The red-diamond symbols found on construction chemicals are widely called COSHH symbols, but their correct name is GB CLP hazard pictograms. They are used on labels to warn that a supplied substance or mixture has one or more hazardous properties.
There are nine standard pictograms. They can identify risks including flammability, acute poisoning, serious long-term health effects, corrosion, oxidising properties, pressurised gas, explosion and environmental damage. A product may carry more than one symbol, and two products displaying the same symbol may still require very different controls.
The nine symbols are a warning system, not a complete COSHH assessment. Always read the product's signal word, hazard statements, precautionary statements and current safety data sheet, then assess how the substance will actually be stored, mixed, applied and removed on site.
Are They Really COSHH Symbols?
On UK sites, the phrase “COSHH symbols” is useful shorthand, but the pictograms come from chemical classification and labelling law rather than from a separate COSHH symbol system. In Great Britain—England, Scotland and Wales—the relevant supply regime is GB CLP. Northern Ireland continues to operate under EU CLP arrangements.
COSHH then governs how employers assess and control exposure to substances hazardous to health during work. The two systems are connected: the supplier classifies and labels the product, while the employer uses that information as part of the workplace assessment. LCM's guide to what substances COSHH covers in UK construction explains why the assessment must also include dusts, fumes and other hazardous substances created by the task, even when no labelled container is present.
The 9 Hazard Symbols at a Glance
| Pictogram | Main Meaning | Construction Examples | Immediate Site Question |
|---|---|---|---|
| Exploding bomb | Explosive, certain self-reactive substances and some organic peroxides. | Specialist blasting products and some highly reactive resin or peroxide systems. | Could heat, impact, friction, contamination or incorrect mixing trigger a violent reaction? |
| Flame | Flammable materials and certain self-heating, self-reactive or pyrophoric substances. | Solvents, thinners, primers, adhesives, fuels, aerosols and some waterproofing products. | Where are the ignition sources, and can vapour accumulate? |
| Flame over circle | Oxidising gas, liquid or solid that can cause or intensify fire. | Oxygen and certain peroxide hardeners, cleaning agents or treatment chemicals. | Is it separated from fuels, oils, timber, solvents and other combustible materials? |
| Gas cylinder | Gas under pressure, including compressed, liquefied, dissolved or refrigerated gas. | Oxygen, nitrogen, carbon dioxide, LPG and welding gases. | Are cylinders secured, protected from heat and handled with the correct equipment? |
| Corrosion | Severe skin burns, serious eye damage or corrosion of metals. | Acids, strong alkaline cleaners, some cement products, drain chemicals and specialist treatments. | How will splashes, contaminated gloves and emergency eye exposure be controlled? |
| Skull and crossbones | Severe acute toxicity; a small exposure may be toxic or fatal. | Some specialist biocides, pesticides, treatment products, hardeners or industrial chemicals. | Can the substance be eliminated, substituted or handled only under specialist controls? |
| Exclamation mark | Harmful acute toxicity, irritation, skin sensitisation or certain effects such as drowsiness and respiratory irritation. | Cleaners, sealants, adhesives, paints, resins and many general construction chemical products. | Which exact hazard statement applies, and what exposure route does it describe? |
| Health hazard | Serious or long-term health effects, including cancer, genetic damage, reproductive harm, respiratory sensitisation, organ damage or aspiration hazard. | Isocyanate products, certain epoxy hardeners, solvents, coatings and specialist treatment chemicals. | Could repeated or low-level exposure cause permanent disease even without immediate symptoms? |
| Environment | Hazardous to the aquatic environment. | Fuels, oils, coatings, biocides, treatment chemicals and some resins. | How will spills, wash water, contaminated absorbents and disposal be kept out of drains and watercourses? |
1. Exploding Bomb: Explosive or Highly Reactive
The exploding-bomb pictogram is used for explosives and for certain self-reactive substances and organic peroxides. These materials can react violently because of heat, impact, friction, contamination or incorrect storage. They are not routine products on most sites, but may arise in specialist demolition, blasting, resin, tunnelling or infrastructure operations.
The pictogram should trigger specialist review rather than a basic glove-and-goggles response. Site teams must establish the correct storage limits, segregation, temperature controls, handling restrictions, competence requirements and emergency arrangements. Where the product also presents a fire or health hazard, other pictograms and hazard statements may appear alongside it.
2. Flame: Flammable
The flame pictogram covers more than liquids that catch fire easily. It can be used for flammable gases, aerosols, liquids and solids, together with certain self-reactive, pyrophoric, self-heating and water-reactive substances. On construction sites it is commonly seen on solvents, thinners, primers, spray products, adhesives, fuels and gas products.
