is an indicaion of he quaniy of combusibles in an enclosure or he energy ha can be liberaed upon complee combusion. However, i mus be borne in mind ha fire load informaion on is own is insufficien o deermine he shape of he hea release rae curve during he pre-flashover sage; he combusibles presen mus be specified and experimenal daa mus also be used, if available. The hea release rae is affeced by he following parameers: a) srengh and locaion of he igniion source; b) ype, amoun, posiion, spacing, orienaion, and surface area of he fuel packages (fire load); c) size and geomery of he enclosure; d) size and locaion of he comparmen openings; and e) hermal ineria of he maerials consiuing he enclosure boundaries. The fire load is commonly expressed as eiher he mass of combusibles (assuming solid combusibles) per uni floor area (kg/m ) or he oal hea energy conen per uni inernal surface area (MJ/m ) or floor area (also commonly referred o as he fire load energy densiy ), and i largely depends on he occupancy. I is recommended ha boh fixed and moveable fire loads (including ransien fire loads) should be aken ino consideraion [17], and ha if daa from represenaive surveys is available, he 90 percenile value should be seleced [18]. Transien fire loads are iems ha are in a space emporarily, for example, Chrismas decoraions [17]. Kloe [17] suggesed a mehod of accouning for ransien fuels in which a fixed hea release rae densiy or hea release rae is assigned o hese fuels. A grea quaniy of fire load daa has been published over he las wo decades, bu due o regional differences in lifesyles and he subjecive manner in which fire loads are quanified; here are large variaions in values. Bwalya e al. [19] presened a survey of fire load daa for residenial occupancies found in he lieraure..1 Pre-Flashover Fires The hea release rae and quaniy of smoke and combusion gases, such as carbon dioxide (CO ) and carbon monoxide (CO), produced are considered o be he mos imporan aribues of pre-flashover fires. During he growh sage, he hea release rae is commonly approximaed by power law correlaions of he form: p Q & = α (1) Q & = Rae of hea release (kw) p = Posiive exponen

4 = Time afer effecive igniion (s) α = fire growh coefficien (kw/s ) The exponen is usually given a value of and he resuling curves are popularly known as fires - he hea release rae varies proporionally o ime squared and hence he name. The growh coefficien is someimes deermined using experimenal daa. Hoglander and Sundsrom [0] discussed such a expression. The maximum hea release rae is he value a which any one of he following evens occurs: a) he fire becomes venilaion-conrolled and combusion proceeds a a seady-sae rae; b) a fire suppression sysem acivaes; c) he decay phase begins (in a fuel-conrolled fire). Fires involving muliple combusibles, which become involved in he fire a differen imes, may exhibi differen behaviour. The fires, which were made popular by he NFPA [1], are given by: Q & = Q& o () o Q & o = Reference hea release rae (kw), usually aken o be 1055 kw o = Growh ime (s) The recommended caegories of fire growh are illusraed graphically in Figure 1. Hea Release Rae (kw) Ulra-fas o = 75 s Fas o = 150 s Medium o = 300 s Slow o = 600 s Time from Igniion (s) Figure 1. Raes of Energy Release of Fires Barne [] suggesed ha he decay phase of a fire can also be represened by a curve wih appropriae decay consans. He presened concepual design fires wih fuel-conrolled growh and decay phases conforming o profiles o represen venilaion-conrolled fires, which proceed o burn a a seady sae afer aaining he peak hea release rae, and fires, which never reach he seady-sae venilaion-conrolled regime. fires, nowihsanding heir widespread use, have been criicized by some auhors [3; 3; 4], parly on accoun of he simple assumpions made in heir derivaion, which are deemed o be unrealisic, and also because, in one auhor s opinion [3], no engineering mehods lend credence o heir applicaion. To he conrary, some fire researchers [5] have repored ha fires mached heir es daa. Schifilii [6] analyzed daa colleced from 40 fire ess [7; 8] conduced in a furniure calorimeer a he Naional Bureau of Sandards (now he Naional Insiue for Sandards and Tesing (NIST)) and found ha fires modeled various sages of he growh period reasonably well when he growh consans were derived from he experimenal daa. The NFPA [1] ouline he assumpions upon which he fires are based and argue ha he approximaion is sufficien for reasonable decisions o be made abou fire safey. Hoglander and Sundsrom [0] gave examples of design fires for muliple upholsered furniure iems creaed by adding up heir individual characerisic hea release rae curves. The hea release rae of each iem

