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The role of fire testing in the use of fire retardants
Polymer Degradation and Stability 30 (1990) 141-152
The Role of Fire Testing in the Use of Fire Retardants Wolfram H. K. Becker BASF Aktiengesellschaft,D-6700 Ludwigshafenam Rhein, FRG (Received 14 December 1989; accepted 19 December 1989)
ABSTRACT Normally the efficiency of fire retardants for improved fire performance characteristics is expressed in terms of a classification based on small scale tests such as UL 94 V-class or A S T M D 2863--LOI values. Such results describe the behaviour of different substances relative to each other under laboratory conditions but do not enable an evaluation of fire safety products in actual use. This paper highlights the possibility and demands for application spec!t~'c testing based on fire hazard related methods.
1 FIRE TESTING AS A MEANS OF CLASSIFYING LEVELS OF FIRE SAFETY Fires are complex phenomena, influenced as they are by very many different factors. No two fires ever follow the same course, and the stages through which a fire goes from being ignited to being extinguished are often very different. The variety of possible scenarios makes it impossible for one test method alone to be used to determine the behaviour of a product in a fire. One or more test methods can be adopted, but the decisive point in choosing methods is the concrete situation for which information is required. Around 800 different standards for fire testing are in force in the industrialized countries of the world, and more are being published each year. Of course, the most important role is played by those methods that put the general principles of legislation or the requirements of other authorities with a regulatory role into practice. This is done by devising the test conditions and the evaluation of results (which normally employs some 141 Polymer Degradation and Stability 0141-3910/90/$03'50 © 1990ElsevierSciencePublishers Ltd, England. Printed in Great Britain
142
Wolfram H. K. Becker
legal requirement
~7
fire test
< ~
,
use
+
classification
waste box Example: DIN 4102, Part 1 (Kleinbrenner) for class B 2 or class B 3
Fig. I. Determinationof undefined legal requirementsby fire tests. system of classification) to take into account all legal and other requirements and to put these on a scientific footing (Fig. 1). It is only when the requirements have been enshrined in legislation that fire tests of this type become valid as a means of evaluating fire safety. A much smaller number of other tests have been devised that provide basic data that can be used in the assessment of fire safety, but do not in themselves enable any evaluation of fire safety to be made: an example is the calorific potential determined according to ISO 1716. Some examples of basic property tests are • • •
calorific potential test; ignition temperature (liquids) test; explosion limits (gases) determination test.
A few test methods have been developed as an attempt to describe the behaviour of different substances relative to each other, but these have been found to have no practical relevance: examples include the standard tests for the horizontal spread of flame described in ASTM D 1692 and the smoke density test (XP2 chamber) described in ASTM D 2843. The following is a list of comparative tests (not recommended for hazard evaluation) • • •
bar test (former ASTM D 1692); XP2 smoke chamber (ASTM D 2843); oxygen index test (ASTM D 2863).
Over the past two decades, it has been realized that the standardization process for fire tests has to take a number of different factors into account (Fig. 2). Differentiations have to be made between the following.
The role of fire testing in the use of fire retardants
143
fire test exposure model--~type of fire (see ISO TR 9122.1)
t
early stages intermediate stages
fully developed
t fuel controlled ventilation controlled
specimen model .-~ final application simulation of environmental conditions choice of test data and their interpretation i procedures for evaluation and classification validation --by large scale tests by means of fire safety engineering
Fig.
2. Hazard related fire tests.
(a)
The fire model, in which the type of fire and the situation in which it takes place are enshrined. (b) The design of test specimens based on their application. (c) The type of data supplied and their interpretation. (d) Procedures for evaluation and classification. It was recognized that each individual test method can only provide information on one discrete type of fire. The further a fire develops away from the initial ignition phase towards a fully fledged conflagration, the more important become the decomposition of the material under test and the various attendant factors, in particular the amount of available oxygen. It has also become recognized that the fire safety of materials can only be evaluated if due regard is given to their final applications. This can be achieved by the choice of test specimens modelling the end use condition, such as in the Brandschacht test described in DIN 4102, Parts 15 and 16. Attempts have also been made to reduce large-scale test configurations down to the laboratory scale and to correlate the results; examples include the Scandinavian Box (Nordtest Method NT Fire 004) and the Australian Early Fire Hazard Test (AS 1530--part 3). This latter approach to solving the problems of methodology only proved successful for certain groups of products, and unsuitable for others, thermoplastics in particular. For products of this latter type, the only solution is to subject them to special
144
Wolfram H. K. Becker
tests in the large-scale model in order to obtain results that are appropriate to their applications. One factor that has to be considered is that large-scale trials are restricted to spaces with a maximum volume of around 20 m 3, because of costs and other factors, as in the room corner test described in ISO/DP 9705; also, there are restrictions on the extent to which results can be extrapolated to provide information on products' behaviour in larger enclosed spaces. A final point is that comparative trials with similar test methods from different countries have been carried out. It was found that the correlation between data obtained in different countries was good in some cases, but products were classified differently because of variations in national legal requirements. This was recognized by Emmons I and Vandevelde, 2 which prompted Blachrre et aL 3 to consider means of adapting the results of tests of building materials in different European Community countries to the ratings systems of others. This has yet to be implemented (Fig. 3).
