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GHS Hazard Classification: Everything You Need to Know

Tghshis article is part of ERA’s three part series on GHS Hazard Classification. Part one outlines the step-by-step process for classifying your hazardous chemicals. 

Under the new Globally Harmonized System (GHS) of SDS and Label authoring, chemical manufacturers, importers, and distributors are required to update the way they classify and communicate the hazards of their products.

This article will give you a crash course in how the GHS handles Hazard Classification and the new hazard categories so that you can be prepared for North America’s GHS implementation. We suggest you use this article in tandem with the official GHS “Purple Book” when classifying your materials.

GHS classification of hazards is divided into class and category. These describe the nature and, if applicable, the degree of hazard of the chemical product.

A chemical will have a hazard class, and within that class are several hazard categories, of which one or more will apply. Section 2 of the new GHS Labels and SDSs require hazard statements which are determined by assigning a hazard class and category.

GHS hazard classification

As a manufacturer, importer, or distributor you’ll need to know how to classify hazards. You’ll also need to know which hazards are classified under GHS guidelines and which hazards are not so you can properly address them in Section 2 of your SDS and on your labels.

The Simple Step by Step Process to Classifying a Hazard

Below are the basic steps in auditing your chemical products to properly classify them under GHS standards:

  1. Identify the relevant data concerning the hazards of the chemical.
  2. Determine if the chemical is hazardous based on its physical hazards, health hazards, and environmental hazards.
  3. Test your chemicals or consult scientific evidence to determine how the above information classifies the material.
  4. Identify each of the hazard classes that apply to each chemical.
  5. Identify the appropriate hazard category within each class for the chemical to identify its severity.

Note: You are not required to test chemicals for the purpose of hazard classification. You may instead consult scientific literature to assess whether your chemical meets the OSHA definition of a hazardous chemical.

GHS Hazard Classification

GHS uses three hazard classes: Health Hazards, Physical Hazards and Environmental Hazards. These aren’t required by OSHA.

Health hazards present dangers to human health (i.e. breathing or vision) while physical hazards cause damage to the body (like skin corrosion). There are 16 physical hazards and 10 health hazards: each hazard is then further divided according to different severity levels.

Chemical manufacturers, importers, and distributors are required to classify their chemicals using the updated HazCom 2012. HazCom 2012 provides specific criteria to address physical hazards, health hazards and the classification of chemical mixtures.

It’s important to note, the HazCom 2012 categories are similar yet contradictory to the HMIS/NFPA ratings: GHS 1 – 4 rating system ranks 4 as the least severe while NFPA’s rank 4 is most severe.  This inverse rating system has created some concern, however OSHA has indicated that the GHS numbers are for hazard classification purposes and do not reflect the rating of the hazard itself.

Additionally, the GHS number will not be required on labels. Nevertheless, NFPA and OSHA have worked to produce a quick card to clarify the issue as much as possible.

Hazard Classes and their Applicable Categories

The following tables can be used as a quick reference once you’ve determined a material’s hazard classification. Each class has one or more associated categories. Once you determine class and category you’ll have the information you need to assign signal words, pictograms, and precautionary statements.

Physical Hazards 

Hazard Class

Associated Hazard Category


Divisions 1.1-1.6 (with 1.1 being the most hazardous, 1.6 the least hazardous)

Flammable gases

Categories 1 and 2

Flammable aerosols

Categories 1 and 2

Oxidizing gases

Category 1

Gases under pressure

4 Groups include: Compressed gas, Liquefied gas, Dissolved gas, and Refrigerated liquefied gas

Flammable liquids

Categories 1 - 4

Flammable solids

Categories 1 and 2

Self-reactive substances

Types A-G

Pyrophoric solids

Category 1

Pyrophoric liquids

Category 1

Self-heating substances

Categories 1 and 2

Substances which in contact with water emit flammable gases

Categories 1 - 3

Oxidizing liquids

Categories 1 - 3

Oxidizing solids

Categories 1 - 3

Organic peroxides

Types A-G

Substances corrosive to metal

Category 1

Health Hazards 

Hazard Class

Associated Hazard Category

Acute toxicity

Categories 1-4 (with 1 being the most dangerous)

Skin corrosion

Categories 1A, 1B, 1C, and 2

Skin irritation

Categories  1A, 1B, 1C, and 2

Eye Effects

 Categories 1, 2A, and 2B

Sensitization (Skin or Eye)

Category 1A and 1B

Germ cell mutagenicity

Categories 1A, 1B, and 2


Categories 1A, 1B, and 2

Reproductive toxicity

Categories 1A, 1B, 2, and additional category for effects on or via lactation

Target organ systemic toxicity: single and repeated exposure

Single: Categories 1-3

Repeated: Categories 1 and 2

Aspiration toxicity

Category 1 and 2                  

Environmental Hazards 

Hazard Class

Associated Hazard Category

Acute Aquatic Toxicity

Categories 1 -3

Chronic Aquatic Toxicity

Categories 1 - 4

 UNECE Classification Summary table

The above tables provide a brief summary of the classification/category relations. However, the United Nations Economic Commission for Europe has compiled a comprehensive list of classification and categories which should be used to verify your classifications. Access it for free online here.

