Formation of Phosgene in Thermal Decomposition of Carbon Tetrachloride' ALICEH A ~ L T OSchool X . of Public Health, Harvard University, Boston, Mass.
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HE possibility of the formation of dangerous gases, of which phopgene is the most important, in the decomposition of carbon tetrachloride under the influence of heat, is a subject that has interested two governments for some years. The United States Bureau of Minm issued five reports on the suh,ject between 1920 and 1923, and the Chemisch-Technixhe Reichsanstalt in Germany issued three between 1926 and 1929. I n 1920 Fieldner, Katz, Kinney, and Longfellow (6, 7 ) published a report of experiments by the Bureau of Mines showing that carbon tetrachloride extinguisher liquids when applied to wood fires produce small quantities of irritating and poisonous gases which may be dangerous in very closely confined spaces if the user cannot escape m-ithout breathing the fumes, This study was made a t the request of the Kavy Department which desired to have tests made of the gases formed by the action of heat on carbon tetrachloride because of an accident that had occurred in Portsmouth Kavy Yard. During the construction of a submarine two men were working in a small, closely confined compartment, escape from which was impossible except through a series of manholes. They were using electric torches, and a piece of hot metal ignited the clothing of one man; the other sprayed a carbon tetrachloride commercial fire extinguisher over him and both were overcome by fumes and were extricated with the utmost difficulty from the poisoned atmosphere. Both recovered from the anesthetic effects arid were also recovering from the burns they had sustained when pneumonia set in and they died, one five and one nine days after the accident. This was in 1919. The histories of the men were sent to me by the U. S. Employees' Compensation Commission for my opinion on the cause of death. At that time all I could say was that the fumes of carbon tetrachloride seemed to have been responsible, since the burns were not severe enough and were healing satisfactorily; but it was not a characteristic picture of delayed carbon tetrachloride poisoning. Later on, when the publications of the Bureau of Mines appeared, I became convinced that the Portsmouth cases were caused by phosgene poisoning and so stated in my book (IO). One of the employees of the Bureau of Mines had been the victim of an accident similar to this, but not so severe. He applied carbon tetrachloride to a fire in an automobile truck and inhaled the fumes, losing consciousness for several minutes and suffering from soreness in the chest for some weeks after. Fieldner and Katz and their colleagues used two methods: (1) applying three types of carbon tetrachloride fire extinguisher and also commercial carbon tetrachloride to actual fires (excelsior) and to hot metals in a closed room of 1000 cubic foot capacity; and (2) passing vapors in air through heated tubes of iron or quartz, n-here humidity and 1 T h e occasion for thip paper ie a complaint made by five commercial companies manufacturing fire extinguishers of t h e carbon terrachloride type t h a t t h e treatment of th:s subject in m y book (fO), published in 1925, is misleading a n d inaccurare. While maintaining m y conviction t h a t t h e information given covered accurately a11 t h a t was available in 1924, I a m unwilling t o let it be supposed t h a t I consider it a n adequate statement of the case a s it is k n o a n today, after a lapse of eight years.
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temperature could be better controlled. Analyses in the first series shon-ed phosgene present in proportions of 15 to 80 parts per million of air when the extinguisher fluids were used (168 p. p. m. when it m s commercial carbon tetrachloride*) and the corresponding figures for vaporized carbon tetrachloride n-ere from 2000 to 5850 p. p. m.; for HC1 they n-ere from 60 to 236 p. p. m. The experiments with heated tubes yielded even higher readings per million parts of air. Since, according to the Chemical Warfare Service (American Vniversity Experiment Station), 25 parts of phosgene per million of air are deadly t o man if exposure is prolonged for 30 minutes, the Bureau of Mines concluded: "Such extinguishers should not be used by persons unprotected from the fumes, who are unable to hold their breath long enough to escape from the dangerous atmosphere." Similar conclusions viere reached by Suckolls (14) in an investigation made for the Underwriters' Laboratories. Later, the Bureau of Mines carried on further experiments (12) applying carbon tetrachloride to electric arcs, burning insulation, etc. They also exposed rats for 15 minutes to gas from burning insulation and to the vapors of carbon tetrachloride alone, finding that the first lot were all seriously affected (three out of seven dying) whereas those in the two other lots suffered no noticeable injury. Several foreign investigators also confirmed the findings of the Bureau of Mines. Thus, in France, Fohlen (9) in 1922 found that the decomposition of carbon tetrachloride with the formation of phosgene occurs a t temperatures between 200" and 800" C.; the yield is small in dry air (maximum obtained, 0.55 per cent of the theoretical yield), but in moist air the yield a t 300" C. is 64 per cent. Therefore, carbon tetrachloride extinguishers should not be used in a moist atmosphere nor in poorly ventilated places, nor should water be applied immediately after. I n Germany, Biesalski ( 5 ) found that phosgene would be produced by the action of carbon tetrachloride on metallic oxides and salts, and that the action of oxygen on this and other chlorinated hydrocarbons (of the methane, ethane, and ethylene series) a t a high temperature would also produce it. The greatest yield resulted from carbon tetrachloride a t 250" C. in the presence of ferrous chloride-namely, 25.41 per cent of the theoretical yield, by weight. In 1926 the first report was issued in Germany of the Chemisch-Technische Reichsanstalt ( 1 ) which had been commissioned by the Mine Safety Board of the Prussian Ministry for Commerce and Industry to clear up the question of whether extinguishers filled with carbon tetrachloride and operated by hand are suitable for use underground, and whether in such use gases injurious to health are formed. The Reichsanstalt found that the question had already been discussed and reports had been published of various experiments, but the opinions expressed were contradictory and resulted in confusion. Thus, for example, Wirth (17), 2
Chloroform had been added t o t a o of the extinguishers t o prevent freez-
ing, and a high-boihng petroleum distlllate t o t h e thlrd, for the same purpose.
