Bridging Principles for Health Hazard Evaluation of Mixtures
(According to OSHA)
In the absence of reliable test data for the whole mixture, the first step in hazard classification of a complex product during SDS writing is looking for available data on similar mixtures and using so called bridging principles as outlined in section A.0.5 of OSHA Appendix A to §1910.1200:
If a known mixture A was diluted with a solvent B of the same or lower toxicity than the least toxic ingredient of the mixture A, then the diluted mixture can be assigned to the same hazard category as the original mixture.
The vast majority of products are manufactured in batches, which could result in some variations in the properties of the product from batch to batch. However, there is usually no need to write separate SDS for each batch of the product as different batches from the same manufacturer are considered equivalent in hazard classification unless there is a good reason to believe otherwise.
Increasing the concentration of the highest hazard ingredients in mixture A, which was assigned to the highest hazard category as the whole, would result in the highest hazard category mixture B. The principle is applicable for acute toxicity, skin corrosion/irritation, serious eye damage/eye irritation, specific target organ toxicity single exposure, specific target organ toxicity repeated or prolonged exposure, and aspiration hazard.
4) Interpolation within one toxicity category
For mixtures A, B, and C with the same ingredients at different concentrations, if mixtures A and B were tested and assigned to the same hazard category, and the concentration of hazardous ingredients in untested mixture B is between A and C, then mixture B should be assigned to the same hazard category as mixtures A and C. This principle is applicable for acute toxicity, skin corrosion/irritation, serious eye damage/eye irritation, specific target organ toxicity single exposure, specific target organ toxicity repeated or prolonged exposure, and aspiration hazard.
5) Substantially similar mixtures
For two mixtures, such as mixture A made of ingredients X and Y, and mixture B made of Y and Z, if the concentration of Y is the same for both mixtures, and the concentration of X=Z, and the toxicity of X=Z, then the corresponding hazard category of mixture A is equivalent to mixture B.