A COSHH assessment should consider exposure to vapour or skin contact, but the fire and explosion risk may also require a DSEAR assessment. Storage cabinets alone are not enough. The method must consider ignition sources, hot works, ventilation, decanting, waste containers, contaminated rags, spill control and whether vapours can collect in basements, risers or other poorly ventilated spaces.
3. Flame Over Circle: Oxidising
An oxidising substance may not burn by itself, but it can cause or intensify a fire by supporting combustion. Oxygen cylinders are a familiar construction example. Certain peroxide products and specialist cleaning or treatment chemicals can also carry the symbol.
The crucial control is segregation from combustible and incompatible materials. Oxygen equipment must be kept free from oil and grease. Storage and transport arrangements should prevent cylinders or containers being damaged, heated or placed beside fuels, timber, packaging and solvent products.
4. Gas Cylinder: Gas Under Pressure
The gas-cylinder pictogram identifies compressed, liquefied, dissolved or refrigerated gases. A pressurised cylinder may rupture or explode if heated. Refrigerated gas can also cause severe cold burns. Some gases create additional hazards, so a cylinder may carry the flame, oxidising or skull-and-crossbones pictogram as well.
Site controls should cover secure upright storage, valve protection, separation of incompatible gases, suitable trolleys, safe connection and disconnection, leak checks and emergency action. The assessment must also consider oxygen displacement or toxic accumulation where gases are used in confined or poorly ventilated locations.
5. Corrosion: Severe Burns and Eye Damage
The corrosion pictogram can indicate severe skin burns, serious eye damage or a substance corrosive to metals. Construction examples include acids, strong alkaline cleaning agents, specialist surface treatments, drain products and some cement-based materials.
The symbol does not specify which body part or exposure route creates the main risk. The hazard statement and safety data sheet must therefore be checked. Controls may include closed transfer, splash protection, correctly selected gloves, face protection, suitable washing facilities and immediate access to eyewash. Contaminated clothing and gloves can continue exposing the skin after the task ends.
6. Skull and Crossbones: Severe Acute Toxicity
The skull-and-crossbones pictogram warns of severe acute toxicity. Exposure through swallowing, inhalation or skin contact may be toxic or fatal, depending on the classification. Products carrying this symbol require a much stronger response than ordinary site chemical handling.
The first question should be whether the product can be removed from the process or replaced with a safer alternative. Where use is unavoidable, access, competence, containment, exposure control, storage, first aid and emergency arrangements must be defined before work begins. Workers should never rely on recognising an odour or experiencing symptoms as an exposure-warning system.
7. Exclamation Mark: Harmful or Irritant
The exclamation mark appears on many familiar construction products, but it does not have one single meaning. Depending on the classification, it can indicate harmful acute toxicity, skin or eye irritation, skin sensitisation, respiratory irritation, drowsiness or dizziness. The supporting hazard statement is therefore essential.
A common mistake is to regard this symbol as minor because the product is widely available. Repeated skin contact with adhesives, resins, sealants and cleaners can contribute to dermatitis or sensitisation. Spraying, sanding or using the same product in an enclosed area may create a much greater exposure than occasional brush application outdoors.
8. Health Hazard: Serious or Long-Term Effects
The health-hazard pictogram shows a human silhouette with a star-shaped mark on the chest. It is associated with serious effects such as carcinogenicity, mutagenicity, reproductive toxicity, respiratory sensitisation, specific target-organ toxicity and aspiration hazard.
This is particularly important in construction because serious occupational disease may develop after repeated exposure rather than after one obvious incident. Isocyanate-containing products are a well-known example where respiratory sensitisation can lead to occupational asthma. Certain epoxy systems, solvents and specialist coatings may carry the pictogram for different reasons, so controls must be based on the exact hazard statement rather than the graphic alone.
9. Environment: Hazardous to Aquatic Life
The environment pictogram shows a dead tree and fish. It identifies substances hazardous to the aquatic environment. It does not, by itself, explain the risk to a worker's health, but it is a critical warning for storage, spill response, drainage protection and waste disposal.
Construction sites can create rapid pollution pathways through surface-water drains, dewatering systems and exposed ground. Fuel, oil, coating, resin or biocide spills must not be washed away. The environmental symbol should prompt a clear plan for bunding, drain protection, spill kits, contaminated absorbents, wash water and licensed disposal.
Why the Hazard Statement Matters More Than the Picture Alone
Each pictogram represents a group of possible hazards. The label's hazard statement explains the specific nature of the hazard—for example, whether a product causes serious eye damage, is harmful if inhaled or may cause allergy or asthma symptoms. The label may also include the signal word Danger for more severe hazards or Warning for less severe classifications.
