COSMETIC PRESERVATIVES 309 LITERATURVERZEICHNIS 1) Rehn, D., D. Groenewegen u. D. Schenckenberg, J. Soc. Cosmet. Chem., im Druck 2) Siebert, C., Parr. u. Kosm. 60, 7, 239--244 (1979) 3) Fa. Zschimmer & Schwarz, Rahmenrezepturen 4) Wallh•iut•er, K.H., in Sterilisation -- Desinfektion -- Konservierung, S. 385, Georg Thieme- Verlag, Stuttgart (1978) 5) Nowak, C. A., Parr. u. Kosm. 60, 1, 8--19 (1979)

j. Soc. Cosmet. Chem., 31,311-321 (November 1980) Electrostatic charge on aerosol cans R. P. WILLIAMS, R. E. REUSSER, and C. R. BRESSON, Phillips Petroleum Company, Research and Development, Bartlesville, OK 74004 Received February 19, 1980. Synopsis The potential ability of an electrostatic charge on an aerosol can to ignite a flammable gas mixture is discussed in terms of electrical capacitor relationships. Energy of the charge determines the INCENDIARY POTENTIAL of the spark and is given by E = Q2/2C, where Q is the coulombic charge and C is the electrical capacitance of the can. To calculate the maximum potential spark energy the significant parameters to measure are: I) the coulombic charge on the can and 2) the minimum capacitance at which the can may discharge. Four CHARGE-MEASURING METHODS under industry study are reviewed with a preference expressed for direct measurement with a coulombmeter. Results of charge measurements on cans of various aerosol products and the minimum capacitance values determined experimentally for several sizes of cans are given. I. INTRODUCTION Electrostatic charging of aerosol cans by release of the contents is not a newly discovered phenomenon, but it has taken on added significance since the 1978-1979 change from fluorochlorocarbon to hydrocarbon propellants in aerosol products. Additionally, the propellant change has focused attention on an industry need for a standard method of measuring the static electrification of aerosol cans. As illustrated in Figure 1, a positive (or negative) charge often develops on a can as a result of releasing all or part of its contents by normal spray operation or from puncture by a mechanical malfunction on an aerosol filling line. Some dry powder-containing products impart relatively large charges to the cans with enough energy to enable a spark discharge to potentially ignite a flammable atmosphere. On the other hand, the electrostatic charge produced by the release of non-powder-containing products is much lower and does not usually reach potentially incendiary energy levels. Fortunately, the likelihood of an ignition is greatest in the case of electrically isolated charged cans which is a condition that does not frequently occur. Chances for ignition are remote during normal use in hand-held spraying since distribution of the charge over the body capacitance 1oivers the energy corresponding- ly. A new investigator in the field of incendiary electrical sparks is confronted by a 311