GHS Classification Explained: Hazard Classes, Categories, and How They Affect Your SDS

Quick Answer

GHS classification identifies the type and severity of a chemical hazard. A hazard class describes the nature of the hazard, such as flammable liquids or acute toxicity, while a hazard category indicates relative severity within that class. The resulting classification helps determine the applicable hazard statements, signal words, pictograms, and precautionary statements required under the relevant regulatory framework and is reflected in Section 2 of the Safety Data Sheet (SDS).

What Is GHS Classification?

The Globally Harmonized System of Classification and Labelling of Chemicals (GHS), developed by the United Nations, provides a common framework for classifying chemical hazards and communicating them through labels and Safety Data Sheets.

The United Nations GHS establishes classification criteria and standardized hazard communication elements designed to improve consistency across markets.

However, GHS is not a single worldwide law. Countries and regions adopt the framework through their own regulations and may use different GHS revisions, hazard classes, categories, or other building blocks. As a result, classification and SDS requirements can vary by market.

In the United States, OSHA’s Hazard Communication Standard (HCS) incorporates GHS-based classification and hazard communication requirements for workplace chemicals.

What Is the Difference Between a GHS Hazard Class and Hazard Category?

A hazard class identifies the type or nature of a hazard. A hazard category further describes the severity or characteristics of that hazard within the class.

A lower category number often represents greater severity within a hazard class that uses numbered categories. However, category numbers should not be compared across different hazard classes.

For example, OSHA classifies acute toxicity into Categories 1 through 4. Other hazard classes may use different categories or subcategories.

What Are the GHS Hazard Classes?

Under the UN GHS, hazard classes fall broadly into three groups:

Physical hazards include hazards such as flammable liquids, explosives, oxidizing substances, gases under pressure, and substances corrosive to metals.

Health hazards include acute toxicity, skin corrosion or irritation, serious eye damage or irritation, respiratory or skin sensitization, carcinogenicity, reproductive toxicity, and specific target organ toxicity.

Environmental hazards are also addressed under the UN GHS. Some countries do not incorporate environmental hazards into their hazard classification systems. For example, U.S. OSHA does not require environmental hazard classification under the Hazard Communication Standard.

The exact hazard classes and categories that apply can therefore depend on the jurisdiction in which a product is placed on the market or used.

How Are GHS Hazard Categories Assigned?

Classification begins with evaluating available information about a chemical against the criteria for each applicable hazard class.

Under OSHA’s HCS, chemical manufacturers and importers must determine the applicable hazard classes and, where appropriate, the corresponding hazard categories for chemicals they produce or import.

Classification requires applying the criteria for the specific hazard class and relevant jurisdiction rather than simply assigning a category number.

How Does GHS Classification Affect a Safety Data Sheet?

Hazard classification directly affects the information communicated in an SDS.

Under OSHA’s Appendix D requirements for Safety Data Sheets, Section 2: Hazard(s) Identification includes the chemical’s classification and applicable signal word, hazard statements, symbols or pictograms, and precautionary statements.

The relationship can be summarized as:

Hazard data → Hazard class → Hazard category → Hazard communication elements → SDS Section 2

The classification and underlying hazard data should also be consistent with relevant information elsewhere in the SDS, including sections covering composition, handling and storage, exposure controls, physical and chemical properties, and toxicological information.

For a broader look at how SDS content is developed in the United States, read CHEMTREC’s How to Create an SDS in the United States.

Is GHS Classification the Same in Every Country?

No. GHS provides a harmonized framework, but individual jurisdictions decide how to implement it.

A country or region may use a different GHS revision, adopt different hazard classes or categories, or require additional information. This means an SDS prepared for one market may need changes before it is suitable for another.

For more detail on how requirements can vary across jurisdictions, read CHEMTREC’s One Chemical, Many Standards: Navigating SDS Variations Worldwide.

How Does OSHA Apply GHS Classification in the United States?

OSHA’s Hazard Communication Standard requires chemical manufacturers and importers to evaluate available hazard information and classify chemicals according to HCS criteria.

Health-hazard classification criteria are addressed in Appendix A, while physical-hazard criteria are covered in Appendix B.

Employers generally may rely on classifications provided by the chemical manufacturer or importer unless they choose to classify the chemical themselves.

OSHA does not enforce the information requirements for SDS Sections 12 through 15 because those areas fall outside OSHA’s jurisdiction.

For more background on recent U.S. classification changes, see CHEMTREC’s OSHA HCS: Physical and Health Hazard Classification Updates.

How Does GHS Classification Affect Labels?

GHS classification also helps determine the hazard communication elements used on applicable labels, including pictograms, signal words, hazard statements, and precautionary statements.

The specific requirements depend on the applicable regulatory framework and classification.

For more on labeling differences, see CHEMTREC’s U.S. Consumer Chemical Labels: How Do They Differ from GHS Labels?

Why Accurate Hazard Classification Matters for SDS Authoring

Hazard classification affects the information workers and downstream users rely on to understand chemical hazards. An incorrect classification can result in inaccurate hazard communication elements or inconsistencies between an SDS and the corresponding label.

For organizations creating, updating, or localizing SDSs, classification should reflect the applicable regulatory framework, available hazard information, and intended market.

CHEMTREC’s SDS Authoring services provide support for SDS creation and maintenance, customized formatting and branding, multi-language needs, and GHS labeling. Learn more about how CHEMTREC can support your SDS authoring needs.