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Fire Research at DBR/NRCC: Proceedings of a symposium held in

September 1981 at the opening of the DBR fire research field station

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Price: $5.00

DIVISION OF BUILDING RESEARCH

FIRE RESEARCH AT DBR/NRCC

Proceedings of a Symposium held in September 1981 to

mark the opening of the DBR Fire Research Field Station

Proceedings No. 5 of the Division of Building Research

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Canada has one of the worst fire records among developed countries. A

study of fire prevention and control ウケウエ・ャセ undertaken by the National

Research Council of Canada in 1978 reported that the yearly loss of lives in fires is over 800, that about four times that number are injured, and that

property losses exceed $500 million. The overall annual expenditure in

destroyed property plus the cost of efforts to control fire was estimated to be over $2.8 billion.

The Division of Building Research has recognized the seriousness of the

situation since it was established in 1947. It formed a Section in 1951

devoted to research on fire-related problems. In 1958 this group occupied a

new building containing laboratory facilities and special test equipment

required for its work. The Section has developed research programs dealing

with major areas of concern including fire resistance of building materials and components, behaviour of materials in fires, flame spread, the toxicity of combustion products and the development of methods for calculating fire risk and fire resistance.

The Division of Building Research has worked closely with committees of the Associate Committee on the National Building Code on the evolution of the fire-related safety requirements of the National Building Code of

Canada. When the development of high-rise buildings introduced the problem

of the control of fire and smoke in tall buildings, expertise in the Fire Research and Building Services Sections of the Division was brought together

to consider action that should be taken. This resulted in the preparation

of Measures for Fire Safety in High Buildings, published as a supplement to the National Building Code in 1977.

The development of smoke control measures and research on fire problems identified the need for larger-scale studies at a location where the

generation of a reasonable amount of smoke could be tolerated. A facility

was designed, a 90-ha (220-acre) site found, and construction undertaken. This work has resulted in a Fire Research Field Station composed of a burn hall, 55 m (180 ft) by 30 m (100 ft) by 12 m (40 ft), to be used for large-scale burns; a ten-storey tower for studies of smoke control and fire in

tall buildings; and a service unit that links the two facilities. The

Station was opened officially 23 September 1981.

A Symposium was held on 22 September in association with the opening of

the Field Station. It provided a summary of the current research activities

of the Division of Building Research on fire and smoke control. A

description of the new Field Station was also presented. This publication

is the proceedings of that meeting. It also contains in an Appendix a

review of the growth of fire research and fire-related activity at the Division during the period 1950 to 1979.

The Division is pleased to record in this wayan important step in the

evolution of fire research capability in Canada. With the opening of the

Field Station, a major national facility that has few equals in the world, has become available for the development of fire technology and testing. The Division looks forward to exploiting fully the opportunities that it will provide.

L.W. Gold

Associate Director,

Division of Building Research, National Research Council.

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NATIONAL RESEARCH COUNCIL OF CANADA cordially invites you

to attend the ceremonies at the opening of the DBR FIRE RESEARCH FIELD STATION

22 and 23 September 1981

TUESDAY, 22 SEPTEMBER WEDNESDAY, 23 SEPTEMBER - A symposium on fire research to be

held in the auditorium of the Division of Electrical Engineering Building M-50, NRC.

- Formal opening ceremonies at the Fire Research Field Station, near Carleton Place, Ontario. - An open house and demonstration

tests at the Fire Research Ottawa Laboratories.

- Open house and demonstration at the Field Station.

Tuesday, 22 September Tuesday, 22 September (Continued) SYMPOSIUM - FIRE RESEARCH AT NRC

Morning Session

Afternoon Session, (22 September)

Chairman - L.W. Gold, Associate Director Division of Building Res.

- Fire resistance of building elements T.T. Lie &M. Galbreath - Some comments on fire cost

control in Canada G. Williams-Leir - COFFEE

- Fire Research Field Station: description and role A.M. Phillips &L.W. Gold - Question period

- Closing remarks - ADJOURNMENT

- Buses depart from Ottawa - Sign guest book

- COFFEE

- OPENING CEREMONIES - LUNCH

- Tours commence - Demonstrations:

fire drainage, room burns, flame deflectors

- First bus returns to Ottawa - COFFEE, Questions and

informal discussions - Remaining buses depart 17:00

OPENING CEREMONIES Wednesday, 23 September

Location - Fire Research Field Station near Carleton Place, Ontario. 16:00 11:15 12:00 12:40 14:00 09:45 10:45 16:30 - C.B. Crawford, Director

Division of Building Res. - Sign guest book

- Introduction - C.B. Crawford - Basic issues of fire science T.Z. Harmathy, Head, Fire Research Section, DBR - Ignition and flammability

studies

M.V. D'Souza, F.R.S. Clark

&W. Taylor

- Smoke and toxic gases produced by fires

K. Sum! &Y. Tsuchiya

- COFFEE

- Studies of the movement and control of smoke in high-rise buildings G.T. Tamut"a

- Question period

- Tours of Fire Research Laboratories, Bldg. M 59 - LUNCH

- The elements of fire safety design

T.Z. Harmathy &J.R. Mehaffey Chairman

Location - Montreal Road campus of NRC Division of Electrical Engineering Auditorium Building M 50. 08:30 09:00 13:00 14:00

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Basic Issues of Fire Science ...••...••....••... 1 T.Z. Harmathy

Ignition and Flammability Studies •••••••••••••••••••••••••••••••• 14 M. V. D'Souza, F.R.S. Clark,

and W. Taylor

Smoke and Toxic Gases Produced by Fires •••••••••••••••••••••••••• 30 K. Sumi and Y. Tsuchiya

Studies of the Movement and Control of ••••••••••••••••••••••••••• 39 Smoke in High-Rise Buildings

G.T. Tamura

The Elements of Fire Safety Design ••••••••••••••••••••••••••••••• 49 T.Z. Harmathy and J.R. Mehaffey

Fire Resistance of Building Elements •••••••••••••••••••••••••••••• 65 T.T. Lie and M. Galbreath

Some Comments on Fire Cost Control in Canada ••••••••••••••••••••• 77 G. Williams-Leir

Fire Research Field Station: Description and Role ••••••••••••••• 87 A.M. Phillips and L.W. Gold

Appendix A: Fire Research at the National Research Council of Canada: 1950 to 1979 G.W. Shorter and T.Z. Harmathy

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by T.Z. Harmathy

ABSTRACT

Fire science provides the foundation for sound design decisions in achieving fire safety. Fire risk

assessment and the assessment of potential for harm are tools for making objective decisions on the safety of products but, as yet, they are of limited utility. The principal drive of fire research today is to supply information on material behaviour and to develop mathematical models of fire tests and fire processes. Some of the models have already achieved predictive capability. The level of fire safety depends a great deal on human behaviour patterns which are responsive to education.

Down through the centuries the word fire had a different connotation than it has today. Building fires often grew into conflagrations destroying whole villages, towns, and cities, and claiming lives by the thousands. The building regulations implemented by the Romans following the great fire of Rome in 64 A.D. to prevent the recurrence of conflagrations were forgotten

in the Middle Ages, and it was not until the fire of London in 1666 that society again became concerned about fire regulations. The next 200 years saw the emergence of so-called "fireproof" constructions, those capable of standing up to a fire and blocking its advance from building to building.