5 was calculaed using an empirical correlaion, which was developed using daa from well-venilaed full-scale (open burning) fire ess involving upholsered furniure. They acknowledged ha here was a lack of daa from complee room fires, and ha i was difficul o prescribe design fires because of he exremely large combinaion of combusibles involved. Based on European saisics, which revealed ha he greaes number of faaliies resuled from fires involving upholsered furniure, hey suggesed ha he influence of such furniure should be included in a design fire if i will be presen in he occupancy under consideraion a view shared by many workers engaged in fire research. Herzberg e al. [4] presened a concep ha was inended o produce more realisic design fires. The mehod used hea release daa from well-venilaed full-scale and bench-scale ess, in conjuncion wih a mahemaical model, which incorporaed he influence of a comparmen on fire developmen and progression. The proposed mehod of incorporaing hea release daa from full-scale ess was similar o ha suggesed by Hoglander and Sundsrom [0]. The fires given by Equaion () are ypically for a single burning iem. I is suggesed, alhough no par of he NFPA [1] recommendaions, o increase he size of he design fire if oher combusibles are wihin he separaion disance, R, defined by Equaion (3) [1]: 1 Q& R = 6.85 π q & i R = Separaion disance from arge o cenre of fuel package (m). q & i = Inciden radian hea flux required for non-piloed igniion (kw/m ). There was no clear guidance given on exacly how he size of he design fire should be increased..1.1 Compuer Tools Two sofware modules, MAKEFIRE and FREEBURN, are available from NIST [9], which are able o generae hea release rae hisories for design fires. These modules are incorporaed ino a fire simulaion program called FPEool. MAKEFIRE uses power law expressions for boh he growh and decay burning phases. FREEBURN is more sophisicaed han MAKEFIRE in ha i calculaes he cumulaive hea release rae hisory for up o five independen fuel iems based on heir individual hea release and burning rae daa, which is read from a file. 1 (3). Pos-Flashover Fires Pos-flashover fires are venilaion-conrolled and produce large quaniies of asphyxiaing gases such as CO and hydrogen cyanide (HCN), in addiion o smoke and oher irrians[30]. During his sage, he design load is characerized by emperaure-ime profiles. The Eurocode [31] parameric equaions are perhaps he mos widelyused equaions for esimaing pos-flashover emperaures. A emperaure-ime relaionship is produced for any combinaion of fire load, venilaion openings and wall maerials. Figure shows one of Magnusson and Thelandersson s [3] ses of curves, from which he equaions were derived. The ses of curves were produced for various opening facors, F o. Buchanan [18] and Karlsson and Quiniere [13] discussed he mehod used by Magnusson and Thelandersson o produce he curves in greaer deail.

6 H F o = A0 0.04m A = 1 - o Temperaure ( o C) Q = 50 MJ/m Time (hr) Figure. Time-Temperaure Curves for Various Fire Loads [3] The Eurocode mehod divides fire developmen ino wo phases: a heaing phase (idenical o he ISO 834 sandard emperaure-ime curve [33]) and a decay phase. The equaion for he heaing phase is: -0.* -1.7* -19* T = e -0.04e -0.47e (4) where T is he emperaure and * is he modified ime (in hours) given by: b = kρ cp (Ws 0.5 /m K) * = ( Fo Fref ) ( bbref ) F o = opening facor (-) F ref = reference value of he opening facor, aken o be 0.04 b ref = reference value of kρ cp, given he value of 1160 Ws 0.5 /m K. Figure 3 shows how he Eurocode emperaure-ime profiles generally compare wih he ISO 834 emperaure-ime curve. The ISO 834 emperaure curve is similar o he ASTM E119 [34] and CAN/ULC S101-M89 [35] emperaure-ime curves. (5)

