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Home , Acrylonitrile, Copolymer, Ethylbenzene, Monomer, Polyacrylonitrile, Polybutadiene

AND MATERIALS, VOL. 10,93-105 (1986)

Acrylonitrile-- (ABS): and Combustion Products and their -A Review of the Literature

Joseph V. Rutkowski and Barbara C. Levint us Department of Commerce, National Bureau of Standards, National Engineering , Center for Fire Research, Gaithersburg, MD 20899, USA

A review of the literature was undertaken to ascertain the current knowledge of the nature of the thermal products generated from ABS and the toxicity of these evolved products in toto. The literature review encompasses English language publications available through June 1984. This literature surveyed showed that the principal ABS thermooxidative degradation products of toxicologic importance are monoxide and . The experimental generation of these and other volatile products is principally dependent upon the combustion conditions and the formulation of the . The toxicity of ABS thermal degradation products has been evaluated by five methods. The LCso (30 min exposure + 14 day post-exposure period) values for flaming combustion ranged from 15.0 mg 1- 1 to 28.5 mg 1-1. In the non-flaming mode of combustion, the LCso values ranged from 19.3 mg 1- 1 to 64.0 mg 1- 1. Therefore, no apparent toxicological difference exists between the flaming mode and the non-flaming mode. The toxicity of ABS degradation products was found to be comparable with the toxicity of the thermal decomposition products of other common polymeric materials.

Keywords: ABS ; ; combustion products; ; literature reviews; thermal decomposition; toxicity.

Acrylonitrile Butadiene INTRODUCTION H H H H I 1 I I Although the hazard posed by toxic gases and vapors C=C-C!!NI I C=C-C=CI I I generated in a fire environment has long been re• H H H H H cognized, 1 information regarding the toxic agent(s) gen• (m.w. = 53.03) (m.w = 54.09) erated from ABS which are responsible for fire deaths not attributable to burns is relatively sparse. The growth of Styrene the science of combustion toxicology over the last ten years has resulted in the generation of a large quantity of information regarding the thermal decomposition pro• O~C=C-H ducts of many natural and synthetic materials, and the I H relative toxicity of those materials' decomposition pro• ducts in toto. This is a review of the English (m.w. = 104.14) literature, available through June 1984, on the thermal Figure 1. Chemical structure of ASS . decomposition products from acrylonitrile-butadiene• styrene (ABS) terpolymers and an evaluation of the predominant atomic species (atomic weight/molecular toxicity data from animals exposed to those products. weight). The only source of in the plastic is The ABS plastics are of particular interest since they are acrylonitrile, which contains approximately 26% nitro• found in numerous household items, such as telephones, gen. The weight percentage of hydrogen is relatively small. appliances, luggage and , as well as in automobile Acrylonitrile is a colorless liquid characterized by a and aircraft interior structures. strong . The of acrylonitrile is 77.3 °C and its freezing point is approximately - 83.55 0c. Acry• CHEMICAL STRUCTURE AND lonitrile is soluble in most , both polar and non• THERMOPHYSICAL PROPERTIES polar. increases with temperature. 2 Acry• lonitrile is capable of undergoing many chemical reac• tions, the majority of which occur at the carbon-carbon ABS are synthesized from three monomeric . It is at this site that the homopolymerization chemicals: acrylonitrile, butadiene, and styrene (Fig. 1); of the acrylonitrile occurs. This reaction takes from which the acronym is derived. The atomic compo• place readily in the presence of initiators through either a nents of these three chemical compounds are, exclusively, free mechanism or an anionic mechanism of carbon, nitrogen and hydrogen, with carbon being the .3 The resultant , polyacrylonit• t Author to whom correspondence should be addressed. rile, is a crystalline-type compound, which is not soluble in

0308-0501j86j030093-13$07.50 Received 20 February 1986 © U.S. National Bureau of Standards Accepted 24 July 1986 94 1. V. RUTKOWSKI AND B. C. LEVIN most common solvents, e.g. , greases, , water and the finished products, generally termed ABS, has been hypochlorite solutions. It will, however, degrade when reported as 466 °ell and between 500 and 575 0c.l3 ABS exposed to concentrated cold or hot dilute alkaline polymers burn readily with the generation of dense solutions, as well as warm 50% sulfuric . Although the , which is characteristic of polymers containing acrylonitrile monomer is significantly toxic by either aromatic rings.l4 ingestion of the liquid or inhalation of the vapor, the In general, the ABS plastics exhibit good durability and homopolymer is considered essentially non-toxic.3 resilience, as well as mechanical strength. In addition, 1,3-Butadiene is a colorless gas. The boiling point of these polymers demonstrate a favorable butadiene is - 4.5 °e and its freezing point is - 108.96 dc. combination of thermal, electrical and mechanical pro• lt is soluble in organic solvents.4 Due to the presence of perties. The different properties may be selectively enhan• two double bonds, butadiene is a very reactive compound, ced for specific applications by modification of the allowing a variety of polymer structures to be formed. All composition and/or relative proportions of the compo• require either an initiator or catalytic nents. Such selective production is usually at the expense factor and occur by a free-radical, an ionic or a coordinate of one or more of the other properties.9•lO,lS mechanism. The end result, , is a rubber polymer formed by addition polymerization. S , Styrene is a colorless to yellowish, oily liquid which has THERMAL DECOMPOSITION a penetrating odor. The boiling point range of styrene is 145 to 146°C and the freezing point is - 30.6°C. Styrene is only slightly soluble in water; however, it is soluble in The type and quantity of the thermal degradation alcohol, ether, , and carbon disulfide. products from ABS plastics depends upon the combus• Styrene is not considered very toxic upon ingestion but is tion chamber utilized and the existing combustion con• a significant irritant when applied to the skin, eyes and ditions, as. well as the composition of the plastic. The mucous membranes. The rate of polymerization of the majority of the studies of the chemical analysis of the decomposition products of ABS has employed a combus• styrene monomer is slow at room temperature and tion with a ring furnace to decompose the material. increases with heat. Since the polymerization is an This type of combustion system is similar to that used in exothermic process, the reaction can become self• the DIN 53 436 toxicity test method (see below). This accelerating. Styrene homo polymerization can occur apparatus has the advantages of being easy to set up and either by free-radical or ionic reactions. The resultant operate and requiring only a small sample for testing. The polymer, , is a clear, crystalline-type combustion atmosphere is easily changed, allowing for compound.6-s ABS polymers (Fig. 2) can be produced by two general pyrolysis studies under inert conditions as well as ther• methods, each of which generates a different type of moxidative degradation experiments. This type of furnace may be programmed either to provide a constant temper• plastic. Type A ABS polymers are produced by a mechan• ical blending of a styrene-acrylonitrile resin ature zone or to heat at a fixed rate. The disadvantages with a butadiene-based (butadiene• within this type of system also must be considered. One of acrylonitrile rubber). The production of Type B ABS the most important limitations is the large internal surface involves a grafting of styrene and acrylonitrile onto area on which combustion products may adsorb or react. polybutadiene. The Type B polymer also contains a In addition, the small sample size, listed as an advantage styrene-acrylonitrile copolymer and ungrafted poly• above, may also be considered a disadvantage since it butadiene. The types of plastics are varied further by does not provide enough material to be conducive to a differences in the relative proportions of the monomer flaming test mode. During the actual combustion, air components. The styrene-acrylonitrile copolymer, for and/or other gases are fed into the system in a manner either type of production procedure, can be composed of which is contrary to the natural convective flow of air observed under natural combustion conditions.16 65-76% styrene and 24-35% acrylonitrile.9•lo Since the formulations of ABS plastics are rarely the same and Other furnace systems have been used less frequently in poorly defined in most of the studies examined for this combustion product generation and analysis. Therefore, review, it is difficult to generalize or compare ABS their pertinent advantages and limitations will be ad• samples. dressed when the experiments conducted in these parti• The temperatures at which ABS processing occurs cular systems are initially discussed. range from 325-550°C, depending upon the type and In the following sections, the results of the chemical grade of plastic being produced as well as the technique analyses of the combustion atmospheres of ABS are being used. The range for grades separated according to the prevailing experimental con• of ABS is 88-120 °C and for the injection grades ditions; i.e. inert or oxidative atmospheres. Although real of ABS, 110-125°CY The autoignition temperature of occur normally under oxidative conditions, very often (especially in large fires) little or no O2 reaches the polymer surface. Therefore, the study of the volatile products generated under inert atmospheres provides I I I I I I I c-c-c c=c-c-c C information on the molecular mechanisms of thermal degradation under controlled experimental conditions. HI CNHI HttHI HI H HI HnHtHI 0A Also, information may be obtained on potential decom• tH x y z position products that could be generated under vitiated Figure 2. Representative chemical structure of an ASS atmospheres or at the polymer surface in real fires. polymer. A summary of all the decomposition products of ABS ACRYLONITRILE-BUTADIENE-STYRENE COPOLYMERS (ABS) 95

