Publisher’s version / Version de l'éditeur:
Vous avez des questions? Nous pouvons vous aider. Pour communiquer directement avec un auteur, consultez la première page de la revue dans laquelle son article a été publié afin de trouver ses coordonnées. Si vous n’arrivez pas à les repérer, communiquez avec nous à PublicationsArchive-ArchivesPublications@nrc-cnrc.gc.ca.
Questions? Contact the NRC Publications Archive team at
PublicationsArchive-ArchivesPublications@nrc-cnrc.gc.ca. If you wish to email the authors directly, please see the first page of the publication for their contact information.
https://publications-cnrc.canada.ca/fra/droits
L’accès à ce site Web et l’utilisation de son contenu sont assujettis aux conditions présentées dans le site LISEZ CES CONDITIONS ATTENTIVEMENT AVANT D’UTILISER CE SITE WEB.
Paper (National Research Council of Canada. Division of Building Research); no.
DBR-P-1213, 1984-03
READ THESE TERMS AND CONDITIONS CAREFULLY BEFORE USING THIS WEBSITE. https://nrc-publications.canada.ca/eng/copyright
NRC Publications Archive Record / Notice des Archives des publications du CNRC : https://nrc-publications.canada.ca/eng/view/object/?id=400692c2-d072-45ac-a4bf-9ba86c0cd2e2 https://publications-cnrc.canada.ca/fra/voir/objet/?id=400692c2-d072-45ac-a4bf-9ba86c0cd2e2
NRC Publications Archive
Archives des publications du CNRC
This publication could be one of several versions: author’s original, accepted manuscript or the publisher’s version. / La version de cette publication peut être l’une des suivantes : la version prépublication de l’auteur, la version acceptée du manuscrit ou la version de l’éditeur.
For the publisher’s version, please access the DOI link below./ Pour consulter la version de l’éditeur, utilisez le lien DOI ci-dessous.
https://doi.org/10.4224/40001719
Access and use of this website and the material on it are subject to the Terms and Conditions set forth at
Toxicity of fire effluents: application of test data
Ser
TH1
IB21d
'
no.
1213,
National Research
Conseil national
C . 2
I
*
Council Canada
de
recherches Canada
B m G
TOXICITY OF FIRE EFFLUENTS: APPLICATION OF TEST DATA
by K. Sumi
ANALYZED
Reprinted from Fire and Materials, Vol. 8, No. 1, 1984 p. 1 - 5
BLDG. RES.
L I B R A R Y
riDBR Paper No. 1213
Division of Building Research
L ' a p p l i c a t i o n d e s r g s u l t a t s d e t o u t e s s a i d e t o x i c i t ' e p a r l e f e u e s t extr2mement d i f f i c i l e e n r a i s o n d e l a complexit'e du probl3me e t d e s l i m i t a t i o n s du domaine d e l ' e s s a i . C e t t e c o m u u n i c a t i o n p o r t e s u r l e s p o s s i b i l i t ' e s d ' u t i l i s a t i o n d e s r g s u l t a t s d ' e s s a i d a n s
l e
p r o c e s s u s d g c i s i o n n e l .Toxicity of Fire Effluents: Application of Test
Data
K. Sumi
Fire Research Section, Division of Building Research, National Research Council Canada, Ottawa, Canada KIA OR6
The application of the results of any fire toxicity test is extremely difficult because of the complexity of the problem and the limitations of the test. This paper will discuss the potential use of test data in the decision-making process.
6
The toxicity of fire effluents (smoke and toxic gases) is Two test methods were considered: the DIN 53436 a subject of major importance in fire research. method (West Germany) and the NBS method Because the majority of fire deaths are caused by (National Bureau of Standards, USA). The DIN inhalation of smoke and toxic gases, research has been method1 utilizes a dynamic or flow-through type carried out with the ultimate objective of decreasing apparatus in which air is introduced into a horizontal fire casualties. One type of investigation that has quartz tube containing the test specimen at one end become widely accepted is the use of animals to and discharges the fire effluents at the other. The determine the toxicity of combustion and pyrolysis specimen is heated by a furnace that moves along the products generated by various materials. More recent- quartz tube. The furnace temperature, the specimen ly, this work has been extended to the development of size and the primary airflow can be varied. The fire stilndard toxicity tests. This paper will present back- effluents leaving the furnace tube are diluted with ground information on the use of the results of toxicity secondary air and transferred to an animal chamber tests in judging the suitability of materials. Difficulties for biological assessment.
