GHS hazard classification is a standardized system for identifying and communicating the dangers of chemical products using uniform labels, pictograms, signal words and Safety Data Sheets (SDS). Developed by the United Nations, the Globally Harmonized System of Classification and Labelling of Chemicals (GHS) ensures that a worker in Texas reads the same hazard information as a worker in Toronto or Tokyo. In North America, GHS is enforced through OSHA's Hazard Communication Standard (HazCom 2012/2024) in the United States and WHMIS 2015 in Canada.
What Is the Globally Harmonized System?
Before GHS, different countries used different systems to classify and label chemicals. A substance considered "toxic" in one country might carry a different warning or no warning at all in another. This created confusion for workers, emergency responders, importers and exporters.
GHS eliminates this inconsistency by providing a single global framework with three main components:
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- Label elements - pictograms, signal words, hazard statements and precautionary statements that appear on every container
- Safety Data Sheets - a 16-section document providing detailed information about each chemical product
GHS Hazard Classes
GHS divides chemical hazards into three broad groups, each containing multiple hazard classes:
Physical Hazards
Physical hazards relate to the chemical and physical properties of a substance. They describe what the chemical itself can do independently of biological exposure:
- Explosives
- Flammable gases, aerosols, liquids and solids
- Oxidizing gases, liquids and solids
- Gases under pressure
- Self-reactive substances
- Pyrophoric liquids and solids
- Self-heating substances
- Substances that emit flammable gas in contact with water
- Organic peroxides
- Corrosive to metals
Health Hazards
Health hazards describe the effects of chemical exposure on the human body:
- Acute toxicity (oral, dermal, inhalation)
- Skin corrosion and irritation
- Serious eye damage and eye irritation
- Respiratory or skin sensitization
- Germ cell mutagenicity
- Carcinogenicity
- Reproductive toxicity
- Specific target organ toxicity (single and repeated exposure)
- Aspiration hazard
Environmental Hazards
Environmental hazards describe the potential impact on ecosystems:
- Hazardous to the aquatic environment (acute and chronic)
- Hazardous to the ozone layer
GHS Hazard Categories Explained
Within each hazard class, chemicals are assigned a category number that indicates severity. Category 1 is always the most severe. The number of categories varies by hazard class - some have two categories while others have five.
For example, acute toxicity is divided into five categories:
| Category | Severity | Signal Word |
|---|---|---|
| Category 1 | Fatal | Danger |
| Category 2 | Fatal | Danger |
| Category 3 | Toxic | Danger |
| Category 4 | Harmful | Warning |
| Category 5 | May be harmful | Warning |
Understanding category numbers is essential for selecting appropriate controls, PPE and emergency response procedures. A Category 1 acute toxicant demands far more stringent handling procedures than a Category 5 substance.
The 9 GHS Pictograms
GHS uses nine standardized pictograms - red-bordered diamonds with black symbols on white backgrounds. Each communicates a specific type of hazard at a glance:
- Exploding bomb - explosives, self-reactive substances, organic peroxides
- Flame - flammable gases, liquids, solids, aerosols, self-reactive and pyrophoric substances
- Flame over circle - oxidizers that can intensify fire
- Gas cylinder - compressed, liquefied or dissolved gases under pressure
- Corrosion - substances that cause skin burns, eye damage or metal corrosion
- Skull and crossbones - acutely toxic substances (Categories 1-3)
- Exclamation mark - irritants, skin sensitizers, acute toxicity Category 4, narcotic effects, respiratory tract irritation
- Health hazard - carcinogens, mutagens, reproductive toxicants, respiratory sensitizers, target organ toxicants, aspiration hazards
- Environment - substances hazardous to the aquatic environment
Workers should be trained to recognize every pictogram and understand the general type of hazard it represents. Detailed information is found on the label text and the Safety Data Sheet.
Signal Words: Danger vs Warning
GHS uses only two signal words:
- Danger - indicates the more severe hazard categories
- Warning - indicates less severe hazard categories
A product can only have one signal word. If multiple hazards are present, the label displays whichever signal word corresponds to the most severe classification. You will never see both "Danger" and "Warning" on the same label.
