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Carbonyl sulphide in fire gases
Ser
TH1
IN21d
Ino.
886
2% ' -- - -National Research
Conseil national
,
Council Canada
de recherches Canada
CARBONYL SULPHIDE IN FIRE GASES
by Yoshio Tsuchiya and
J.G.
BoulangerReprinted from Fire and Materials
Vol. 3,
No.
3, September 1979p. 154 155
DBR Paper No. 886
Division of Building Research
SOMMAIRE
Les gaz toxiques produits par la combustion ou la pyrolyse de la laine comprennent du CO, du HCN et quatre composds contenant du soufre. Des essais sur animaux laissent supposer que la toxicit6 des compos6s du soufre est importante. Les auteurs pyrolysent de la la'ine et analysent les gaz par chromatographie en phase gaseuse et par spectrom6trie de
masse (CGISM). Le SO est le principal gaz contenant du soufre produit
par la combustion 1 ?a £1-e en atmosphsre enrichie dloxygSne. Dans
diff6rentes conditions de pyrolyse, le COS est un produit majeur cont-
enant du soufre. Msme si le COS est un gaz tres toxique, il n'a pas
encore fait l'objet de rapports par lea chercheurs oeuvrant dans le
domaine de la toxicit6 des gaz d'incendie. Les auteurs recommandent
que le COS soit inclus dans la toxicologie analytique des polym2res
Carbonyl Sulphide in Fire Gases
Yoshio Tsuchiya and J. G. Boulanger
Fire Research Section, Division of Building Research, National Research Council of Canada, Ottawa, Canada KIA OR6
The toxic gases released by combustion/pyrolysis of wool include CO, HCN and four compounds containing sulphur. Animal test data suggest that the toxicity of the sulphur compounds is significant. Wool was pyrolysed and the gases were analysed by GC-MS. SO2 was the main sulphur-containing gas produced by flaming combustion in an oxygen-enriched atmosphere. In pyrolysis under various conditions COS was a major sulphur-containing product. Although it is a highly toxic gas, COS has not so far been reported by workers engaged in the toxicity of 6re gases. It is suggested that analysis of COS be included in the analytical toxicology of sulphur-containing polymers.
INTRODUCTION
Combustion and pyrolysis gases from wool have proved to be very toxic in animal tests.l* 2 Both wool and nylon have similar chemical composition and at high tem- peratures3 produce highly toxic hydrogen cyanide (HCN) and carbon monoxide (CO). Wool, however, was found to be the more toxic of the two.2 The main reason for this difference may be the presence of sulphur in wool. Yamamoto has compared the toxicity of combustion products of polyacrylonitrile, silk and wool, using animal tests.4 COHb values in the blood of dead animals were almost the same for the three fibres, but blood cyanide for wool was much lower than that for the others. This suggests that sulphur in wool has a significant toxic effect.
Both hydrogen sulphide (H2S) and sulphur dioxide (SO$ are known to be major toxic gases from the combustion of sulphur-containing polymers. In fact, 4 in the study of environmental pollution caused by the ' combustion of sulphur-containing fossil fuels, HzS, I SOz, carbon disulphide (CSz) and carbonyl sulphide (COS) were the major toxic sulphur compounds.5 They are probably present in the combustion gases of sulphur-containing polymers. In the present study, sulphur-containing gases in the combustion gases of wool are determined, and attention is focused on COS, which has not been mentioned previously in reports of fire gas toxicity.
EXPERIMENTAL
1
A specimen of wool fibre was burned or pyrolysed under various conditions. For flaming combustion it was ignited in a limiting oxygen index tester under a flow of a mixture of 35% oxygen and 65% nitrogen. It was also pyrolysed in a heated quartz tube at a tem- perature of 600 or 800 "C under a flow of air or nitrogen. In these conditions wool flashed for only 1 or 2 s or did not flame at all. In both experiments combustion/
pyrolysis gases were collected in a plastic bag for analysis.
A Finnigan Model 3100D GC-MS (gas chromato- graph-mass spectrometer) equipped with Model 6100 Data System was used for the gas analysis. GC separa- tion was performed at 100 "C isothermal condition, using a + i n (6.3 mm) o.d., 6 ft (2 m) long glass column packed with Chromosorb 104. The sulphur compounds were not completely separated by 'total ion chromato- graphy' at this condition. 'Single ion chromatography' of mass number 76, 64, 60 and 34, however, clearly separated all the sulphur compounds. This analysis is semi-quantitative because the quantities of gas were simply assumed to be proportional to the areas under each peak. For separate determination of the combined amount of COS and HzS, gases were scrubbed with 200 ml of 0.1 N NaOH solution and the concentration of sulphide ions was determined with a sulphide ion electrode.
