Document DDkkO45q4vxZBDp3a4j2KaD0N

1 * V J) ^ Oxidative Thermal Degraoationof Selected Polymeric Compositions K. L. PACIOREK, R. H. KRATZER, J. KAUFMAN and A. M. HARTSTEIN* Ultrasystems, Inc., 2400 Michetson Drive, Irvine, Ca, 92664 Tola *m performed on (a) polyvinyl chloride-containing materials, (b) neopeena composition!, (c) polyurethane foams, and (d) miscellaneous materials (including Jute and fiber glass) using a stagnation burner arrangement. In the case of the chlorinated materials, significant quantities of hydrogen chloride were detected. Us rate of evolution being strongly temperature dependent. Once glow occurred, carbon monoxide became the predominant toxic species formed. Urethane foams produced CFClj and COz together with some HC1 and chlorinated hydrocarbons; whereas Jute compositions liberated methyl chloride as well as other products. A composition of resin reinforced with glass fibers ignited spontaneously at 487'C and produced significant quantities of carbon monoxide. Introduction THE RESEARCH IN THE AREA OF FIRE toxicology and material off-gassing has been proceeding uninterruptedly ever since World War II as can be attested by the review summarizing the work from 1945 to 19511 and other publications.2'4 The more recent emphasis on this type of an investiga tion was necessitated by the considerations of hazards inherent to confined locations such as, e.g., aircraft, spacecraft, submarines, and underground mines.17'15 Under thermal oxidative conditions, or ganic compositions decompose to form a variety of gaseous products the nature of which is largely dependent on the composi tion of the original material and to a cer tain degree on the concentration of oxygen in the surrounding atmosphere, e.g., the presence of air or pure oxygen. Furthermore, the most widely used flame resistant mate rials do contain halogens, particularly chlo rine. The latter upon thermal degradation is liberated mainly in the form of hydrogen chloride. u. $. Bureau of Mines, Pittsburgh Mining and Safety Research Center, Pittsburgh, Pennsylvania. In a broad sense the problem of forming decomposition products, including toxic sub stances, during the pyrolysis and combustion of natural and synthetic materials in a coal mine is the same as that for any other indus trial facility. In a coal mine the same type of materials are used under similar conditions as in an industrial plant; therefore, from iden tical items the same type of toxic products in the same quantities will be formed. In view of the confinement in an underground coal mine and the creation of a defined air flow pat tern by the required ventilation, several aspects become of importance that normally can be neglected in above-ground operations. In contrast to above-ground operations, the available space in coal mines is limited, and in case of an accident, egress is not readily accomplished. In addition, the lim ited space available is taken up to a much larger extent than in an above-ground facil ity by equipment necessary to carry out the various mine operations such as mining, haulage, and ventilation. Thus, despite ven tilation, the danger of accumulating toxic decomposition products at or above thresh old limit values is much greater in an under ground mine than in an above-ground facil- 175 / ucc 03747 176 ity, since larger amounts of materials per unit volume of available space are capable of oxidative thermal decomposition accom panied by toxic product formation. Accord ingly, the temperature at which specific ma terials produce significant quantities of volatiles, the nature and toxicity of these vo latiles, the onset of glow or the tempera ture of autoignition, the loss of flame resistance through normal use, and the na ture and toxicity of combustion products are of much greater importance in an under ground mine than in most other locations. Most of the aforementioned studies cited above were conducted at rather gradually increasing temperatures either in static sys tems or at relatively low gas flow rates. In the work reported here more severe condi tions were employed to approximate more closely situations that could occur in a mine. To simulate overheating, a preheated, tem perature equilibrated test cell was employed. To approximate the condition in which a stream of hot gas, originating from a fire, causes the decomposition of a material down stream, preheated air was passed at a known flow rate over the test specimen. As de March, 1974 scribed in the experimental section, inter mittent sampling was employed to determine change of product composition with time and to estimate the rate of toxic product forma tion as a function of temperature. The studies reported here were preliminary in nature; more extensive investigations are being cur rently pursued. Experimental