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Evaluation of the toxicity of combustion products
Ser
TH1
N21r2
no.
507
NATIONAL RESEARCH COUNCIL OF CANADA
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2
CONSEIL NATIONAL DE RECHERCHES D U CANADA
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Y 7 E D
EVALUATION OF THE TOXICITY OF COMBUSTION PRODUCTS
by
Yoshio Tsuchiya and Kikuo Sumi
Reprinted from
Journal of Fire and Flammability
Vol. 3, No. 1, January
1972
p.
46
Research Paper No. 507 of the
Division of Building Research
OTTAWA
January
1972
L'EVALUATION DE LA TOXICITE DES PRODUITS COMBUSTIBLES
Les gaz et les vapeurs toxiques degages lors des incendies causent de nombreuses pertes de vie. Les dangers que presentent les produits
a
combustion toxique augmenteront peut-etre cause de I'emploi crois- sant de nouveaux materiaux. L'auteur propose un indice de toxicitk maximum afin d'evaluer et de comparer les dangers de gaz toxiques produits par la combustion. On calcule I'indice de toxicite maximum d'un materiel d'apres les donnees exp6rimentales sur la quantite de produits a combustion toxique et sur leur concentration mortelle.ANALYZED
Evaluation of
the
Toxicity of
Combustion Products
Yoshio Tsuchiya and Kikuo Surni
Na fional Reseurcll Corlrlcil o
f'
CSlr~atla,
Otfarva. Ca11a~1u
Fire Researcll Section, Divisiorl of' Brlildirlg Rescarcll
Evaluation of the Toxicity of
Combustion Products
Yoshio Tsuchiya and Kikuo Sumi
National Research Council o f Canada, Ottawa, Canada Fire Research Section, Division o f Building Research
(Received July 26, 1971)
ABSTRACT
T o x i c gases a n d vapors produced f r o m f ~ r e are responsible f o r a large number o f f i r e deaths. The potential danger caused b y t o x i c combustion products may be increasing because o f t h e increasing use of new materials. F o r the purpose o f evaluating and comparing the potential danger f r o m t o x i c gases produced b y combustion o f materials, " m a x i m u m t o x i c i t y index" is proposed. The m a x i m u m t o x i c i t y index o f a material is calculated f r o m experimental data o n the q u a n t i t y o f t o x i c combustion products a n d the lethal concentration o f the oroducts.
INTRODUCTION
T o x i c gases and vapors produced by oxidation and thermal decomposition re- actions that occur during a fire are responsible for a large number of fire deaths. The potential danger of toxic combustion products may be increasing because of the increasing use of new materials, especially synthetic polymers, both as building materials and in goods and furnishings that make up the contents of buildings. Consequently, many fire authorities believe that some restrictions should apply t o the use of materials that are capable of producing large amounts of toxic combustion
products.
In a previous paper
[ I
I ,
the authors suggested a method for evaluating the toxicity of combustion products from quantitative experimental data and literature data dealing with the lethal concentrations of these products. In the present paper, the possible use of the evaluation method in restricting materials based on their potential for producing large quantities of toxic gases at fires is discussed.DEVELOPMENT OF METHOD OF EVALUATION
Toxicity, t, due t o a gaseous or volatile compound is assumed to be proportional t o i t s concentration and t o its relative toxicity, t,.
Evaluation of the Toxicity of comb us ti or^ Prodzlcts
Relative toxicity is defined as
where cf i s the concentration o f gases fatal t o man in 30 minutes exposure. The toxicity of a decomposition product, based o n b o t h the nature of the compound and the quantity evolved, then becomes
By comparing values o f c/cf f o r different decomposition products evolved under one set of conditions, toxicity f r o m each product could be assessed. In order t o present data on toxicity i n a consistent manner the authors suggest using the equation
where T i s the toxicity index and c, is the concentration of a volatile or gaseous product evolved when one gram o f original material i s decomposed and the decompo- sition products are diffused in a volume o f 1 m 3 . Concentrations, c, and q , are expressed in ppm. The toxicity index f o r a material is obtained from the sum of the toxicity indices o f the combustion products. That is,
The toxicity index o f a material depends on the experimental conditions under which the material i s burned. The maximum value, T,, obtained f r o m experimental data or derived f r o m theoretical consideration provides a useful basis of comparison.
DETERMINATION O F T O X I C I T Y INDEX
Toxicity index i s usually determined f r o m quantitative data o f gases obtained after a closely controlled combustion experiment. The main toxic combustion products must first be identified and then quantitatively analyzed. The nature o f these products often can be predicted f r o m knowledge of the composition of the material and the mechanism o f thermal decomposition o f polymers. The quantitative data on combustion products and t h e resulting toxicity index depend on the experi- mental conditions under which a material i s burned. The combustion temperature, duration o f heating, availability o f oxygen and other factors influence the formation of toxic products. The authors believe that the maximum toxicity indices obtained f r o m experimental data should be useful in comparing the potential hazard o f different materials i n producing toxic gases at fires. Much o f the data obtained b y previous investigators are unsatisfactory f o r evaluating this hazard because there is no way o f knowing whether the toxicity index determined was maximum for the par- ticular material.
Yoshio Tsuchiya and Kikuo S u m i
Values for c,, the concentrations of compounds that are fatal t o man in a short exposure of the order of 30 minutes, are available in the literature for a number of toxic compounds that are produced at fires. There is a need for animal studies t o establish cf values of other compounds and t o re-examine some of the data that have been reported. When cf is not found in the literature, an estimate often can be made for the compound from data on similar compounds. For others, an estimate can be made from Threshold Limit Values (TLV) that have been reported for a large number of compounds[21.