With the increasing use of fireproof constructions and the

establishment of well-equipped and disciplined fire brigades, disastrous conflagrations all but disappeared shortly after the turn of the century, recurring only briefly during the Second World War. With the probability of spread of fire between buildings greatly diminished, the objective of fire defence was redefined as prevention of spread of fire beyond the boundaries of the compartment involved. The concept of fire-resistant compartmentation emerged; it still holds its ground. Increasing technological objectivity demanded test-supported evidence on the fire-resistance performance of compartment boundaries. Speculation concerning the utility of the fire-resistance test and other performance tests that followed, and the

interpretation of test results, inevitably led to the evolution of fire science. Although fire science started as a discipline closely tied to fire performance testing, it has now assumed a more or less independent role.

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DECISIONS ON FIRE SAFETY

The objective of the branch of fire science that concerns the DBR Fire Research Section is the creation of a sound foundation for the provision of fire safety in buildings. A fire-safe building can be defined as one in which:

- the probability of fire occurring is low,

- if fire does occur, all occupants will probably survive without injury, and

- property damage will be confined to the immediate vicinity of the fire.

Fire safety depends on many factors. Some of them are related to building design, e.g., the layout and dimensions of a building, the selection of building materials, and the use of safety devices and

facilities. Others are related to the occupants' behaviour patterns: how they select and arrange various articles, mainly furniture, that are brought into the building, and how aware they are of the danger of fire. The design of buildings and their contents can be influenced to some extent by lawful coercion. In North America, the most important fire safety requirements are covered in building codes that regulate design and construction materials, and fire codes that control what can be brought into a building. Decisions concerning the arrangement of building contents and others related to the occupants' awareness of the danger of fire are essentially beyond the reach of the law; yet they too can be influenced by education and persuasion.

As far as building design and use of construction materials are concerned, there is a tendency today, in the interest of providing better protection at lower cost, toward relaxing the coercive power of building codes and giving the building designer a greater say in how to achieve fire safety. Although, as will be discussed later, certain aspects of the

overall fire problem do suggest particular design solutions with almost compelling force, there are other aspects that must be treated with an open mind. To aid the designer, "decision trees" have been developed to identify

the numerous techniques available for achieving fire safety and to suggest possible trade-offs between them (1).

Many of the available techniques are well understood and can be

designed on the basis of long available general knowledge or the specialized knowledge developed more recently by fire science. A conscientious designer is concerned not only with the effectiveness of the techniques to be

employed but also with the costs involved. As with most other design problems, the designer's decisions are motivated largely by his knowledge and experience. From an effort to allow major design decisions to be made on objective bases, has evolved a branch of fire science referred to as "fire risk assessment".

The general aim of fire risk assessment is to minimize the overall fire-related costs, usually regarded as comprising the expected value of

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fire losses and the costs of measures to prevent these losses. Calculation methods discussed by Lie (2) and Ramachandran (3) are typical of

probabilistic techniques employed in fire risk assessment. Although the "logic tree" and the algorithm are fairly well established t the practical value of fire risk assessment is greatly restricted by the paucity of

reliable input information. Perhaps it is one version of Murphy's law that statistical data never come broken down in the way needed for the solution of one's problem. Without hard-fact statistical data any fire risk

assessment degenerates into a sophisticated statement of subjective judgement.

POTENTIAL FOR HARM

In minor design decisions t e.g. t selecting one or another building product for a specific application t monetary considerations are usually ignored; attention is focused on the merits of making particular choices from the point of view of overall fire safety. SimilarlYt fire safety and not the cost is the principal consideration in selecting various articles t e.g., furniture t to be brought into the building. The test-based evaluation of the overall peril created by installing in t or bringing a product into t a building is referred to in North America as assessment of "potential for harm" (4) or as assessment of "reaction to fire" in Europe (5). The potential-for-harm numbers are not regarded as strictly quantitative

statements of the peril but rather as product descriptors that ensure that t after starting with a set of standard test data, all designers will arrive at more or less the same safety decisions. The combination of the test data into a product descriptor is based on systematically developed "expert

opinion" rather than statistical data.

The procedure to assess the potential for harm starts with identifying the product in question with respect to the nature of the peril with which it is associated. The following four product groups have been suggested

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Group A: Group B: Group C: Group D:

clothing and bedding products,

furnishing or floor covering products t miscellaneous other items,

wall and ceiling lining products, building components.

The potential for harm (PH), is visualized as consisting of a number of components. A tentative list is:

(1) ignition by plausible ignition source,

(2) intense smoke production,

(3) production of toxic gases,

(4) high burning rate or high flame spread shortly after ignition,

(5) high burning rate or high flame spread at a more advanced

phase of fire,

(6) structural failure, and

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It is assumed that the results of a set of a number of well-chosen performance tests will quantify these PH components. Based on the results, the overall PH number will be obtained by an agreed-upon algorithm, e.g., by the weighted summation of the PH component numbers:

where PH1, PH2, ••• PH7 are component potentia1-for-harm numbers, and a, b, ••• g are weighting factors. These weighting factors may eventually be decided on by experts using the Delphi technique (6). A tentative list of those values, suggested by this author, is given in Table I (4).

Table 1. Weighting Factors

Factor for PH Product Group

component A B C D a (ignitabi1ity) 0.•40 0:-20 0:-20 0:-20 b (smoke) 0.05 0.30 0.20 0.05 c (toxicity) 0 0.10 0.05 0.05 d (burning, initial) 0.40 0.35 0 0 e (burning, advanced) 0 0 0.50 0 f (structural failure) 0 0 0 0.65 g (extinguishment) 0.15 0.05 0.05 0.05 , -1.00 1.00 1.00 1.00

To be acceptable for a particular application the potentia1-for-harm number for the product in question must fall below a critical level. This level should be defined either by an appropriate body having jurisdiction, or (preferably) by groups of experts using the Delphi analysis. The

critical level is visualized as dependent primarily on the type of occupancy, and other factors relating to safety of life.

PERFORMANCE TESTS

A meaningful reaction to fire index or potentia1-for-harm number can only be derived from the results of a set of meaningful tests.

Unfortunately, most of the existing fire test standards grew out of

practical necessities at times when the problems they were designed to solve were not fully understood. None was intended for use in conjunction with others to form a segment in a mosaic of understanding. Developing a set of good, relevant performance test standards that complement one another is clearly the prerequisite of any attempt to attain a coherent philosophy of assessment of peril.

A few years ago ASTM Subcommittee E05.32 on Research appointed a task group to formulate a set of criteria for evaluating standard fire tests, those existing or to be developed. This task group has formulated a tentative list of the traits of good performance standards and a "success tree" (logic diagram) serving essentially the same purpose as the list. The Subcommittee has also undertaken the checking of all existing performance standards against the list and the success tree, and thus to determine the

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value of the test standard from the point of view of assessment of potential for harm. Even the optimists realize, however, that this work, together with the development of new standards to replace those to be discarded or to fill in some gaps, may take several decades. Thus the future of decision-making based on performance tests does not look particularly bright.

As so often happens, the ability of performance tests to yield early answers without a thorough insight into a problem diminishes with time as basic research catches up with developments. Eventually it will be more practical to derive solutions, direct from basic studies, to all but a handful of the most complex problems. Although those solutions are still far off as far as fire safety is concerned, they will probably be achieved before the problems of the test-based assessment of the perils of fire are all sorted out.

