How many GHS hazard classes are there?

GHS Revision 7 defines roughly 29 hazard classes, split among physical hazards (about 17), health hazards (about 10), and environmental hazards (2).

Can a chemical have more than one hazard class?

Yes. Most hazardous chemicals fall into several classes at once — for example flammable, irritant, and target-organ toxicant — and each contributes its own elements to the label.

What's the difference between a hazard class and a hazard category?

The class is the nature of the hazard (e.g., flammable liquid); the category is the severity within that class (Category 1 most severe). A full classification names both.

GHS / HazCom term · Glossary

Hazard Class

Verified vs OSHA sources · 2026-10-05

The nature of a hazard a chemical presents — for example flammable liquid, oxidizer, acute toxicity, carcinogenicity, or aquatic toxicity. GHS groups hazard classes into physical, health, and environmental hazards (roughly 29 classes in Revision 7). A single chemical can fall into several hazard classes at once.

29 CFR 1910.1200(c)

Also known as: GHS hazard class

Hazard Class at a glance

Three families: physical hazards, health hazards, environmental hazards.
GHS Revision 7 defines roughly 29 hazard classes in total.
Each class is then divided into hazard categories by severity.
One chemical can belong to several classes (e.g., flammable + irritant + STOT).

In plain English

The “what kind of danger is it” label — flammable, corrosive, cancer-causing, toxic to fish, and so on. GHS sorts every hazard into one of three families (physical, health, environmental), and a chemical can belong to several classes at once.

What the rule says

“Hazard class means the nature of the physical or health hazards, e.g., flammable solid, carcinogen, oral acute toxicity.”
29 CFR 1910.1200(c)

In context

A classification or labeling concept from the UN Globally Harmonized System, adopted into US law through OSHA's Hazard Communication Standard (29 CFR 1910.1200) and its appendices.

29 CFR 1910.1200

Where this is written in OSHA's rules

29 CFR 1910.1200(c)Read on eCFR / OSHA.gov

Example

Acetone belongs to the “flammable liquid” hazard class (a physical hazard) and also to the “eye irritation” and “specific target organ toxicity — single exposure” health-hazard classes. Each class then has its own category, and together they decide acetone's full label.

Why it matters

The hazard class is the starting point for the whole label — it dictates which pictogram family and statements apply. Missing a class a chemical belongs to (e.g., overlooking its health hazard) leaves workers unwarned and is a classification error under 1910.1200.

Hazard class vs. hazard category

The class is the type of hazard (flammable liquid). The category is the severity within it (Category 1, 2…). Think “class = what kind,” “category = how bad.” A classification names both.

GHS hazard-class families

Family	Example classes	Count (approx.)
Physical	Flammable liquid, oxidizer, gas under pressure, explosive	~17
Health	Acute toxicity, carcinogenicity, skin corrosion, STOT	~10
Environmental	Hazardous to the aquatic environment (GHS09)	2

Hazard Class: frequently asked questions

How many GHS hazard classes are there?: GHS Revision 7 defines roughly 29 hazard classes, split among physical hazards (about 17), health hazards (about 10), and environmental hazards (2).
Can a chemical have more than one hazard class?: Yes. Most hazardous chemicals fall into several classes at once — for example flammable, irritant, and target-organ toxicant — and each contributes its own elements to the label.
What's the difference between a hazard class and a hazard category?: The class is the nature of the hazard (e.g., flammable liquid); the category is the severity within that class (Category 1 most severe). A full classification names both.

Free tools for this

GHS Label Generator Flammable Liquid GHS Category Classifier

Governing OSHA standards

OSHA Hazard Communication Standard (HazCom)OSHA HazCom Standard for Construction

More GHS terms

Acute Toxicity

A GHS health-hazard class for the harmful effects that follow a single dose, several doses within 24 hours, or a 4-hour inhalation exposure. Chemicals are sorted into categories by route (oral, dermal, inhalation) using LD50/LC50 cut-offs — Category 1 is the most toxic. OSHA's HazCom standard uses Categories 1–4.

Aspiration Hazard

A GHS health-hazard class for chemicals that can be fatal if swallowed and then enter the airways — directly or by vomiting — causing chemical pneumonia or lung injury. Thin, low-viscosity hydrocarbons (gasoline, kerosene, lamp oil) are the classic example. It is Category 1, with the health-hazard pictogram (GHS08) and signal word “Danger.”

Carcinogenicity

A GHS health-hazard class for chemicals that cause cancer or increase its incidence. GHS (and OSHA's HazCom standard) sorts carcinogens into Category 1A (known human carcinogen), 1B (presumed, from animal evidence), and Category 2 (suspected). Carcinogens carry the health-hazard pictogram (GHS08) and a hazard statement such as H350 (“May cause cancer”).

Chemicals Under Pressure

A physical-hazard class added by OSHA's 2024 HCS update (aligning with GHS Revision 7) for liquids or solids pressurized with a gas, held in pressure receptacles other than aerosol dispensers and not classified as gases under pressure. It is categorized by the flammability of its contents and always carries the gas-cylinder pictogram (GHS04) for the pressure hazard.

Classification

The process of evaluating the available scientific evidence for a chemical against the GHS criteria to decide whether it is hazardous and, if so, the hazard class and category of each effect. Classification is the first step in HazCom — its result determines every label element (pictogram, signal word, hazard and precautionary statements) and SDS content.

Corrosive to Metals

A GHS physical-hazard class for chemicals that, by chemical action, will materially damage or even destroy metals. It is a single category (Category 1), determined by corrosion-rate testing on steel and aluminum, and uses the corrosion pictogram (GHS05) with the hazard statement H290. It is a separate hazard from skin corrosion, even though both use GHS05.

Desensitized Explosives

A physical-hazard class added by OSHA's 2024 HCS update (GHS Revision 7) for solid or liquid explosives that have been phlegmatized — wetted or diluted — to suppress their explosive properties for safe transport and storage. It has four categories based on the corrected burning rate, and uses the flame pictogram (GHS02), not the exploding-bomb.

Globally Harmonized System (GHS)

An internationally agreed framework created by the United Nations (first adopted in 2003) that standardizes how chemical hazards are classified and communicated — using common hazard classes, pictograms, signal words (Danger / Warning), and coded hazard (H) and precautionary (P) statements on labels and safety data sheets. The US adopted GHS into law through OSHA's 2012 Hazard Communication Standard update.

Sources & verification

Reviewed by HazComFast against eCFR, OSHA.gov, NIOSH, and the Federal Register. Last reviewed 2026-10-05. This glossary is general information, not legal advice; OSHA State-Plan states (e.g. California, Michigan) may adopt stricter requirements.

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