was not detectable when this ABS sample was decom• Table 1. Degradation products of ADS posed under the described inert pyrolysis conditions, Product Atmosphere' References Hoff et al.19 analyzed by gas chromatography-mass I. 0 19 spectrometry the volatile products generated from two Acids (-COOH) o 24 I, 0 19,23,24 different ABS samples decomposed under an inert at• Acrylonitrile I, 0 19,23,24 mosphere. The two ABS samples were identified as Aldehydes (total) (HCHO) o 24 Ugikral RA 10331 (Ugine Kulman; referred to as ABS-l) 1,0 19,23 and Cycolac AM 25139 (Borg-Warner; referred to as o 13,17 ABS-2). ABS-l and ABS-2 were pyrolyzed at 210°C in a Carbon monoxide o 13,17,18,21,24 Pyrex glass degradation tube with a nitrogen gas flow of Cresol 1,0 19 20-30mlmin-1. The two ABS polymers demonstrated Dimethylbenzene I, 0 19 different properties upon thermal degradation. ABS-2, the Ethanal 1,0 19 less thermostable of the two, decomposed considerably 1,0 19 faster and formed nearly three times as much styrene as Ethylmethylbenzene 1,0 19 o 24 ABS-l (Table 2). ABS-2 also released higher amounts of Hydrogen cyanide 1,0 13,17,21,24 other volatiles common to both plastics as degradation Isopropyl I, 0 19 products, such as 2-phenyl-2-propanol, acetophenone, !Y.•

C(- Methylstyrene I. 0 19 methylstyrene and isopropylbenzene. ABS-l did not P - Methylstyrene 1,0 19 generate any volatile products other than styrene in o 21 quantities greater than 100 flg g - 1 of ABS sample pyro• o 21 Iyzed. Some of the degradation products from the ABS Phenol I, 0 19 samples pyrolyzed under inert conditions contain , I, 0 19 Phenyl indicating the presence of oxygen-containing additives. I, 0 19 2- Phenyl-2-propanol The extensive list of volatile products identified by Hoff 3-Phenyl-1- 1,0 19 et at. 19 (Table 2) may be a result of the experimental n- Propyl benzene I, 0 19 Styrene I, 0 19,23,24 methodology. The decomposition products evolved dur• 4- Vinyl-1 - I, 0 19 ing the thermal degradation of the polymer were removed from the furnace/combustion site by the nitrogen gas flow 'I = Inert pyrolysis atmosphere. (20-30mlmin-1), potentially reducing their further de• 0= Oxidative combustion atmosphere. gradation. Also, the temperature used is typical ofthose in industrial processing and, at most, may represent the identified under all the described experimental conditions temperature conditions during the early phase of a fire. is presented in Table 1, in which the combustion at• The different amounts of styrene evolved from the two mosphere (inert or oxidative) is indicated as are the ABS plastics may be related to a difference in the studies which identified each product. The data indicate acrylonitrile content of the plastic, as it has been shown that the majority ofthe products generated are character• that an increase in acrylonitrile content of styrene• istic of both inert and oxidative conditions. acrylonitrile polymers favors a higher styrene yield during degradation.2o

Thermal degradation in inert atmospheres Table 2. Thermal degradation products of two types of ABS This section will cover experiments performed in at• decomposed in nitrogen 19 mospheres devoid of oxygen. This experimental atmos• Degradation product ASS.1 a ABS-2b phere, in effect, limits the type of degradation products Styrene 2400C 7400 formed, as oxidative decomposition is prevented. 2- phenyl-2 -propanold 20 580 Sumi and Tsuchiya 17 measured the amount of hydro• Acetophenoned 23 420 12 230 gen cyanide (HCN) generated when chopped ABS C(- Methylstyrene was exposed to a temperature of 800°C in a combustion Iso-propylbenzene 42 190 tube furnace with a nitrogen flow of II min -1. The 4-vinyl-1-cyclohexane 13 88 75 evolved HCN was collected in a 0.4% Benzaldehyded 33 23 54 (NaOH) trap and quantified with a cyanide ion (CN -) Ethylbenzene Ethylmethylbenzene 11 39 specific electrode. The maximum concentration of HCN n- Propyl benzene 18 32 generated under these experimental conditions was 18 fJ- Methylstyrene <10 0.034 g HCN g-l ABS sample. The generation of HCN Acrylonitrile 15 <10 under nitrogen did not differ quantitatively from that Cresold 48 generated under oxidative conditions (see below). Phenold 33 The amount of carbon monoxide (CO) generated by Phenylcyclohexane 18 pyrolysis of an ABS sample in a atmosphere was Di-methylbenzene 14 <10 determined by Michal.18 A horizontal combustion tube 3-Phenyl-1-propene was used with a moving ring oven set at 550°C. Helium 'Ugikral RA 10331, Ugine Kulman. gas was fed into the combustion chamber at a flow rate of bCycolac AM 25139, Borg-Warner. 30 ml min -1. The ABS used was identified as Forsan 752E cValues are micrograms of product evolved per gram of material (Kaucuk, Kralupy, Czechoslovakia): The results in• pyrolyzed. dicated that CO (as measured by gas chromatography) dOxygen-containing products. 96 J. V. RUTKOWSKI AND B. C. LEVIN