2 M O D I F Y I N G THE PROPERTIES OF PRODUCTS FROM THE FIRE SAFETY ASPECT Industrial products have to satisfy minimum standards of fire safety before they can be brought into circulation. These requirements normally apply to the particular material in question only, without taking into account the applications of the products made from it. If these minimum standards cannot be attained, the only solution is to resort to fire retardants. This approach has been adopted for some cellular plastics in the building industry and the paper used for laminating insulating material made from mineral fibres. The choice of fire retardant, especially in regard to the range of temperatures at which it is expected to be effective, is determined by the test methods and the requirements that these are designed to test. The main requirement is mostly to prevent fire breaking out at all, and test methods are therefore designed to simulate the initial development phase. Even if these minimum requirements are met, further improvements can be made to extend the range of applications to which products can be put (Fig. 4). The following examples are worthy of special mention. (i)
Composites, such as sandwich-type elements, consisting of a cellular plastic core clad on both sides with metal. (ii) Composites, such as gypsum plasterboard, which consist of a combustible outer covering and a mineral core with high enthalpy. (iii) Mixtures of combustible and mineral materials, Such as insulationgrade plaster.
The role of fire testing in the use of fire retardants
(1966) - comparison of ranking
Emmons
~ Va!develde
classification
(1973) ~ t e s t
145
, no
use
D no
use
data
Blachere, Tephany et al. (1984/90) interpretative doc. fire modelling (CIB/W14) since 1970's) l--Eurefic program (1989-1992 ?) fire safety engineering (IS0/TC92/SC4
1990 ?)
Fig. 3. Validation of fire test data.
(iv) Flame-retardant coatings applied to wood and wood-based materials, etc. Fire retardants are only one of the means by which improved fire safety can be achieved, and they are often unnecessary in situations in which the energy generated by fire can be dissipated and rendered harmless, or when
exposure under initial stage of fire
I , <~
"-"fail ~ fire retardants
pass
I
I product I exposure under developed stage of fire
fail ~ i improved fire retardance composite pass mixtures increased enthalpy intumescent coatings J
application Fig. 4. Example of the use of fire retardants.
146
Wolfram H. K. Becker
the decomposition of the flammable components can be delayed. In practice, the prescribed test methods often stand in the way of purely physical solutions of this type if, for example, the specimen bears no relation to the material's application or if composites, or composite building materials made up on site, are evaluated according to their individual components. In cases such as these, the test method used for classification---especially the type, intensity and duration of exposure to fire--is the only factor determining the composition and quantity of flame retardant required. 3 T H E I N F L U E N C E O F TEST M E T H O D S ON T H E USE OF F I R E RETARDANTS The aim of the following section o f this paper is to illustrate the means by which legal requirements determine whether or not test methods can provide alternatives in terms o f design and other application-related measures that can be adopted, as opposed to using fire retardants (Fig. 5).
3.1 Requirements and tests specific to materials If requirements are accompanied by tests specific to the materials in 1. test related to s p e c i f i c
materials
- examples: UL 94 limited oxygen index Swiss requirements on building materials consequence: increased use of fire retardente 2. application specific
test methods
- examples: Bran'dschechttast,
DIN 4 t 0 2 ,
Part 15/18
flooring radiant panel test, l e o
9239
external exposure r o o f test, DIN 4102, Part 7 e. consequence: several solutions, fire retardente
one of them is the use o f
3. tests under extreme c o n d i t i o n s - examples: c a l o r i f i c potential
test, ISO 1716
cone calorimeter, ISO/DP
5 8 6 0 (-SkW/m=)
room corner test, ISO/DP
9706 (-100kW/burner)
*" consequence: ftre retardants provide only limited or even no improvement
Fig. 5. The influence of test methods on the use of fire retardants.
