AEROSOL PROPELLANTS 409

410 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS (iii) In all cases where phosgene was produced, appreciably greater concentrations of the acidic gases were formed, confirming that these would have given adequate warning. All the compounds tested have been used in aerosols and in most cases the quantities involved could conceivably be discharged from standard aerosol containers in the home. Under certain circumstances toxic products are undoubtedly produced with all the compounds, but consideration of (i)-(iii) above, and the fact that deliberately unfavourable conditions were created, suggests that this would not constitute a hazard to health. CHLOROCARBON PROPELLANTS Methylene Chloride (CH2Cl2) Methylene chloride is a non-flammable liquid boiling at 40.2øC. It is one of the least toxic of the chlorinated solvents (MAC=500 ppm v/v, Underwriters Laboratories Group 4-5). Although it has an anaesthetic effect if breathed at high concentrations, the quantities involved in aerosols do not constitute a real user hazard in this respect. It is used in aerosols in its own right as a so!vent, to depress the flam- mability of other solvents, as a co-solvent to increase the solubility of some ingredients in propellants and as a cheaper substitute for part of the pro- pellant 11 in 12/11 mixtures. As a pressure depressant for propellant 12 its effect is very similar to that of propellant 11. It has, however, a number of technical disadvantages which limit its use in aerosols. It hydrolyses more readily than propel!ant 11 which can increase corrosion problems. It has a more defined smell and this, coupled with the higher hydrolysis rate, can seriously affect fragrances and perfumes used in aerosols. It has a marked solvent and swelling effect on elastomers 5, and resistant materials must be used in valves, etc. Its strong solvent action also occasions caution when used in household aerosols we have found that the misuse of an aerosol containing more than 15% methylene chloride, by applying from a short distance, can damage synthetic fibres such as acetate and triacetate rayons. Although these disadvantages limit its range of applications and the proportion which may be used, methylene chloride has already established itself as a valuable raw material in the aerosol industry. 1.1.1-Trichloroethane (CCl•. CH•) Stabilised grades of this non-flammable solvent are sold under the trade names "Genklene" (ICI) and "Chlorothene" NU (Dow). 1.1.1-trichloroethane has a similar low toxicity to that of methylene chloride (MAC =500 ppm, v/v) but its higher boiling point (ca.76øC) makes it a rather safer solvent for cold cleaning. It is believed, in general, to have less effect on the elastomers