The oxidative studies were performed us ing the stagnation burner arrangement, a schematic of which is given in Figure 1. A quartz probe equipped with three ampoules (shown also in Figure 1) was used for sam pling. During sampling, the stopcock A to the vacuum pump was^losed, and a given ampoule (previously evacuated) was opened to the probe for a period of 5 seconds. All the temperatures presented in Table I are the temperatures recorded by the thermo couples B (gas temperature) and C (block temperature). In Table I only one tempera ture is denoted, since in all the experiments performed both temperatures were identi cal. The temperatures were recorded using a CEC 5-124A recording oscillograph after i ire 037476 American Industrial Hygiene Association Journal ucc 037477 Sample Idemiticaiion PVC-Nylon PVC-Nylon PVC-Nylon PVC-Nylon PVC-Nylon PVC-Nylon Neoprene Composition Neoprene Composition Neoprene Composition Neoprene Composition Neoprene Composition Neoprene Composition iute lute Jute Jute Polyurethane Foam Polyurethane Foam Polyurethane Foam Polyurethane Foam Fiber Glass Fiber Glass Fiber Glass Fiber Glass Temp c 400 400 490 490 570 570 390 390 485 485 555 555 475 475 555 555 485 485 545 545 487 487 550 550 TABLE1 Summary of Thermal Oxidative Tests Performed on Representative Materials* Sample Wl M Heavy Smoke Dufatkm uc SampUnf Time KC HCI ft CO ft CO, % C,H,b % CftA CHgCl ft 904 45-90 40-45 trace 0.04 904 925 925 932 932 2187 2187 2448 2448 2286 2286 607 607 45-90 33-85 33-85 28-65 28-65 165-205 165-205 60-130 60-130 50-90 50-90 65-150 65-150 60-65 3.62 35-40 3.07 55-60 1.36 5055 0.06 170-175 165-170 210-215 2.34 100105 19.63 125-130^ 3.11 65-70 7.33 150155* 0.38 45-50 55-60* 0.23 0.36 0.18 0.38 0.10 0.48 1.51 3.74 1.06 2.53 0.37 0.79 0.16 0.29 0.26 0.29 0.19 0.07 1.07 in 9.97 2.74 5.63 1.96 2.18 0.15 0.18 0.25 0.09 0.21 0.05 0.21 0.01 0.46 trace 2.17 0.02 0.45 trace 1.57 0.01 0.10 0.20 0.44 0.31 0.20 755 30-45 755 30-45 279 10-40 279 10-40 260 3-20 260 3.20 770 75-127 770 75-127 791 35-39 791 35-39 35-40 65-79* 8-13 18-23 5-10 15-20 107-112 1301351* 35-40 42-47' 0.24 0.13 0.65 0.18 0.14 0.09 0.19 0.71 2.79 1.88 4.14 2.02 0.59 2.41 0.25 1.91 0.32 1.09 10.60 5.79 9.45 0.14 trace 0.11 0.01 0.07 0.05 1.91 3.89 1.45 9.44 n.d.1 n.d. n.d. n.d. 0.15 0.03 0.19 0.40 0.07 * All tbe analyses are mole percents of gaseous sample, the remainder is N,. (X, Ar. b The hydrocarbons compiled under C,H, are ethylene, propylene with lesser amounts of propane and acetylene. c Glow from 4 to 28 min. d Glow from 2 min 10 sec to 28 min; this sample was taken just prior to glow onset. * Glow from 1 min 50 sec to 35 min; this sample was taken during glow. 'Glow from i min IS sec to 3 min; this sample was taken just prior to the glow. * Glow from 58 sec to 8 min; this sample was taken during glow. 11 Combustion from 2 min 7 sec to 2 min 23 sec; this sample was taken during combustion. `Combustion from 39 sec to 1 min 20 sec; this sample was taken during combustion. 1 n.d.: not determined. CFCI, ft 0.06 0.04 trace so, C.H.C1, %* ... ,,,, 0.04 0.05 0.04 0.04 0.02 0.11 0.07 0.01 *V 17S steady state was attained just prior to polymer insertion. In view of the air temperature range of 200-550C, the actual gas flow varied from 80-1S0 cc/sec. All times listed in Table I were measured from the moment of polymer insertion. The volatiles collected in the ampoules were analyzed using mass spectrometry (modified CEC Model 21-620) and infrared spectroscopy. Results and Discussion In Table I are compiled the results ob tained for four representative material com positions used in mines. These were brattice cloth samples (PVC-nylon, jute, "fiber glass"), conveyor belts and cable insulation (neoprene), and ventilation stop sealants (polyurethanes). The fiber glass composition was included to illustrate the unexpected flammability and toxic product formation (in this case CO) from what would appear to be a "safe" material. The actual number of compositions studied under this program was much larger, however, since the data obtained for related compositions (e.g., the various types of brattice cloths -composed essentially of polyvinyl chloride-nylon) were not significantly different to alter the general trend only one representative member of each series is discussed. On both polyvinyl chloride-nylon and the neoprene compositions, tests were per formed at 200C; however, in each instance, after 10 minutes residence in the hot zone, only 1 % of sample weight was lost, and no volatile products could be detected by mass spectrometry. In the experiments summar ized in Table I at least one sampling at a given temperature was performed during the most intense smoke formation. Examining the data it is apparent that in polyvinyl chloride and neoprene compositions the ob