The role of fire testing in the use of fire retardants
147
question, the only course of action left open for particular groups of products is to use fire retardants. The Underwriters' Laboratories' (UL) rules governing products for electrical engineering are a case in point. The results of tests on rod-shaped specimens in either a vertical or horizontal configuration are used for evaluation. The highest attainable rating for solid plastics according to U L 94 is the rating VO, and this sets the standard in the industry. Systems of classification such as these do not in themselves imply any degree of fire safety, but systems of practical criteria backed by tests are a convenient guide for electrical engineers in choosing between different groups of materials. Manufacturers of materials in their unfinished state are also provided with a relatively low-cost set of quality control tests. Simple systems of material-specific criteria are based on the assumption that, by eliminating hazards in the fire development phase, some degree of fire safety will be achieved. The question of whether the measures taken justify the expense required for success remains unanswered. The situation is similar in regard to test criteria that take no account of materials' applications, and cases in which finished products are evaluated according to the various materials from which they are made, rather than considering the composite as a whole. The Swiss regulations on building materials are a case in point. In this type of situation, requirements can usually be met by adding fire retardants to selected components of composites.
3.2 Application-specific requirements and test methods More elaborate test methods need to be used if the required standards of fire safety specifically refer to finished products or finished products in situ. The main difference between these and the material-specific tests is in the test specimens. Specimens are prepared with a thickness and shape that correspond to their final applications, and they are mounted on an appropriate substrate. In the case of building materials, fastenings or adhesives are also used to secure the samples. Examples of tests of this type in the building sector include the Brandschacht test described in DIN 4102, various tests on roofing in DIN 4102, part 7 and flooring in ISO 9239 and, for the electrical sector, the hot wire test and bad connection test described in the IEC standards. The results obtained from application-specific tests are determined by the sum total of the components from which the specimen is assembled. It often makes no difference whether a particular component is non-combustible, such as an internal insulating layer, or contains fire retardants. The final assembly tested, put together in a manner corresponding to practical conditions, plays the decisive part in influencing results.
148
Wolfram H. K. Becker
Advertising that makes claims for one particular component of a composite material that is classified or has been classified as belonging to a particular group of materials is inappropriate or even misleading, as are legal requirements that refer to single components only. Application-specific testing has the advantage that successful, economical solutions can be developed, and their contribution to fire safety can be tested directly. The disadvantage is that the results obtained are unique to the specimen tested, and there are restrictions on the extent to which they can be applied to other designs. In the industrial sector, and in countries that prefer application-specific testing, fire prevention methods that involve fire retardants have to be resorted to less frequently. Some components, of roofing structures for example, may be made from materials containing fire retardants, but the main consideration may be the prevention of fire on the building site or during manufacturing: the fire retardants themselves have no bearing on the burning behaviour of the finished product as defined by the relevant test methods and criteria for evaluation. 3.3 Tests under extreme conditions
Most test methods for building and other materials are concerned with ignitability, the spread of flame after ignition, and the heat generated when the specimen is exposed to a fire in the development stage. A tendency towards testing under extreme conditions has also been observed, and some methods have been published. The best-known example is the determination of calorific potential as described in ISO 1716. The material to be tested is ground up and burned under pressure in pure oxygen. It is obvious that flame retardants have no significant influence on the results obtained, unless they have the effect of increasing the enthalpy of the material. Similar considerations apply to the time-of-ignition test described in ISO DP 5660, which makes use of a cone calorimeter, if specimens are irradiated at densities well in excess of 50 kW/m 2. Fire retardants have no significant effect on the time it takes for specimens to ignite the more intensely they are irradiated. 3.4 Summary
The purpose of the preceding examples has been to show that the choice of test methods and conditions has a very considerable influence on whether or not fire retardants are appropriate for particular materials or the products made from them, and on the type of fire retardants used.
149
The role of fire testing in the use of.fire retardants
In material-specific testing, the practice has been to choose the type and quantity of fire retardants from the point of view of the technicalities of testing, which are in turn determined by legal requirements, rather than purely from the aspect of fire safety.
4 T E S T I N G F I R E P R E V E N T I O N M E A S U R E S IN T E R M S OF T H E EFFECTIVENESS OF F I R E R E T A R D A N T S Because of their complicated nature, tests are rarely carried out on the same article with and without fire retardants under both laboratory and largescale conditions. However, two examples of this type of testing are discussed below.