MATERIALS RESEARCH

Fire science is concerned with materials, processes, probabilities, and patterns of human behaviour. Because of the specific way fire scientists look at material behaviour, it has become a very significant part of fire science.

From the point of view of the problems that arise, a material may be looked upon as a fuel (source of fire), an insulating material, or a

structural material. These three groups are not mutually exclusive; a given material may belong to one or all depending on its role in the problem at hand.

In the case of fuels, the material properties of interest depend to some extent on the nature of the problem to be considered: ignition, flame spread, steady-state burning, or propensity for the production of smoke or toxic gases.

As will be discussed in another paper presented at this Symposium (7), the mechanism of burning of solid fuels depends to a great extent on whether the fuel is char-forming or non-charring. For non-charring materials the rate of steady-state burning is controlled mainly by factors intrinsic to the material, such as temperature and heat of pyrolysis, heat of combustion of volatile decomposition products, and luminosity of flame. For char-forming materials the prime controlling factor is extraneous, i.e., the rate of air supply to the fuel surface; the just enumerated material-intrinsic factors are of lesser importance. In burning processes of a strongly

transient nature, such as ignition and flame spread, the heat capability and thermal inertia of the material should be added to the earlier list of

process-controlling factors.

Obscuration of vision by smoke is deemed to be the most important threat to life safety in building fires (8). For a specialist the

structural formula of a fuel may give a faint clue about its smoke-producing propensity, as well as its propensity to produce toxic gases. These

propensities depend, in ways not fully understood, on a large number of material-intrinsic and extraneous factors.

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When dealing with the performance of building elements in fire t an overwhelming majority of non-combustible materials and a fair portion of combustible materials are usually looked upon as "insulating" materials t even though they may also perform structural functions. Concrete t gypsum t brick t and wood are the most common examples. Unlike some metals and ceramic materials t most building materials are not usually required to function satisfactorily at elevated temperatures for extended periods. ConsequentlYt their physico-chemical stability at higher temperatures is

rarely considered in normal engineering or architectural design. But the fire safety specialist must be aware of the problem. Many of these

materials are unstable at temperatures higher than lOO°C. On heating t most of them undergo changes that are always accompanied by absorption or

evolution of heat t and may bring about substantial transformations in their microstructures and properties. Concrete at SOO°C and concrete at room temperature are entirely different materials.

ClearlYt the generic information available on the properties of

building materials at room temperature is seldom applicable in designing for fire safety. Those who use it may arrive at grossly erroneous conclusions and risk distrust by the layman in other than experimental techniques of performance assessment.

The thermal properties of insulating materials that are of particular interest in the design of building elements for fire resistance are thermal conductivitYt densitYt and apparent specific heat (which includes the basic sensible heat contribution and a latent heat contribution over temperature intervals of physico-chemical instability). A list of these properties over the temperature range of 20 to lOOO°C would be of great value.

For materials in the structural group that form the load-bearing components in building elements (steel t concrete t and wood are prime

examples)t rheological behaviour at elevated temperatures is of interest to the designer. A great deal is already known about the creep behaviour of steel at elevated temperatures; the behaviour of concrete and wood is less well understood.

COHERENCE OF FIRE-RELATED PROBLEMS

The ultimate goal of fire research is to provide the means to improve fire safety by conscious design decisions rather than by lawful coercion. The development of meaningful design methods has long been hindered by the multiplicity of fire-related problems in complex buildings. It has been customary to divide these problems into manageable units t to seek solutions to the unit-problems separatelYt and to assume that the solution to the overall problem is simply a spatial or temporal composition of the unit-solutions. The inadequacy of this concept has been clearly brought out by numerous reports on fires in high-rise buildings. What has been learned from these reports is that some important aspects of fire can only be studied if the entire building is looked upon as a single unit.

The distribution of air currents in a building prior to the outbreak of fire is profoundly important information. These currents t whose intensity

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increases with building height, are brought about by two factors: the temperature difference between the building interior and the outside atmosphere, and the "air-leakiness" of the building envelope. Because of the former, these currents are especially strong during the winter heating season. The intensity and direction of air currents in a nine-storey building on a calm winter day are illustrated in Fig. lao

The spread of fire tends to follow the path of air currents. Thus, if fire breaks out in a compartment below the mid-height of a building, it will first enter the corridor, then rise in the stairwells or elevator shafts. If fire begins in the upper storeys, on the other hand, the spread will be towards the building envelope. On reaching the envelope, flames emerging from the windows may ignite the exterior cladding (if it is combustible) or may break the windows above and set a compartment on the next storey on fire.

The effect of air currents on the spread of smoke is similar to their effect on the spread of fire. Because smoke is not a combustion-carrying medium but an aggregate of combustion gases and airborne particles, it is much more mobile than the fire that breeds it and can disperse throughout

the building in a much shorter time. Figure lb shows how air currents would distribute smoke on various levels of a building within a mere 10 to 15 minutes of the onset of a fire on the first floor. (The smoke contamination of the second floor would be the result of vertical leakage currents, not discussed in this paper.)

MATHEMATICAL MODELING

The primary aim of research into fire processes is to gain an

understanding of how such elementary processes as heat and mass transfer or physical and chemical changes, the laws of which are fairly well understood, are intertwined in various fire phenomena. The theoretical synthesis of these elementary processes, supplemented by physical and chemical

principles, is usually referred to in the field of fire science as

mathematical modeling. The objects of mathematical modeling include: fire tests, e.g., the fire-resistance test and the flame-spread test; unit fire processes, e.g., ignition and real-world fire spread; and composite fire processes, e.g., pre-flashover and post-flashover compartment fires, and intercompartmental fire spread.

The ultimate purpose of mathematical modeling is to provide reliable information to the fire safety designer. The immediate goals are usually more modest: to identify the parameters that playa part in the fire

process, evaluate their influence, and determine whether they are intrinsic to the process or incidental. When related to fire tests, a good model will help in the understanding of whether a test addresses a component of the potential for harm, and whether it is correctly devised; in other words, whether the test results are meaningful and reproducible.

Inasmuch as a real-world fire is usually an aggregate of unit processes, understanding the mechanisms of unit processes is extremely

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important. Considerable success has been achieved in modeling the air currents in high buildings and the distribution of airborne fire gases. Mathematical modeling was instrumental in acquiring insight into such

pivotal unit processes as fire plume and flame spread over combustible surfaces.

From a practical point of view, the modeling of compartment fires is of principal interest. Work on fully-developed (post-flashover) compartment fires has made it possible to estimate the potential of compartment fires for spread by the destruction of compartment boundaries and by the

convection of fire gases (7). When the combustibles in a compartment consist mainly of char-forming materials, cellulosics in particular, as a rule a fire will have a higher tendency to spread by destruction than when the combustibles consist of non-charring materials, such as most plastics. On the other hand, when the combustibles consist mainly of non-charring materials, the potential of fire to spread by convection through corridors and along the facade of a building will be considerably higher. Through today's calculation techniques, these findings can be put to use in fire safety design.