Thermooxidative degradation A ten-fold increase in the maximum generation of CO was demonstrated under flaming conditions as compared with When sufficient oxygen (02) is present in the atmosphere, the CO levels generated in the non-flaming or smoldering the primary gases formed during the combustion of r.lost conditions (Table 3). materials, including ABS, are CO and carbon die xide Similar findings are evident in the data from the (C02), Hydrogen cyanide generation from nitrogen• interlaboratory evaluation (ILE) of the National Bureau containing materials occurs during thermo oxidative de• of Standards (NBS) Toxicity Test Method (Table 3).13 gradation as well as during thermal degradation under Four used the same ABS material and inert atmospheres. Other thermo oxidative products from essentially the same combustion conditions. However, ABS are listed in Table 1. variations in the results can be attributed to individual Table 3 summarizes the quantitative data in the litera• laboratory modifications of the designed experimental ture on the generation of CO, CO2 and HCN from ABS protocol. An ABS copolymer in pellet form was ther• decomposed under oxidative conditions. Although vari• mooxidatively degraded in a crucible (or cup) furnace. ations in test methods and ABS samples do not allow for The amount of air flow around the test sample in the direct, quantitative comparisons between studies, gener• furnace is unknown and not controlled. This may ally more CO and CO2 were generated in the flaming affect the formation of secondary combustion products mode than in the non-flaming one. The production of and the completeness of combustion of evolved products. HCN is approximately the same in both modes. The In the ILE of this test system, toxic gas analysis was following sections will discuss the experimental studies on performed by continuous flow, non-dispersive infra-red each of these primary gases separately. analysis or gas chromatography for CO and CO2 and either gas chromatography or specific ion electrodes were Carbon monoxide. Gross et al.21 measured the amount of used for HCN measurement. The observed CO levels CO generated during the combustion of two generic generated in the flaming mode generally exceeded levels samples of ABS. The composition ratio of the monomers measured in the non-flaming mode of combustion of the in the plastics was the same for both samples; however, the ABS; however, the differences were not as great as those samples did differ in their physical characteristics and found by Gross et al. (i.e. ten-fold).21 One of the four ILE appearance. ABS sample 1 was 0.045 inches thick, participating laboratories who examined ABS reported weighed 1.33 kg m - 2 and was a semi-rigid sheet with a no significant difference in mean CO levels (laboratory dark gray matte finish. The second ABS sample was 0.08 #3). The reason for the differences between the data of inches thick, weighed 2.35 kg m - 2 and was a rigid sheet Gross et al.21 and of Levin et al.13 is unknown. with a green polished surface. Each ABS sample was Sumi and Tsuchiya 17 used gas chromatography to placed in an 18 ft3 chamber and was subjected to thermal measure the amount of CO generated from chopped ABS irradiation at a level of 25kWm-2 to the normal-use pipe subjected to a series of increasing temperatures in a exterior (or front) surface. Gas analysis during the course combustion tube furnace (Table 3). An initial increase in of experimentation was performed using colorimetric CO production was observed when the temperature was indicator tubes.b The maximum value from two separate raised from 500-600 0c. Further elevation of temperature determinations was reported; if these values differed by a in 100° increments up to a maximum of 800°C resulted in factor of two, additional measurements were performed. a decrease in CO levels. However, when the O2 con-

• 792270 ±) 86160 F FbF414±144954900±342990160126RadiantCombustion95486±76±25±HCN'1715±2440.63621250.729727225419223co:za0.812±12±0.56±0.5217±32958±3.21d±6±1TemperatureCO'3Apparatus62.0-±756radiant10425kWm-218414753185396atmosphereheating800°C500°CAirfluxNFModetubeor 9±1 Air 3648522755 550°CF 13 Table 3. Primary306Sample± 27toxicants621± 26'from experimental ABS thermooxidative degradation Reference NFcNF Cup 21furnance 17 Air:N250:50 800°C600°C700°C694-700°C475°C530°C725°C600°C500°C525°C Sample 2 'ValuescNon-flamingdThebFlamingnumbersarecombustion.thecombustion.respondmean ± tostandardthe laboratorydeviation.Combustioncode of those laboratories participating in the interlaboratory evaluation. "Expressed as milligrams per gram of sample. ACRYLONITRILE-BUT ADIENE-STYRENE COPOLYMERS (ABS) 97

centration was decreased by 50% by nitrogen, the CO Organic volatiles. The classes of organic volatiles and the level increased two-fold over that found at 800°C in air summed quantities of the individual agents generated alone. The authors provide no indication of whether or during the experimental thermo oxidative degradation of not the specimens flamed during their tests. However, as various samples of ABS are presented in Table 4 and noted above, the quartz tube furnace is not conducive to discussed below. Some of these compounds, such as flaming combustion. acrolein and styrene, have known irritant properties and may be present in high enough concentrations to com• Hydrogen cyanide. The generation of HCN, like that of CO, pound the hazard of the fire environment by affecting the is dependent upon the combustion conditions. The data mucous membranes and respiratory tracts of exposed from the previously described work of Gross et aFl and indi vid uals. Levin et al,u (laboratory #6 of the ILE) demonstrate no Zitting and Heinonen23 measured the levels of styrene, difference between the evolution of HCN gas during benzaldehyde, acrolein and acrylonitrile when Cycolac flaming combustion and during non-flaming thermal T 10000 (Borg Warner) was decomposed in air at 250, 300 degradation (Table 3). However, some data (laboratories 1 and 350°C in a combustion tube furnace with an air flow and 3 ofthe ILE) indicate a somewhat greater production of 0.51 min - I. Styrene and benzaldehyde were measured of HCN in the flaming mode of combustion than in the by gas chromatography, acrolein by high pressure-liquid non-flaming one (Table 3).13 Sumi and Tsuchiya 17 de• chromatography (HPLC) of its 2,4-dinitrophenylhydra• monstrated an increase in HCN production as the zone derivative and acrylonitrile by colorimetric indicator temperature increased from 500 to 800°C. The incidence tubes.b The aromatic yield (in this , of flaming combustion, however, was not noted. For the styrene) increased with each 50°C increase in temperature, 300 °C increase in temperature, the generation of HCN as did the aldehydes (benzaldehyde and acrolein) and increased approximately two-fold. At 800°C, a 50% acrylonitrile (Table 4). The amount of benzaldehyde decrease in the O2 content of the combustion atmosphere present exceeded the measured amount of acrolein one increased HCN production by approximately 20%. hundred-fold. Zitting and Savolainen24 determined the quantity of Carbon dioxide. Sumi and Tsuchiya 17 examined the effect various organic volatiles when Cycolac T 1000 was ther• oftemperature on the production of CO2, Carbon dioxide mooxidatively degraded at temperatures of 300 and production was approximately five- to ten-fold greater 330°C. Gas chromatographic analyses of styrene (listed as than CO production (Table 3). The CO2 production at all an aromatic hydrocarbon in Table 4) indicated that the temperatures was approximately the same, ranging from concentration doubled with the 30°C increase in degrad• 223 to 297 mg g-l sample. The occurrence of flaming ation temperature. The same relative increase was seen combustion was not reported. In a combustion atmosph• with acrylonitrile and the organic acids which were ere of air and nitrogen (50/50; 10% O2), the yields of CO measured by back titration with NaOH. The aldehyde and CO2 were of the same order of magnitude (52 and concentrations (acrolein, formaldehyde and total alde• 58 mg g - 1 sample, respectively). hydes) also increased with the increase in temperature; The data reported by Levin et al.13 also demonstrated a however, this increase was less than two-fold. Acrolein preponderance of CO2 over CO generated in the combus• was measured by the method of Cohen and Altshuller. 25 tion of ABS (Table 3). Except for the results reported by Formaldehyde concentration was determined by a one of the participating laboratories (laboratory #3), CO2 chromatropic method26 and total aldehydes by sodium production was greater in the flaming mode than in the bisulfite titration. non-flaming one. The mean CO2 values differed between Hoff et al.19 thermo oxidatively decomposed two ABS combustion modes by a factor of two to three. plastics, Ugikral RA 10331 (ABS-l) and Cycolac AM

