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Hazard Classes

Last updated: September 26, 2018

What Does Hazard Classes Mean?

A hazard class is a group of hazardous chemical substances that share similar properties. Systems of hazard classes are used to group hazards together in a manner based on an internally consistent set of technical criteria.

Hazard classification systems allow individuals to efficiently identify and understand the dangers that are posed by a chemical, as well as ensure that this information is communicated between individuals in a uniform manner.

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Safeopedia Explains Hazard Classes

Classification systems are often associated with a standardized set of pictograms, multilingual warning statements, and alphanumeric index identifiers. These ensure that the meaning of each class and the hazards associated with their respective substances can be easily communicated across jurisdictions and language barriers. The alphanumeric indexes associated with each class allow additional information about the hazard to be accessed in an efficient manner, and they ensure that the information will come from a source that is common to all users of the classification system.


The United Nations’ Globally Harmonized System of Classification and Labelling of Chemicals (GHS) provides the most prevalent set of hazard classes in use today. The GHS has been adopted by federal occupational health and safety agencies in most major countries around the world, as well as by related safety and health agencies.

The GHS sorts hazard classes into three groups: physical hazards, health hazards, and environmental hazards. For occupational health and safety purposes, it is common for regulatory agencies (including OSHA) to only utilize the first two groups for hazard classification. The standard version of the GHS includes 17 physical hazard classes and 10 health hazard classes, which are then subdivided into categories that describe specific severities of hazards that are associated with each class.

Other Standards

Individual jurisdictions may incorporate some or all of the classes from these groups into their hazard communication standards, and they may also add additional classifications that are organized with reference to the GHS scheme. For instance, Canada’s Workplace Hazardous Materials Information System (WHMIS) does not include the GHS explosives class and adds a “Hazards Not Otherwise Classified” class to both the health and physical hazard groups.

The U.S. Department of Transportation also provides a hazard classification system for the shipment of dangerous goods within the United States. This system uses nine different classes, all of which correspond to classifications present in the physical hazards group of the GHS scheme except for the ninth class, "Miscellaneous Dangerous Goods." The specific criteria for this standard are defined under 49 CFR 172.101 and 173.

Hazard classification is a key component of workplace health and safety programs. OSHA requires the completion of a rigorous hazard classification process under its Hazard Communication Standard. Similar hazard classification processes, in line with the tenets of the GHS, are required in other jurisdictions.



HAZMAT Classes, Hazardous Materials Classification, HAZMAT Placards, Classification of Hazards, Hazardous Waste Labels, HAZMAT Labels

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HazardsHAZMATSafety HazardStandardsChemical Resistant (CR)

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