Although the nature of a fire during the post-flashover period is the determining factor in the structural design of a building, from the point of view of life-safety the pre-flashover period is equally or even more

significant. The time-to-flashover is a very important piece of information because it indicates the maximum length of time available to the occupants of a compartment to escape or to be rescued. For this reason, a thorough understanding of the chain of events that connect the ignition of the first item with the flashover has become a major goal of fire research (9).

Among the mathematical models applied to pre-flashover fires, the modular (or zonal) models are the most widely employed. These models

consider a compartment on fire as consisting of discrete control volumes: the lower spaces occupied mainly by air near atmospheric temperature, the burning item, the fire plume, the upper spaces occupied mainly by combustion and decomposition gases, the heated compartment boundaries and possibly other heated objects. The mathematical models are constructed by writing conservation equations for each control volume, and expressing fluxes of mass, momentum, and energy across the boundaries of the control volumes.

The models that have so far been developed do not take account of the presence of air currents. Because of this, and because of the insufficiency of knowledge concerning two key modules, the burning item and the fire

plume, the practical utility of the models is as yet rather limited. It is hoped that they will eventually become valuable tools in predicting the course of fires in compartments of strictly arranged furniture, e.g., prison cells, theatres, and hotel rooms. Under general conditions, the predictive capability of these models will always remain restricted, owing to the large number of stochastic variables (such as those characterizing the

compartment, the furnishings, the ignition source, the air currents, and even the occupants of the compartment) needed in the description of pre-flashover fires. In fact, the true purpose of modeling is not so much to

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achieve this capability as to develop certain guidelines with respect to the do's and don't's of interior design.

Even when modeling simpler processes, some input variables may turn out to be of a stochastic nature. It is always a sound principle to restrict probabilistic considerations to the specification of these stochastic input variables. A complex process, such as fire, can only be understood if the relations between the input and process (output) variables are known. Such an understanding cannot be achieved through probabilistic modeling of the entire process or a major part of it.

Naturally, this argument is applicable only if the modeling is done with a view to developing predictive methods or design guidelines.

Insurance companies are not concerned with decisions related to individual situations, but rather with mean values, distributions, and probabilities. For their purposes, modeling fire processes by probabilistic techniques is more suitable. Probabilistic models usually regard a fire as a sequence of states or realms, e.g., ignition, initial item burning, interactive burning, and consider the transitions between these states in terms of time and

probabilities of occurrence (1). FIRE SAFETY DESIGN

As already mentioned, the potential of fire for destructive and

convective spread can be quantified. Knowing the expected characteristics of the fire and the probable course of the spread of flames and smoke, if attempts to confine the fire to the compartment of fire origin fail,

appropriate countermeasures can be designed. An effective and inexpensive tool to prevent the spread of smoke in high buildings is the pressurization of the building or a major part of it. Preventing the flames from spreading from the fire compartment to other parts of the building can be achieved by the use of self-closing doors on the lower floors and flame deflectors on the upper floors. Flame deflectors are insulated metal boards mounted above the windows. When activated by the flames emerging from windows, they fall down to assume a horizontal position, and thus shield the storeys above from the flames and radiant heat.

There is considerable pressure nowadays to make the installation of sprinklers mandatory in high buildings. Resistance to this comes from those who resent stereotyped safety measures and would like to see more

encouragement given to knowledge-based building design. Sprinklering is a rather expensive defence method. If, in the affected area, the sprinkler system fails or merely "controls" the fire without extinguishing it, the building is left defenceless against the dispersion of smoke.

Provision of smoke detectors, sufficiently wide escape routes, and pressurized refuge areas are part of the overall fire safety system in tall buildings.

It is widely recognized that designing for fire safety is a many-sided problem, perhaps more so than most other problems in building design.

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cases it takes meticulous deliberation on all details of the building design to arrive at the correct solutions.

PSYCHOLOGICAL AND SOCIOLOGICAL FACTORS

The question naturally arises as to how much fire safety is really necessary. The answer to this is not only a matter of science and

economics, it also concerns psychology and sociology. Human adaptation is an important factor. Countless examples show that people can live safely in extremely flammable shacks, using candles or oil-lamps for illumination; they can also fall victim to fire in modern buildings equipped with all amenities and fire safety facilities. An average person is subject to a behaviour pattern reminiscent of the principle of action-reaction in

physics. Perhaps it could be described as the following generalized form of Parkinson's law: human laxity expands to fill the space allowed by the

restraining factors.

There are, however, great deviations from this behaviour pattern, governed primarily by the understanding by the individual of his

responsibilities toward society which, in turn, depend on his educational level. That this point has not yet been brought out clearly is probably due to the fact that statistical data on fire losses are often collected on the wrong bases, e.g., area, racial origin of the occupants, or type of housing. A striking example that there is a profound underlying factor behind these statistical data is a British report (10) which revealed that the propensity for high fire losses in an area with a low level of household amenities did not decrease after a massive redevelopment of the area including provision of amenities.

The high incidence of fires in modern times is due largely to

negligence, which is a symptom of a deficient sense of responsibility. It manifests itself in various ways and is the chief source of the troubles

that plague society. Education is the cure. Problems that have a strong social component cannot be solved by technology alone.

SUMMARY

With respect to the provision of fire safety in buildings, there is a tendency today to relax the coercive power of building codes and give building designers greater freedom in their decisions. In design, the personal qualification of the designer is still the most important factor. Owing to the paucity of statistical data, cost-effective solutions can rarely be arrived at by fire risk analyses.

The potentia1-for-harm number (or reaction to fire index) have been proposed as test-based descriptors of the peril created by installing or bringing a product into a building. The test-based assessment of peril is not yet possible, however, for lack of a set of good performance test standards that complement each other.

The aims of materials research depend on the role of various materials in a fire. For fuels - their thermodynamic properties, for insulating

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materials - their thermal properties, and for structural materials - their rheological properties are of principal interest to the designer.

The bulk of research efforts now consists of the mathematical modeling of fire tests, unit fire processes, and complex fire processes. Predictive capability has already been achieved on the problem of fully developed fires. This capability provides a foundation in the design of buildings against spread of fire by destruction and convection. Efforts are under way to develop predictive capability with respect to pre-flashover fires.

Statistical modeling of developing and spreading fires is an approach that yields useful information to insurance companies.

The nature of fires in high-rise buildings can be fully understood only if the entire building is regarded as the unit system. Drafts in the

building strongly influence the course of the fire and the dispersion of smoke. A reasonable amount of knowledge is available for quantifying the various components of the overall fire problem and developing the technology' to cope with the problem.

The optimum level of fire safety depends strongly on patterns of human behaviour. Bettering human behaviour at an impressionable age would be a powerful tool in improving fire loss statistics.

REFERENCES

1. Roux, H.J. and G.N. Berlin. Toward a knowledge-based fire safety system. In Design of buildings for fire safety, E.E. Smith and T.Z. Harmathy, Eds., American Society for Testing and Materials, ASTM STP 685, Philadelphia, 1979, p. 3.

2. Lie, T.T. Economic design for fire safety. Build International, Vol. 7, 1974, p. 289-304 (NRCC 14364).

3. Ramachandran, G. Statistical methods in risk evaluation. Fire Safety Journal, Vol. 2, 1979/80, p. 125.

4.

Harmathy, T.Z. assessment.