Table 4. Organic volatiles from experimental ABS thermooxidative degradation Combustion Temp. Aromatic Reference Apparatus atmosphere (Oe) hydrocarbons Alcohols Ketones Aldehydes Acids Acrylonitrile <<1mgm-3120mgm-34mgm-39mgm-31Ol1gg-'13mgm-3b24.5ppm11.8ppm'26mgm-343mg11.5ppm- m-3 8.4ppm' 19 821199-'10250208300I1g-Combustion351199-'4ppm2.12ppm93.9ppm69-,ppmdI1g--825611gg-'2445--g-'35mgm-3'87mgm-3I1gAirtube21811gg-'191199-'g-'700l1g721199-'- 9 Air-, 450l1g197g-' ASS-22423 350330300 ASS-1

·Styrene. bSenzaldehyde with small amount of acrolein. 'Acrolein. formaldehyde and total aldehydes. dOrganic acids (as -COOH). 98 1. V. RUTKOWSKI AND B. C. LEVIN

laboratory comparison of data difficult. However, suffi• Table 5. Thermooxidative degradation products of two types of ABS19 cient toxicity data obtained using different test methods ABS-" exist to compare the toxicity of the thermal degradation Degradation product<10450190130ABS-Z'8238357800565070012017 2300c<1043203511162510141837121519 products of ABS to those of other materials such as AcroleinEthymethylbenzenen-propylbenzeneEthanalEthylbenzeneex-methylstyrene4-vinyl-1-cyclohexeneAcetophenoneBenzaldehydeIso-propylbenzene2-StyrenePhenyl-2-propanol AcrylonitrileP - methylstyreneCresol Di-methylbenzenePhenolPhenylcyclohexane Douglas fir. (Although it is recognized that Douglas fir is not a substitute for ABS in commercial products, the large realm of toxicological data on wood provides a point of reference with which the relative toxicity of materials can be compared.) Certain other characteristics of the com• bustion product toxicity can also be inferred. A brief description ofeach test system will precede a discussion of the data.

National Bureau of Standards (NBS) toxicity test method

The NBS test method27 utilizes a static exposure system in which the combustion products accumulate in the exposure chamber for the duration of the exposure. The stystem employs a cup furnace which , generates combustion products directly into the 200 1 'Ugikral RA 10331, Ugine Kulman. exposure chamber. The material to be tested is decom• bCycolac AM 25139, Borg Warner. posed at a cup furnace temperature 25°C above (flaming cValues are micrograms of product per gram of material pyrolyzed. mode) and below (non-flaming mode) the predetermined autoignition temperature of that particular material. The 25139 (ABS-2) at 208°C and 197 °C, respectively, and experiments may also be performed at furnace tempera• measured a number of organic volatiles (Tables 4 and 5). ture of 440°C if the autoignition temperature exceeds Styrene was the principal degradation product measured. 490°C. The design of the exposure chamber provides for ABS-1 generated six times more styrene than the total of head-only exposure of six rats, as well as sampling of the all other combustion products combined and ABS-2 chamber atmosphere for chemical analyses. Carbon generated four times more styrene than the total of all the monoxide, CO2 and Oz are monitored continuously. other volatiles. Thus, the aromatic hydrocarbons were the Hydrogen cyanide is measured approximately every 3 predominant class of organic volatiles. During the ther• min when a nitrogen-containing material is tested. mooxidative degradation of ABS-1 no other measured The biological/toxicological endpoints that have been compound appeared in the fire atmosphere in quantities used with this test method are incapacitation and leth• equal to or greater than 100,ug g-1 of sample. ABS-2 ality. Incapacitation is determined by the hind limb generated significant amounts (greater than 100J-lg g-1 of flexion conditioned avoidance response for which an sample) of 2-phenyl-2-propanol, acetophenone, isopro• EC so value is determined. For lethality, an exposure LCso pylbenzene, benzaldehyde and a-methylstyrene in ad• value (the mass loading of material per unit volume of the dition to styrene; the other measured compounds ap• chamber necessary to cause 50% ofthe test animals to die) peared in quantities less than 100 J-lg g-1 of sample is determined, as well as an LCso value for both the (Table 5). Comparison of Tables 2 and 5 indicates that exposure and post-exposure observation periods. The similar degradation products evolved during the degrad• procedure also calls for the observation of toxic signs ation of ABS-1 and ABS-2 under both inert and oxidative during the 30-min exposure period and the 14-day post• conditions, which demonstrates no significant oxidative exposure period, during which daily animal body weights effect on the products. Therefore, either no oxidation are recorded. Carboxyhemoglobin (COHb) levels are occurs under the described thermooxidative combustion measured before, during exposure and just before the end conditions or the combustion apparatus prevented oxida• of the exposure period in two animals, which are cannu• tion from occurring. lated 24 h prior to exposure. The toxicity data from Levin et al.13 and Anderson et al.28 show that the degradation products from ABS ) COMBUSTION PRODUCT TOXICITY may be more toxic when decomposed under flaming ¥ thermooxidative conditions than non-flaming ones In laboratory experiments designed to assess the toxicity (Table 6). The within-exposure (LCso (30min)) and the of combustion products of either natural or synthetic within plus post-exposure (LCso (30min + 14 days)) materials a number of factors must be considered, includ• results are equivocal in the comparison of toxicity under ing the experimental design, the physical apparatus, the the two modes of combustion. The animal deaths did combustion conditions and the material sample. A review occur during both the exposure and post-exposure of the literature on ABS combustion product toxicity is periods. The incapacitation data (ECso) demonstrate that presented below with appropriate consideration given to the flaming and the non-flaming modes produced com• these important factors. bustion products of approximately equal toxicity. In The variety of ill-defined material formulations, experi• addition, Anderson et al.28 reported that some animals mental systems and conditions that have been used to demonstrated a degree of corneal opacity when ABS was assess ABS combustion product toxicity makes inter- degraded in the non-flaming mode. ACRYLONITRILE-BUTADIENE-STYRENE COPOLYMERS (ABS) 99

