Chemical hazards and the GHS label

Awareness level only. This lesson explains the ideas so you recognise them. It does not qualify you to do this work. Before you handle chemicals, biological materials or lab equipment for real, you need the training your employer or institution requires, and you must work under supervision until they sign you off.

Why it matters

A lab may hold hundreds of chemicals, and many look alike: clear liquids, white powders. The label is your first warning of what a container can do to you. Before 1992, labels varied by country and supplier. The Globally Harmonized System of Classification and Labelling of Chemicals (GHSThe Globally Harmonized System of Classification and Labelling of Chemicals, a UN-developed single format for chemical labels and Safety Data Sheets.), developed through the United Nations, gives the whole world one format. In the United States, OSHA's Hazard Communication Standard (HazCom, 29 CFR 1910.1200) adopts GHS for workplace labels and Safety Data Sheets. Most other countries have adopted it too (for example, CLP in the EU and WHMIS in Canada).

Hazard classes

GHS sorts hazards into three groups:

• Physical hazards: flammable, explosive, oxidising, self-reactive, pyrophoric (ignites in air), gases under pressure, corrosive to metals.
• Health hazards: acute toxicity, skin corrosion or irritation, serious eye damage, sensitisation, carcinogenicity, mutagenicity, reproductive toxicity, organ toxicity, aspiration hazard.
• Environmental hazards: harmful to aquatic life (and, outside the US, the ozone layer).

Within a class, a categoryThe severity level within a GHS hazard class, where category 1 is the most severe. gives severity. Category 1 is the most severe: acute toxicity category 1 can kill in tiny amounts; category 4 is harmful.

The six parts of a GHS label

1. Product identifier: the chemical or product name, matching its Safety Data Sheet.
2. Signal wordThe one word on a GHS label that shows severity: Danger for more severe hazards, Warning for less severe ones.: Danger (more severe) or Warning (less severe). A label has only one.
3. Hazard statementsStandard coded phrases (H-codes) that describe the nature of a chemical's hazard, such as H225 Highly flammable liquid and vapour.: standard phrases describing the hazard, each with a code, such as H225 Highly flammable liquid and vapour or H314 Causes severe skin burns and eye damage.
4. Precautionary statementsStandard coded phrases (P-codes) that say how to prevent harm and how to respond, store and dispose of the chemical.: what to do, with P-codes: prevention (P210 Keep away from heat, sparks, open flames), response (P305+P351+P338 IF IN EYES: Rinse cautiously with water for several minutes...), storage and disposal.
5. Pictograms: red-bordered diamonds with a black symbol.
6. Supplier information: name, address and phone number of the manufacturer or importer.

The nine pictograms

Worked example: reading a label

A bottle of acetone shows: signal word Danger; the flame and exclamation mark pictograms; H225 Highly flammable liquid and vapour, H319 Causes serious eye irritation, H336 May cause drowsiness or dizziness; and precautions including P210 (no ignition sources) and P233 (keep container tightly closed).

What it tells you: keep it away from hot plates and flames, use it where vapours are controlled, wear eye protection, and close the bottle after use. The label does not tell you which glove material works or how to clean up a large spill; for that you go to the Safety Data Sheet (next lesson).

Secondary containers

When you pour a chemical into a beaker, wash bottle or smaller bottle, that secondary containerA beaker, wash bottle or smaller bottle a chemical is poured into, which must also be labelled by the lab's rules. must also be labelled according to your lab's rules: at least the chemical name and main hazards, often the date and your initials. Unlabelled containers are one of the most common findings in lab inspections, and the cause of many "what was in this?" incidents.

Other labels you will see

• NFPA 704 diamond (blue health, red flammability, yellow instability, white special hazards, rated 0 to 4) on doors and storage areas, aimed at emergency responders.
• DOT/transport labels on shipping boxes.
• Biohazard, radiation and laser warning signs, covered elsewhere in this course.

Note that the NFPA scale runs the opposite way to GHS categories: in NFPA, 4 is the most severe; in GHS, category 1 is.

Common mistakes

• Judging by smell or looks. Many dangerous chemicals have no warning odour.
• Ignoring the signal word. "Danger" means take extra care.
• Confusing GHS categories with NFPA numbers.
• Leaving secondary containers unlabelled, even "just for a minute".

Quick recap

• GHS gives one label format worldwide; OSHA HazCom requires it in US workplaces.
• A label has six parts: identifier, signal word, hazard statements, precautionary statements, pictograms, supplier.
• Learn the nine pictograms and what each means.
• Labels are the summary; the Safety Data Sheet has the detail.

Official source: OSHA Hazard Communication, https://www.osha.gov/hazcom (Checked on 2026-10-23.)