Fire performance standards and the problem of fire risk Fire and Materials, Vol. 4, 1980, p. 173 (NRCC 19209). 5. Minne, R. The Belgian point of view on testing reaction to fire of

building materials. In Ignition, heat release, and noncombustibi1ity of materials, American-Society for Testing and Materials, ASTM STP 502, Philadelphia, 1972, p. 35.

6. Da1key, N.C. The Delphi method: an experimental study of group opinion. Rand Rept. No. RM-5888-PR, 1969.

7. Harmathy, T.Z. and J.R. Mehaffey. The elements of fire safety design (this Symposium volume).

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8. Friedman, R. Quantification of threat from a rapidly growing fire in terms of relative material properties. Fire and Materials, Vol. 2, 1978, p. 27.

9. Pape, R. and T.E. Waterman. Understanding and modeling preflashover compartment fires. In Design of buildings for fire safety, E.E. Smith and T.Z. Harmathy, Eds., American Society for Testing and Materials, ASTM STP 685, Philadelphia, 1979, p. 106.

10. House Fires and Social Conditions, Building Research Establishment, Great Britain, BRE News, Autumn 1979, p. 49.

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Figure 1 Illustration of smoke problem in a 9-storey office building

(a) air currents

(b) smoke distribution (fire on first storey)

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IGNITION AND FLAMMABILITY STUDIES

by

M.V. D'Souza, F.R.S. Clark and W. Taylor

ABSTRACT

The fire hazard of products can be described in three ways: by assigning merit values on the basis of results of standard small-scale tests; by observing results of full-scale tests simulating specific scenarios; and by combining all fire-related properties of products into a number that will place the product on a unique fire hazard scale. This paper discusses examples of all three approaches, based on recent studies at NRCC. Examples of deriving fire hazard classification by the first approach are the application of a modified version of the Steiner Tunnel test to accommodate foam plastics and the use of a small corner wall test employed

concurrently with the tunnel. Two examples of developing information by scenario-type tests are discussed: the effect of covering foam plastics with metal foil and more conventional materials; and fire

spread through vertical cavities. Results from the latter test indicate that air gap and fire stop provisions are the most important factors in fire

spread. Finally, the ignitability of simple polymers in a flame has been studied by monitoring the light emitted at the conclusion of the ignition delay; this represents a first step in the identification of intrinsic fire properties, suitable for a fire hazard scale.

The word "fire" evokes the sense of hazard, a dangerous state, whose control is the major interest of some public and private agencies. Complete control of such a hazard is not easily achieved, however, due in part to lack of knowledge.

Despite its usually harmless beginnings, a fire can grow very rapidly to engulf the entire room of origin, to spread through a building and, in the extreme, to involve other buildings as well. Early work in the control of fire was directed primarily at the prevention of fire spread between buildings; more recent efforts have sought to contain fires within the compartments of origin. The field of fire resistance evaluation, which addresses one aspect of the problem of fire containment, is now fairly well established, because a fully-developed fire is a relatively steady-state phenomenon.

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Recent attention has been focused on understanding the growth period of a fire, i.e. the period preceding full-room involvement or flashover. This period comprises a complex interaction of physical and chemical processes occurring under highly transient conditions. For a fire to grow and spread, sufficient heat must be released to sustain the pyrolysis process. Gas-phase mixing and combustion and, possibly, solid-gas oxidation reactions which produce the heat required to maintain pyrolysis are highly dependent on the physical constraints of the system.

The many variables that influence the course of the fire process can be divided into three groups: the thermophysica1 properties of the materials involved, the geometric characteristics of the fuel-bed and the enclosure, and the variables that describe the prevailing environmental conditions. All three should be considered in any prediction of performance of a fire during its growth stage. Since each real-world fire scenario is essentially unique, it is not surprising that progress in understanding the earliest

period of fires has been slow.' HAZARD ASSESSMENT

Fire hazard can be assessed in three ways. The traditional approach has been to use standardized, small-scale, performance tests. These tests assign empirical values on arbitrary merit scales to certain fire

characteristics of a material, e.g., its ignitabi1ity and propensity to spread flame, to generate smoke and toxic gases, and to release heat. The tests are conducted under specified conditions that often bear little

resemblance to conditions of use. These tests were developed as needs arose and, for many, no theories exist to enable prediction of results.

Regulatory authorities set upper limits of acceptability for materials used in specified locations, based on the values developed from these tests. Experimental evidence, experience and expert judgement are normally used to support the selection of these limits of acceptability.

For some time, no problems were encountered in relating test data to practical experience and, consequently, this approach has been widely used. Recent experience has shown, however, that the behaviour of some lightweight materials, foamed plastics in particular, is quite different from behaviour predicted from results of performance tests (1,2).

The second approach to hazard assessment is to conduct full-scale fire tests, which attempt to simulate a given fire scenario in its entirety. They are used whenever existing small-scale tests or practical experience are inadequate to make a correct assessment. The principal drawback of this approach is its limited relevancy. The selection of a suitable scenario of wide applicability is difficult if not impossible, while the evaluation of all possible scenarios is prohibitively expensive.

The third (and preferred) approach to hazard assessment requires a sound knowledge of the fire process which would make it possible to design tests that measure intrinsic fire-related properties of materials.

Regulations could then be formulated by combining these property data through an algorithm representative of the chosen scenario, to provide a

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suitable measure of hazard potential (3,4). It is hoped that eventually it will be possible to predict the course of a fire in any enclosure solely

from information related to the enclosure and the physical and thermochemical properties of the materials in the enclosure.

This paper is an account of efforts by the DBR Fire Research Section, using each of these approaches, to provide answers to current flame spread problems as an aid to the regulatory process.

SHORT-TERM SOLUTIONS

The inadequacies of many established procedures for evaluating flame spread have resulted in test agencies adopting a defensive posture by including disclaimers in the test specifications. The same inadequacy has led regulatory bodies to require certain materials, prone to rapid flame spread, to be protected against accidental ignition. Although such measures have done little to improve the understanding of the basic problem, they have provided solutions to current difficulties.

Further steps taken in Canada include the modification of existing test methods and the development of complementary tests. In the U.S.A., on the

other hand, so-called diversified testing was permitted, whereby full-scale demonstration test results were accepted in lieu of standard test data. MODIFICATIONS OF TUNNEL TEST

The ULC* 7.6 m tunnel test is the principal means used in Canada for developing information on the flame spread characteristics of materials (5). The credibility of this test was questioned when it was applied to foamed plastics after observation of the behaviour of these materials during tunnel tests. The flame front initially advanced rapidly, but slowed down

substantially before reaching the end of the tunnel. This resulted in much lower values for flame spread classification (FSC) for foamed plastics than were indicated from experience.

The anomaly was thought to be associated with the very low thermal inertia of foamed plastics compared with that of more customary materials (6). A much smaller heat flux is required to raise the surface temperature of materials of low thermal inertia to the level of pyrolysis than is

necessary for more traditional materials. The heat of combustion per unit volume of these lightweight materials is considerably less, however, than that for other high density combustibles. Consequently, although plastic foams are easier to pyrolyse, the heat generated by the combustion of their pyrolysis products is insufficient to maintain flame spread if the

surrounding surfaces have high thermal inertia. Because of this, the conventional tunnel test was unsuitable for evaluating the flame spreading propensity of foamed plastics.