servance of smoke is associated with hydro gen chloride evolution. As would be ex pected, at the higher temperature hydrogen chloride is evolved at a much faster rate than at lower temperatures. Consequently. March, 1974 after a shorter time interval the material is depleted of chlorine, resulting in an earlier glow onset. During glow the gaseous effluent was found to be grossly depleted of hydrogen chloride, whereas the relative concentration of carbon monoxide was significantly in creased. Thus it seems safe to state that in the case of chlorinated composition, in par ticular materials such as neoprenes or PVC, hydrogen chloride is the main toxic species produced during the initial stages of decom position prior to the occurrence of a glow. By the time glow or autoignition can be observed, carbon monoxide, not hydrogen chloride, poses the real toxic hazard. Sulfur dioxide, in case of neoprenes, is produced in sufficiently high concentration to be de tected in the highly diluted samples collected. However, in comparison with the hydrogen chloride and carbon monoxide concentra tions measured, sulfur dioxide is not the major toxic hazard although it definitely is a contributing factor. On the other hand, in our current studies to be reported at a later date, other toxic sulfur-containing constitu ents were observed also, such as carbon disulfide, carbonyl sulfide, and hydrogen sulfide. Thus, the sum of all sulfur-contain ing species amongst the decomposition prod ucts may represent a considerable danger in the case of highly cured compositions, since threshold limit values are very low for some of them and the effects are additive. Jute has been used extensively in the mines, particularly in the form of brattice cloths. As would be expected carbon mon oxide is the main toxic species produced here; the surprising aspect is the formation of methyl chloride. This compound most likely arises from the reaction of calcium chloride, incorporated as a fire retardant, with the organic constituents of jute. Four different polyurethane foam samples were investigated. The mixture of decom position products found was very similar in each instance. It was known that Fluorocar bon-1 1 (CFCI.i) was the blowing agent used , ' American Industrial Hygiene Association Journal 179 to produce the rigid foams, thus the find ing of this material in the volatile off-gases was not surprising. However, it is noteworthy that it is a potential phosgene precursor. The presence of dichloroethane and hydrogen chloride was unexpected unless it can be assumed that chlorinated hydrocarbons were components of the urethane mixture. Com paring sample weights employed, it is ob vious that these products were formed in sig nificant quantities on weight/weight basis. The Tiber glass" sample used in these investigations is actually an organic resin reinforced with glass fibers to increase structural integrity. The particular sample tested was one of the few materials that were found to burst into flames when ex posed to temperature (487C). It also pro duced high concentrations of carbon mon oxide. As a matter of interest, a typical coal sample failed to glow under these condi tions. It should be pointed out that this study was not concerned with material ignition behavior, therefore ignition of this "fiber glass" sample obviously can occur at tem peratures lower than 487C. This material accordingly presents a danger both in view of its ready flammability and its production of large amounts of carbon monoxide. Hy drogen cyanide is of great importance from the toxicology standpoint, yet it is not listed in Table I since the mass spectrometer em ployed did not resolve the peaks at m/e 27 and 26 to show whether these were HCN and CN or CxH* and OH* derived. No hydrogen cyanide was detected using infra red spectroscopy, which means that, if it was present, its concentration was below 0.1%. It should be emphasized that this was an exploratory study concerned mainly with the production of the major toxic com ponents as influenced by temperature and exposure duration. The experimental con ditions chosen did not lend themselves to detection and identification of toxic com ponents formed in small quantities, e.g,, in concentrations of less than 0,01% in the ' gaseous effluent. More extensive work aimed at lowering of detection limits and quantita tive determination of all major products formed is presently in progress. Acknowledgemeiit This work was supported by the Bureau of Mines, Pittsburgh Mining and Safety Re search Center, under Contract HO 122009. References ^ 1. -------------- Nature and Quantity of Giae* Emitted by Plastic Materials Subjected to Flammability Tests. Nat. Tech. Info. Ser. AD 493460 (1952). 