User Guide to Thresholds and Classification - Environmental ...

167User Guide for Thresholds and ClassificationsGenerally, however, the propellant should not be taken into account when classifying aerosols, as thegaseous propellant will not be present in the liquid that comes into contact with the skin.11.3.3. Classification of mixtures when data are available for all or some components of themixtureTo make use of all available data for when classifying the skin corrosion or irritation hazards of mixtures, thefollowing assumption has been made and is applied where appropriate in the tiered approach.The ‗relevant ingredients‘ of a mixture are those that are present in concentrations (including impurities andadditives) of 1% (by weight for solids, liquids, dusts, mists, and vapours, and by volume for gases) or greater,unless there is a presumption (for example, in the case of corrosive ingredients) that an ingredient present ata concentration of less than 1% can still be relevant for classifying the mixture for skin corrosion or irritation.In general, the approach to classifying mixtures as corrosive or irritant to skin when data are available on thecomponents, but not on the mixture as a whole, is based on the theory of additivity. In additivity, for subclass6.3 (8.2), each corrosive or irritant component contributes to the overall corrosive or irritant properties of themixture in proportion to its potency and concentration. A weighting factor of 10 is used for corrosivecomponents when they are present at a concentration below the generic concentration limit for classificationwith an 8.2 classification, but are at a concentration that will contribute to the classification of the mixture asan irritant. The mixture is classified as corrosive or irritant when the sum of the concentrations of suchcomponents exceeds a concentration limit.Table 11.2 provides the generic concentration limits to be used to determine if the mixture is considered tobe an irritant or a corrosive to the skin.Particular care must be taken when classifying certain types of chemicals such as acids, bases, inorganicsalts, aldehydes, phenols, and surfactants. Many of these substances are corrosive or irritant atconcentrations < 1%. For mixtures containing strong acids or bases, the pH should be used as classificationcriteria since pH will be a better indicator of corrosion than will the concentration limits in Table 11.2. Amixture containing corrosive or irritant ingredients that cannot be classified based on the additivity approach,because chemical characteristics make this approach unworkable, should be classified as 8.2A, 8.2B, or8.2C if the mixture contains 1% of a corrosive ingredient(s) or as 6.3A or 6.3B if the mixture contains 3%of an irritant ingredient(s). Table 11.3 outlines the approach for substances where additivity does not work.On occasion, reliable data may show that the skin corrosion or irritation hazard of an ingredient will not beevident when present at a level above the generic concentration limits mentioned in Table 11.2 and Table11.3. In these cases, the mixture is classified according to that data. On occasion, when it is expected thatthe skin corrosion or irritation of an ingredient is not evident when present at a level above the genericconcentration limits mentioned in Table 11.2 and Table 11.3, testing of the mixture may be considered. Inthose cases the tiered weight-of-evidence strategy should be applied, as described in section 11.3.3 andillustrated in Table 11.1.January 2012 EPA0109