This document also includes decision flow charts and numerical limits/thresholds that will be essential if you are required to author GHS-compliant SDSs and/or labels.

Classification of Mixtures

The GHS classifies mixtures using a tiered approach. To classify your mixtures you should use available testing data for the mixture itself along with the GHS classification guidelines. An exception to this is if your mixture is a carcinogen, a mutagen, or a reproductive toxin where classification may be based on the strength of evidence and modified on a case-by-case basis.

For untested mixtures the GHS suggests applying bridging principles with similar tested mixtures or using the cut-off approach with the values described in the specific end point. Bridging principles exist for Dilutions, Batching, Concentration of Highly Toxic mixtures, Interpolation within One Toxic Category, Substantially Similar Mixtures and Aerosols.

More information about the GHS bridging principles and Mixture classification can be found online. 

How to Communicate Hazards: Hazard Statements

Once you have classified and categorized your substances and mixtures you will be able to apply the correct hazard statements to your Safety Data Sheets and Labels. GHS Hazard statements were designed to replace OSHA R-Phrases.

Each hazard statement has a specific hazard code, although your SDSs and Labels must include the entire statement and not simply the code number. This ensures that anyone reading the document knows exactly what to expect immediately without having to refer to a long list of codes.

Section A3.1.2.1 of the UNECE document  explains the codification of the hazard statements:

  1. Each code begins with the Letter “H” for Hazard Statement
  2. The first number designates the type of hazard the hazard statement is assigned
    1. 2 = physical hazard
    2. 3 = health hazard
    3. 4 = environmental hazard
    4. The second and third numbers refer to the intrinsic properties of the substance
    5. Some hazard codes and statements can be combined/ conjoined using a  “+” which means “or”

For example, the hazard code H200 refers to an unstable explosive. It’s clear from the first letter of the code, 2, that the explosive property of the material is a physical hazard.

Take a look at all the hazard statements here.

What if a Hazard is Not Classified under GHS?

Some hazards are not classified under GHS, but that doesn’t mean they can be ignored. These types of hazards are divided into 2 groups: “Pyrophoric Gases, Simple Asphyxiants, and Combustible Dusts”; and Hazard not otherwise classified.

Pyrophoric Gases, Simple Asphyxiants, and Combustible Dusts

These hazards have their own unique requirements and generally do not have any specific GHS pictograms associated with them (the one exception being pyrophoric gas which can use the flame GHS pictogram).

Nevertheless, they must still be included under Section 2 in the SDS and on the label as follows:

Pyrophoric gases (in addition to the Flame GHS pictogram)

  • Signal word - Danger
  • Hazard statement - Catches fire spontaneously if exposed to air
  • Signal word - Warning
  • Hazard statement - May displace oxygen and cause rapid suffocation
  • Signal word - Warning
  • Hazard statement - May form combustible dust concentrations in the air

Simple asphyxiants

Combustible dusts

The “Hazards not otherwise classified” Category

Some materials may have hazards not classified by the Globally Harmonized System that cannot be defined as Pyrophoric Gases, Simple Asphyxiants, and Combustible Dusts.

If a chemical product contains a Hazard Not Classified by the GHS (HNOC), it must be addressed on section 2 of the SDS and may or may not be included on the label under Supplemental information.

The Most Effective Way to Classify Hazards

The Globally Harmonized System offers manufacturers, importers, and distributors a better way of understanding and communicating information about their materials.

However, this shift will also present a challenge because the systems most businesses have in place will need to be updated. Classifying a single material can require a great deal of testing and research, and uses an unfamiliar set of thresholds and requirements.

Many companies are looking for ways to automate this GHS classification process using an electronic system that already has the new GHS rules built in. Rather than building a whole new set of internal chemical management guidelines under a tight deadline, using a GHS SDS/Label authoring software can ease the transition by automatically classifying your materials while you properly implement and master the GHS.

That way you’ll have accurate and compliant GHS documents, you’ll save time, money, and avoid stress, and your transition to GHS will be smoother and more successful. Download our guide to find out more about the most effective way to become GHS Compliant.

Ask an ERA Expert:

Are you transitioning to the GHS in your business? Do you have any questions or concerns about the topic covered in this article? Want more insight? Now is your chance to ask one of ERA’s Environmental Specialists. Please leave your question or comment below and we’ll make sure one of our expert scientists responds. 

 Get the Ultimate GHS Hazard Classification Guide