4.1 Tests performed at the State Materials Testing Laboratory of North Rhine Westphalia (MPA NRW) One of the aims of this work was to test the results obtained for wall and ceiling cladding obtained in the DIN 4102 Brandschacht test, which is application-specific, on a larger scale, i.e. in enclosed spaces of 30 m a and 640 m 3 volume (Fig. 6). Klingelh6fer has already reported on this work. 4 All test data have also been submitted to ISO/TC 92/SC 1/WG 7, which means that they are also available to CEN/TC 127/WG 2 for the furtherance of their work. The following results are of particular interest. (a)
The dimensions and volume of the space enclosed by the wall and ceiling claddings can exert a great influence on results. Fire retardants proved to be more necessary in the smaller room. upscaling: Brandschacht
, small
lm '
room
, large
30m'
room
640m '
results: • great • fire
influence retardants
of
room
proved
size
more
necessary
in s m a l l e r
rooms
• o n l y f o r t i m b e r o n e - s i d e - c o a t e d with intumescents: t h e s m a l l r o o m test was more severe than the Brandschacht-test • quick acting and intense fire exposure a n y c a s e t h e m o r e severe condition
is not in
Fig. 6. Proving effectiveness of fire retardants (tests in Dortmund, early 1970s).
150
Wolfram H. K. Becker
(b) The results obtained in the 'Brandschacht' test in respect of spread of flame and flashover were confirmed on a larger scale. (c) The thermal conditions in the smaller room were less favourable than in the Brandschacht test when wood, treated with a flame-retardant coating on one side only, was tested. (d) The wall and ceiling claddings do not necessarily make a greater contribution to the development of fire if they are exposed to a more intensive, quick-acting fire. The net result of these experiments was to show that design features can be adopted to prevent fire being spread along cladding, and that these can be regarded as being equally effective as treating the materials with fire retardants. The German standards for building materials with limited spread of flame (Class B1-DIN 4102) were used for evaluation. 4.2 Experiments at NBS (now NIST) in Gaithersburg (USA) These experiments were concerned with comparing the fire behaviour of some very different products in a cone calorimeter, a furniture calorimeter, and a room of c. 2 0 m 3 with a corridor leading to an adjacent room. Babrauskas et al. have reported on this work5 (Fig. 7). It became apparent that there was a correlation between results obtained in the laboratory and those obtained in larger-scale tests on homogenous building materials in slab form, but not in tests performed on heterogeneous -
upscaling: cone c a l o r i m e t e r lOOcm ' sample
,
small room and c o r r i d o r 20m'
results in general: • good correlation
with materials
• little or no correlation • difficult to optimize -
comparison • survival
with h e t e r o g e n e o u s
fire retardants
of F.R. materials time
in the c o n e test
with non-F.R,
materials
15 times longer
• mass c o n s u m e d • heat g e n e r a t e d
only only
• total toxic products • no increase
products
50% 25% only 3 3 %
of smoke generated
Fig. 7. Proving effectivenessof fire retardants (tests at NIST, Gaithersburg, 1988).
The role of fire testing in the use of fire retardants
151
materials. It was difficult to optimize the fire retardant if only the results of the cone calorimeter tests were taken as the guide. The author is of the opinion that more research and development work is required to refine this method. This is further emphasized by the fact that, unlike untreated products, no flashover was observed when products were treated with flame retardants. The latter also displayed the following properties. (i) (ii) (iii) (iv)
The survival time was 15 times longer. The mass consumed during combustion was only half. Only a quarter of the heat was generated. The total toxic combustion products generated were less by two thirds. (v) There was little difference in the amount of smoke generated.
The above tendencies were also observed in experiments with the cone calorimeter, but quantitative factors and results expressed in terms of mass diverged considerably. It would seem that reliable predictions cannot be made on the basis of laboratory results using the cone calorimeter alone.
5 CONCLUSIONS Classifications made on the results of fire tests can exert a great influence on the use of fire retardants, especially if systems of classification are based on legal requirements or the requirements of insurers. This is especially true of material-specific tests, as no design or other measures can be adopted to improve the fire retardation of the material under test. The material-specific test methods in use today are only based on experience, and not on quantitative risk analyses. They are still important, but application-specific testing is becoming increasingly more popular for testing fire retardants. The latter methods have the advantage that they enable products to be tested under conditions that correspond to their final application. There is currently a trend towards larger-scale tests and calculations based on the corresponding models, and it is to be hoped that this will have a beneficial effect on the quality of results that can be obtained in the laboratory. This will enable the contribution of fire retardants to fire safety to be judged more accurately, and it will make it easier to optimize fire retardants. It is to be hoped that it will thus be possible to avoid some of the misguided developments that can still be observed.
152
Wolfram 1-1.K. Becker
REFERENCES 1. Emmons, H. W., Fire Research. A Trip Report No. 1, Harvard University, 1966-1967. 2. Vandevelde, P., Fire and Materials, 5 (1981) 77-84. 3. Blachere, G., Tephany, H., Trottein, Y. & Martin, J., APropos des Essais de Reaction au feu dans la Cee. Commission of the European Communities, Brussels, 1988. 4. Kiingelh6fer, H. G., VFDB-Zeitschrift, 27 (1978) 102-3. 5. Babrauskas et al., NBS Special Publication 749. US Department of Commerce, National Bureau of Standards, Gaithersburg, MD, USA, 1988.