7 Eurocode Temperaure ( o C) ISO Time (min) Figure 3. Comparison of he Eurocode Design Fire wih he ISO 834 Temperaure-Time Curve (fire load: 500 MJ/m 1 ; opening facor: 0.05 m ) Feasey and Buchanan [36] used a simple compuer model o generae a series of pos-flashover design fires wih he help of daa from real fires and carefully defined fire loads (primarily wood cribs and real furniure) as inpu. Their inenion was o modify he burning and decay phases of he Eurocode empirical fire curves in order o improve he esimaion of emperaures in pos-flashover comparmen fires, which, hey fel, were under-prediced, especially for venilaion-conrolled fires. Mehaffey [37] presened a simple framework for underaking performance-based design for fire resisance in wood-frame residenial and office buildings, which employed design fires based on he Eurocode equaion and an empirical pos-flashover model ha was developed in Japan: T() - T(0) = 3.0 T(0) A F v kρc p (6) T = emperaure of he ho gas (K) = ime from igniion (s) The applicaion of he mehod was illusraed by using a hree-sorey wood-frame hoel building. Ma and Makelainen [38] presened an empirical emperaure-ime curve for represening small o medium pos-flashover fire emperaures based on daa from various laboraories. Their equaion is: T-T g o = exp 1 - T -T g,max o m m δ (7) T g = ho gas emperaure ( o C) T g,max = maximum ho gas emperaure ( o C) T o = reference emperaure ( o C) m = ime a which maximum emperaure occurs (min) δ = shape consan for he curve (-)

8 Barne [] presened a echnique for modelling emperaures, oued as being easy o use because only one equaion represened he emperaures of boh he growh and decay phases of a fire, and only hree facors were required in he equaion: maximum gas emperaure, he ime a which i occurred and a shape consan for he source. Barne s equaion is: (log - log m ) - sc maxe T = T + T (8) s c = shape consan for he emperaure-ime curve (-) T = emperaure a any given ime ( o C) T = ambien emperaure ( o C) T max = maximum emperaure generaed above T (calculaed using he mehods given in he SFPE handbook [14]) = ime from igniion of fire (min) m = ime a which T max occurs (min) The shape consan was correlaed wih he pyrolysis coefficien using experimenal daa. Equaion (8) was developed using daa from 14 fire ess from various sources, he majoriy of which were conduced wih wood cribs. The fuel masses ranged from 3 o 5100 kg and he emperaures measured ranged from 500 o C o 100 o C. The growh raes ranged from ulra-slow o ulra-fas, in accordance wih he NFPA [1] caegories of fire growh. 3 HEAT RELEASE RATES Given he imporance of he hea release rae in quanifying a design fire, hea release rae daa for a wide range of combusible iems are some of he mos sough-afer combusion daa. The invenion of he furniure calorimeer [7] and he ISO 5660 cone calorimeer [39] in he early 1980s led o an increase in he amoun of published hea release daa for many combusible iems, especially upholsered furniure. Some sources of daa on hea release raes and oher combusion daa, such as CO and CO producion raes, are [40-43]. Compilaions of hea release rae and combusion species producion rae daa can also be obain from fire research organizaions such as he Building Research Esablishmen Ld [44] and NIST [9]. I is imporan o noe ha almos all of hese daa were obained from fire ess performed under well-venilaed condiions. There is a school of hough ha such fire ess may no represen realisic models for he developmen of life hazards from many fires occurring in muli-comparmen buildings [45]. The hea release rae is affeced by many facors such as: venilaion, fire load, locaion of fire load wih respec o he walls, and igniion mehod. Furniure consrucion deails and maerials are known o subsanially influence he peak hea release rae, such ha hea release rae daa are no available for all combusible iems or for generic combusible iems [1]. The concep of hea release densiy (kw/m ), which is he hea release rae of a fire divided by he base area of he fuel package, is imporan in esimaing he peak hea release rae of similar fuel packages occupying differen base areas. Gemeny and Wiasek [46] gave an example of he use of hea release densiies obained from Cone Calorimeer [39] ess o esimae he peak hea release rae of a large iem, which was hen used o specify a design fire. Gemeny and Wiasek also gave anoher example of a design fire produced by a summaion of he individual hea release hisories of componen combusible assemblies. This design fire was used as inpu o deerminisic models o predic smoke filling and o calculae smoke exhaus requiremens for an arium lobby. The predicion of hea release raes from informaion obained from he burning characerisics of individual iems obained in small-scale ess such as he Cone Calorimeer, has been of ineres ever since i was firs aemped by Babrauskas and Krasny [47]. However, many effors have so far been me wih limied success mainly because of he difficuly of scaling complex phenomena from small-scale o full-scale iems [18]. The European Commission-sponsored projec, Combusion Behaviour of Upholsered Furniure (CBUF) [43] produced one of he larges collecions of combusion daa for upholsered furniure. In he CBUF projec, he furniure calorimeer was used for esing full-scale furniure iems, while he cone calorimeer was used for small scale esing of furniure componens. Three differen numerical models were developed for predicing hea release raes for full-scale furniure using cone calorimeer daa. Equaions o predic he peak hea release rae, ime o reach unenable condiions, oal energy released and smoke producion raes were developed afer an exensive saisical analysis of he daabase. Babrauskas e al. [48] presened a deailed discussion of he hree models developed in he CBUF work. Much work [49; 50] has been carried ou in New Zealand o deermine he

