16.4. Classification Procedure

This section explains the methods and procedures used to determine the hazard classification of the substance or mixture. It provides transparency about how classifications were derived, whether through testing, calculation methods, expert judgment, or other approaches, helping users understand the basis for the hazard information presented in the SDS.

Purpose and Importance

Documenting the classification procedure in a Safety Data Sheet serves several important functions:

Transparency

Provides clarity about how hazard classifications were determined, allowing users to understand the scientific basis for safety information.

Verification

Enables users to assess the reliability of classifications and potentially reproduce the classification process if needed.

Compliance

Demonstrates adherence to regulatory requirements for hazard classification and documentation.

Risk Management

Helps users make informed decisions about risk management measures based on the robustness of the classification.

Regulatory Requirements

According to the Globally Harmonized System (GHS) and regulations such as REACH in the EU and HazCom in the US, Safety Data Sheets should include information about the methods used for classification, particularly for mixtures. This information is especially important when classifications are based on calculation methods, bridging principles, or expert judgment rather than direct testing.

Classification Process Overview

Data Collection

Gather all available information on physical, chemical, toxicological, and ecotoxicological properties

Data Evaluation

Assess data quality, reliability, and relevance to classification criteria

Method Selection

Choose appropriate classification method based on available data and substance type

Classification

Apply criteria to determine hazard classes and categories

Documentation

Record classification results and methodology in the SDS

Classification Methods

Different methods can be used to classify substances and mixtures, depending on the available data and the type of hazard being assessed:

Method	Description	Typical Applications	Advantages/Limitations
Test Data	Classification based on results from standardized tests performed on the substance or mixture	Physical hazards (flammability, explosivity) Acute toxicity Skin/eye irritation Aquatic toxicity	Advantages: Most reliable and direct evidence Preferred by regulatory authorities Limitations: Expensive and time-consuming May raise ethical concerns for animal testing
Calculation Methods	Classification based on mathematical formulas using data from individual components of a mixture	Acute toxicity Skin/eye irritation Specific target organ toxicity Environmental hazards	Advantages: No testing required Relatively straightforward for well-characterized mixtures Limitations: Requires reliable data for all components May not account for synergistic or antagonistic effects
Bridging Principles	Classification based on similarity to tested mixtures with minor variations in composition	Dilution Batching Concentration of highly hazardous mixtures Interpolation within one toxicity category Substantially similar mixtures Aerosols	Advantages: Reduces need for testing similar mixtures Scientifically sound approach Limitations: Requires sufficient data on similar mixtures Limited to specific scenarios
Expert Judgment	Classification based on evaluation by qualified experts using weight of evidence approach	Complex or novel substances Conflicting data Data gaps Non-standard test results	Advantages: Can integrate multiple lines of evidence Useful when standard approaches are inadequate Limitations: Subjective elements Requires specialized expertise May be challenged by authorities

Calculation Methods for Mixtures

When classifying mixtures, specific calculation formulas are often used to determine hazard classifications based on the properties of individual components:

Acute Toxicity Estimate (ATE)

For acute toxicity classification:

ATEmix = 100 / Σ (Ci / ATEi)

Where:

Ci = concentration of component i (%)
ATEi = Acute Toxicity Estimate of component i

Additivity Formula

For skin/eye irritation/corrosion:

Σ (Ci / SCLi) ≥ 1

Where:

Ci = concentration of component i (%)
SCLi = Specific Concentration Limit for component i

Summation Method

For environmental hazards:

Σ (Ci × M) ≥ Concentration limit

Where:

Ci = concentration of component i (%)
M = M-factor for component i

Cut-off Values/Concentration Limits

For carcinogenicity, mutagenicity, reproductive toxicity:

If Ci ≥ Generic/Specific Concentration Limit, then classify

Where:

Ci = concentration of component i (%)
Generic limits: typically 0.1% or 1%
Specific limits: substance-specific values

Case Study: Classification of a Complex Mixture

A manufacturer needed to classify a new cleaning product containing multiple ingredients:

Mixture composition:
- Substance A (10%): Classified as Acute Tox. 4 (oral), Skin Irrit. 2, Eye Dam. 1
- Substance B (5%): Classified as Acute Tox. 3 (oral), STOT SE 3
- Substance C (2%): Classified as Skin Sens. 1, Aquatic Chronic 1 (M=10)
- Substance D (1%): Classified as Carc. 2
- Water and other non-hazardous ingredients (82%)
Classification approach:
- Physical hazards: Determined through testing of the final mixture
- Acute toxicity: Calculated using the ATE formula
- Skin/eye effects: Applied additivity formulas
- Sensitization: Applied cut-off values
- Carcinogenicity: Applied generic concentration limits
- Environmental hazards: Applied summation method with M-factors
Results:
- Physical hazards: Not classified (based on test data)
- Acute Tox. 4 (oral): ATEmix = 2500 mg/kg (calculation method)
- Eye Dam. 1: Concentration of Eye Dam. 1 components ≥ 3% (additivity)
- Skin Irrit. 2: Concentration of irritant components ≥ 10% (additivity)
- Skin Sens. 1: Component C ≥ 1% (cut-off value)
- Carc. 2: Component D ≥ 1% (generic concentration limit)
- Aquatic Chronic 2: (2% × 10) = 20% equivalent of Chronic 1 (summation)
Documentation in SDS: Section 16.4 clearly stated the classification methods used for each hazard class, including references to the specific calculation formulas, cut-off values, and test methods applied.

Example of Section 16.4 Content

16.4 Classification Procedure

The classification of this product was determined using the following methods:

Physical Hazards:

Flammable Liquid Category 2: Based on flash point test data (closed cup method) according to ASTM D56
Not classified for other physical hazards based on test data and product properties

Health Hazards:

Acute Toxicity (oral) Category 4: Calculation method using Acute Toxicity Estimate (ATE) values of components
Skin Irritation Category 2: Additivity approach based on concentrations of irritant components
Eye Damage Category 1: Additivity approach based on concentrations of corrosive/irritant components
Skin Sensitization Category 1: Cut-off value method based on concentration of sensitizing component
Specific Target Organ Toxicity - Single Exposure Category 3: Cut-off value method based on concentration of STOT SE 3 components

Environmental Hazards:

Aquatic Chronic Category 2: Summation method using concentrations and M-factors of classified components

Classification according to: Regulation (EC) No 1272/2008 [CLP], GHS Revision 8 (2019)

Evaluation method: The classification was performed according to the calculation methods set out in Annex I of the CLP Regulation and the GHS, using data from reliable sources for all components. Where appropriate, expert judgment was applied using a weight of evidence approach.

Common Issues with Classification Procedures in SDSs

When preparing or reviewing Section 16.4 of an SDS, be aware of these common issues:

Lack of specificity about which methods were used for which hazard classes
Failure to document the basis for classifications when using expert judgment
Inconsistency between the classification procedure described and the actual classifications in Section 2
Incomplete information about calculation methods or formulas used
Outdated classification criteria that do not reflect current regulations
Failure to account for specific concentration limits or M-factors
Lack of transparency about data gaps or uncertainties in the classification

Best Practices for Section 16.4

Clearly specify which classification method was used for each hazard class
Provide details of calculation formulas when used for mixture classification
Reference the specific version of regulations or guidelines followed (e.g., GHS Rev. 8, CLP Regulation with amendments)
Document the rationale when expert judgment or weight of evidence approaches are used
Indicate when bridging principles are applied and the basis for their application
Note any specific concentration limits, M-factors, or ATEs used in calculations
Ensure consistency between the classification procedure and the classifications in Section 2
Update the classification procedure when new data becomes available or regulations change
Include information about classification reviews or validation processes

Important: Transparency about classification procedures is essential for the credibility and reliability of a Safety Data Sheet. Users should be able to understand how hazard classifications were determined, especially for complex mixtures or when non-standard approaches were used. This information helps users make informed decisions about risk management and ensures compliance with regulatory requirements.