in the application of such test results to real-world The NBS method2 is a static method in which a
problems will be discussed. common chamber is used for both product generation
and animal exposure. The material is heated in a small open-cup furnace, similar in design to that described by Potts and ~ e d e r e r , ~ at a pre-selected temperature. BACKGROUND INFORMATION At present the proposal is to conduct experiments at
three temperatures as follows: Ifmhprnent of standard tests
(1) 25 "C above auto-ignition temperature (gases A great deal of information has been developed, formed by flaming combustion);
especially in the past fifteen to twenty years, on the (2) 25 "C below auto-ignition temperature (gases inhalation toxicity of fire effluents. Experiments have formed by pyrolysis);
been carried out to evaluate the propensity of (3) At 440 "C for materials with auto-ignition temper- materials to release toxic gases. Such experiments ature greater than 515°C (gases formed by usually involve generation of fire effluents and a pyrolysis).
biological assessment of their effect. The results of
these investigations have shown that the mode of Condition (3) is intended for the evaluation of generation of gases has a significant ifiuenw on the materials whose ignition temperature is higher than ranking of materials. Because of variation in proce- that of Douglas fir at the specified temperature level. dures, it is difficult to compare results from di£ferent It should be noted that WG 12 no longer exists.
lqboratories. ISO/TC 92 was reorganized recently into subcommit-
TSO/TC 92 (International Organization for tees and working groups, and the duties of WG 12 Standardizationmechnical Committee
92)
formed a have been transferred to a new Subcommittee 3 (Toxic working group (WG 12) to develop a standard test for Hazards in Fire). The activities that were carried out evaluating materials, based on the toxicity of fire by WG l2 are being SC and its four effiuents. A method was required that would rank working groups.materials according to relative toxicity of pyrolysis and combustion products. Such an objective is very
difficult to realize, however, because of the limitations Prediction of toxicity of fire gases from the results of of present knowledge. WG 12 therefore focused chemical analysis
attention initially on the development of methods of
I identifying materials that produce fire effluents signi- A method based on combined use of chemical I
ficantly more toxic than those of conventional mate- analytical data and toxicological information of the analysed products was proposed by Tsuchiya and
CCC-0308-0501/84/0008-0001$02.50
sumi4,' some time ago. They suggested that quantita- tive analysis of a few key toxicants can often provide a reasonable estimate of the toxicity of a mixture of oxidation and pyrolysis products. The method may be used in parallel with animal exposure tests to improve the understanding of the subject. It may also be used for initial screening of materials to reduce the number of animal tests.
Briefly, the method is as follows. The toxicity of a single product is obtained by decomposing or burning a known amount of material and allowing the products to disperse into a known volume. The toxicity index, T, for any toxic compound can be calculated from the equation
/
where c, = experimentally determined concentration of a toxic product; cf = concentration of the same toxic product that is fatal or dangerous to man in 30 min; V = known volume into which the products are dispersed; W = weight of material, and v = volume of toxic products generated.
The toxicity index of the pyrolysis and combustion products of a material can be predicted from the sum of the indices of the individual harmful components, with appropriate factors incorporated where synergis- tic effects exist.
The foregoing index reflects the toxicity of products released from a given weight of material. For practical purposes the rate of release of toxic gases is often more important than the quantity of toxic products produced from unit weight of material. On this consideration the concept of a dynamic toxicity factor was developed that is based on rate of generation of 'toxicity' during pyrolysis or c o m b ~ s t i o n . ~ The dyna- mic toxicity factor, TD, is defined as
where lj = volumetric rate of generation of a toxic product, and A = surface area of material.
The chemical analytical method for predicting toxicity is useful in generating information but has obvious limitations if used alone for decision-making. For further development of the toxicity index concept, co-ordinated studies using the chemical analytical approach and biological measurements are needed.
