GHS Hazard Pictograms Explained

Pick up almost any chemical bottle, from lab reagents to household bleach, and you’ll see one or more red-bordered diamonds with black symbols inside. These are GHS hazard pictograms, and they’re the same in most countries around the world. Once you know them, you can understand the main hazards of a substance in seconds, even if the label is in a language you can’t read.

What GHS is

GHS stands for the Globally Harmonized System of Classification and Labelling of Chemicals. It was developed by the United Nations and first published in 2003, to replace the many different national labelling systems that made international trade and safety information confusing.

Countries adopt GHS into their own laws. For example, the European Union’s CLP Regulation (2008) and the United States OSHA Hazard Communication Standard (2012 revision) are both based on GHS. The pictograms look the same everywhere, although countries may adopt slightly different subsets of the hazard categories.

The nine pictograms

Each pictogram is a black symbol on a white background inside a red diamond.

1. Exploding bomb: explosives

Meaning: explosive; may explode from fire, heat, shock or friction. Examples: some organic peroxides, picric acid when dry, fireworks, certain azides.

2. Flame: flammable

Meaning: flammable gases, liquids, solids or aerosols; substances that catch fire spontaneously in air (pyrophoric); substances that release flammable gases with water; self-heating substances. Examples: ethanol, propanone (acetone), petrol, hydrogen, sodium metal, butane.

3. Flame over circle: oxidising

Meaning: oxidiser; can cause or intensify fire by providing oxygen. Examples: potassium nitrate, hydrogen peroxide (concentrated), potassium permanganate, oxygen gas, concentrated nitric acid.

Note the difference from the flame pictogram: oxidisers don’t burn themselves but make other things burn more fiercely.

4. Gas cylinder: gases under pressure

Meaning: contains gas under pressure; may explode if heated; refrigerated gases can cause cold burns. Examples: cylinders of nitrogen, carbon dioxide, oxygen, helium; liquid nitrogen containers.

5. Corrosion: corrosive

Meaning: causes severe skin burns and eye damage; may corrode metals. Examples: concentrated hydrochloric, sulfuric and nitric acids; sodium hydroxide; many oven and drain cleaners.

6. Skull and crossbones: acute toxicity (severe)

Meaning: fatal or toxic if swallowed, inhaled or absorbed through the skin, even in small amounts. Examples: methanol (in some categories), mercury(II) chloride, sodium cyanide, hydrofluoric acid.

7. Exclamation mark: less severe hazards

Meaning: harmful (less acutely toxic); irritant to skin, eyes or respiratory tract; may cause skin allergy; narcotic effects (drowsiness or dizziness); hazardous to the ozone layer (in some regions). Examples: dilute acids and alkalis at moderate concentrations, copper(II) sulfate, many household cleaning products.

8. Health hazard: serious long-term health hazards

Meaning: may cause cancer, genetic defects, harm to fertility or unborn children, organ damage through prolonged exposure, or respiratory sensitisation (asthma-like reactions); aspiration hazard (can be fatal if swallowed and enters the airways). Examples: benzene, potassium dichromate, formaldehyde, some solvents, lamp oil.

The symbol is the outline of a person with a star-shaped burst on the chest.

9. Environment: hazardous to the aquatic environment

Meaning: toxic to aquatic life, often with long-lasting effects. Examples: copper(II) sulfate, silver nitrate, many pesticides, zinc compounds.

The symbol shows a dead tree and a dead fish. In some countries, this pictogram is not mandatory for all products.

Quick reference table

Pictogram	Hazard group	Common lab examples
Exploding bomb	explosives	dry picric acid, some peroxides
Flame	flammable	ethanol, acetone, hydrogen, sodium
Flame over circle	oxidising	KNO₃, KMnO₄, concentrated H₂O₂
Gas cylinder	gases under pressure	gas cylinders
Corrosion	corrosive	concentrated acids, NaOH
Skull and crossbones	acute toxicity	cyanides, mercury(II) salts
Exclamation mark	irritant, harmful	dilute acids, CuSO₄
Health hazard	long-term health	benzene, dichromates
Environment	aquatic toxicity	CuSO₄, AgNO₃

One substance can carry several pictograms. Concentrated nitric acid, for example, is both corrosive and oxidising. Copper(II) sulfate is both an irritant and hazardous to the environment.

Signal words

Every GHS label with a hazard also carries one signal word:

• Danger: for more severe hazards.
• Warning: for less severe hazards.

If a substance has both types of hazard, only Danger is shown.

Hazard (H) and precautionary (P) statements

Labels and safety data sheets use standard coded phrases:

H-statements describe the hazard:

• H225: Highly flammable liquid and vapour
• H290: May be corrosive to metals
• H314: Causes severe skin burns and eye damage
• H319: Causes serious eye irritation
• H400: Very toxic to aquatic life

P-statements describe how to use the substance safely:

• P210: Keep away from heat, hot surfaces, sparks, open flames and other ignition sources. No smoking.
• P280: Wear protective gloves, protective clothing, eye protection and face protection.
• P305 + P351 + P338: IF IN EYES: Rinse cautiously with water for several minutes. Remove contact lenses, if present and easy to do. Continue rinsing.

The numbering is standard, which means the same H- or P-number always has the same meaning, in any country’s version of the label.

How to read a chemical label

A full GHS label typically includes:

1. Product identifier: the chemical name (and sometimes a CAS number, a unique registry number for the substance).
2. Pictograms: one or more red diamonds.
3. Signal word: Danger or Warning.
4. Hazard statements: what could go wrong.
5. Precautionary statements: how to prevent it and what to do if it happens.
6. Supplier details: name, address and phone number.

Always check the concentration. The hazard classification depends on it. Concentrated hydrochloric acid is corrosive; 0.1 mol/dm³ hydrochloric acid may carry no hazard pictogram at all in some classification systems.

For more detail than a label can hold, look up the safety data sheet (SDS), which every supplier must provide. An SDS has 16 standard sections, covering everything from first aid and fire-fighting to storage, disposal and toxicology.

Older symbols you may still see

Before GHS, many countries used different symbols, such as orange squares in the EU (with letters like C for corrosive, T for toxic, Xi for irritant) or various national systems. You may still see these on older bottles in stores and some textbooks. They carry similar meanings but aren’t used on newly supplied chemicals in most GHS-adopting countries.

Transport labels are different

Chemicals being transported by road, rail, sea or air carry transport labels under the UN Recommendations on the Transport of Dangerous Goods. These are also diamonds but are coloured (for example, red for flammable liquids, black-and-white for corrosives) and carry a class number at the bottom. They’re related to GHS but not identical.

Key takeaways

• GHS uses nine standard pictograms: explosive, flammable, oxidising, gas under pressure, corrosive, acutely toxic, irritant/harmful, serious health hazard and environmental hazard.
• “Danger” signals a more severe hazard than “Warning”.
• H-statements describe hazards; P-statements describe precautions, with standard numbering worldwide.
• Hazard depends on concentration, so always read the full label.
• Combine labels with good practice from lab safety rules.