Table 6. ABS toxicity data-NBS toxicity test methodl3•28 EC",(mgl-') 440'CNFFNF LC",(30min)>20.830.0>38.415.0N.D.9(15.9-27.2)(23.1-47.9)(54.2-75.5)(21.2-45.0)64.0(12.3-18.3)(13.9-26.9)(26.5-34.0)>38.037.630.919.315.633.3>38.0>32.5(mgl-')(22.8-47.8)(17.6-27.5)33.022.0 (16.7-22.3)(13.2-18.4)LC",(30min+ 14d)(mgl-') Laboratory17.4 F' F NFb 440'C (13.9-21.9)(20.1-24.4(18.9-22.9)(13.2-18.415.6)) 22.1 20.8 (23.6-34.5)28.5 1c 10.6 ~21.0d ~20.2 (7.4-15.2)" [15.1-25.2] [15.1-25.2] 3 6.0 5.8 9.0 (4.1-8.9) (2.8-8.4) (4.7-17.3) 5 ~17.0 ~23.0 <37.6 [15.0-20.0] [18.5-27.5]

'Flaming mode of combustion. bNon-flaming mode of combustion. cThe numbers respond to the laboratory code of those laboratories participating in the NBS interlaboratory evaluation.'3 dEstimated value; numbers in brackets used for estimate. 895% confidence limits. f NBS large furnace. gNot determined. hData from Anderson et af.2·

NF13080FF Fd 1200 Table 7. 55070-ABS>18>28>22~50130NF'3202344><23-1806160330290-1602418445906026374207008505018001500900toxicityHCN(ppm)'COHb(%)'COHb(%)bCO(ppm)'data: NBS toxicity test method-carbon EC",(30min)monoxide, COHb and HCN!3 Laboratory 51 f3 69 CO(ppm)' LC",(30min)

'Average calculated for 30 min exposure at LCso (30 min). bCOHb values measured just prior to end of 30 min exposure. CAverage calculated for 30 min exposure at EC.o' dFlaming mode of combustion. "Non-flaming mode of combustion. fNumbers respond to the laboratory code of those laboratories participating in the NBS interlaboratory evaluation.'3 9NBS large furnace.

38.433.021.7 Non~flaming -1-1 Laboratory 35.0>(mgl~24.9130HCN(mgl(ppm)HCN3100340018001500-360016022.0180LCso38.0>(ppm)32.5(ppm)>>850420330-390039.83400>44003000CO900(ppm)50(ppm)CO2700(ppm)160700(mgl)20.822.117.415.6) >46.5) 37.329.0 Non·flaming-I Flaming Douglas fir Table 8. RelativeCOb toxicityLCso of ABS and Douglas fir-NBS test method 13 1 53 6c -1 LCso' Flaming HCNb bAveragecN BS largeCOfurnace.calculated for the 30 min exposureASS at the LCso (30 min). 'LCso for the 30 min exposure period.

The concentrations of CO and HCN in the combustion that either individually or together were too low to atmosphere are measured according to the protocol of the account for the observed within-exposure deaths. NBS test method and the results are presented in Table 7. Whereas, laboratories 3 and 6 reported HCN levels More CO was generated in the flaming than the non• sufficiently high enough to have caused within-exposure flaming exposure atmospheres and correspondingly deaths, in actuality, no deaths were observed (Table 7). higher COHb levels were noted in the exposed animals; Under flaming conditions, the LCso values for ABS however, the amount of CO was not sufficient to account were lower than those found for Douglas fir by approxi• for the lethality of the animals.29 On the other hand, the mately a factor of two (Table 8). This difference may not measured HCN concentrations in the exposure atmosph• be regarded as toxicologically significant. There is no eres were sufficient by themselves or with the additional significant difference in toxicity between ABS and Doug• CO to account for the deaths that were observed in las fir when combusted in the non-flaming mode, even laboratories 1,3 and 6 in the flaming mode. In the non• though the wood generates a significantly greater amount flaming mode, laboratory 1 reported HCN and CO levels of CO under both combustion conditions. These results 100 1. V. RUTKOWSKI AND B. C. LEVIN