An index based on the initial rate of flame spread in the tunnel was proposed in 1977, as a result of work conducted at the National Research *Underwriters Laboratories of Canada.

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Council of Canada (2). The more general validity of such an index (Fig. 1) was demonstrated by results of full-scale and half-scale corner-wall tests. A subsequent examination of data obtained by the ASTM E-162 flammability

test apparatus also seemed to support the use of the newly defined index (Ref. 7 and Fig. 2). Since 1978, the tunnel test has been complemented by a 1.2 m corner-wall test in the determination of flame-spread index according to ULC procedures (8).

The information presented in Fig. 1 on the flame-spread characteristics of foil-covered foamed plastics suggested that the fire performance of a product is also dependent on the time scale of the test fire. During a brief exposure to a fire the depth of thermal involvement of a material is small, so that the influence of a high thermal capacity surface cover is significant. Thus, a short duration test, such as a corner-wall test, would give a foil-covered foam a rating superior to that of its unfaced

counterpart, whereas the tunnel test, which is of longer duration, may not distinguish between the two (9).

These tests, and indeed most current material performance tests, are designed primarily to evaluate a particular fire characteristic (flame spread here) of a single-component material. Relatively simple composites, such as laminated foams, can be accommodated, but assemblies, e.g., complete wall sections, are difficult to test and the results difficult to interpret. In most tests, the material in question is tested with an adequate supply of air. If, however, the material (usually foam plastic) is covered by a

protecting layer of some other material, the supply is restricted and the material's performance can be markedly different.

PROTECTIVE COVERINGS FOR PLASTIC INSULATION

In low buildings that are designated by the National Building Code of Canada (NBCC) as "non-combustible constructions," the use of certain types and quantities of combustible material is allowed in specified areas. Foam plastics, however, must be provided with a protective cover which is capable of preventing them from becoming involved in a fire for a period of at least 10 minutes. Fire involvement is defined as a rise in temperature above 140°C at the protective-cover-foam interface, when the assembly is subjected to a "standard" fire. Gypsum board, at least 12.7 mm thick, is regarded as an acceptable protective cover. In buildings referred to as "combustible constructions" by the NBCC, gypsum boards having a minimum thickness of 9.5 rom may be used, as well as certain plywoods, particleboards, hardboards and fibreboards, provided their flame spread ratings do not exceed 150.

Two series of studies have been conducted to examine the performance of protected foamed plastics in fire. The first looked into the effectiveness of some coverings accepted by the NBCC (10). Tests were conducted in the 1.2 m corner test apparatus (8) on combinations of typical interior lining materials over polystyrene foam and, for the purpose of comparison, over glass fibre batt insulation. The results showed that the spread of fire was slower for assemblies employing a thin plywood, hardboard, particleboard or gypsum wallboard cover over polystyrene foam than for the uncovered foam

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was found to be the most effective cover material of those tested, as it not only protected the insulation from direct exposure to the fire but also limited surface flame spread to within the confines of the apparatus. In contrast, all the wood linings examined were eventually breached and

therefore could not prevent the insulation from being exposed to the fire. Exposure of the insulation did not occur, however, until the flames had spread over the surface of the lining and emerged from the canopies, i.e., after a flashover condition had been reached.

The type of construction used had little effect on the rate of fire growth. Stud-framed assemblies with wood lining performed slightly better than those in which the protective lining was glued directly to the plastic foam (see Table I). The glued assemblies did not come apart in any of the tests.

When thin linings cover insulation, the thermal properties of the insulation influence the fire performance. Generally, the denser the

substrate the longer the time for the fire to reach flashover conditions (as indicated by flames issuing from the canopy). Thus the lightest insulation of those tested, glass fibre batt, produced the shortest time to flashover when used with a given wood cover material and in a given type of

construction.

The experiments demonstrated that although thin plywoods, hardboards and particleboards do not provide extended thermal protection to the

insulation, they delay direct exposure of the insulation to the fire until after flashover conditions have been attained in the room of origin (Table II). Thus, if occupant safety is of prime concern, these lining materials may be regarded as providiing satisfactory protection for plastic foams. It must be remembered, however, that thin linings will probably be breached shortly after flashover, resulting in the ignition of any combustible material beneath.

In the case of tall buildings, greater than 18 m in height, the NBCC specifies a much more stringent requirement for the protective lining. To prevent the plastic insulation from spreading fire from floor to floor, a covering providing thermal protection for a period of 45 min is stipulated. To fulfil this requirement, the installation of a protective lining

consisting of two layers of 15.9 mm thick fire-resistant gypsum board, or equivalent, is required. Experimental evidence indicates, however, that protection of the insulation for 45 min is not really needed in a typical compartment fire, as the intensity of the fire will peak within 30 minutes. The extent of thermal protection offered by various thicknesses and types of gypsum board was therefore examined at the authors' laboratory by way of small-scale furnace and corner-wall tests (11).

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Table I. Selected Results of 1.2 m Corner Tests of Protected Thermal Insulation No. A3 AS A7 B2 B3 B4 B5

B6

C1 C2 C3 Lining (thickness,mm) Wood panel (3.7) Hardboard (5.1) Gypsum board (9.7) Cork tiles (13.5) Wood panel (3.7) Gypsum board (9.7) Wood panel (3.7) Gypsum board (9.7) Wood panel (3.7) Gypsum board (9.7) Nil Nil Wood panel (3.7) Insulation (thickness,mm) Polystyrene beadboard (49.5) Polystyrene beadboard (49.5) Polystyrene beadboard (49.5) Polystyrene beadboard (49.5) Nil Nil Polystyrene beadboard (49.5) Polystyrene beadboard (49.5) Glass fiber

+

paper (51. 0) Glass fiber

+

paper (51.0) Polystyrene beadboard (49.5) Extruded poly-styrene (50.8) Nil (lining in contact with asbestos board) Time until flames issued from canopy, s 120.0 190.2

*

26.4 148.8

*

139.8

*

138.6

*

78.0 87.0 148.2 Time until substrate exposed, s 180.0 272.4 **

**

157.2 ** 165.0

**

164.4

**

FSCI of exposed surface 166 153 <25 353 166 <25 166 <25 166 <25 167 168 166

IF1ame spread classification as per ULC tunnel test.

2Test series A: All wall components glued. Ceiling components stud-framed.

3Test series B: All components stud-framed.

*Test terminated before flames issued from canopy. **Test terminated before substrate was exposed.

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Table II. Protected Thermal Insulation Performance Comparison: Flammability vs Protection

Time flames Time when lining-insulation interface Test duration t

issue from temperature exceeds 160°C, s s

No.1 canopYt s Above burner Ceiling centre

Al 120.0 114.0 168.6 187.8 A3 190.2 257.4 277 .2 301.8 A5

*

682.2

*

1260.0 A7 26.4

*

*

65.4 Bl 148.8 111.62 177.02 216.0 B2

*

*

*

1218.0 B3 139.8 130.8 170.4 198.0 B4

*

*

*

600.0 B5 138.6 124.2 178.2 189.0 B6

*

*

*

600.0 Cl 78.0 No interface 153.0 C2 87.0 No interface 93.0 C3 148.2 141.02 181.82 195.0

lSee Table I for interpretation of test number. 2Temperature of unexposed surface of lining used.