One also contained turpentine
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a recognized authority, whose article is often quoted, came to the conclusion that the use of carbon tetrachloride on fires in confined narrow spaces (boats, mines, cellars) should be forbidden. On the other hand, tests made by Fire Director Kaiser of the Mining Board of Breslau (1)led him to say that phosgene could be found only in small amounts not dangerous to health, even underground, in all spaces which are swept by ventilation. Again, the experiments made by a German association of engineers (Reichsverein Deutscher Feuerwehringenieure) in 1923 yielded phosgene contents of 140, 300, and 1400 mg. per cubic meter of air (or 34, 73, and 340 p. p. m.) from the decomposition of carbon tetrachloride when applied to burning wood, sawdust, and glowing metals, as reported by Stahl (16) who emphatically condemned its use in cellars and other badly ventilated places. The first report of the Reichsanstalt (I) gives the possible results from the decomposition of carbon tetrachloride in the following equations :
VoI. 25, No. 5
the operator. The Reichsanstalt hopes that it may be found practical to add ammonia to the carbon tetrachloride and thus prevent the formation of phosgene, but a t present technical difficulties make this impracticable, for ammonia has a corrosive action on the metal of the apparatus. The analytic method used by the Bureau of Mines for the quantitative determination of phosgene was the alcoholsodium hydroxide method-namely, the removal of hydrochloric acid by silver nitrate on granular pumice, removal of chlorine by antimony trisulfide, absorption of phosgene by sodium hydroxide in 85 per cent alcohol, and titration of the excess alkali or determination of the chlorine. The Germans used two methods: the first was a saturated solution of aniline in water, causing the precipitation of diphenylurea which is filtered off and weighed. The second method is based on the fact that phosgene in the absence of water reacts quantitatively with iodides with the separation of an equivalent amount of iodine. A solution of sodium iodide in acetone was used and the liberated iodine titrated 2cc1, = C2C16 Clz with a standard thiosulfate solution. 2CCL = CtCll 2c1. Olsen (15)and his colleagues have tested the above methods and conclude that the first, the soda-alcohol, is untrustworthy :c1* 02 = 2cc for quantitative estimation because other chlorine compounds beside phosgene are present in the vapor formed by the thermal decomposition of carbon tetrachloride, and because they also undergo hydrolysis and thus add to the sodium chloride Which of these reactions will actually occur depends on from vhich the quantitative estimation is made. Olsen, several factors among which are the gases from the fire itself. therefore, holds that the amounts found in the Bureau of Moreover, the phosgene formed is itself decomposed into Mines’ experiments are too high, and he shows that, when the carbon monoxide and chlorine to an extent of about 60 per same gas is tested by the three methods given above, the cent a t 500” C. and about 90 per cent a t 600” C. readings for the first are much higher, 58.92 per cent, as The German experiments. were made with burning oil, against 36.72 for the acetone method and 36.68 for the aniline burning benzene, and burning carbide, in the presence of method. iron, and were carried out in a tunnel constructed for the This review of the available literature, to which may be purpose with controlled air supply and movement ( 2 ) . added statements in accepted textbooks, such as those of Later, burning wood, journal waste (boxes), cables, etc., Henderson and Haggard (11)and Flury and Zernik (8), show were used. The phosgene content of the air proved to be as that carbon tetrachloride and other chlorinated hydrocarbons follows: decompose under the influence of heat, and especially in the presence of metals and of moisture, with the formation of Oil: 3 liters with 7 kg. of iron yielded from less than 5 mg. per dangerous gases of which phosgene is the most important; cubic meter to 15 mg. Benzene: 4 liters with 7 kg. of iron yielded from less than 5 mg. and that, while the danger is usually negligible in connection to 19 mg. with the use of fire extinguishers of this type, there are Carbide: 0.5 to 1.5 kg. with 7 kg. of iron yielded from less than circumstances under which serious effects may be produced5 mg. t o 178.8 mg. for instance, an unusually prolonged stay in a poorly ventiIn the absence of iron no measurable amount of phosgene was lated space where such a liquid has been used. As to the actual occurrence of cases of phosgene poisoning produced by burning carbide. The report also calls attention to the fact that, with a from the use of fire extinguishers of this type, the information greater fire area and the use of too much liquid, the situation is scanty. Cases are often mentioned, but not in detail, nor would be different. If the fire is extinguished with diffi- is the source of information given. Most authors, American culty-for instance, a carbide fire-the air may become much and foreign, refer to the Portsmouth submarine cases, which contaminated with the extinguishing liquid, and will vaporize were apparently the first to be reported and have remained through the flame, with the formation of phosgene. The the most c~nspicuous.