GHS / HazCom term · Glossary
Hazard Category
Verified vs OSHA sources · 2026-10-05
The division of severity within a GHS hazard class. Within a class, Category 1 is the most severe, with higher numbers less severe; some classes add sub-categories (1A, 1B). Categories compare severity only inside the same class — a Category 1 flammable is not “as bad as” a Category 1 carcinogen.
Also known as: GHS category
Hazard Category at a glance
- Lower number = more severe; Category 1 is the most severe in its class.
- Some classes use sub-categories: 1A and 1B (e.g., carcinogenicity).
- Severity is comparable only within the same hazard class, not across classes.
- Category drives the signal word and the specific hazard statement.
In plain English
Once you know what kind of hazard a chemical is (the class), the category says how bad it is within that kind. Category 1 is the worst; bigger numbers are milder. It only ranks severity inside one class, not across different hazards.
What the rule says
“Hazard category means the division of criteria within each hazard class, e.g., oral acute toxicity and flammable liquids include four hazard categories. These categories compare hazard severity within a hazard class and should not be taken as a comparison of hazard categories more generally.”
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.
Where this is written in OSHA's rules
- 29 CFR 1910.1200(c)Read on eCFR / OSHA.gov
Example
Carcinogenicity splits Category 1 into 1A (known human carcinogen) and 1B (presumed). Both get the signal word “Danger” and H350, while Category 2 (suspected) gets “Warning” and H351. The class is the same — carcinogenicity — but the category sets the severity.
Why it matters
The category determines whether a label says “Danger” or “Warning” and which hazard statement appears. Assigning too high a category number (milder) under-warns workers; OSHA treats an incorrect category as a classification error citable under 1910.1200.
Hazard class vs. hazard category
The class is the type of hazard (flammable liquid, carcinogen, acute toxicity). The category is the severity within that class (1 = most severe). A chemical has a class and, within it, a category — e.g., “Flammable Liquid, Category 2.”
How hazard categories rank severity
| Notation | Meaning | Example |
|---|---|---|
| Category 1 | Most severe in the class | Acute toxicity Cat 1 (LD50 ≤ 5 mg/kg) |
| Category 1A / 1B | Sub-divisions of Category 1 | Carcinogen 1A (known) / 1B (presumed) |
| Category 2, 3, 4… | Decreasing severity | Flammable liquid Cat 2 → Cat 4 |
Hazard Category: frequently asked questions
- What is the difference between hazard class and hazard category?
- The class is the nature of the hazard (e.g., flammable liquid, carcinogen). The category is the severity within that class, with Category 1 the most severe. A full classification names both, e.g., “Acute Toxicity (oral), Category 2.”
- Is Category 1 the most or least severe?
- Most severe. GHS numbers categories so that 1 is the highest hazard within a class and larger numbers are less severe.
- What do 1A and 1B mean?
- They are sub-categories of Category 1 used in some classes (such as carcinogenicity and germ cell mutagenicity), where 1A reflects stronger (often human) evidence and 1B reflects presumed (often animal-based) evidence.
Related terms
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Governing OSHA standards
More GHS terms
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 HazardA 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.”
CarcinogenicityA 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 PressureA 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.
ClassificationThe 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 MetalsA 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 ExplosivesA 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
- 29 CFR 1910.1200(c) (eCFR / OSHA.gov)
- OSHA — Appendix A/B to §1910.1200 (classification criteria)
- 29 CFR 1910.1200 (eCFR)
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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