The Role of Fire Testing in the Use of Fire Retardants Wolfram H. K. Becker BASF Aktiengesellschaft,D-6700 Ludwigshafenam Rhein, FRG (Received 14 December 1989; accepted 19 December 1989)
ABSTRACT Normally the efficiency of fire retardants for improved fire performance characteristics is expressed in terms of a classification based on small scale tests such as UL 94 V-class or A S T M D 2863--LOI values. Such results describe the behaviour of different substances relative to each other under laboratory conditions but do not enable an evaluation of fire safety products in actual use. This paper highlights the possibility and demands for application spec!t~'c testing based on fire hazard related methods.
1 FIRE TESTING AS A MEANS OF CLASSIFYING LEVELS OF FIRE SAFETY Fires are complex phenomena, influenced as they are by very many different factors. No two fires ever follow the same course, and the stages through which a fire goes from being ignited to being extinguished are often very different. The variety of possible scenarios makes it impossible for one test method alone to be used to determine the behaviour of a product in a fire. One or more test methods can be adopted, but the decisive point in choosing methods is the concrete situation for which information is required. Around 800 different standards for fire testing are in force in the industrialized countries of the world, and more are being published each year. Of course, the most important role is played by those methods that put the general principles of legislation or the requirements of other authorities with a regulatory role into practice. This is done by devising the test conditions and the evaluation of results (which normally employs some 141 Polymer Degradation and Stability 0141-3910/90/$03'50 © 1990ElsevierSciencePublishers Ltd, England. Printed in Great Britain
142
Wolfram H. K. Becker
legal requirement
~7
fire test
< ~
,
use
+
classification
waste box Example: DIN 4102, Part 1 (Kleinbrenner) for class B 2 or class B 3
Fig. I. Determinationof undefined legal requirementsby fire tests. system of classification) to take into account all legal and other requirements and to put these on a scientific footing (Fig. 1). It is only when the requirements have been enshrined in legislation that fire tests of this type become valid as a means of evaluating fire safety. A much smaller number of other tests have been devised that provide basic data that can be used in the assessment of fire safety, but do not in themselves enable any evaluation of fire safety to be made: an example is the calorific potential determined according to ISO 1716. Some examples of basic property tests are • • •
calorific potential test; ignition temperature (liquids) test; explosion limits (gases) determination test.
A few test methods have been developed as an attempt to describe the behaviour of different substances relative to each other, but these have been found to have no practical relevance: examples include the standard tests for the horizontal spread of flame described in ASTM D 1692 and the smoke density test (XP2 chamber) described in ASTM D 2843. The following is a list of comparative tests (not recommended for hazard evaluation) • • •
bar test (former ASTM D 1692); XP2 smoke chamber (ASTM D 2843); oxygen index test (ASTM D 2863).
Over the past two decades, it has been realized that the standardization process for fire tests has to take a number of different factors into account (Fig. 2). Differentiations have to be made between the following.
The role of fire testing in the use of fire retardants
143
fire test exposure model--~type of fire (see ISO TR 9122.1)
t
early stages intermediate stages
fully developed
t fuel controlled ventilation controlled
specimen model .-~ final application simulation of environmental conditions choice of test data and their interpretation i procedures for evaluation and classification validation --by large scale tests by means of fire safety engineering
Fig.
2. Hazard related fire tests.
(a)
The fire model, in which the type of fire and the situation in which it takes place are enshrined. (b) The design of test specimens based on their application. (c) The type of data supplied and their interpretation. (d) Procedures for evaluation and classification. It was recognized that each individual test method can only provide information on one discrete type of fire. The further a fire develops away from the initial ignition phase towards a fully fledged conflagration, the more important become the decomposition of the material under test and the various attendant factors, in particular the amount of available oxygen. It has also become recognized that the fire safety of materials can only be evaluated if due regard is given to their final applications. This can be achieved by the choice of test specimens modelling the end use condition, such as in the Brandschacht test described in DIN 4102, Parts 15 and 16. Attempts have also been made to reduce large-scale test configurations down to the laboratory scale and to correlate the results; examples include the Scandinavian Box (Nordtest Method NT Fire 004) and the Australian Early Fire Hazard Test (AS 1530--part 3). This latter approach to solving the problems of methodology only proved successful for certain groups of products, and unsuitable for others, thermoplastics in particular. For products of this latter type, the only solution is to subject them to special
144
Wolfram H. K. Becker
tests in the large-scale model in order to obtain results that are appropriate to their applications. One factor that has to be considered is that large-scale trials are restricted to spaces with a maximum volume of around 20 m 3, because of costs and other factors, as in the room corner test described in ISO/DP 9705; also, there are restrictions on the extent to which results can be extrapolated to provide information on products' behaviour in larger enclosed spaces. A final point is that comparative trials with similar test methods from different countries have been carried out. It was found that the correlation between data obtained in different countries was good in some cases, but products were classified differently because of variations in national legal requirements. This was recognized by Emmons I and Vandevelde, 2 which prompted Blachrre et aL 3 to consider means of adapting the results of tests of building materials in different European Community countries to the ratings systems of others. This has yet to be implemented (Fig. 3).
