Mastering GHS Classification Decisions: Technical Flowchart

After years of consulting on GHS compliance, I've found that accurate classification remains one of the biggest challenges for safety professionals. Many spend hours manually diagramming decision paths, only to encounter errors when regulatory updates invalidate their work.

Below is a comprehensive technical diagram I've created to guide chemical classification according to GHS standards. This flowchart covers physical hazards (including flammable liquids and explosives), health hazards (such as acute toxicity), and environmental hazards, mapping out the critical decision points for accurate classification.

While this diagram is helpful for visualizing GHS classification paths, many safety teams struggle with the complexity of these decisions, especially for chemical mixtures where multiple hazard categories may apply simultaneously.

This technical diagram maps out the core decision points in GHS classification, but implementing these decisions consistently across your chemical inventory remains challenging. As regulatory requirements evolve, maintaining these complex decision trees manually becomes increasingly difficult.

In my experience working with dozens of chemical manufacturers and distributors, those who achieve the best compliance outcomes are transitioning to digital solutions that can automate these classification processes while maintaining a clear audit trail.

Key GHS Classification Challenges in 2025

When working with safety professionals across various industries, I've noticed several recurring challenges that make GHS classification particularly demanding:

1. Complex Mixture Rules

The GHS system includes detailed rules for classifying mixtures based on their components. For mixtures containing multiple hazardous substances, these calculations quickly become complex. For example, when classifying a mixture for acute toxicity, you must apply the Acute Toxicity Estimate (ATE) formula, which requires knowing precise LD50/LC50 values for each component. Making these calculations manually introduces significant risk of error.

2. Overlapping Hazard Categories

Many chemicals fall into multiple hazard categories simultaneously. For example, a substance might be both a flammable liquid and acutely toxic. When creating technical documentation, you need to ensure all applicable hazard categories are identified and properly communicated. Our diagram above helps visualize these distinct classification paths, but keeping track of them all for complex chemicals remains challenging.

3. Regulatory Interpretation Differences

While GHS aims to harmonize chemical classification globally, different countries and regions have adopted varying versions and interpretations. For example, the EU's CLP regulation, US OSHA HazCom Standard, and Canada's WHMIS all implement GHS slightly differently. These variations make maintaining accurate classification technical diagrams increasingly difficult for companies operating in multiple markets.

GHS Physical Hazards: Technical Implementation

As shown in our technical diagram, physical hazards represent a significant portion of GHS classification complexity. The diagram maps out the decision pathways for key physical hazards like flammable liquids, explosives, and oxidizers.

Flammable Liquids Classification

For flammable liquids, the classification process requires specific test data including flash point and boiling point. The diagram shows how these values determine classification into Categories 1-4, each with corresponding hazard statements (H-codes) and pictogram requirements. In practice, these tests must follow standardized methods like ISO 2719 (closed cup flash point) and ISO 3924 (boiling point determination).

Explosive Properties Testing

The explosives classification pathway follows the UN Test Series 1-7, which evaluates properties including sensitivity to impact, thermal stability, and mass explosion hazard. These technical tests require specialized equipment and expertise, making this one of the more complex areas of GHS classification.

Health and Environmental Hazard Classification

The health and environmental sections of our technical diagram illustrate the decision points for acute toxicity and aquatic hazards, both critical aspects of chemical safety communication.

Implementing Acute Toxicity Classification

Acute toxicity classification requires LD50/LC50 data from standardized tests like OECD 423/425 (oral), OECD 402 (dermal), and OECD 403 (inhalation). For mixtures, the classification process involves complex calculations using concentration limits and the acute toxicity estimate (ATE) formulas specified in GHS Chapter 3.1.

Aquatic Toxicity Technical Requirements

Environmental classification under GHS requires data from aquatic toxicity tests (OECD 201-203, 211) that measure effects on fish, daphnia, and algae. The classification criteria shown in our diagram are based on LC50/EC50 values for acute toxicity and NOEC values for chronic toxicity. For substances that rapidly degrade in the environment, additional factors must be considered.

Special Classification Considerations

The "Special Cases" section of our technical diagram highlights additional classification considerations that safety professionals must address:

Mixture Classification Using the Additivity Formula

For mixtures containing components with known hazards, the GHS provides specific calculation methods. The additivity formula shown in our diagram is particularly relevant for environmental hazards, where the concentration of each hazardous component is multiplied by its M-factor (which accounts for high toxicity) to determine if the mixture meets classification thresholds.

Nanomaterial Classification

The emerging field of nanomaterial safety presents unique classification challenges. As shown in our diagram, materials with primary particles measuring ≤100nm in ≥50% of the particle count distribution may require specific hazard considerations beyond standard GHS criteria.

Practical Implementation of GHS Classification

While our technical diagram provides a valuable visual reference for classification decisions, implementing these processes consistently across a chemical inventory requires systematic approaches:

Documentation Requirements

For each classification decision, safety professionals must maintain documentation that includes:

• Test data sources and reliability assessment
• Classification rationale, especially for borderline cases
• Calculations used for mixture classifications
• References to specific GHS criteria and decision points

Updating Classifications

GHS classification is not a one-time activity. Classifications must be reviewed and potentially updated when:

• New hazard information becomes available
• Formulation changes occur, even minor ones
• Regulatory updates are published
• The product is introduced to new markets with different requirements

Moving Beyond Manual Classification

While technical diagrams like the one above have traditionally been essential tools for safety professionals, the increasing complexity of GHS requirements has pushed many companies to seek more efficient solutions. Modern approaches include:

Digital Classification Tools

Digital tools can automate complex classification calculations while maintaining a detailed audit trail of decision logic. By integrating regulatory rules directly into the classification engine, these tools can adapt quickly to GHS updates without requiring complete redesign of classification diagrams.

Component-Based Classification

By maintaining a database of accurately classified components, safety professionals can more consistently classify mixtures and reformulations. This approach relies on accurate component data but significantly reduces the time required for routine classifications.

Our SDS Copilot platform combines these approaches, helping safety professionals reduce time spent on manual classification while improving accuracy and documentation. The system handles the complex calculations and regulatory logic shown in our technical diagram, freeing safety teams to focus on higher-value safety activities.

Final Thoughts

The GHS classification technical diagram above serves as an excellent reference for understanding the key decision points in chemical hazard classification. It visualizes the complex pathways that safety professionals must navigate to ensure compliance with global regulations.

As regulations continue to evolve and chemical formulations become increasingly complex, the challenge of maintaining accurate classifications grows. Whether you're using technical diagrams like this one or adopting automated solutions, the goal remains the same: communicating chemical hazards accurately to protect workers, communities, and the environment.