Use of individual fire performance tests
It is not clear whether a toxicity test will ever be developed that is suitable for regulatory purposes. Those concerned with regulations, however, will be keeping under continuous review the possible use of such tests as knowledge of the subject increases. Because the application of the results of any toxicity test is extremely difficult, it is important to consider how the test data may be applied. One obvious method of application is to use the test as a direct decision-making tool, in much the same way that other fire performance tests are used today. The approp-
riateness of this course of action therefore needs to be examined.
In Canada, the flame spread test performed in the Steiner tunnel is the principal 'reaction to fire' test used to regulate building materials. Two standards are available. One is similar to ASTM E84, in which material to be tested is mounted on the ceiling of the tunnel (CAN4 Sl02);' in another, the material is placed on the floor (CAN4 ~102.2).' The latter is used for flooring and floor coverings and for materials for which the ceiling mounting is not considered appropri- ate, e.g. thermoplastics or loose-fill insulation mate- rials. The flame-spread classifications calculated from the test results give a ranking of materials under the conditions specified by the method. For regulatory purposes it is assumed that ranking would be essential- ly the same for many conditions encountered in real-world fires.
An analogous assumption should not be made with a toxicity test because the ranking of materials is strongly influenced by the fire conditions.
Combined use of small-scale tests in fire
risk
assessment
Many fire tests used for regulatory purposes have been severely criticized in recent years on the ground that they do not represent real-world fire situations. The limitations of individual tests are recognized, but a satisfactory means of using them in evaluating overall fire risk has not yet been developed. A comprehensive risk assessment should consider many factors, includ- ing those dealing with fire characteristics such as ease of ignition, spread of flame, rate of heat release, toxicity, smoke development, etc., those dealing with the mass, form, shape and orientation of the combusti- ble item and others such as the type of occupancy, the mobility of the occupants, etc.
It has been suggested that a set of complementary 'reaction 'to fire' tests be developed whose results can be used collectively in evaluating the total fire risk presented by a product. A major study using this approach was carried out in Belgium by ~ i n n e ~ in 1971. The methodology involved the determination of a 'reaction to fire' index from a material's relevant properties, relating them to the growth of fire and the resuIting damage to life and property.
The reaction to fire index of a material (Id) is given by the general formula
where A, B, C,
. . .
are relevant fire properties, and k,, kb, kc,.
. .
are coefficients of relative importance.A method was developed for the determination of a number of relevant properties from a single test. These properties are ignitability, heat release, flame spread and smoke density. The results of tests performed on twenty-one materials were reported. In calculating the reaction to fire index, all coefficients of relative importance were taken as one.
Recently, Herpol and vandevelde1° carried out a
TOXICITY OF FIRE EFFLUENTS
study in which the results of a toxicity test were also included among the relevant fire properties. The reaction to fire characteristics, excluding the aspect of toxicity, was obtained using the method adopted by the Belgian Standards Institute, and the toxicity data were obtained using the movable furnace test de- scribed earlier. In combining the relevant fire prop- erties in a reaction-to-fire index, the coefficients of relative importance (k's) were again assumed to be unity.
The assessment of fire risk from the results of a set of 'fire characteristic' tests and from other parameters has also been considered by Rouxl' and ~ a r m a t h ~ . ' ~ Roux defined the fire risk associated with the use of a product in terms of its potential for harm (PH) and the probability of exposure (E) of people or property to a fire involving it. The P H of a material could be determined from the results of one or more fire characteristic tests and from other parameters. Ten fire characteristics were tentatively identified for use with this hazard assessment scheme. It has been suggested that for product-approval a P H of a product may be combined with an estimate of probability of exposure.
Harmathy analysed the problems associated with fire risk assessment and made a number of sugges- tions. He divided the phases of a fire with which a test is associated into (1) incipient phase, (2) advanced pre-flashover phase and (3) fully-developed phase, and identified for groups of products the phase in which the P H is maximum. He adopted the following conventional definition for the fire risk:
Fire risk = probability of occurrence
x
probability of exposure x potential for harmOf the three components of fire risk assessment, only the third, the potential for harm, can be assessed from fire performance tests. The other two are to be derived from statistical data.
The proposals of both Roux and Harmathy are variations of the earlier work carried out in Belgium. They offer suggestions for developing a sound method for assessing the overall fire risk associated with the use of products. Clearly, much more work is needed.
