For all the diverse categories of safety symbols, hazard and warning signs are the ones to watch out for most of all.

People are exposed to dangerous hazards on a daily basis, which is why we all need to be aware of the risks and how to avoid them.

As sign experts, 3 Signs are happy to let you know the top 9 hazard and warning signs you need to know about.


Signs depicting a bomb blowing up warn us about the presence of unstable, explosive substances. From the more obvious likes of fireworks or ammunition, things like paint or adhesives emit flammable fumes which can cause explosions when mixed with air or heat. Explosion signs accompany materials or items that require especially careful handling.


What do gasoline, alcohol, wood or paper have in common? They can all catch fire very easily. All materials and products with high fire risk should be stored safely, far from anything that could potentially ignite flames and cause great damage. ‘Flammable’ signs are as straightforward as can be: recognisably illustrated by a little flame.

Oxidising substances

Signs featuring a circle with a flame above it inform us about a substance’s tendency to react exothermically (releasing heat or light) with other chemicals. Substances such as hydrogen peroxide or nitrate compounds, also known as oxidisers, are not a fire hazard by themselves; the main danger lies in them getting introduced to other flammable chemicals.

Gas under pressure

In the alphabet of safety signage, ‘pressurised gas’ is represented by a black cylinder. You are most likely to find these signs in medical settings or scientific laboratories where these gases are used for a variety of tasks (e.g. for welding, or to power certain machines). Many of the gases compressed within cylinders are explosive, while others can bring on various health problems due to their toxicity or displace breathable air and cause asphyxiation.


A pictogram of a chemical being poured on a hand and a surface can only mean one thing: corrosive chemicals. These substances, usually strong acids, cause a chemical reaction and irritate whatever surface they encounter. By dehydrating the skin and producing heat, corrosive chemicals cause burns. Cleaning products and other solutions labelled with a ‘corrosive’ sign must therefore be handled carefully, with suitable protective gear.


A pirate flag-like sign, featuring a skull with crossbones, warns of materials that are extremely dangerous to health. These symbols can be found on substances that can be fatal when ingested, inhaled, or absorbed through the skin – even in the smallest of doses. Anyone who comes in contact with a chemical labelled like this must seek emergency medical care.

Health hazard

The exclamation mark of ‘health hazard’ signs can be found on many cleaning products, meaning simply that those substances can cause harm if handled incorrectly. While not quite as dangerous as chemicals labelled with ‘toxic’ signs, touching, swallowing or inhaling these substances can still result in substantial health issues.

Serious health hazard

Chemicals that may damage the internal organs, cause genetic defects or otherwise harm unborn children, trigger asthma/allergy or cause cancer, carry the symbol of a human silhouette with an exploding star shape within. Asbestos or turpentine are two examples of substances that pose a long-term health risk.

Dangerous for the environment

Finally, a dead tree and an equally lifeless fish feature on a sign reserved for substances dangerous to the environment. Fuel, pesticides, mercury, lead, and many others, all require extremely cautious handling as their toxicity has long-lasting, widespread effects on all lifeforms.

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