support the earlier implication of the involvement of the results of the experiments with the dynamic exposure another toxicant (presumably HCN) in the toxic action of system rank both ABS and ABS-FR of approximately ABS combustion products. equal toxicity with red oak (Table 9). When one considers the relative of ABS and in the static exposure system, polypropylene is equal in toxicity University of Michigan test methods to ABS; whereas in the dynamic exposure system it is more toxic (Table 9).32 Therefore, these data indicate that Two test systems, one static and one dynamic, each with a change in combustion systems will affect different distinct characteristics, were developed by Cornish and materials differently. coworkers.30-32 The static system consists of a 15001 The LAso values from the experiments using both the stainless steel exposure chamber in which mice are dynamic and the static systems30.31 do not show much exposed in a whole-body fashion to the combustion difference between the apparent toxicities of the combus• products for a period of 4 h. Combustion products are tion products of ABS and those of ABS-FR (Table 9). generated by placing the test material in a Vycor tube However, the specific mortality results, taken in a separate wrapped with resistance wire which produces a combus• study,32 do indicate a difference. For example, when rats tion temperature of 700-800 DC in 1-2 min. The LC50 is were exposed in the static system to the combustion determined after a 7-day observation period. Additional products of a 20 g sample of ABS- FR, 14 out of 15 animals animals may be tested and sacrificed following exposure (93%) died. Three of four rabbits also died when subjected for histological/pathological examination. to the same exposure conditions.32 This mortality is The dynamic University of Michigan test system somewhat greater than anticipated, since a 20 g sample is , consists of a flow-through Pyrex glass tube chamber with essentially equivalent to the reported LA 50 value.30.32 In side ports for the head-only exposure of rats. The contrast, no rats or rabbits died from the exposure when a combustion products are generated from materials placed 20 g sample of non-fire retarded ABS was decomposed,32 in ceramic boat in a combustion furnace. The furnace although the reported LAso value is also approximately temperature is programmed to increase 3 to 5 DC per 20 g30.31 or slightly greater (33 g).32 These inconsistencies minute to a maximum temperature of700-800 0c. Carrier which are evident between the mortality data32 and the air is passed through the combustion apparatus at a rate LAso values30-32 for ABS and ABS-FR are not of 11min - 1 and an additional diluting air stream of explained. 21 min -1 is added before the combustion products enter the exposure chamber. The exposure period parallels the time course of combustion product generation during the University of (PITT) method degradation of the material sample. The amount of material consumed which kills 50% of This dynamic test system was developed by Alarie and the exposed animals (LA 50)C from a number of studies on Anderson.33 A Lindberg furnace programmed to heat at ABS decomposed in both the static and the dynamic test 20°C min -1, starting at room temperature, is responsible systems are listed in Table 9. The specimens were not for the generation of combustion products. The test identified sufficiently to determine if the ABS material material starts in the non-flaming mode and will flame tested was identical in all three studies. The data provide when the material's autoignition temperature (under some information on the relative toxicity of fire retardant these combustion conditions) is exceeded. Animal expo• (unspecified) treated ABS (ABS-FR) and non-fire retarded sure begins in the non-flaming mode when 0.2% of the ABS samples and other materials used in these studies. material has decomposed. An air flow of IIImin - 1 is Because of the great differences in design and operation of maintained through the furnace during the combustion of the static and dynamic exposure systems the specific the material. Total air flow entering the exposure chamber toxicity of anyone material in either system should not be amounts to 201 min -1 following dilution of the combus• compared. However, the relative toxicities of different tion gases with cooling air. The 2.31 glass exposure materials studied within one system should be compar• chamber accommodates four mice in the head-only able with that found in others. This does not always exposure mode. The biological endpoints/parameters hold.32 which are determined include the RDso (i.e. the con• In the static exposure system red oak is a factor of two centration of smoke that produces a 50% decrease in more toxic than ABS and ABS-FR (Table 9). However, respiratory rate), a sensory irritation stress index (SISI), asphyxiant effects, lethality and histopathological changes. Analyses of the combustion atmosphere for ./ Table 9. Toxicity data-University of Michigan test method primary toxicants and O2 depletion are also performed. 3.6DynamicReference2.20.92.31.81.7313032 Static28189 LAso values' 20 A very limited amount of ABS toxicity information ABS-FRbRedABSoak Material 213322 polypropylene derived from this test system is available. Alarie and Anderson34 determined an LCso of 6.3g (1O.5mgl-1)d where the LCso is the amount of material loaded in the furnace that is required to kill 50% of the animals within an exposure period of 30 min and a post-exposure period of 10 min. The ABS sample used was only described as 'standard acrylonitrile-butadiene-styrene'. The L Tso, the time at which 50% of the animals die at the sample weight "Amount (grams) of material consumed necessary to cause the death of 50% of the exposed animals. killing 50% of the animals (or the sample weight nearest bFire-retarded treated sample. above it), was recorded as 9 min. According to the ACRYLONITRILE-BUT ADIENE-STYRENE COPOLYMERS (ABS) 101

evaluation criteria incorporating both the concentration• in the atmosphere, the level was too low to account for the response and time-response, the ABS is classified as being deaths. The carboxyhemoglobin levels in the rats exposed more toxic than wood (i.e. Douglas fir) and toxic actions to ABS being degraded at 400°C were also higher occur faster upon exposure to ABS combustion products than the other groups but still well below toxic levels, than upon exposure to the combustion products of wood. which were shown by Levin et at. to be above 80%.29 The Anderson et al.28 also tested ABS using the PITT increased HCN concentration from 100 to 150ppm, method in their report to the New York State Office of however, was enough to cause lethality in 30min.29 Fire Prevention and Control. An LCso valued of An ABS differed from the above described solid 9.3 mg I-I was obtained for the ABS sample used. The ABS in that the increase in mortality at the elevated LTso range during which the deaths occurred was 0• temperature was much less for the foam. No change in CO 40 min with an additional death reported during the concentration was recorded when the foam was degraded period of 49 h to 14 days post exposure. Again, the ABS at the higher temperature, and the five-fold increase in also proved to be more toxic than Douglas fir. HCN concentration resulted in a final concentration of only 100 ppm. It is, therefore, not surprising that fewer rats died in the 30-min exposure to the combustion DIN 53 436 method-Federal Republic of Germany products of the ABS foam as compared with the solid. These results show that the solid ABS combustion This apparatus was developed in the Federal Republic of products appear to be more toxic than those of the ABS Germany and adopted as a standard test method by the German Commission of Standards.35 The combustion foam when exposed to temperatures of 400°C. At this temperature, lethal levels of HeN are generated from the apparatus consists of a silica tube with a ring oven which solid ABS sample while sublethal levels are produced moves along the combustion tube at a rate of from the ABS foam. In both cases, HCN concentrations 10 mm min - 1. In these flow experiments the key para• increased at the higher temperature. The differences in meters are residence time in the heated zone and air/fuel toxicity between the two ABS samples can be attributed to (gas) ratio. Air flow through the combustion tube is possible variations in the formulation of the solid and provided at a rate of 100 I h - 1 in a direction counter to the foam. movement of the oven. The combustion products are Herpol37 also utilized the DIN test apparatus to diluted, cooled and carried into the exposure chamber by evaluate the toxicity of an ABS sheet. However, the a total air flow of 200 I h -1. Various exposure chambers chamber system was modified to allow for individual can be used to provide for either whole body or head-only whole-body exposure of the rats. This ABS sample was exposures. The toxicological endpoint is animal death. In degraded at three different temperatures (400,600 and addition, the animals are observed for toxic signs during 800°C) and the mortality found at each temperature is and following the exposure. Gross pathological examin• given in Table 11. The toxicity of ABS increases with an ations are performed when appropriate. The typical increase in combustion temperature. However, at the two protocol consists of a 30-min exposure period and a 7-14• higher temperatures more material degraded. This tem• day post-exposure observation period. perature phenomenon was also described to some degree Kimmerle36 used the head-only exposure system to by Kimmerle36 (see above). A significant mortality was evaluate the toxicity of two samples of ABS, a solid and a evident at 400°C and not at 350 °C in the results for the foam. The mortality data are presented in Table 10. It ABS solid.36 However, Herpol did not observe any appears that a substantial increase in mortality occurred animal deaths until a temperature of 600°C was when the decomposition temperature of the solid ABS reached.37 This may reflect a difference in material sample was increased from 350-400 0c. Although the CO concentration at 400°C was increased more than two-fold concentration, formulation or any number of possible variations in the experimental conditions. Herpol37 de• monstrated an increase in the CO and CO2 indices as the COHbHCN CO Table (#10.(ppm)10014.220150dead/#7.36.25.8(%)13/20MortalityASS1001500/202/20350tested)(ppm)toxicity350(0C) data-DIN 53 436 method36 temperature increased from 400-600 0c. These indices are ASSSampleASS foamsolid 400400 Temp. calculated by summing the recorded values at each minute and indicate the amount of gas liberated by the test material during the test period. A slight decrease was evident when the temperature was further increased to 800°C (see Table 11). In pure CO experiments, Herpol37 found that the CO index necessary to cause death during a

of(ppm.69550d51940d(#Mean10.0samplewt(g)(%v/v.dead/#48Samplea904056Mortalitymin)2.0COHbbNumber(%)min)exposed)(%)tests453 of 2950 Table 11. ASS Weight9/293/240/18mortalityCO2110.9CO86.0indexcindexcloss and toxicity data-DIN 53 436 method37 400('C) 600800 Temp.