In the furnace tests composite specimens were used t 790 mm x 840 mm t and the temperature of the furnace adjusted to follow the standard ASTM temperature-time curve. It was found (Table III) that a single layer of regular gypsum board t 12.7 mm thick t failed according to the interface temperature criterion (a rise in temperature of 140°C) within 16 mint regardless of the type of insulation used underneath t and did not prevent flaming of gases released by the insulation. A single layer of 15.9 mm fire-resistant gypsum board also failed at 23 min but it did prevent

flaming. Two layers of the latter material extended the protection period to 60 mint well in excess of the NBCC requirement. By comparisont in

corner-wall tests t a single layer of gypsum wallboard t whether of regular or fire-retardant type t showed little difference in performance.

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Table III. Results of Furnace Tests of Protected Thermal Insulation

Max. Time for Max. Time

Gypsum Thermal Barrier Temperature Flames

Type Thickness, rom Insulation Rise of 140°C Observed, s

Regular 12.7 Polyurethane A 900 1110

Regular 12.7 Polystyrene beadboard 960 1140

Type X 2 x 15.9 Polyurethane B 3480 »4500

Type X 2 x 15.9 Polyisocyanurate 3540 »4500

Type X 2 x 15.9 Polystyrene bead board 3600 »4500

Type X 2 x 15.9 Polystyrene extruded 3480 »4500

board

Type X 15.9 Polyurethane A 1380 » 2100

Type X 15.9 Polyisocyanurate 1320 »2100

Type X 15.9 Polystyrene bead board 1380 »2100

Type X 15.9 Polystyrene extruded 1320 »2100

board

Type X 15.9 Polystyrene extruded 1500

board

Type X 2 x 15.9 Polystyrene extruded 3600

board

FIRE SPREAD TO VERTICAL CAVITIES

Another investigation, using scale-model testing of a specific scenario, was initiated in response to a request from the Fire Test

Committee of Underwriters' Laboratories of Canada, for test data on the fire involvement of plastic insulations in a wall cavity, once fire had entered the cavity. The NBCC places some limits on the area of concealed spaces between fire stops where combustible materials are installed and on the flame spread ratings of those materials. The fire stops specified in the Code, however, seem to have been selected with wood-frame construction in mind and in some cases may not be effective. Furthermore earlier work at NRCC indicated that the extent of flame spread within cavities could be controlled by suitable design of the cavity (12).

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Under a DBR/Industry Research Fellowship arrangement with the Society of the Plastics Industry, Canada, a comprehensive test program was conducted at NRCC with the objective of determining whether a fire, once having

entered a wall cavity, could be contained within the cavity of origin, either by engineering design or by the regulation of materials used (13). The test rig used to simulate typical wall designs is illustrated in Fig. 3. It comprised a vertical duct, bounded with Marinite, and measuring 5 m high by 1.25 m wide. The front face of the rig was movable to accommodate

different cavity thicknesses, geometries and materials. Constructions referred to as combustible and non-combustible were simulated in the tests as well as a number of possible fire-stop arrangements.

The fire source, consisting of a natural gas burner rated at 25 kW, was introduced through a 25 mm slot at the base of the cavity; the exhaust gases exited through a similar opening at the top of the cavity. The arrangement, as shown in Fig. 3, is suitable for simulating a fire that enters a cavity from the exterior of the building, e.g., flames emerging from a window, where the air space is likely to be located.

A wide variety of foamed plastic and glass fibre batt insulations, ranging in flame-spread classifications from 45 to 1000, were tested. The materials used for the movable front face of the rig, representing the

cladding, included asbestos cement board, gypsum wallboard and plywood. The fire stops were made from asbestos cement board, wood and sheet metal.

For thermosetting foams, the thickness of the air space between foam and cladding had a much more significant influence on fire spread than the flame spread rating of the foam. In the (nominal) absence of an air space, fire damage was confined to the immediate vicinity of the igniting burner. Even with foams whose flame-spread classification (FSC) was 450, fire spread was limited to the lower 25% of the cavity provided the air space was not thicker than 25 mm. The extent of involvement of material increased dramatically, however, if the thickness of the air space was increased beyond 25 mm, even for foams having an FSC as low as 45.

Fire stops that offered drainage but not ventilation of the cavity (Fig. 3b) were very effective in limiting flame spread in cavities with large air spaces (25 mm). In contrast, when ventilation of the cavity was included (Fig. 3c), only the asbestos board and metal stops were capable of restricting fire growth to the cavity of origin. The amount of overhang of the fire stop was seen to be an important design parameter, a value of 75 mm being adequate. Fire stops of 38 rom thick lumber retarded, but did not stop, the passage of fire up the assembly. With polyurethane insulation, excessive quantities of smoke were produced, resulting in complete

obscuration of a light beam across the top of the test rig in less than 3 min, in the extreme case.

Expanded polystyrene foams melt and flow when subjected to heat. If there was no intervening air space between foam and cladding, the heat

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supplied by the burner was absorbed within the cavity created by the melting material. The melt collected on the horizontal base of the cavity and

eventually ignited, thereby further accelerating the melting and the involvement of material in the pool fire.

With any form of ventilation (Figs. 3a and c) an appreciable quantity of heat was lost from the cavity by convection. The rate of this heat loss seemed to depend on the thickness of the cavity and the density of the insulation. With lighter weight polystyrene beadboard a severe pool fire resulted at an air space of 25 mm, whereas a space of 38 mm was required before the heavier extruded board performed similarly.

The collection of molten material at the bottom of the cavity, which was central to the pool fire process, could be eliminated by the

installation of sloping fire stops. Irrespective of the material they were made from, sloping fire stops offered satisfactory performance, and limited the fire involvement to the cavity of origin.

In another test series, the performance of a popular form of

combustible construction utilizing foamed plastic insulation, the so-called super-insulated stud wall, was examined. In this assembly, the wall stud space is filled with glass fibre batts and enclosed by gypsum wallboard on the interior of the building, and by foamed plastic board on the exterior in place of the customary fibreboard sheathing. The cladding is then attached to furring strips affixed through the plastic insulation to the wood studs. Although extruded polystyrene board is the most widely used material,

polystyrene, polyurethane and wood fibreboard sheathings were used in the DBR tests.

In these tests, the flame was introduced into the cavity between the sheathing and the cladding from the outside of the assembly. The extent of vertical propagation was influenced by the available air space between the sheathing and the cladding. With no appreciable air space, wood fibreboard and polyurethane foam exhibited only limited smouldering; the polystyrene behaved as described earlier.

When an air space was included in the assembly, more active and

extensive burning developed in the cavity with the primary propagation path being along the wood stud framing. The situation was particularly bad when a combustible cladding such as plywood or PVC was used, as the fire in the cavity eventually penetrated the cladding and, circumventing the fire stop, continued propagating up the exterior surface of the assembly. Assemblies containing polystyrene behaved noticeably worse than others.

LONG-TERM APPROACH

The foregoing illustrates the limited value of current approaches to the assessment of the flame-spread hazard. Performance test data are often applicable only in scenarios similar to that addressed by the test. To circumvent this difficulty, one solution would be to develop new tests with very narrow but specific applications. If the controlling mechanisms of the processes to be simulated by the tests are known, the limitations of such

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tests are clearly discernible. An example is the spread of fire from a room along the carpet of an adjoining corridor. In that scenario, the principal means of heat transfer to the pyrolysing carpet is radiation from the hot gases near the ceiling. The flooring radiant panel test (14) addresses this scenario. From it the minimum incident radiant heat flux required to

sustain flame propagation over the upper surface of a horizontal specimen can be assessed.