2 M O D I F Y I N G THE PROPERTIES OF PRODUCTS FROM THE FIRE SAFETY ASPECT Industrial products have to satisfy minimum standards of fire safety before they can be brought into circulation. These requirements normally apply to the particular material in question only, without taking into account the applications of the products made from it. If these minimum standards cannot be attained, the only solution is to resort to fire retardants. This approach has been adopted for some cellular plastics in the building industry and the paper used for laminating insulating material made from mineral fibres. The choice of fire retardant, especially in regard to the range of temperatures at which it is expected to be effective, is determined by the test methods and the requirements that these are designed to test. The main requirement is mostly to prevent fire breaking out at all, and test methods are therefore designed to simulate the initial development phase. Even if these minimum requirements are met, further improvements can be made to extend the range of applications to which products can be put (Fig. 4). The following examples are worthy of special mention. (i)
Composites, such as sandwich-type elements, consisting of a cellular plastic core clad on both sides with metal. (ii) Composites, such as gypsum plasterboard, which consist of a combustible outer covering and a mineral core with high enthalpy. (iii) Mixtures of combustible and mineral materials, Such as insulationgrade plaster.
The role of fire testing in the use of fire retardants
(1966) - comparison of ranking
Emmons
~ Va!develde
classification
(1973) ~ t e s t
145
, no
use
D no
use
data
Blachere, Tephany et al. (1984/90) interpretative doc. fire modelling (CIB/W14) since 1970's) l--Eurefic program (1989-1992 ?) fire safety engineering (IS0/TC92/SC4
1990 ?)
Fig. 3. Validation of fire test data.
(iv) Flame-retardant coatings applied to wood and wood-based materials, etc. Fire retardants are only one of the means by which improved fire safety can be achieved, and they are often unnecessary in situations in which the energy generated by fire can be dissipated and rendered harmless, or when
exposure under initial stage of fire
I , <~
"-"fail ~ fire retardants
pass
I
I product I exposure under developed stage of fire
fail ~ i improved fire retardance composite pass mixtures increased enthalpy intumescent coatings J
application Fig. 4. Example of the use of fire retardants.
146
Wolfram H. K. Becker
the decomposition of the flammable components can be delayed. In practice, the prescribed test methods often stand in the way of purely physical solutions of this type if, for example, the specimen bears no relation to the material's application or if composites, or composite building materials made up on site, are evaluated according to their individual components. In cases such as these, the test method used for classification---especially the type, intensity and duration of exposure to fire--is the only factor determining the composition and quantity of flame retardant required. 3 T H E I N F L U E N C E O F TEST M E T H O D S ON T H E USE OF F I R E RETARDANTS The aim of the following section o f this paper is to illustrate the means by which legal requirements determine whether or not test methods can provide alternatives in terms o f design and other application-related measures that can be adopted, as opposed to using fire retardants (Fig. 5).
3.1 Requirements and tests specific to materials If requirements are accompanied by tests specific to the materials in 1. test related to s p e c i f i c
materials
- examples: UL 94 limited oxygen index Swiss requirements on building materials consequence: increased use of fire retardente 2. application specific
test methods
- examples: Bran'dschechttast,
DIN 4 t 0 2 ,
Part 15/18
flooring radiant panel test, l e o
9239
external exposure r o o f test, DIN 4102, Part 7 e. consequence: several solutions, fire retardente
one of them is the use o f
3. tests under extreme c o n d i t i o n s - examples: c a l o r i f i c potential
test, ISO 1716
cone calorimeter, ISO/DP
5 8 6 0 (-SkW/m=)
room corner test, ISO/DP
9706 (-100kW/burner)
*" consequence: ftre retardants provide only limited or even no improvement
Fig. 5. The influence of test methods on the use of fire retardants.