~ Lehmann (IS),in an article dealing with the practical asabove results were taken after a comparatively short burning time, 0.5 t o 1 minute; practically, one should reckon, in the pect of the question, doubts whether even the Portsmouth case of fires underground, with a burning time of a t least 3 to cases were caused by phosgene alone, and he has been unable to discover more than some sixteen instances of accidental 5 minutes. The summary of the findings shows that the vapors formed injury of this sort (none of them serious) although such in extinguishing difficult fires in mines with carbon tetra- extinguishers have been used in large numbers for years. He chloride may contain relatively high concentrations of phos- believes, therefore, that the danger has been much exaggergene. Examples of this are fires in piled up pieces of cable, ated. It is undeniable, he mites, that phosgene may be carbide fires, and wood fires. Higher concentrations are formed by the contact of carbon tetrachloride with glowing favored on the one hand if the carbon tetrachloride comes in coals, metals, flames, etc., but the hydrochloric acid which contact with highly heated metals, on the other hand, when also forms acts as a warning, causing enough irritation to force the fire must be fought with large amounts of liquid ex- the man to escape, and phosgene poisoning can occur only tinguisher, and also when a fire, thought to be extinguished if the stay in the poisoned atmosphere is prolonged. He with “tetra,” blazes up again with the influx of fresh air. would instruct the user of such an extinguisher to hold his These are, in general, the fires in which the use of “tetra” 8 I have never been able to verify the statement, quoted in my book (IO), extinguishers should be avoided. Similar fires occurring in of an industrial insurance man to the effect that six death8 had occurred from the open aboveground gave too little phosgene to endanger the use of this form of fire extinguisher.
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May, 1933
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INDUSTRIAL AND ENGINEERING CHEMISTRY
SUMMARY
breath till he can get out, to use it only on beginning fires which can be extinguished so quickly (0.5 to 1 minute) that he need not breathe while doing it, and not to use carbon tetrachloride on fires in narrow spaces where escape cannot be made quickly. Negative evidence as to the occurrence of occupational poisoning is of little value in this country, but it certainly is significant that no cases of phosgene poisoning from this source have been reported by German factory inspectors. (One fatality attributed to phosgene was caused by the thermal decomposition of trichloroethylene, 1923-24.) Flury and Zernik say that in addition to the Portsmouth accident there have been some accidents involving German firemen, but they give no detail^.^ . On the other hand, the French have lately been emphasizing the danger of carbon tetrachloride as an industrial poison and of phosgene gas formation from its decomposition when used as a fire extinguisher. The Paris correspondent of the Journal of the American Medical Association (3) states that the latter use of carbon tetrachloride has given rise to the most serious accidents, “several examples of which have been reported recently in various parts of France.” The only case histories given are those of two men (reported by Mollaret of Grenoble) who used a rather large quantity of carbon tetrachloride extinguisher on a fire caused by a short circuit in a poorly ventilated room. The description of their symptoms, nausea, gastric disturbances, jaundice, prostration, is suggestive of carbon tetrachloride rather than of phosgene. At a recent meeting of the Medical Society of Paris (4) the subject was discussed, various cases reported, and the organization resolved to demand the inclusion of carbon tetrachloride among the dangerous poisons.
Foreign experiments have borne out the findings of the Bureau of Mines with regard to the formation of phosgene and other toxic gases in the decomposition of carbon tetrachloride byheat, and, while the number of cases of actual injury reported from this source seems t o be very small, the conclusion to be drawn from the literature is that fire extinguishers of the carbon tetrachloride type should not be used in inclosures where the ventilation is not sufficient to dilute the products of thermal decomposition below the danger point, especially if quick escape from the place is not assured.
