If data for a mixture are not available, use bridging principles in paragraphs 19-24. If bridging principals do not apply, classify as Category 1 if: for substances with additivity - the sum of the concentrations of substances classified as corrosive to the skin and/or eye Category 1 substances in the mixture is > 3%; or if the sum is > 1%, for substances to which additivity does not apply (See paragraph 28).