FLAMMABILITY OF PROPELLANTS 497 COMPARISON WITH OTHER l•ESULTS Kempe • has recently published a paper giving a comparison of flam- mability of chlorofluorohydrocarbons, vinyl chloride and isobutane, with a range of organic solvents and had shown that the addition of flammable solvent to flammable propellants can result in iormulations which give very severe flammabihty risks, and the "blow torch" type of flame. It is interesting to note, however, that in all his examples both the flame extension and the flame temperature relate fairly uniformly to the total amount of flammable material present in the formulation. Thus, for example, in a system consisting of 50/50 Frigen 11/12, isopropyl alcohol, methylene chloride, and isobutane, the volume/volume concentration of Frigen is held constant while the ratio of isopropyl alcohol to methylene chloride in the mixture constituting the remainder of the fill is increased, giving rise to a corresponding increase in flame extension and flame temperature. On replacement of the final mixture (50% v/v Frigen, 50% v/v isopropyl alcohol) with 50 v/v vinyl chloride, 50% v/v methylene chloride, little change occurs in either of the measured quantities, in spite of the fact that methylene chloride, while being virtually nonflammable under normal conditions, has an auto-ignition temperature (1224øF, 662øC) a well below the flame temperature at this stage (approx. 850øC). As Kempe points out, replacement of methylene chloride by isopropyl alcohol (or other flammable material) has relatively little effect on the flame temperature or extension at this stage. Kiibler, in the final article of an interesting series 4'*'6, gives results showing a similar pattern for a range of propellant/solvent systems. Kiibler (loc cit) also gives descriptions of the effects of placing dispensers filled with a range of formulations in a fire, and his findings are in general agreement with our own. (a) (b) CONCLUSIONS It is possible to make aerosol products which are completely non- flammable or intensely flammable, or anywhere in between. While specific materials have widely differing fire promoting or fire suppressing properties, the fire hazard presented by any particular product in the hands of a consumer will depend on the balance achieved between these properties in the complete formulation. It should be noted here that formulation is not necessarily the only feature contributing to the possible fire risk, and that proper selection of other components, such as the valve, may in some instances be especially important. (c) Extensive experience has shown us, and other marketers of pressure

498 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS (d) (e) packs in this country, that packs containing up to 60% or 70% of flammable material are used safely by the general public. The results of our own tests, and those of others, show that butane- propelled packs can be formulated to present certainly no more, and probably less, fire hazard to the consumer than is already widely accepted. The final test on any consumer product is its performance in the hands of the user and judgement of it should be made accordingly. ACKNOWLEDGEMENTS I should like to acknowledge with thanks Mr. R. 3/. Mumford's en- couragement and advice in preparing this paper, and Messrs. D. Hollinshead's and A. Glass' intrepid assistance in carrying out the experiments. (Received: 19th February 1963) REFERENCES Aerosol Guide 11 (1957) (C.S.M.A., New York) Kempe, W. Aerosol Age 8 28 (January 1963) Sax N. I. Dangerous Properties of Industrial Materials 893 (1957) (Reinhold Publishing Corporation, New York) Kfibler, H. Aerosol Age 7 33 (May 1962) Kfibler, H. Aerosol •lge 7 34 (August 1962) Kfibler, H. Aerosol •lge 7 92 (October 1962) Introduction by the lecturer The paper presented relates only to hazards in the users' hands, and not to any that may exist in bulk storage or transport. I do not intend to discuss this aspect, which is one where other considerations may be of importance. My main thesis is that an aerosol pack should be considered as a whole, and that no undue attention should be paid to the inclusion or omission of any particular ingredient as such. If a pack is shown to be safe in use, then there is no point in taking exception to the inclusion of any material that may be dangerous on its own. The risk associated with a product will depend on suitable choice of materials, proper formulation and proper use of the product, as will be illustrated by three accidents which have come to my notice since my paper was written. All concern hair sprays, one pressure packed and the others in squeeze bottles. (1) A pressure pack was used in an American bathroom where both a gas fire and a gas water heater were going. Vapours from the spray were ignited, and the bathroom was quickly involved in flames.