August i, 1901.] 



THE INDIA RUBBER 'JVORLD 



323 



EXPLOSIONS OF VOLATILE VAPORS IN FACTORIES. 



By H. L. Terry, F. I. C. 



THERE was recently a serious explosion at the hat fac- 

 tory of Messrs. Wilson & Sons, at Denton, near Man- 

 chester, whereby fourteen persons were killed. Al- 

 though discussion of affairs relating particularly to the 

 hat trade does not come within the purview of this journal, 

 yet there was so much identity between this catastrophe and 

 others which have happened, and may not improbably happen 

 again in India-rubber works, that I feel that it is not superflu- 

 ous to say a few words on some of the salient points investi- 

 gated at the inquest. The explosion occurred in the drying 

 stove, where the hats, after being dipped in a solution of shellac 

 in methylated spirit, were placed in order that the vapor might 

 be evaporated. This operation is one that is common to the 

 trade, and although some slight explosions have been recorded, 

 nothing at all serious seems to have happened to demonstrate 

 to the manufacturers the latent possibilities of disaster. In gen- 

 eral the alcoholic vapors have been allowed to escape, through 

 ventilators, into the atmosphere, but now in several works both 

 in England and the United States are to be found recovery in- 

 stallations, the vapors being condensed for use over again. 

 That the recovery process when in operation lessens any risk 

 of explosion, the evidence which has been given by a hat manu- 

 facturer of America who has several of these recovery plants in 

 operation tends strongly to show, but unfortunately in the 

 case of the recent explosion, which happened on a Monday fore- 

 noon, the recovery plant was not working, a fact which un- 

 doubtedly formed a prominent factor in the situation. 



The case was thoroughly investigated by the chief inspector 

 of explosives to the Home office, and as there were several 

 points in his evidence at the inquest which are of technical in- 

 terest, I shall proceed to touch on some of them. Commencing 

 with a generality I quote his statement that the full extent of 

 the danger in these stoves did not appear to have been realized 

 by the majority of hat makers. This is no doubt true. Probably 

 the majority of hat makers know little or nothing about the 

 laws of chemical combination that operate when certain pro- 

 portions of oxygen or air and of volatile vapors come mto contact 

 with a flame. The reference need not be limited to hat manu- 

 facturers as far as ignorance of such scientific detail goes. It may 

 fitly be extended to many trades where volatile vapors are used 

 in some form or other. In addition to the rubber manufacturer 

 with his naphtha and carbon bisulphide, there is the dry cleaner 

 who uses benzoline instead of soap, and there are many concerns 

 where volatile solvents are used as extractive media. 



Now it goes without saying that practically all from the mas- 

 ter to the humblest employe know that such solvents will take 

 fire if brought into contact with a light, but in many cases this 

 represents the sum total of their knowledge ; the fact that a 

 material may take fire and burn quietly when one set of con- 

 ditions prevail and that the same material may explode with 

 disastrous consequences when the conditions are altered, may 

 be but to only a alight extent, is not one that has impressed itself 

 at all generally upon the minds of those who hold positions of 

 authority in works where such dangerous elements are found. 

 Take any of these volatile solvents, naphtha, carbon bisulphide, 

 methylated spirit, etc., and set fire to a small quantity either in 

 the open or in a vessel filled with them and communicating 

 with the air by means of a tube and what happens : a flame is 

 produced and burns quietly. Suppose, however, we alter the 



conditions and shake up a small quantity of the liquid in a ves- 

 sel with a definite quantity of air ; on firing it either by a flame 

 or by electric spark we get a violent explosion. The latent en- 

 ergy that vapors possess and which reveals itself under the con- 

 dition just named is not sufficiently widely known, and I think 

 that the government inspectors would be doing useful service 

 if they issued information of the sort to the various factories 

 where volatile solvents are used. 



In two fatal explosions which have occurred in the dry clean- 

 ing process, the evidence went as in the present case to show a 

 lamentable lack of knowledge on the part of the principals as 

 to the potency of the agents they employed, and it certainly 

 seems desirable that the workmen should not be exposed to 

 risks by reason of the failure of their employers to recognize the 

 possibilities of disaster. The inspector said that from the vio- 

 lence of the explosion it was evident that the theoretical mix- 

 ture of air and alcoholic vapor must have been present, and 

 this proportion, he went on to say, was one of vapor to twelve 

 of air. Later on he says in his evidence, when discussing the 

 details, that there was several times as much spirit as would 

 be required to form the most explosive mixture. Now, I have 

 had no acquaintance with the explosion of alcoholic vapors, 

 but I cannot quite reconcile these statements to theory. To get 

 explosion or instantaneous combustion in a limited area, the 

 theoretical proportions of air and vapor are necessary ; if one 

 or the other is in excess, the explosion is either very feeble or 

 does not occur at all. I know in the experiments which 1 have 

 made with carbon bisulphide and naphtha that an excess of air 

 or of vapor prevents the explosion, and the remark quoted 

 above, that the alcoholic vapor was in excess, does not har- 

 monize with the facts of the explosion. Of course, the excess 

 in this case may only have been to such an extent as to modify 

 without preventing the explosion, though this supposition 

 hardly coincides with the statement as to the atmosphere of 

 greatest explosibility being present. The necessary conditions 

 for an explosion are : (i) The proper amount of air ; (2) due 

 admixture of this air with the vapor; (3) a sufliciently high 

 temperature to set fire to it. Perhaps the best example of this 

 is to be seen in cases of colliery explosions of marsh gas or fire 

 damp, and at the risk of boring my readers by going too much 

 into detail, I append the combustion equation of such an ex- 

 plosion : 



CH4 + 2(0,)-i-8(No)=Co,-f-2(H,o) + 8(N,). 



Here we see that complete combustion takes place, the pro- 

 portion of fire damp and air by weight being i in 20, and by 

 volume I in 10, which is the most explosive mixture. To pur- 

 sue the subject further on scientific lines would require much 

 more space than the present occasion affords, and it might, 

 moreover, not prove of general interest. That it is of impor- 

 tance will, however, I think, be generally conceded, and the 

 three conditions mentioned above should be duly noted. Re- 

 ferring for a moment to No. 3, the temperature of ignition will 

 be found to vary within wide limits in the case of different 

 vapors. For instance, marsh gas requires a flame or electric 

 spark, and so does alcoholic vapor, while carbon bisulphide va- 

 por, on the other hand, will ignite by a hot — not by any means 

 a red hot — piece of iron. The temperature required in the hat 

 explosion is stated to be 1200° C, and therefore a light must 

 have come into contact with the vapor, though by what agency 



