Why Hazard Symbols Matter
Chemical hazard symbols are a universal language. Regardless of whether you read English, Mandarin, or Spanish, a skull-and-crossbones on a container communicates danger instantly. The Globally Harmonized System of Classification and Labelling of Chemicals (GHS) was introduced by the United Nations to standardize these symbols worldwide, replacing dozens of conflicting national systems.
Understanding these pictograms is essential for anyone working with, transporting, or storing chemicals — and is a core component of responsible laboratory practice.
The 9 GHS Hazard Pictograms
GHS uses nine standardized diamond-shaped pictograms with a red border and white background. Each represents a category of chemical hazard:
1. Flame 🔥
Hazard: Flammable substances, including flammable gases, liquids, solids, and self-reactive materials. Examples: ethanol, acetone, hydrogen gas.
2. Flame Over Circle
Hazard: Oxidizing substances that can intensify fires by releasing oxygen. Examples: hydrogen peroxide (concentrated), potassium permanganate.
3. Exploding Bomb
Hazard: Explosive materials or substances that can rapidly decompose, deflagrate, or detonate. Examples: ammonium nitrate, organic peroxides.
4. Compressed Gas Cylinder
Hazard: Gases under pressure — compressed, liquefied, dissolved, or refrigerated. Examples: oxygen cylinders, propane tanks, dry ice (CO₂).
5. Corrosion
Hazard: Corrosive substances that destroy living tissue or damage metals. Examples: sulfuric acid, sodium hydroxide, hydrofluoric acid.
6. Skull and Crossbones
Hazard: Acutely toxic substances that are fatal or toxic in small doses (oral, dermal, or inhalation routes). Examples: hydrogen cyanide, methanol.
7. Exclamation Mark
Hazard: Lower-level hazards including irritants, skin/eye sensitizers, and substances with specific target organ toxicity (single exposure). Examples: isopropanol, acetaldehyde.
8. Health Hazard (Silhouette with Starburst)
Hazard: Serious or chronic health hazards, including carcinogens, reproductive toxins, respiratory sensitizers, and substances causing organ damage. Examples: benzene, asbestos, formaldehyde.
9. Environment (Dead Tree and Fish)
Hazard: Substances that are acutely or chronically hazardous to the aquatic environment. Examples: tributyltin compounds, certain pesticides.
Reading a GHS Chemical Label
A complete GHS label includes more than just pictograms. You should also look for:
- Signal Word: "Danger" (more severe hazard) or "Warning" (less severe).
- Hazard Statements: Standardized phrases describing the nature of the hazard (e.g., "H225 – Highly flammable liquid and vapour").
- Precautionary Statements (P-codes): Instructions for safe handling, storage, and disposal.
- Supplier Identification: Name and contact of the manufacturer or importer.
Legacy Systems Still in Use
While GHS is globally adopted, older hazard symbols still appear on legacy equipment, storage facilities, and some regional products. Familiar orange-square symbols from the older EU system (depicting flames, oxidizers, and toxic skulls) may still be encountered. Familiarizing yourself with both systems is worthwhile.
Practical Tips for the Lab or Workplace
- Never remove or obscure labels from chemical containers.
- Re-label secondary containers (e.g., spray bottles) with the chemical name and applicable hazard symbols.
- Inspect labels before every use — degraded or missing labels are a hazard in themselves.
- Cross-reference labels with the chemical's SDS for full hazard information.
Summary Table
| Pictogram | Hazard Class | Common Examples |
|---|---|---|
| Flame | Flammable | Ethanol, acetone |
| Exploding bomb | Explosive | Ammonium nitrate |
| Skull & crossbones | Acute toxicity | HCN, methanol |
| Corrosion | Corrosive | H₂SO₄, NaOH |
| Health hazard | Carcinogen/CMR | Benzene, formaldehyde |
| Environment | Aquatic toxicity | Some pesticides |
Recognizing and respecting these symbols is one of the simplest, most effective ways to promote safety in any environment where chemicals are present.