GHS Label Requirements
Every container of a hazardous chemical must display a GHS-compliant label with the following elements:
- Product identifier - the chemical name or product name
- Signal word - Danger or Warning
- Pictogram(s) - the applicable red-bordered diamond symbol(s)
- Hazard statement(s) - standardized phrases describing the nature and severity of the hazard (e.g., "Highly flammable liquid and vapour")
- Precautionary statement(s) - standardized phrases for prevention, response, storage and disposal
- Supplier identification - name, address and phone number of the manufacturer or distributor
Workplace labels - those applied to secondary containers when a chemical is transferred from its original packaging - must include at minimum the product identifier and hazard information. Many jurisdictions accept pictograms plus the product name as a valid workplace label.
Safety Data Sheets: The 16-Section Format
The Safety Data Sheet is the detailed companion to the label. GHS standardizes the SDS into 16 sections in a fixed order:
- Identification
- Hazard(s) identification
- Composition/information on ingredients
- First-aid measures
- Firefighting measures
- Accidental release measures
- Handling and storage
- Exposure controls/personal protection
- Physical and chemical properties
- Stability and reactivity
- Toxicological information
- Ecological information
- Disposal considerations
- Transport information
- Regulatory information
- Other information
Employers must maintain an SDS for every hazardous chemical in the workplace and ensure they are readily accessible to workers during their shift. A centralized document management system makes it easy to store, search and update your SDS library without relying on physical binders that quickly become outdated.
For a deeper look at managing your SDS library, see our Safety Data Sheets guide.
GHS and North American Regulations
United States: OSHA HazCom
OSHA adopted GHS through its revised Hazard Communication Standard (29 CFR 1910.1200). The most recent update aligns more closely with GHS Revision 7 and introduces changes to classification criteria and label elements. Employers must ensure their written HazCom program, labels and SDS libraries reflect the current standard.
Canada: WHMIS 2015
Canada integrated GHS through WHMIS 2015 (Workplace Hazardous Materials Information System). The system uses the same pictograms, label format and 16-section SDS structure as GHS. Canadian regulations also include physical hazard classes not in the UN GHS, such as "combustible dust" and "physical hazard not otherwise classified."
Training Workers on GHS
Effective GHS training covers three areas:
- Label comprehension - reading and understanding every element on a GHS label
- SDS navigation - knowing where to find critical information in the 16-section format
- Protective measures - translating hazard information into safe handling, storage and emergency response actions
Training must occur before workers are exposed to hazardous chemicals and whenever new hazards are introduced. Document all training sessions with dates, attendees and topics covered.
Common GHS Compliance Mistakes
Even organizations that take chemical safety seriously can fall into these traps:
- Outdated SDS files - keeping Safety Data Sheets on file that are more than three years old or do not reflect current formulations. Manufacturers are required to update SDS documents when new hazard information becomes available, but employers must actively request and replace outdated versions.
- Incomplete chemical inventories - failing to include cleaning products, maintenance chemicals, office supplies (toners, adhesives) and samples in the inventory. If it is hazardous and it is on site, it belongs on the list.
- Unlabeled secondary containers - transferring chemicals into spray bottles, buckets or other containers without applying a workplace label. Workers cannot protect themselves from hazards they cannot identify.
- One-time training - delivering GHS training during orientation and never revisiting it. Refresher training is essential when new chemicals are introduced, when job roles change or when incident data suggests knowledge gaps.
- Inaccessible SDS libraries - storing Safety Data Sheets in a locked office or a shared drive that workers cannot access during their shift. SDS documents must be available immediately, not after a 10-minute search.
- Ignoring workplace labels - focusing on supplier labels while neglecting the secondary containers that workers handle daily.
Building a Chemical Hazard Management Program
GHS classification and labeling is one component of a broader chemical hazard management program. A complete program also includes:
- Chemical approval process - reviewing new chemicals before they enter the workplace to assess hazards, storage requirements and PPE needs
- Storage compatibility - ensuring incompatible chemicals are stored separately according to their hazard classifications (oxidizers away from flammables, acids away from bases)
- Spill response procedures - written plans for containing and cleaning up chemical releases, including required equipment and PPE
- Exposure monitoring - air sampling and biological monitoring where regulatory thresholds exist for specific substances
- Medical surveillance - health monitoring programs for workers exposed to regulated substances such as lead, benzene or crystalline silica
Each of these elements relies on accurate GHS classification data. When you know exactly what hazards a chemical presents and how severe they are, you can design controls that match the actual risk level.
Keep Your Chemical Hazard Program Current
Chemical inventories change, regulations update and new products enter the workplace regularly. A GHS compliance program is not a one-time project. Schedule quarterly reviews of your chemical inventory, SDS library and label conditions. Audit your written HazCom/WHMIS program annually and retrain workers whenever significant changes occur.
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