500 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS packs of simi!ar types. Rather, they compare flame extension of Arcton propelled packs containing a highly flammable matehal with those of butane- propelled packs containing water. THE LF. CTURER: On a point of detail in 3gr. Phillips' question: I have not used 100/120 petrol with butane and water. This was used with Arcton- 11/12 mixture, and the butane/water mixture formed a separate series of tests. However, his first point is similar to that of 3gr. Dyson and serves to demonstrate the importance of correct formu!ation. It also demonstrates the importance of correct testing. I believe that with the mixture containing 70% butane and 30% water very rapid settling of the water in the emulsion has occurred in spite of shaking the dispenser, and most of the water was used up early in the life of the dispenser. This point should have been made explicitly in the text. 3gr. Dyson's emulsions were, no doubt, more stable than those described. I believe that this also covers 3gr. Phillips' second question. I do not think that any great significance should be attached to the cross- ing of the curves relating to the butane packs. It is difficult to measure the flame length with accuracy, and I suspect that all are in fact converging to the same asymptote. I cannot agree with 3gr. Dyson's comment on the caption of Figure 2. This shows flame extensions found with two series of packs containing the same ratios of flammable and non-flammable materials. In one instance, they are Arcton and petroleum ether in the other they are water and butane. It is quite true that some of these mixtures are unlikely to be of any great commercial interest, and this applied equally to both types insofar as I am aware. If taken to the extreme one might say "because a pack contains Arcton it must be safe" and "because a pack contains butane it must be dangerous". Either of these bald statements is untenable, one no more so than the other. The fallacy is, I think, in the tacit assumpt/on that there is some magic difference between propellants and solvents, or other ingredients. I strongly suggest that the only difference between the two classes lies in their vapour pressure, and that even here the dividing line is not well defined. This takes us to 3gr. Phillips' final question. I consider it not only legitimate, but essential, to consider hydrocarbon gases together with all the other ingredients present, not only those with flammable yapours, and that the behaviour of the complete pack should be considered as a whole. MR. A. HERZI•A: Would someone care to comment on the remarks made in the paper that "leakage from pressurized packs presents no greater hazard than from other common household articles"? Gr. F. PHILLIPS: The lecturer quotes four (presumably U.K.) in-

FLAMMABILITY OF PROPELLANTS 501 cidents involving aerosol containers: Explosions caused by steam, or ex- posure to sunlight, inversion of the base by direct heating, side-seam failure by solar heat. He refers briefly to other explosions in hotter climates. He knows of no fires primarily due to domestic use of aerosol dispensers. I find it hard to believe that there can have been only four such incidents, and •)ne concludes that the majority of incidents have not led to serious con- .sequences. For example, I cotfid supply the lecturer with two more from my private experience. One, an explosion of a veterinary preparation in the storage portion of a pigeon loft left closed over a weekend. This resulted in a considerable mess and frightened the pigeons but caused no fire in a second incident, an aerosol container left in a closed cabinet over a hot Bank Holiday weekend, suffered inversion of the dished base sufficiently violently to .damage adjacently stored glassware. This could have been more dangerous, (tepending on the contents of the other vessels. But even this excellent record does not supply a premise for the lecturer's conclusion. The evidence appears to show that the containers he has con- sidered are satisfactory it does not imply that leakage of the contents would present "no greater hazard than that from other common household articles". One might agree where the most hazardous component present is, say, kerosene but leakage of butane in an unventilated cupboard in which, for example, electrical switches were present, could represent a considerable hazard. It would only require the leakage of 3 oz of butane in a cupboard •)f dimensions 5'x 4'x 3' to furnish an explosive atmosphere (2% v/v). I therefore cannot entirely agree with the lecturer. MR. E. EBE•: Surely the flammability of the cretonne cloth might be influenced by other factors such as the humidity of the air? TI•E LECTURER: While I accept the value of flame temperature as a possible means of indicating hazard associated with flammable material, I feel that the duration of a flame is also of great importance and in the burst/fire tests the tendency has been for, what I suspect to be, the relatively low temperature flame produced by fairly heavy flammable material to be more likely to ignite the curtain, than the possibly higher temperature quick- flash obtained with some volatile materials. MR. E. EBEn: The flash point of the formulation is a very important property. Tests using the Abel-Pensky flash point meter with subcooled (--40øC) contents of aerosols have shown that formulations with flammable propellants have flash points of the order of below -- 40 to --30øC. But the use of fluorinated hydrocarbon propellants raises the flash point beyond room temperature. THE LECTURER: I agree that flash point is important, but its importance