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Globally Harmonized System for Classifying Hazardous Chemicals

The Globally Harmonized System (GHS) is an internationally adopted system for the classification and labeling of hazardous chemicals that:

  • Includes established criteria for classifying hazards and for further categorizing (or rating) the hazards according to their relative risks
  • Provides established language and symbols for each hazard class and each category within a class

Examples of GHS Hazard Symbols with their definitions.

GHS language includes:

  • A signal word (such as “danger” or “warning”)
  • A symbol or pictogram (such as a flame within a red-bordered diamond)
  • A hazard statement (such as “causes serious eye damage”)
  • Precautionary statements for safely using the chemical

An important part of this hazard classification system is the set of criteria that describe a given class of hazard (e.g., flammable liquids) and the ratings (categories) of the hazards within each hazard class.

The hazard categories are numbered from 1 to 5. The LOWER the number, the GREATER the severity of the hazard. So, category 1 hazards are the most dangerous.

Note: This GHS numbering system is the opposite of the NFPA rating system
under the NFPA system, the most dangerous rating is 4 , while 0 would pose a minimal hazard

The GHS was developed to identify to the user of a material both the hazards and the risks associated with chemicals. The EPA, OSHA, and U.S. Department of Transportation have adopted the GHS for use in the United States.

Science teachers are expected to understand and use the GHS signal word, symbol, hazard statement, and precautionary statement. These items are appropriately placed on commercial labels found on chemical containers and in Safety Data Sheets (SDSs). The prudent practice would be to transfer the signal word and symbol to the labels on secondary containers.

GHS Hazard Symbols and Their Definitions1

GHS hazard symbol for Explosive


  • Explosives
  • Self-reactive substances
  • Organic peroxides
GHS Hazard symbol for Flammable


  • Flammable gases, aerosols, liquids, and solids
  • Pyrophoric liquids or solids
  • Self-heating substances
  • Self-reactive substances
  • Substances that emit a flammable gas upon contact with water
  • Organic peroxides
GHS Hazard symbol for Corrosive


  • Skin corrosion/burns
  • Eye damage
  • Corrosive to metals
GHS Hazard Symbol for Oxidizer


  • Oxidizing gases, liquids, and solids
GHS Hazard Symbol for Compressed Gas

Compressed gas

  • Gases under pressure
GHS Hazard symbol for Irritant


  • Irritant (skin and eye)
  • Skin sensitizer
  • Acute toxins
  • Narcotic effects
  • Respiratory tract irritants
  • Hazardous to ozone layer (non-mandatory)
GHS Hazard symbol for Toxic Substance

Toxic Substance

  • Acutely toxic substances that may be fatal or toxic if inhaled, ingested, or absorbed through the skin
GHS Hazard symbol for Environmental Hazard

Environmental Hazard (non-mandatory)

  • Acute aquatic toxins
  • Chronic aquatic toxins
GHS Hazard symbol for Health Hazard

Health Hazard

  • Respiratory sensitizers
  • Carcinogens
  • Mutagens
  • Reproductive toxins
  • Target organ toxins, single exposure or repeated exposure
  • Aspiration toxins

Source: UNECE. Globally Harmonized System of Classification and Labelling of Chemicals, 2015. (accessed Dec 1, 2015).

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