Precautionary statements describe recommended measures to prevent or reduce harm. These can include wearing eye protection, avoiding release to the environment or using respiratory protection where ventilation is inadequate. However, the supplier's wording still needs to be translated into a safe construction method that reflects the quantity, work location, duration, application process and people exposed.
What Information Should Be Read on the Label?
A compliant hazard label is more than the red diamond. Before use, the site team should identify the product, supplier, pictograms, signal word, hazard statements and precautionary statements. These elements work together. Reading only the image can lead to the wrong control because the same pictogram may represent several different hazard classes or severities.
Where the product has been decanted, the secondary container must remain clearly identifiable and suitable for the substance. Unlabelled bottles, cups and improvised containers create foreseeable risks during use, storage, cleaning and emergency response.
How the Safety Data Sheet Supports the COSHH Assessment
A current safety data sheet provides further information on classification, composition, first aid, fire response, accidental release, handling, storage, exposure controls, stability, toxicology and disposal. Sections 2, 7 and 8 are often particularly useful at the start of a site assessment, but the full document may contain information relevant to the activity.
The safety data sheet does not describe every construction scenario. It cannot know whether the product will be sprayed above operatives, mixed in a basement, applied beside hot works, used for eight hours or removed by grinding. The employer must combine the supplier information with the real method and environment.
No Symbol Does Not Mean No COSHH Risk
Many significant construction exposures are generated by the work rather than supplied in labelled packaging. Cutting concrete can release respirable crystalline silica. Welding generates fume. Diesel plant produces exhaust emissions. Damp or contaminated environments can expose workers to biological agents. These hazards may have no red-diamond pictogram at the point of exposure.
This is why a site COSHH register based only on purchased products will be incomplete. LCM's analysis of silica exposure during dry cutting demonstrates how the work process can create the dominant health risk even where the original material looks ordinary.
What Site Teams Should Do When They See a Hazard Symbol
Identify the exact hazard: read the hazard statement rather than relying on the pictogram name.
Obtain the current safety data sheet: confirm that the product and revision match what is on site.
Consider elimination or substitution: ask whether the product or application method can be replaced with a safer option.
Assess the real task: consider quantity, frequency, duration, ventilation, temperature, spraying, mixing, sanding, cutting, cleaning and waste.
Control exposure at source: use enclosure, extraction, ventilation, segregation, closed transfer or other engineering measures before relying only on PPE.
Address overlapping risks: products carrying flame, explosion, oxidising or gas symbols may require fire, cylinder or DSEAR controls in addition to COSHH.
Brief and supervise the workforce: operatives should understand the specific product, exposure routes, controls, emergency actions and disposal method.
Common Construction-Site Mistakes
Treating the pictogram as the complete assessment: the image identifies a hazard group but does not assess the work.
Assuming the exclamation mark always means low risk: repeated or poorly controlled exposure can still cause significant ill health.
Choosing gloves or masks from the symbol alone: PPE selection requires the substance, exposure route, breakthrough time, concentration and task to be understood.
Ignoring several pictograms on one product: the controls must address every applicable health, fire, pressure and environmental hazard.
Keeping old or generic paperwork: changed formulations, revised safety data sheets and different application methods can invalidate the assessment.
Allowing unlabelled decanted products: workers and emergency responders may be unable to identify the substance or select the correct action.
The Practical Answer
The nine hazard pictograms are the exploding bomb, flame, flame over circle, gas cylinder, corrosion, skull and crossbones, exclamation mark, health hazard and environment symbols. On construction sites they provide an immediate warning about the hazardous properties of supplied chemicals, but they do not explain the full risk of the work.
The correct approach is to read the whole label, check the current safety data sheet and complete a task-specific assessment. The symbol tells the site team to investigate. The hazard statement explains what the danger is. The COSHH assessment then determines how exposure will be prevented or controlled under the actual site conditions. LCM's review of recurring failures identified through HSE prosecutions reinforces the wider lesson: recognised hazards must be converted into physical controls, competent supervision and verifiable compliance evidence.
Sources and methodology: This guide was checked against current Health and Safety Executive guidance on GB CLP hazard pictograms, hazard labels, hazard and precautionary statements, the relationship between COSHH and CLP, and the GB and Northern Ireland CLP regimes. The article reflects guidance available on 19 July 2026 and does not replace a product-specific safety data sheet, COSHH assessment, DSEAR assessment or competent occupational-hygiene advice.
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Expert Verification & Authorship: Mihai Chelmus
Founder, London Construction Magazine | Construction Testing & Investigation Specialist |