The development of performance tests for application to other aspects of the fire process requires a similar insight into the control mechanisms. A study has recently been initiated to gain some insight into perhaps the most important phase of fire: ignition.

The technique employed in this study is rapid transient flame emission spectrometry. A polymer specimen is ignited with a controlled flame of a burner and the radiation emitted by the sample flame is studied during its early stages using a spectrometer and photomultiplier tube. At present, the spectrometer is set to monitor the emissions of the C2 radical, common in flames of carbon-containing polymers, and absent from the emissions of the igniting flame.

It has been found that for poly(methyl methacrylate) the growth of C2 emission is approximately exponential over a period of perhaps 0.5 S after the ignition starts, but that a consistent oscillation with a frequency of 100 Hz is superimposed upon the emission curve in some conditions. The oscillations approximate those in laminar flame studies. They are sensitive to the relative orientation of the igniting burner and specimen and

disappear when the specimen is placed in the reaction zone of the burner flame; in that condition, a single ignition pulse is observed. No

definitive explanation of these findings can yet be given. The ignition process is essentially a local phenomenon not

significantly influenced by the environment of the object. Subsequent phases of the fire growth process, however, are influenced. Although some progress has been made in understanding certain modes of flame propagation,

there are conflicts of opinion concerning the dominant mechanisms. In his study of laminar diffusion flame spread, which occurs in

downward or horizontal propagation, deRis (15) assumed that mass transfer of reactants rather than combustion kinetics controlled the rate of the

process. He suggested that radiation and gas-phase conduction parallel to the solid surface, rather than solid-phase conduction, were the principal means of raising the temperature of the fuel bed to the pyrolysis value. Lastrina et al (16) restricted their attention to a small ignition region at

the leading edge of the spreading flame where, they postulated, the controlling phenomena occurred. They claimed that in this region, heat conduction through the gas phase, perpendicular to the solid surface, was large compared to that parallel to the surface, and the flame velocity was proportional to environmental pressure and oxygen concentration. Fernandez-Pello and Williams (17) offered experimental evidence that heat

conduction through the solid fuel bed was the principal transfer mechanism for thick fuel beds.

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Vertical upward fire spread t the most usual form of spread in rea1-world fires t is highly turbulent. Much work on unconfined vertical spread has been carried out at the Factory Mutual Research Corporation (18 to 21). Flame radiation is recognized as the dominant mode of heat transfer to the fuel surface t contributing 75 to 80% of the total value absorbed. According to preliminary mode1s t spread rates increase exponentially with time for thermally thick solids t while local burning rates are strongly dependent on the height of the pyrolysis zone t probably due to the influence of flame radiation. A model for confined vertical spread of fire has been suggested recently (22).

Historica11Yt the characteristics of principal concern have been

ignitabi1ity in regulating the nature of building contents and flame spread in selecting building materials. From the point of view of life safetYt however t smoke and toxic gas generation are the most important aspects of product behaviour. A considerable effort will be required to understand the factors influencing smoke and toxic gas generationt and to develop suitable test methods.

CONCLUDING REMARKS

A thorough assessment of fire hazard presented by a given situation requires consideration of several factors not addressed by current test procedures. Although significant progress has been made in understanding the growth of a fire in enc10sures t the related problems and research topics are numerous and the theory is not expected to produce a viable means of fire growth control in the near future.

The methods for predicting fire growth based on performance tests will probably continue for some time. As there are clear limitations in the use of the present assortment of tests t several new methods need to be

deve10ped t relevant to well-defined components of the over-all hazard t and to be incorporated in a unified assessment. A start has been made at DBR t NRCC t in studying the basic mechanisms of the ignition process.

For the time being t existing standard tests t suitably modified t will have to suffice. The ad hoc t scale model test is seen as a useful means of satisfying the needs of the regulation process as it stands today.

REFERENCES

1. Wil1iamson t R.B. and F.M. Baron. A corner fire test to simulate

residential fires. J. of Fire and F1ammabi1itYt Vol. 4 t 1973 t p. 99-105.

2. D'Souza t M.V. and J.H. McGuire. foamed thermosetting plastics. 1977 t p. 85-94.

ASTM E-84 and the flammability of Fire Techno10gyt Vol. 13 t No. 2 t 3. Roux t H.J. The role of tests in defining fire hazard: a concept.

Procs. of a NBS/ASTM Symposium on Fire Standards and SafetYt Gaithersburg t Mary1and t April 1976. ASTM Special Technical Publication 614 t 1976 t p. 194-205.

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4. Rarmathy, T.Z. assessment.

Fire performance standards and the problem of fire risk Fire and Materials, Vol. 4, No.4, 1980, p. 173-176. 5. Standard method of test for surface burning characteristics of building

materials. ULC-S102-1978.

6. McGuire, J.R. and M.V. D'Souza. Significance of flame spread results. National Research Council of Canada, Division of Building Research, Building Research Note No. 137, December 1978.

7. McGuire, J.R. and M.V. D'Souza. The E162 radiant panel flammability test and foamed plastics. Fire Technology, Vol. 15, No.2, 1979, p. 102-106.

8. Standard corner wall method of test for flammability characteristics of non-melting building materials. ULC-S-127-1978.

9. McGuire, J.R. and M.V. D'Souza. Flammability merit sequence and

specimen homogeneity. Fire Technology, Vol. 14, No.4, 1978, p. 273-278.

10. D'Souza, M.V., M.A. Kasem, and M. Galbreath. Performance of protective linings for polystyrene insulation in a corner wall test. Fire

Technology, Vol. 17, No.2, 1981, p. 85-97.

11. Taylor, W. Evaluation of thermal barriers for foam plastics insulation. In preparation.

12. Lie, T.T. Contribution of insulation in cavity walls to propagation of fire. DBR/NRCC, Fire Study No. 29, 1972 (NRCC 12878).

13. Taylor, W. The spread of fire in vertical concealed spaces containing foamed plastic insulation. In preparation.

14. Standard test method for critical radiant flux of floor-covering systems using a radiant heat energy source, ASTM E648,78. 15. deRis, J. Spread of a laminar diffusion flame. Procs. 12th

(International) Symposium on Combustion, Poitiers, France, 1968, p. 241-252. The Combustion Institute, Pittsburgh, 1969.

16. Lastrina, F.A., R.S. Magee, and R.F. McA1evy. Flame spread over fuel bed: solid phase energy considerations. Procs. 13th (International) Symposium on Combustion, Salt Lake City, Utah, 1970, p. 935-148. The Combustion Institute, Pittsburgh, 1971.

17. Fernandez-Pe110, A. and F.A. Williams. Laminar flame spread over PMMA surfaces. Procs. 15th (International) Symposium on Combustion, Tokyo, Japan, 1974, p. 217-231. The Combustion Institute, Pittsburgh, 1975.

Figure

Table III. Results of Furnace Tests of Protected Thermal Insulation
Figure 2 Modified flame-spread index;
Figure 3 Sketch of apparatus used to study ,vertical spread of fire in concealed spaces
Figure 2 Thermal decomposition apparatus
+7

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