Quantification of fire threats
Another concept that has been considered involves fire risk assessment from 'fire threats' (heat, smoke and toxic gases). The fire threats can be expressed in terms of the time to reach dangerous levels for specific situations. In this assessment ignitability is treated as a separate issue.
The problem of ranking materials according to their threat to life in fire was addressed by ~ r i e d m a n . ' ~ He evaluated for several materials the time available for escape (or rescue), defined as the time interval between detection and blockage of the escape route by heat, smoke or toxic gases. He also analysed ex- perimental data to identify the most severe threat variable. In his paper the threat variables were quantified in terms of temperature rise, optical density (smoke) and CO concentration (toxicity). Each vari-
able was normalized by dividing it by selected critical values. Friedman's study was based on experimental data obtained by Tewarson and pion14 from small- scale flaming combustion experiments under well- ventilated conditions.
The results of full-scale burn experiments conducted in a room enclosure were used by ~ a v i s ' ~ to evaluate various mattresses, on the basis of arbitrary criteria for human tenability, with respect to heat flux, smoke density and toxicity (CO, C 0 2 concentration and lack of
04.
In the foregoing examples of fire risk assessment based on fire threats the results of small-scale fire experiments and full-scale room burns have been considered. It should be noted that there have also been attempts to use the results of mathematical modelling in risk assessment. In mathematical models of fire processes all variables relevant to the fire situation are addressed. For given room geometries, construction materials, furnishings and ignition sources, the models are capable of predicting the time to reach untenable gas temperature. The predictions for the other two fire threats, i.e. untenable smoke obscuration and untenable gas concentrations, are less reliable.
DISCUSSION
Complexity of toxicity test
The evaluation of the propensity of materials for releasing smoke and toxic products is very sensitive to environmental conditions. Simple changes can make major differences in the amount of smoke produced and the toxicity of the generated products. It is therefore difficult to relate test data to real-world fire conditions.
The toxicity test has problems that are different from those of other fire performance tests. One notable example is the measuring technique based on animal exposure. Biological assessment does not give instantaneous information during the progress of fire. Although one can monitor variations in temperature and smoke density during a fire test, one cannot monitor variations in toxicity. As chemical analysis does permit instantaneous measurement of key tox- icants or oxygen, co-ordinated studies involving biolo- gical assessment and chemical analysis are necessary. Even if near-perfect correlation of the two kinds of measurement were obtained, and this is almost impossible, one question would still remain: can results based on the response of animals be related to human beings?
Current regulatory strategy based on individual lire tests
It is traditional to control the use of materials or products in buildings based on fire performance tests. As mentioned, the Steiner tunnel is used in Canada to determine the flame spread classification of materials under a specified set of conditions. It is assumed that
that classification gives a ranking of materials essen- tially the same under the conditions encountered at real fires.
A similar concept for the control of materials based on smoke generation or toxicity is not satisfactory. The amount of smoke produced by a small-scale test (or an experimental fire) depends to a significant extent on variables such as oxygen concentration and gas temperature in the test apparatus.16 The choice of variables affects the ranking of materials obtained by the test. The toxicity of fire effluents also depends on oxygen concentration and gas temperature; the two parameters will determine, for example, whether a material will pyrolyze or undergo flaming combustion. The resultant combustion atmosphere and its toxicity
w
i
l
l
vary with these parameters to the extent thatunder one set of conditions the products generated from a given material will be very toxic and under another set of conditions almost non-toxic. Thus, direct application of the results of a toxicity test in decision-making may not be appropriate until a relation has been established between the test condi- tions and real-world fires.
Regulatory strategies for the future
The use of reaction to fire tests in promoting fire safety is not completely satisfactory. The ranking of materials obtained by these tests does not indicate the relative degree of risk. As discussed earlier, new concepts are being considered for a more rational approach to fire hazard assessment. These include: (1) Overall fire risk assessment of materials, based on
the combined use of a number of 'reaction to fire tests', and
(2) Evaluation of materials, based on fire threat components (heat, smoke and toxicity).
Assessment based on the combined use of a number of small-scale fire performance tests has been discus- sed at ISOITC 92 meetings for at least fifteen years,g but relatively little progress has been made. Because of the complexity of the problems, one of which involves subjective judgement in establishing weight- ing factors for the various fire characteristics, it is uncertain when an acceptable assessment method will become available for practical use.