LITERATURE CITED (1) Anonymous, Jahresbericht chem-tech. Reichsanstalt, 5, 11-20 (1926). (2) Ibid., 6,57-63 (1927). (3) Anonymous, J . Am. Med. Assoc., 98, 2299 (1932). (4) Ibid., 99, 1276 (1932). (5) Biesalski, E., 2. angew. Chem., 37, 314-17 (1924). (6) Fieldner and Kats, Bur. Mines, Rcpt. Investigations 2262 (1921).
(7) Fieldner, Katz, Kinney, and Longfellow, J . Franklin Inst., 190, 543 (1920). (8) Flury, F., and Zernik, F., “Schiidliche Gase, DRmpfe, Nebel, Rauch- und Staubarten,” pp. 222, 502, Springer, 1931. (9) Fohlen, J., Tech. moderne, 14, 593-6 (1922). (10) Hamilton, Alice, “Industrial Poisons in the U. S.,”hlacmillan, 1925. (11) Henderson, Yandell, and Haggard, H. TV., “Noxious Gases,” Chemical Catalog, 1927. (12) Katz, Gleim, and Bloomfield, Bur. Mines, Rept. Investigations 2499 (1923). (13) Lehmann, K. B., Zentr. Gewerbehyg. Unfallverhiit., 17, 123-33 (1930). (14) Kuckolls, H. H., Quart. Xatl. Fire Protect. Assoc., 14 (3), 221-36 (1921). (15) Olsen, J. G., Ferguson, G . E., Sabetta, V. J., and Soheflan, L., IXD. EXG.CHEY.,Anal. Ed., 3, 189-91 (1931).
4 Neitzel [Geaundh. Ing., 51, 561 (1928)l writes of a n accident t o six firemen in Westphalia, who mere overcome by the fumes of carbon tetrachloride extinguishers, lost consciou~ness,and later complained of irritation of the upper air paasages a n d of inflamed eyes: however, Neitzel thinks t h a t phosgene was not the causative agent, b u t rather vapors of carbon tetrachloride with hydrochloric acid a n d chlorine.
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(16) Stahl, R., Zentr. Gewerbehyg. Unfallsverhiit., [N.S.1, 5, 78-80 (1928). (17)
Wirth, F., Chem.-Ztg., 49, 615-17 (1925).
RECEIVED January 19, 1933. e
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Discussion of “Formation of Phosgene in Thermal Decomposition of Carbon Tetrachloride” J. C. OLSEN,~The Polytechnic Institute of Brooklyn, Brooklyn, N. Y.
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T MAY not be clear to the reader of A. Hamilton’s article in what respect her book “Industrial Poisons in the United States” was termed “misleading and inaccurate’’ in the complaint which she cites, or t o what she has reference when she explains that “the information given (in the book) covered all that was available in 1924.” The following paragraph from the letter making the complaint to which she refers may serve to make this point clear: On page 444,Dr. Hamilton alleges that “according to an industrial insurance man, six deaths are known to have occurred recently from the use of this form of fire extinguisher.*** We have tried t o ascertain the source of Dr. Hamilton’s information but she has failed to give these data. In this connection it is interesting to note that one of our number alone, who has the summation readily available, has itself sold some 5,770,000 charged extinguishers and some 7,500,000 refills of liquid therefor over the period from 1910 t o 1930. No one of our companies has ever received any evidence whatsoever of a single fatality due t o the use of an extinguisher of the carbon tetrachloride type. Hamilton has stated in her article: “I have never been able to verify the statement, quoted in m y book (IO) of a n 1 Technical representative of the Vaporizing Liquid Division, Chemical Fire Extinguisher Association.
industrial insurance man t o the effect that six deaths had occurred from the use of this form of fire extinguisher.” This statement has the effect of removing from the literature this error which is of a type that occurs too often. Another pertinent paragraph from the letter making the complaint, t o which Hamilton refers, is as follows: In speaking of t? Portsmouth incident also on page 443, Dr. Hamilton states: *** the other threw Pyrene (sic) fire extinguisher over the clothing to put it out. Both men were overcome by the fumes so that they could not save themselves ***.” The innuendo and inference that the fumes which overcame these men were those of Pyrene we most definitely deny. It is well known that peo le are often overcome by smoke and fumes from fires, and deatxs from this cause are not infrequent. Hamilton has clarified and amplified this statement by saying that she first explained the death of the two men concerned as caused by inhalation of carbon tetrachloride vapor, whereas later she became convinced that death was caused by phosgene poisoning. As the physiological action of these compounds is quite different, it is obvious that no scientific medical basis existed for either of these diagnoses. Hamilton gives no evidence that phosgene is produced by spraying