'Wt of sample charged. bMean COHb levels of those animals which died. 'The CO and CO2 indices are calculated from the measurements at each minute interval and summing the values. The indices provide an estimate of the total amount of toxicant liberated during the exposure period. dCO index at the moment of death. 102 1. V. RUTKOWSKI AND B. C. LEVIN

30-min exposure was 120000 ppm. min (equivalent to a ABS. Only selected representative work by Hilado 30-min exposure to 4000 ppm). A CO2 index of 300%. min et a1.38•39 will be presented here in an effort to avoid (equivalent to a 30-min exposure to 100000 ppm) will redundancy. result in the inhibition of respiration. It is evident from the The data for ABS toxicity are presented in Table 12. data (Table 11) that the CO was not present in amounts The endpoints used by Hilado are the following: that can solely account for the observed mortality. These (1) Time to incapacitation (the first observation of stag• data suggest, as has the work of other authors, that CO is gering, prostration, collapse or convulsions); not the only toxicant involved. (2) Time to staggering (the initial observation of loss of equilibrium); (3) Time to convulsions (the first observation of University of (USF) method convulsive-type movement); (4) Time to collapse (the first observation of muscular The apparatus for this method consists of a Lindberg support loss); and horizontal tube furnace which is either programmed to (5) Time to death (the time at which cessation of move- heat at a rate of 40°C min -1 from 200°C to a maximum of ment and respiration are observed). 800 °C or set at a fixed temperature. The toxic combustion The mean values and standard deviations of times to products which are generated are carried into the expo• sure chamber with or without a forced air flow. The specified animal responses presented in the studies by exposure chamber is a 4.21 hemisphere constructed of Hilado et at. are derived from the means of two or more , polymethylmethacrylate and provides for whole-body replicate tests and reflect between-experiment variation exposure offour mice. The biological endpoints which are rather than individual animal variability. The ABS used in this system are time intervals to various observed material used by Hilado et al. was identified as Dylel 702, signs of intoxication, such as incapacitation, staggering, natural, lot A54000 from Sinclair-Koppers, Co., Kobuta, convulsions, collapse or death. The mortality is recorded. PA. The data in Table 12 compare various experimental Analysis of CO and CO2 in the chamber atmosphere is conditions and their influence on the toxicity of ABS. The performed at the conclusion of the experiment. Oxygen amount of ABS pyrolyzed under each set of experimental levels, however, are monitored periodically during the conditions was approximately 1.0 g. From these results it exposure. is evident that the determination of the relative toxicity of The principal disadvantage to this system is that all ABS depends largely upon the test conditions used. With endpoints are based on the subjective measurements of this test system the most toxic exposure condition is a the one individual conducting the test. In addition, these fixed furnace temperature of 800°C with forced air flow, at endpoints provide no insight into the cause of the which animals respond most rapidly. This short animal observed response. Since CO and CO2 are measured at response time is most likely due to the more rapid the end of the exposure period, limited inference can be generation of toxic decomposition products at this tem• made concerning the role of these gases in the observed perature. The addition of a forced air flow through the toxic effects. Moreover, time to effect is not a true combustion system into the exposure chamber also toxicologic parameter and, in this case, is related to both augments the degree of toxicity, as reflected in the shorter the time necessary for material degradation and that time to response at 600 and 800 dc. The apparent CO required for the toxic insult to take effect. Toxicity is based concentration (ppm) in the animal chamber at the end of on the quantity of a substance required to elicit a certain the exposure period did not correlate with the time to measurable effect. The 'time to effect' is more appropri• response. In fact, at 800°C with forced air flow, the ately considered important in the overall hazard assess• amount of CO was lower at the shorter response times, an ment of a material in a particular use rather than being an observation that was not evident at a furnace temperature index of toxicity. of 600°C. Hilado and co-workers have amassed a sizeable In another study of ABS by Hilado and Huttlinger39 a amount of data on the toxicity of materials, including material sample size-dependent phenomenon was de-

Table 12. ADS toxicity data-USF method38 Experimental(Imin-')FlowincapacitationTime(#COdead/#numbertoTime(ppm)TimedeathconvulsionsTimecollapsestaggering(min)toexposed)toto(min)(min)(min)(min) Mortality Air 13.523.092.302.841.691.475.83±2.10243537002405297516950313600± 0.050.490.040.0617.62±4.773.46b1.573.80(2)(1)1.76(1)18.522.033.415.027.713.479.514.5315.53550±1.258.39±4.466.50(2)16.48(5)C(2)16/161.72±1.5318.0920/208/8±1.12±0.268/8±0.080.30±0.723.680.394.090.16±5.08±(1)1.90(2)2.831.994.09(5)(1)6.44(1)(2)(2)(4)(2)(4)(4)(2)(4)(2)(5)(2)5.961.722.933.39± 2.61±± 0.090.210.41(2)(2)(2) ('C)800'800d600d 600dTemp. conditions "

'Ramped heating mode. bMeans± S. D. cNumber in parentheses representsthe number of experiments from which the means were used to calculate the means± S. D. dFixed heating mode. ACR YLO -BUT ADIENE-STYRENE CO PO LYMERS (ABS) 103

monstrated under fixed and ramped temperature con• of CO was calculated to be 31 020 ppm. min, indicating ditions in the time to death of the animals (Table 13).Two that the amount of CO generated by the thermal decom• samples of ABS, Dylel 702 natural Lot A54000, Sinclair• position of ABS was barely in the critical range (30000• Koppers Co., Kobuta, PA (ABS-1), and Lustran, Mon• 45000 ppm. min for a 30-min exposure period is charac• santo Co., St Louis, MO (ABS-2), were tested. As the mass teristic of materials whose principal toxicant is C041). ofthe pyrolyzed sample increased, the mean time to death (Caution should be used, however, in extrapolating of the experimental animals decreased, a result which is concentration-time products to other exposure times not surprising since the amount of toxic gases produced is since this value is not a constant.) While CO was found to directly correlated with the amount of sample decom• be an important contributor to ABS combustion product posed. The decrease is directly correlated with the amount toxicity,40 Hilado and Huttlinger39 did not consider it to of sample decomposed. The decrease in time of death be the sole toxicant. observed with both samples under ramped and fixed temperature conditions was comparable. Hilado and Huttlinger compared the relative toxicity of ABS to various woods under ramped temperature con• SUMMARY ditions and no air flOW.41The results are presented in Table 14. The data presented by Hilado41 show that the CO concentration generated by the ABS sample at the The processes of pyrolysis and combustion under various time of death is less than that generated by any of the nine atmospheric conditions result in the production of many wood samples tested under similar conditions. Also, the decomposition products, some which are known toxi• concentration-time product for ABS is lower than that of cants and others whose toxicities have not been inves• any wood sample tested. The concentration-time product tigated. In addition, there may be toxic products gen• erated that have not been identified. The conditions under which decomposition occurs are important in determin• Table 13. Time to death dependency on sample size- USF test ing which degradation products will be generated and at method 39 what concentrations. 2.003930.05005.002272.003555.001700.999742.001440.103842.002715.002625.004811.002831.000111.0008026.6620.5825.2818.52±4.8110.88±0.44PyrolyzedCharged4.975720.984130.993740.987044.954910.996484.871664.891120.05001.762491.991330.103372.001542.58±0133.172.659.512.277.10±1.129.419.96TimeWeightdeath± to0.661.87b0.110.00.080250.011.091.75(g)of(min)sample10.02 ± 0.36 In the case of ABS, twenty-seven chemical experiments Number of 22143612 Sample Temperature compounds have been identified as combustion ABS-1' ramped products.13,17-19,21,23,24 It is obvious that more com- bustion products are generated, but have not been identified or investigated to date. The degradation pro• ducts which appear to be of primary toxicologic concern ABS-2C ramped are CO and HCN.13,36 These two decomposition pro• ducts have been detected under a wide variety of experi• mental conditions and are likely to be generated under