The evaluation of materials based on individual fire threats is less complicated. The selection of tenability limits is arbitrary, but it is likely to be less controver- sial than the selection of weighting factors needed in the previous approach. Another factor that simplifies the fire threat approach is the consideration of ignitability as a separate issue.
It should be noted that the results of the current toxicity tests based on biological assessment cannot be applied directly to this assessment scheme.
Restricting the use of a toxicity test
Many fire tests are more suitable for research and development than for regulatory use. The two toxicity tests being considered by ISOITC 92 support this view.
The question of whether use of a candidate test method should be restricted to research is often discussed at meetings of standards-writing organiza- tions. For lack of agreed-upon theories relating test data to real fires, there is concern that the standard may be inappropriately used. Obviously, serious errors in application must be avoided; yet restricting the use of standards could lead to a situation where only a small number of fire tests would be available for regulatory use. Unfortunately this situation will persist until meaningful and rational methods of assessing fire risk, based on 'good' fire performance tests, are developed.
Responsibility for the appropriate use of a standard test
Another question concerns responsibility for ensuring that a standard fire test is used appropriately. The developers of a standard, e.g. a toxicity test, have some idea of how the test method may be used by the decision-makers, but they do not know of all the conceivable situations for which use of the standard may be considered. Responsibility for determining the relevance and appropriateness of a test method to a particular application should be with the user. The developers of the standard may assist the users by preparing good guidance documents and by dialogue, but they cannot be held responsible for misuse of a standard test.
Alternate ways of controlling materials
Although fire incidence data show that the majority of fire deaths are caused by inhalation of smoke and toxic gases, the control of materials based on a toxicity test may not be the best regulatory strategy. The goal of increasing fire safety in buildings could also be served by reducing the probability of outbreak of fire (judged on the basis of results of an ignitability test) or by moderating the growth of fire (judged on the basis of results of a flame-spread test or a heat-release test). If such strategies were pursued, the need for regulation based on a toxicity test would lose its urgency, except for certain 'unwanted' materials that may be missed by alternate test methods.
Unnecessary animal suffering
Animal exposure studies are increasingly used in the development of information on the toxicity of fire effluents. They may provide the only practical way of determining the integrated biological effect of pyroly- sis and oxidation products of materials. Although the use of animals for research is generally accepted, there is concern that adoption of a standard toxicity test for decision-making
will
lead to unnecessary suffering ofanimals.
A British Standards Institution committee on the toxicity of combustion products has suggested the use of analytical screening, based on the toxicity index concept discussed earlier, to reduce the need for
TOXICITY OF FIRE EFFLUENTS
animal experiments. Animal experiments are to be conducted only if analysis indicates an apparent absence of toxicants at critical concentrations.
A variation of this approach might reduce the number of routine animal tests even further. It is suggested that materials that (based on analytical studies) indicate either the presence or absence of toxicants at specified concentrations be rejected or accepted without animal experiments. Biological test- ing would then be carried out only on the remaining materials, i.e. those whose performance in the toxicity test is most uncertain.
Caution in using a toxicity test
To date, regulatory agencies have been cautious in the use of results of small-scale tests of fire effluents (smoke generation and toxicity). They should continue to exercise caution because of the inadequacy of the existing tests and the lack of a satisfactory method of risk assessment. It is an unsatisfactory situation likely to continue for some time. During this period some correlation between test conditions and real-world fires should be established so that tests would be more useful to decision-makers.
Assuming that a certain test method is found to be appropriate for yielding information, caution should still be exercised by carefully selecting the criteria of acceptability. Two alternatives could be considered. The first would set the acceptability limit so that practically all 'unwanted' materials (based on subjec- tive judgment) would be judged unacceptable. In using this concept a number of materials that are borderline cases with regard to toxicity but otherwise possess acceptable or good fire performance character- istics might be sacrificed. The second alternative would set the acceptability limit at a less restrictive level and thereby keep the number of materials to be rejected to a minimum. 'The author is in favour of the second alternative.
CONCLUSIONS
(1) The application of the results of toxicity tests is extremely difficult because of the complexity of the problem and the limitations of the tests. (2) The use of a toxicity test will probably receive
more consideration by the regulatory community when standard tests are developed and knowledge of the subject is more complete.
