Guide
SDS for Mixtures: How Hazards Are Classified and Reported
An SDS for a mixture classifies the product as supplied, using either test data on the whole mixture or calculation methods based on its ingredients. Section 3 lists the hazardous ingredients and their concentrations or ranges, but the hazard classification in Section 2 describes the mixture as a whole, so it can differ from the classification of any single ingredient.
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How a mixture is classified
The GHS and HazCom allow three routes. First, if test data exist for the mixture itself, those are used. Second, if data exist for similar mixtures, the supplier may apply "bridging principles", for example classifying a slightly diluted version in the same category as a tested product. Third, the supplier calculates the classification from the ingredients using cut-off values and formulas, known as the additivity approach for many health hazards. The exact method varies by hazard class.
That is why a mixture with an irritating ingredient may not itself be classified as an irritant if the ingredient is present below the relevant cut-off. Conversely, a mixture of several moderately hazardous ingredients may require a more serious classification.
What Section 3 shows for a mixture
Section 3 must identify the ingredients that are classified as health hazards and present at or above their cut-off levels, as well as those that present a health risk below the cut-off. Each is listed with its chemical name, a unique identifier such as a CAS number, and a concentration or concentration range. Non-hazardous ingredients, such as water, may be omitted. See Section 3 for details.
If an identity or an exact concentration is withheld as a trade secret, the sheet must say so. Read trade secrets on SDSs to learn how.
Dilutions and ready-to-use products
A sheet for a concentrate does not describe the diluted product. When you dilute a chemical, the classification may fall to a lower category or to none, but not always; some hazards, such as skin sensitization, persist at low concentrations. Check whether the supplier provides a sheet for the ready-to-use product. If you blend or dilute on site, you may need to label the secondary container and consider whether you have become a manufacturer. See secondary container labels.
Exposure limits for mixtures
Section 8 may list limits for individual ingredients rather than for the mixture. If a product contains several solvents, the exposures may add up. The usual professional approach is to evaluate the combined effect when ingredients act on the same organ system, but there is no single number on the sheet. If you are unsure, ask the supplier or an occupational hygienist. See reading exposure limits.
If you blend chemicals yourself
- You may be a manufacturer under HazCom and need to classify the blend and prepare an SDS if it leaves your site, or at least provide the hazard information to your own employees.
- Record the recipe, the date and the person responsible.
- Check compatibility before blending. Some combinations release toxic gas or heat.
- Label the container with the product identifier and the hazards. See labeling requirements.
- Apply other regimes where relevant, for example TSCA for a product you sell.
Red flags in a mixture SDS
- A hazardous ingredient in Section 3 with no corresponding hazard in Section 2, and no explanation of the cut-off.
- Ingredient lists in which percentages total much more or less than 100 with no note.
- Hazard classification copied from a pure ingredient, ignoring dilution.
- No statement of how the classification was derived, such as "calculation method" or "test data".
Frequently asked questions
Does an SDS have to list all the ingredients of a mixture?
No. It must list the ingredients that are classified as hazardous above their cut-off levels, plus those posing a health risk below the cut-off. Non-hazardous components may be omitted.
Can a mixture be less hazardous than its ingredients?
Yes, particularly when a hazardous ingredient is diluted below the cut-off for a hazard class. Some hazards, such as sensitization, can persist at low concentrations.
Do I need an SDS for a mixture I make myself?
If you use it only in your own workplace, you need to provide the hazard information to employees. If you sell or ship it, you are a manufacturer and must prepare an SDS and label.
Why do two similar cleaners have different classifications?
Because they contain different ingredients or concentrations, or because suppliers used different data and methods.