2. Berger, L. B.. H. H. Schienk, I. A, Gale. R. W. Stewart, and L. E. Sieffert: Report of Investi gations, Toxicity and Flame Resistance of Thermosetting Plastics. Nat. Tech. Info. Ser. AD 493861 (1947). 3. Zapp, J, A.: The Toxicology of Fire. Armed Services Technical Information Agency 104487 (1951). 4. Thinius, K., E. Schroder, and A. Gustke: The Pyrolysis of Plastics in the Presence of Air. Plaste und Kautschuk 11:61 (1964). 5. Hagen, E.: Compostion of Pyrolysis Gases of Plastics. Plaste und Kautschuk 75:711 (1968). 6. Dotreppe-Grisard. N.: Compounds Obtained by Combustion of Plastics. Trib. CBBEDEAU 294:141 (1968). 7. Boettner, E. A.. G. Ball, and B. Weiss: Anal ysis of the Voltatile Combustion Products of Vinyl Plastics. 7. Appl. Potym. Sci. 13:311 (1969). 8. Kobyashi, Y.. et al.: Combustion Gases Gen erating from Polyvinyl Chloride and Its Prod ucts. Model Experiments in Case of Fire. Japan Plastics 5:40 (1971). 9. Dufour, R. E.: Survey of Available Informa, lion on the Toxicity of the Combustion and Thermal Decomposition Products of Certain Building Materials Under Fire Conditions. U. S. Underwriters Laboratories, Inc., Bulle tin of Research No. 53, Chicago (1963). 10. Autian, I.: Toxicologic Aspects of Flammabil ity and Combustion of Polymeric Materials. 7. Fire Flammability 7:239 (1970). 11. Ausobsky, S.: Danger Rating of Combustion Gases from Plastics, Ver. Foerder. Deut. Brandschutzes, Z. 76:58 (1957). 12. Romberg, E.: Decomposition Products and Smoke Formation from Synthetic Materials During Fires. Ver. Deut. Ingr. Z. (Dusseldorf) 777:20(1971). 13. Hyvarinen, P.: Poisonous Pyrolysis Products of Some Plastics Formed During Fires. Vallion Tek, Tutkimuslaitos, Sarfa 111 ft, 93:3 (1965). 14. Rasbash. D. J.: Smoke and Toxic Products < 180 . March, 1974 Produced at Hies, Platt. Inst. Trans. /., Conf. Soppt. No. 2. pp 55-61 (1967). 15. Botl, B., J. G. Firth, and T. A. Jones: Evolu tion of Toxic Gases from Heated Plastics. Brit. Polym. J. 1:203 (1969). 16. Hagen, E.: The Composition of Fire Gases from Polyurethane Foams and Polycarbonates. Plane and Kautschuk 14: S. 391 (1967). 17. Marcy, J. F., E. Nicholas and J. E. Demaree: Flammability and Smoke Characteristics of Aircraft Interior Materials. Federal Aviation Agency Report ADS-3 (1964). 18. Marcy, J. F., et al.: Flaming and Self-Extin guishing Characteristics at Aircraft Interior Materials. Nat. Tech. Info. Ser. AD 673084 (1968). 19. Pryor, A. J., and C. H. Yuill: Mass Fire Life Hazard. Nat. Tech. Info. Ser. AD 642790 (1966). 20. Proceedings of the NASA Conference on Ma terials for Improved Fire Safety, held at NASA MSC, Houston, Texas, May 6 and 7, 1970. 21. Conference on Fire Retardant Polymeric Ma terials, NASA-OART and NASA-Ames, held at the National Bureau of Standards, October 30, 1970. 22. Marcy, J. F.: A Study of Air Transport Pas senger Cabin Fires and Materials, Nat. Tech. Info. Ser., AD 654542 (1965). 23. Paciorek, K. L., and L. B. Zuttg: Fundamental Ignition Study for Material Fire Safely Im provement, NASA CR 114357 (1970). 24. Paciorek, K. L, R. H. Kratzer, and J. Kauf man: Fundamental Ignition Study for Material Fire Safety Improvement, NASA CR 114402 (1971). 25. Paciorek, K. L. R. H. Kratzer, and J. Kauf man: Oxidative Thermal Degradation of Polytetrafluoroethylene, /. Polymer Sci. 11.-1465 (1973). Horace W. Gerarde, M.D., Ph.D. Dr. Horace Gerarde and his wife. Dotty, died in an airplane crash at Izmir, Turkey, on January 26, 1974. Horace, a long standing member of AIHA, was well known to us for his many significant scientific contribu tions to our field and for his unstinting work for AIHA committees and projects. He is, perhaps, best known for his extensive research on the toxicology of the hydrocarbons among his many and varied researches. He was graduated from Beloit College in 1940, then received his M.D. from the University of Wisconsin in 1948 and his Ph.D. from the Uni versity of Iowa in 1951. In 1952, he joined the Medical Research Di vision of Esso Research and Engineering Co., where he did much of his work on the hydrocarbons. Then in 1966 he became the Medical Director of B-D Division of the Becton, Dickinson and Co. and pursued the devel opment of his invention the Unopette. He was Corporate Medical Director for Occupational Health for Becton, Dickinson and Co. and consultant to a number of other firms at the time of his tragic death. Dr. Gerarde also combined his research and industrial medical activities with a considerable interest in teaching. At various times he held teaching appointments at Fairleigh-Dickinson University, Rutgers University, New York University, and Harvard University. We join his coworkers and many friends in their grief and loss in the passing of Horace Gerarde, for whom we hold the highest respect as a scientist, as an individual, and most of all as our professional confrere. m ucc 037480