COMPARISON OF TOXICITY INDICES
How does the potential hazard from the toxic combustion products of a material compare with that from wood or other cellulosic materials? Wood is often used as one of the reference standards for such discussions because it and other cellulosic materials have been and continue t o be consumed in quantity at most building fires. Carbon monoxide (CO) is the most important toxic gas produced by the combustion of wood; carbon dioxide ( C 0 2 ) is of secondary importance.
The amounts of CO and C02 produced by combustion, and the resulting toxicity index, vary with experimental conditions. For example, various weights of white pine samples were burned in a 5-liter flask, containing air, at 800°c, and CO and C02 were analyzed quantitatively [31. The maximum toxicity index for wood obtained from these data was 0.09.
A theoretical calculation of the maximum toxicity index of a combustion product is often possible i f the composition of the original material is known. The results of these calcc~lations often provide useful information where experimental data are lacking, e.g., the relative importance of two different toxic combustion products. They also point out cases where quantitative analysis of a compound is not important for the evaluation of toxic products because the theoretical maximum toxicity index of this product is small.
When polyvinyl chloride (PVC) i s involved in fire, the chlorine atoms combine with hydrogen atoms t o form hydrogen chloride (HCI) [ I ] . The theoretical maxi- mum toxicity index for HCI from unplasticized PVC is
where cf for HCI is 1000 ppm [ 4 ] . This theoretical value was found t o agree with the maximum toxicity index that was obtained from experimental data.[l]
.
The simple method of evaluation discussed in this paper does not consider syner- gism of two or more toxic products that may occur together. Because of possible synergism, the toxic effect of a mixture may be greater than the sum of the toxic effect of each component. The authors believe that synergism is often over- emphasized and do not consider i t to be important when the toxicity indices of two components differ by a factor greater than ten. In any case, animal experiments offer
Evaluation of the Toxicity of Coinbustion Products
a method of finding combinations of toxic gases that produce significant synergistic effect.
RATE O F PRODUCTION O F T O X I C GASES
The maximum toxicity index discussed thus far represents the toxic hazard created by burning a unit weight of material under conditions that are most favorable for produ'cing toxic gases. Restrictions for building materials or contents of buildings based on maximum toxicity index could be considered in future fire regulations.
The authors believe that these regulations on toxic gas producing properties of materials could be made even more meaningful if the rate of production of toxic combustion products were also considered. This is, however, not practical a t present because of a lack of understanding of the rate of combustion of solid materials. Calculations on the behavior o f fire in an enclosure with openings representing a typical room show that one complete air change takes place in about one minute during a fire. Because the rate of air change is rapid, the rate of toxic gases leaving the room involved in a fire and spreading to other parts of the building can be assumed t o be proportional to the rate of production of toxic gases. This information suggests that i t is appropriate to evaluate toxic combustion products by multiplying the maximum toxicity index by the burning rate when the latter becomes available for various materials found in buildings.
When wood is burned in a compartment, the rate of combustion depends on the area of opening and is expressed by the equation
where R is rate of combustion, A is area of opening, H is height of opening and k is a constant that has been found experimentally t o be about 6 kg min-' m-'.'. Similar information for other combustible materials is needed. For example, more data are required for polyurethane foam, one of the newer materials, that is widely used as thermal insulation in buildings and cushioning material for furniture. The rate of combustion of this material in a compartment fire with restricted supply o f air is not known. Data on the burning characteristics of polyurethane, foam rubber, and various other combustible materials should be obtained, so that a better measure of toxicity would be possible.
SUMMARY
Maximum toxicity index, which indicates the potential danger of materials in forming toxic combustion products i s recommended a s a yardstick for the evaluation of materials. The lethal concentrations, cf, of gases and vapors which are required for this evaluation are often not a s consistent as they should be because they are based on animal experiments conducted by different investigators under different experi- mental conditions for different purposes. The authors therefore recommend that
Yoshio Tsuchiya and Rikuo Surni
systematic animal experiments be conducted for the establishment of cf values. One important factor that has been omitted in the present evaluation of toxic combustion products is the rate of production o f toxic gases from the combustion of different materials. The authors suggest that the rates of combustion (and rates of production of toxic gases) should be studied for various materials so that this information may be included in the evaluation of toxic combustion products.
This paper is a contribution from the Division of Building Research, National Research Council of Canada, and is published with the approval of the Director of the Division.
REFERENCES
1. Y. Tsuchiya, and K.Sumi, J. Appl. Chem, 17, 364 (1967).
2. Documentation o f Threshold L i m i t Values, American Conference of Governmental Industrial Hygienists, Committee on Threshold L i m i t Values, Cincinnati, 223 pp. (1966).
3. K. Sumi, and Y. Tsuchiya, Toxic Combustion Products o f Wood and Polystyrene, National Research Council o f Canada, Division of Building Research, BRNote 76, (1971).
4. Y. Henderson and H. W. Haggard, Noxious Gases and the Principles of Respiration Influ- encing their Action, The Chemical Catalog Co. Inc., New York, 212 pp. (1927).
Yoskio Tsuckiya
Yoshio Tsuchiya is a Research Officer of the Division of Building Research, National Research Council of Canada. He received his Bachelor of Engineering and Doctor of Engineering degrees in Applied Chemistry from the University of Tokyo in 1953 and 1962 respectively. He joined the National Research Council i n 1965. He has experience in the fields of industrial explosives, organic peroxides and fire re- search.
Kikuo Sumi
Kikuo Sumi i s a Research Officer of the Division of Building Research, National Research Council of Canada. He received his B.A.Sc. degree in Applied Science from the University of Toronto and his Ph.D. degree in Chemical Engineering from the University of London. He joined the National Research Council in 1951 and has experience in various aspects of fire research such as thermal decomposition of polymers, fire extinguishment and fire prevention regulations.
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