PHYSIOLOGICAL PROPERTIES OF PROPELLANTS 341 PHYSIOLOGICAL PROPERTIES OF PROPELLANTS H. KfJBLER, Dr. rer. nat.* Presented at the $•ymposium on "Aerosols", organised by the Society, at Southport, Lancs., on 2$th April The properties, MAC an(l LD 50 values of the various propellants, all of which belong to t•e less toxic Groups 5-6, are referred Inhalation tests indicate that up to 5% by volume of propellants 11, 12, 113, 114 and vinyl chloride is tolerate(l. The quantity of halogenate(l acids formed (luring t•e t•ermal (lecomposition of the propellants between 100øC an(l 1000øC is so great, that their irritation prevents the inhalation of carbon monoxi(le an(l phosgene. The results obtaine(l by various workers confirm the absence of skin irrita•on. T•ZRF. ZXIST about forty chemical compounds which are in a gaseous state at room temperature, and which can easily be liquefied. From these, the propellants for aerosol packs are chosen, and the essential features are vapour pressure, boiling point, solubility, chemical resistance, flammability and low toxicity. Only a few of the gases fulfil the greater part of these requirements. The most important property of a propellant is the low order of toxicity, especially bv inhalation. Only a few substances can be tolerated by human individuals in any quantity, whereas other substances which are of decisive importance for metabolism, have a pronounced toxic action in higher concentrations. For instance, carbon dioxide can cause weakness or even suffocation of humans. We must therefore determine the toxic threshold or the concentration at which injuries to health occur. The only gases suitable as propellants are those where this concentration is far below the amount likely to be used in the most extreme circumstances. Complete non-toxicity in any con- centration cannot be demanded for this purpose. The MAC-value characterises the compatibility of a substance, while the LD 50 limit indicates the toxicity. These values differ in so far that by exceeding the MAC-value one does not necessarily cause any harmful effects, but a substance can be lethal even before the LD 50 value is reached. One must differentiate between the toxicity due to the differing intake of a substance, i.e., by mouth, subcutaneous, percutaneous, intravenous, and *Spriihtechnik GmbH, Rheinfelden/Baden, Germany.

342 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS by inhalation. In practice only inhalation tests can be performed with gaseous substances. The concentration, by volume, of the gas in the atmosphere which after a definite inhalation period has a lethal effect or causes injuries to health, takes the place of the LD 50 value. A very high propellant concentration could be harmful, because it results in a reduction of the oxygen content of the atmosphere. The so-called "interference level" is of the order of about 12.5 volume % oxygen. We do not know such a case it cannot occur during shipment or during the storage of pressurized dispensers, but it could happen due to a sudden leakage from large propellant cylinders, or during cleaning of the latter. Undoubtedly, the MAC-value does not give a definite indication for the physiological suitability of a gas, but the propellants commonly used have an identical value of at least 500 ppm. While the MAC-value indicates the concentration by volume (cc), which is tolerated in 1 m 3 of air daily for inhalation in 8 hours, e.g., in a filling plant, an individual is exposed only temporarily to a certain concentration of vapour while a pressure pack is used. As a result, the use of a solvent with a MAC-value below 500 pprn may be permissible, particularly as there are often very good technical reasons for doing so. In the event that one is faced with two equivalent substances having different MAC-values, one or both of which are below 500 ppm, then one would select the substance with the higher value. Toxicity Groups Group 1: Group 2: Group 3: Group 4: Gases at a concentration in air from 0.5-1.0% by volume have a lethal effect by inhalation after 5 minutes, or cause serious, irreversible damage, e.g., phosgene, sulphur dioxide. Gases at a concentration in air from 0.5-1.0% by volume have a lethal effect by inhalation after 30 minutes or cause serious, irreversible damage, e.g., ammonia, methyl bromide. Gases at a concentration in air of 2-2.5% by volume have a lethal effect by inhalation after 1 hour, or cause serious, irreversible damage, e.g., carbon tetrachloride, chloroform, methyl formate. Gases at a concentration in air of 2-2.5% by volume have a lethal effect by inhalation after 2 hours, or cause serious, irreversible damage, e.g., dichloroethylene, methyl chloride, ethyl bromide.