The role of fire testing in the use of fire retardants
147
question, the only course of action left open for particular groups of products is to use fire retardants. The Underwriters' Laboratories' (UL) rules governing products for electrical engineering are a case in point. The results of tests on rod-shaped specimens in either a vertical or horizontal configuration are used for evaluation. The highest attainable rating for solid plastics according to U L 94 is the rating VO, and this sets the standard in the industry. Systems of classification such as these do not in themselves imply any degree of fire safety, but systems of practical criteria backed by tests are a convenient guide for electrical engineers in choosing between different groups of materials. Manufacturers of materials in their unfinished state are also provided with a relatively low-cost set of quality control tests. Simple systems of material-specific criteria are based on the assumption that, by eliminating hazards in the fire development phase, some degree of fire safety will be achieved. The question of whether the measures taken justify the expense required for success remains unanswered. The situation is similar in regard to test criteria that take no account of materials' applications, and cases in which finished products are evaluated according to the various materials from which they are made, rather than considering the composite as a whole. The Swiss regulations on building materials are a case in point. In this type of situation, requirements can usually be met by adding fire retardants to selected components of composites.
3.2 Application-specific requirements and test methods More elaborate test methods need to be used if the required standards of fire safety specifically refer to finished products or finished products in situ. The main difference between these and the material-specific tests is in the test specimens. Specimens are prepared with a thickness and shape that correspond to their final applications, and they are mounted on an appropriate substrate. In the case of building materials, fastenings or adhesives are also used to secure the samples. Examples of tests of this type in the building sector include the Brandschacht test described in DIN 4102, various tests on roofing in DIN 4102, part 7 and flooring in ISO 9239 and, for the electrical sector, the hot wire test and bad connection test described in the IEC standards. The results obtained from application-specific tests are determined by the sum total of the components from which the specimen is assembled. It often makes no difference whether a particular component is non-combustible, such as an internal insulating layer, or contains fire retardants. The final assembly tested, put together in a manner corresponding to practical conditions, plays the decisive part in influencing results.
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Advertising that makes claims for one particular component of a composite material that is classified or has been classified as belonging to a particular group of materials is inappropriate or even misleading, as are legal requirements that refer to single components only. Application-specific testing has the advantage that successful, economical solutions can be developed, and their contribution to fire safety can be tested directly. The disadvantage is that the results obtained are unique to the specimen tested, and there are restrictions on the extent to which they can be applied to other designs. In the industrial sector, and in countries that prefer application-specific testing, fire prevention methods that involve fire retardants have to be resorted to less frequently. Some components, of roofing structures for example, may be made from materials containing fire retardants, but the main consideration may be the prevention of fire on the building site or during manufacturing: the fire retardants themselves have no bearing on the burning behaviour of the finished product as defined by the relevant test methods and criteria for evaluation. 3.3 Tests under extreme conditions
Most test methods for building and other materials are concerned with ignitability, the spread of flame after ignition, and the heat generated when the specimen is exposed to a fire in the development stage. A tendency towards testing under extreme conditions has also been observed, and some methods have been published. The best-known example is the determination of calorific potential as described in ISO 1716. The material to be tested is ground up and burned under pressure in pure oxygen. It is obvious that flame retardants have no significant influence on the results obtained, unless they have the effect of increasing the enthalpy of the material. Similar considerations apply to the time-of-ignition test described in ISO DP 5660, which makes use of a cone calorimeter, if specimens are irradiated at densities well in excess of 50 kW/m 2. Fire retardants have no significant effect on the time it takes for specimens to ignite the more intensely they are irradiated. 3.4 Summary
The purpose of the preceding examples has been to show that the choice of test methods and conditions has a very considerable influence on whether or not fire retardants are appropriate for particular materials or the products made from them, and on the type of fire retardants used.
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The role of fire testing in the use of.fire retardants
In material-specific testing, the practice has been to choose the type and quantity of fire retardants from the point of view of the technicalities of testing, which are in turn determined by legal requirements, rather than purely from the aspect of fire safety.
4 T E S T I N G F I R E P R E V E N T I O N M E A S U R E S IN T E R M S OF T H E EFFECTIVENESS OF F I R E R E T A R D A N T S Because of their complicated nature, tests are rarely carried out on the same article with and without fire retardants under both laboratory and largescale conditions. However, two examples of this type of testing are discussed below.
4.1 Tests performed at the State Materials Testing Laboratory of North Rhine Westphalia (MPA NRW) One of the aims of this work was to test the results obtained for wall and ceiling cladding obtained in the DIN 4102 Brandschacht test, which is application-specific, on a larger scale, i.e. in enclosed spaces of 30 m a and 640 m 3 volume (Fig. 6). Klingelh6fer has already reported on this work. 4 All test data have also been submitted to ISO/TC 92/SC 1/WG 7, which means that they are also available to CEN/TC 127/WG 2 for the furtherance of their work. The following results are of particular interest. (a)
The dimensions and volume of the space enclosed by the wall and ceiling claddings can exert a great influence on results. Fire retardants proved to be more necessary in the smaller room. upscaling: Brandschacht
, small
lm '
room
, large
30m'
room
640m '
results: • great • fire
influence retardants
of
room
proved
size
more
necessary
in s m a l l e r
rooms
• o n l y f o r t i m b e r o n e - s i d e - c o a t e d with intumescents: t h e s m a l l r o o m test was more severe than the Brandschacht-test • quick acting and intense fire exposure a n y c a s e t h e m o r e severe condition
is not in
Fig. 6. Proving effectiveness of fire retardants (tests in Dortmund, early 1970s).