(3) The results of individual fire performance tests are
widely used today in deciding various separate aspects of fire safety. Similar use of the results of a toxicity test will probably also be considered by regulatory agencies in the future.
(4) More caution needs to be exercised in the use of
the results of a toxicity test for regulatory purposes than, say, those of a flame-spread test because knowledge of fire toxicity is less advanced than that of other aspects of reaction to fire.
(5) A control strategy based on ease of ignition and
growth of fire may be more appropriate than a strategy based on toxicity tests for most situations. An additional requirement based on a toxicity test would not be needed except in very special situations.
(6) Research on the environmental conditions of the
test methods and their influence on the formation of combustion/pyrolysis products from various materials is considered to be a high priority. The relation between the test conditions and some aspects of real fires should be established before any regulatory decisions are taken.
(7) Rational methods of fire risk assessment of
products are needed for the future. If fire risk assessment is based on the results of a number of 'reaction to fire' tests, data from any toxicity test could be used. If the assessment is based on individual fire threats, it is uncertain whether toxicity data developed from biological experi- ments could be incorporated. Both Friedman13
and ~ a v i s ' ~ used data from chemical analyses to
quantify toxic threat instead of data from biologic- al assessment.
REFERENCES
1. DIN 53436, Producing thermal decomposition products from materials in an air stream and their toxicological testing. Part 1. Decomposition apparatus and determina- tion of test temperature. Part 2. Thermal decomposition method (1979).
2. M . M. Birky, M. Paabo, B. C. Levin, S. E. Womble and D. Malek. Development of recommended test method for toxicological assessment of inhaled combustion products. National Bureau of Standards, Washington, NBSlR 80-
20777 (1 980).
3. W. J. Potts and T. S. Lederer, J. Comb. Toxicol. 4, 114 (1977).
4. Y. Tsuchiya and K. Sumi, J. Appl. Chem. 17, 364 (1967). 5. Y. Tsuchiya and K. Sumi, J. Fire Flammability 3, 46 (1972). 6. Y. Tsuchiya, Japanese Association of Fire Science and
Engineering 28, 1 (1 978).
7. CAN4-S702-79, Standard method of test for surface burn- ing characteristics of building materials, Underwriters' Laboratories of Canada, Toronto (1979).
8. CAN4-S102.2-79, Standard method of test for surface
burning characteristics of flooring, floor covering and miscellaneous materials, Underwriters' Laboratories of Canada, Toronto (1979).
9. R. Minne, ASTM STP 502, American Society for Testing and Materials, Philadelphia, pp. 35-55 (1972).
10. C. Herpol and P. Vandevelde, J. Comb. Toxicol. 2, 135 (1981).
11. H. J. Roux, ASTM STP 674, American Society for Testing and Materials, Philadelphia, pp. 194-205 (1977).
12. T. 2. Harmathy, Fire Mats 4, 173 (1980). 13. R. Friedman, Fire mats 2, 27 (1978).
14. A. Tewarson and R. F. Pion, Combust. Flame 26, 85 (1976). 15. S. Davis, Assessment of fire hazards from furniture, Presented at International Fire, Security and Safety Exhibi- tion and Conference, London, 24-28 April 1978.
16. Y. Tsuchiya and K. Sumi, J. Fire Flammability 5, 64 (1974). This paper was presented at lnterflam '82 held at the University of Surrey, Guildford, UK, 30 March-I April 1982
T h i s p a p e r , w h i l e b e i n g d i s t r i b u t e d i n r e p r i n t form by t h e D i v i s i o n of B u i l d i n g R e s e a r c h , remains t h e c o p y r i g h t of t h e o r i g i n a l p u b l i s h e r . It s h o u l d n o t be reproduced i n whole o r i n p a r t w i t h o u t t h e p e r m i s s i o n of t h e p u b l i s h e r . A l i s t of a l l p u b l i c a t i o n s a v a i l a b l e from t h e D i v i s i o n may be o b t a i n e d by w r i t i n g t o t h e P u b l i c a t i o n s S e c t i o n , D i v i s i o n o f B u i l d i n g R e s e d r c h , N a t i o n a l R e s e a r c h C o u n c i l of C a n a d a , O t t a w a , O n t a r i o ,