ABS-l fixed real fire situations. Although each toxicant alone may not be present in adequate concentrations to pose a health threat, recent studies at NBS on the interaction of CO and ABS-2 fixed HCN indicate that these two toxicants may act in an additive fashion.29 The data presented in this review have been evaluated to determine the extent to which CO and HCN together could account for the combustion product 'Dylel 702 Natural lot A54000, Sinclair-Koppers Co., Kobuta, PA. toxicity. It appears that the concomitant generation of bMean ± standard deviation. CO and HCN is responsible for the toxic/lethal effects of CLustran, Co., St Louis, MO. the combustion products of ABS. However, the involve• ment of other toxicants cannot be precluded prior to Table 14. Relative toxicity of ABS compared with various comprehensive analyses of the degradation products. , wood41 In general, the degradation products of ABS from the Cone.(ppm.(ppm)COtimemin) Time to flaming mode produced LC 50values that were lower than 35790339203358031020135001030010200120001140015000485004527036980393903971052720910067009200 15.5614.7615.4214.5013.8214.3714.9115.0914.0618.52(min) death those of wood (either Douglas fir or red oak) Sample/materialbWesternYellowAspenSouthernBeechEasternDouglasRedASSoakpoplarbirchwhitehemlockredfiryellowcedarpinepine (Fig. 3)/3,32,34 however, some findings to the contrary have been noted,32 The magnitude of the differences in LCso values ranges from a two-fold difference in a static exposure system13 to a ten-fold difference in a dynamic test system.34 The ABS LCso values for flaming combus• tion ranged from 10,5 mg 1-134 to 22.1 mg 1- 113 for a 30-min exposure period and 15.0 mg 1- 113 to 28.5 mgl-128 for the 30-min exposure and 14-day observ• ation period. In the non-flaming mode, both ABS and Douglas fir combustion products are equally toxic.13 In the non-flaming mode of combustion, the ABS LCso 'Concentration-time products (ppm. min) for CO. values ranged from 22.0 mg 1- 113 for a 30-min exposure bSamples were pyrolyzed with a ramped furnace temperature at 40°C min -, to a maximum of 800°C with no forced air flow through the to 64.0 mg I-lor greater13,28 for the 30-min exposure and system. 14-day observation period. 104 1. V. RUTKOWSKI AND B. C. LEVIN

Concentration - response Much more : More toxic : As toxic toxic than : thon wood ; as wood wood' . 0.1 1000.0

r r Grams •••••••••••• Io •• ~

g:J 30.0 1;; UFGM57cellUlose] t [Df" ••..0"00 ",0 «3 .~~125]GM 2' ...•...•- ~rr[Q::;PE wood[ Q) ••••••••••• ., ••••. I ~ C MO:"-J. PVC ~ PE I o ,g 10.0 PVC-A~t Closs A a. +- '" GM 47 :u'\ I III Q) •... PVC-CN ~.(G~49 GM 23 Q) +• Class B Q)'O ::l •I ABS-3 GM zl PE •...I +-0 C "'0 T Q) PCP-CN E ~3 •••••••••••• I••• ~

~ •...

Q)"O 1;; g 3.0 .E3 Closs C I ~c Uo :>~

~.~ ••••••• 1 •••••. Closs 0 to

Figure 3. Relative toxicity of ABS-Pitt method.33 Each point represents the amount of material (grams on the X-axis) which produced sufficient smoke to kill 50% of the animals (LC50) and the time (minutes on the Y-axis) required to kill 50% of the animals (L T50) using that amount of material. Reading the graph vertically, each material is classified in terms of potency while each material is classified in terms of onset of action by reading horizontally. To combine both, parallel quadrants separate classes A-D. (Reproduced with the permission of the authors. Copyright 1981 Academic Press, Inc.)

CONCLUSIONS (3) The thermal degradation products of ABS plastics demonstrate a measureable degree of toxicity. How• The currently available literature on ABS combustion ever, the toxicity of ABS combustion products is product toxicity provide a great deal of data; however, comparable with the toxicity of the degradation these results have only very limited usefulness. The full products of other common polymeric materials. assessment of the relative toxicity of the combustion products of ABS is complicated by a large number of Acknowledgements potential variations in the chemical formulations of ABS and a variety of test systems and experimental protocols. The authors gratefully acknowledge the help of Ms N. Jason, Ms M. However, the following generalizations are possible: Diephaus, Ms A. Durham and Ms C. S. Bailey who performed the literature search and compiled the references. This experimental work (1) Many combustion products are generated during the was performed under Contract CPSC-IAG-74-25, Task Order 84-8 decomposition of ABS. from the US Consumer Product Safety Commission, Bethesda, Mary• (2) The principal gases which appear to be responsible for land 20207, with Dr Rita Orzel as Project Officer. The opinions the observed toxicity are HCN and CO. expressed herein are those of the authors and not those of CPSc.

NOTES

a Certain commercial equipment, instruments or materials are C The use of the convention, LC50 by Cornish et at. to describe a identified in this paper in order to adequately specify the experi• value expressed in grams and not grams per unit volume is mental procedure. In no case cioes such identification imply inappropriate. The convention LA", (lethal amount",) is used as a recommendation or endorsement by the National Bureau of more appropriate substitute in the discussion of these data. Standards, nor does it imply that the equipment or material d Alarie reports his toxicological results in grams of material. For identified is necessarily the best available for the purpose. comparison purposes the gram units have been converted to b Indicator tubes, such as Draeger Tubes, do provide a convenient mg 1-1 units by the following equation: and inexpensive indication of the presence of measureable wt (g) amounts of individual combustion products; however, if interfer• ing gases are present in the test atmosphere, a high degree of chamber air flow rate (I min-1) x exposure time (min) precision and accuracy is not attainable. x1000mg/g ACRYLONITRILE-BUTADIENE-STYRENE COPOLYMERS (ABS) 105

REFERENCES

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