9 applicabiliy of he hea release rae predicion mehods developed in he CBUF work. I was found ha he correlaions were no as accurae for upholsered furniure used in New Zealand, which exhibied higher peak hea release raes. Hea release rae daa for elecronic equipmen and appliances, such as elevision ses, compuer moniors and inkje priners can be obained from he Naional Associaion of Sae Fire Marshals websie [51]. 4 DISCUSSION AND CONCLUSION The ISO publicaions, ISO/TR and [4; 5] provide an excellen overview of he general principles ha should be followed when underaking he ask of creaing design fires. However, apar from he pre-flashover design fire, he publicaions do no ye provide any oher quaniaive mehods for pre-flashover and pos-flashover fires. The erm design fire is used variously o refer o jus abou any fire characerisic perceived o give a measure of he fire environmen, such ha even a mere saemen of he average hea release rae over he expeced duraion of a fire, for example, is a design fire. In he absence of widely acceped sandards, he amoun and accuracy of he quaniaive informaion provided abou a design fire is decided somewha subjecively. A presen, he calculaion schemes available are largely empirical in naure and unsophisicaed insofar as using mehods founded on rigorous fire science principles is concerned. This is one source of uncerainy when such mehods are used o generae inpu daa for fire models. The wo main quaniies used o describe design fires are usually he hea release rae (pre-flashover scenario) and emperaure-ime profiles (pos-flashover scenario). The mos widely-used pre-flashover design fires are fires, whereas a hos of empirical correlaions are available for calculaing emperaures in he pos-flashover sage. Alhough enabiliy is he main concern during he earlier sages of a fire, here were no simple mehods found ha could be used o quanify design fires in erms of he concenraion of asphyxiaing gases wih ime. The hea release rae is regarded o be he mos imporan quaniy ha describes a design fire. Hea release rae daa for many combusibles is available from he various sources cied earlier. However, i is impracical o presen all he resuls in a single forum in a nea and organized fashion due o he exremely large variaions in he physical characerisics of real combusibles. 5 FUTURE WORK Fires involving real combusibles are inherenly difficul o model accuraely using curren mehods parly due o he complexiy of fire dynamics, and also because he combusibles are no homogeneous in maerial composiion and oher physical aspecs. A research projec is being conemplaed o sudy fires in simulaed rooms, using suiably seleced fuel packages, wih a view o developing well-founded design fires for various occupancies. The iniial focus will be on residenial occupancies and he fire loads o be used in he sudy would be based on daa colleced from a Canadian fire load survey ha is currenly being underaken for by he auhors. 6 NOMENCLATURE A o Area of a venilaion opening ( m ) A Toal inernal area of bounding surfaces of an enclosure ( m ) b A parameer in Equaion (5), = kρ cp (W.s 0.5 /m K) b ref Reference value of b (W.s 0.5 /m K) c p Specific hea capaciy (kj/kg.k) H o Heigh of venilaion opening ( m ) F o Ao Ho 1 Opening facor = ( m ) A 1 F ref Reference value of he opening facor ( m ) F v Venilaion facor = Ao H o 5 ( m ) k Thermal conduciviy (kw/m.k) Q & Hea release rae (kw) Q & o Reference hea release rae (kw)

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