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(b) The results obtained in the 'Brandschacht' test in respect of spread of flame and flashover were confirmed on a larger scale. (c) The thermal conditions in the smaller room were less favourable than in the Brandschacht test when wood, treated with a flame-retardant coating on one side only, was tested. (d) The wall and ceiling claddings do not necessarily make a greater contribution to the development of fire if they are exposed to a more intensive, quick-acting fire. The net result of these experiments was to show that design features can be adopted to prevent fire being spread along cladding, and that these can be regarded as being equally effective as treating the materials with fire retardants. The German standards for building materials with limited spread of flame (Class B1-DIN 4102) were used for evaluation. 4.2 Experiments at NBS (now NIST) in Gaithersburg (USA) These experiments were concerned with comparing the fire behaviour of some very different products in a cone calorimeter, a furniture calorimeter, and a room of c. 2 0 m 3 with a corridor leading to an adjacent room. Babrauskas et al. have reported on this work5 (Fig. 7). It became apparent that there was a correlation between results obtained in the laboratory and those obtained in larger-scale tests on homogenous building materials in slab form, but not in tests performed on heterogeneous -
upscaling: cone c a l o r i m e t e r lOOcm ' sample
,
small room and c o r r i d o r 20m'
results in general: • good correlation
with materials
• little or no correlation • difficult to optimize -
comparison • survival
with h e t e r o g e n e o u s
fire retardants
of F.R. materials time
in the c o n e test
with non-F.R,
materials
15 times longer
• mass c o n s u m e d • heat g e n e r a t e d
only only
• total toxic products • no increase
products
50% 25% only 3 3 %
of smoke generated
Fig. 7. Proving effectivenessof fire retardants (tests at NIST, Gaithersburg, 1988).
The role of fire testing in the use of fire retardants
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materials. It was difficult to optimize the fire retardant if only the results of the cone calorimeter tests were taken as the guide. The author is of the opinion that more research and development work is required to refine this method. This is further emphasized by the fact that, unlike untreated products, no flashover was observed when products were treated with flame retardants. The latter also displayed the following properties. (i) (ii) (iii) (iv)
The survival time was 15 times longer. The mass consumed during combustion was only half. Only a quarter of the heat was generated. The total toxic combustion products generated were less by two thirds. (v) There was little difference in the amount of smoke generated.
The above tendencies were also observed in experiments with the cone calorimeter, but quantitative factors and results expressed in terms of mass diverged considerably. It would seem that reliable predictions cannot be made on the basis of laboratory results using the cone calorimeter alone.
5 CONCLUSIONS Classifications made on the results of fire tests can exert a great influence on the use of fire retardants, especially if systems of classification are based on legal requirements or the requirements of insurers. This is especially true of material-specific tests, as no design or other measures can be adopted to improve the fire retardation of the material under test. The material-specific test methods in use today are only based on experience, and not on quantitative risk analyses. They are still important, but application-specific testing is becoming increasingly more popular for testing fire retardants. The latter methods have the advantage that they enable products to be tested under conditions that correspond to their final application. There is currently a trend towards larger-scale tests and calculations based on the corresponding models, and it is to be hoped that this will have a beneficial effect on the quality of results that can be obtained in the laboratory. This will enable the contribution of fire retardants to fire safety to be judged more accurately, and it will make it easier to optimize fire retardants. It is to be hoped that it will thus be possible to avoid some of the misguided developments that can still be observed.
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REFERENCES 1. Emmons, H. W., Fire Research. A Trip Report No. 1, Harvard University, 1966-1967. 2. Vandevelde, P., Fire and Materials, 5 (1981) 77-84. 3. Blachere, G., Tephany, H., Trottein, Y. & Martin, J., APropos des Essais de Reaction au feu dans la Cee. Commission of the European Communities, Brussels, 1988. 4. Kiingelh6fer, H. G., VFDB-Zeitschrift, 27 (1978) 102-3. 5. Babrauskas et al., NBS Special Publication 749. US Department of Commerce, National Bureau of Standards, Gaithersburg, MD, USA, 1988.