RESULTS A N D DISCUSSION
Among the four sulphur compounds analysed, SO2 is the most oxidized, COS is intermediate, and H2S and CS2 are the least oxidized. At higher temperatures and with more available oxygen, more SO2 is expected. In the present experiments SO2 was the only major product in flaming combustion in an oxygen-enriched atmosphere. In pyrolysis conditions there was HzS, CS2 and COS, but no SO2; of the three present, COS was always the highest in quantity. Table 1 lists the quantities of the four gases produced at four different conditions. Organic sulphur compounds such as mer- captans and alkylsulphides were searched at the appro- priate mass numbers, but only methyl mercaptan was detected in a small quantity when wool was pyrolysed in Nz. They were not found in an environmental pollution study. 5
COS is soluble in an alkaline solution and produces sulphide in the following reactions, which are complete
CCC-0308-0501/79/0003-0154 $01.00
CARBONYL SULPHIDE IN FIRE GASES
Table 1. Quantities of sulphur-containing gases from the pyrolysis/combustion of wool (products mg g-l of wool)
H2S C2S COS SO2
800 "C, under Nz flow 3 . 7 0 . 9 3 . 9 0
800 "C, under air flow 4 . 4 1 . 8 4 . 9 0
600 "C, under air flow 2 . 5 1 . 0 8.4 0
Flaming in 02-enriched atmosphere 0 0.09 0.08 14.8
in a few minutes?
Thus, COS and HzS are determined together. In the present experiments the highest combined amount of COS and H2S that could be determined was 1 mg-mol per gram of wool in pyrolysis at 600 "C under a flow of Nz. This means that most of the sulphur is converted to these gases, and does not remain in the residue, because the sulphur content of wool is known to be
2.5-5
%
by weight.There are several kinds of sulphur-containing polymers
phase and the toxicity of sulphur-containing gases such as COS could be significant in fires.
Toxicity data for COS in the literature are as follows. One textbook states that COS has been found to be
more poisonous than H z S , ~ another that toxicity of
H2S is comparable to that of HCN.8 Data on the acute inhalation toxicity of COS in animals6 are as follows, listing kind of animal, concentration of COS in the atmosphere, and time for a lethal effect: mice, 2900 ppm, 1.5 min; mice, 1200ppm, 35 min; rats, 20000 ppm, 45 min; rabbits, 3200 ppm, 35 min. The limiting long-term averaged concentration recommended for protection against adverse health effects is 0.15 ppm for CoS.6
CONCLUSION
The authors suggest that carbonyl sulphide be included in future studies in the analytical toxicology of the combustion products of sulphur-containing polymers.
A quantity of carbonyl sulphide was produced in the
pyrolysis of wool, and this compound has not so far been mentioned in studies of fire gas toxicity.
with sulphur contents ranging from 5
%
to 80%: vul- ~ ~ ~ ~ ~ ~ 1 ~ d ~ ~ , , , ~ ~ ~canired and 'ynthetic rubbers, P ~ ~ YThis paper ~ is a ~contribution ~ from P the Division ~ ~ of Building Re- ~ ~ ~
and polysulphide Unless there is provision search, National Research Council of Canada, and is published
to fix sulphur in the solid phase, it goes into the gas with the approval of the Director of the Division.
REFERENCES
1. F. Saito, J. Assoc. Fire Sci. Eng. 23, 25 (1973) [in Japanese]. 2. C. J. Hilado and C. R. Crane, J. Combust. Toxicol. 4, 56
(1 977).
3. Y. Tsuchiya, J. Combust. Toxicol. 4, 271 (1 977).
4. K. Yarnamoto and Y. Yamamoto, Z. Rechtsmed. 81, 173 (1 978).
5. Y. Hosika, I. Koyima, K. Koike and K. Yoshiomoto, Bunseki Kagaku 23,1393 (1974) [in Japanese].
6. T. 0. Peyton, R. V. Steele and W. R. Mabey, Carbon Disulfide, Carbonyl Sulfide: Literature Review and Environmental
Assessment. NTlS PB-257947. National Technical Inforrna- tion Service, Springfield, Virginia (January 1976).
7. M. Shrnidt and W. Siebert, in Comprehensive Inorganic Chemistry, ed by A. F. Trotman-Dickenson, Vol. 2, p. 825. Pergamon, Oxford (1 973).
8. N. A. Lange, Handbook of Chemistry, 10th Edn., p. 1755. McGraw-Hill, New York (1961).
Received 15 May 1979
0 Heyden 8 Son Ltd, 1979
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