Hazard pictograms represent a wide range of dangers beyond the most familiar symbols for flammable or toxic materials. Across workplace labels, shipping containers, and laboratory chemicals, pictograms cover nine categories of chemical hazard, plus additional symbols for radiation and biological risks. Here’s what each one means and when you’re likely to encounter it.
The Nine GHS Chemical Hazard Pictograms
The Globally Harmonized System (GHS) is the international standard for labeling chemical hazards. It uses nine pictograms, each a red diamond-bordered symbol on a white background. OSHA updated the U.S. Hazard Communication Standard in May 2024 to align with the seventh revision of this system, so these symbols now appear on virtually every chemical product label in workplaces and stores.
Each pictogram covers one or more hazard categories. Some are straightforward, others represent a surprisingly broad set of risks.
Physical Hazard Pictograms
Exploding Bomb
This symbol covers explosives, self-reactive substances, and organic peroxides that can detonate or explode. Explosives are further divided into six divisions based on severity. Division 1.1 substances can cause a mass explosion affecting an entire load instantaneously. Division 1.4 presents only a minor hazard largely confined to the package. Divisions 1.5 and 1.6 cover very insensitive or extremely insensitive materials with negligible risk of accidental detonation under normal conditions.
Flame
The flame pictogram is one of the most common. It applies to flammable gases, flammable liquids, flammable solids, flammable aerosols, self-reactive chemicals, pyrophoric substances (which ignite on contact with air), self-heating chemicals, substances that emit flammable gases when wet, and certain organic peroxides. If a product can catch fire under normal or slightly elevated conditions, it gets this symbol.
Flame Over Circle
This one looks like a flame sitting on top of a ring and represents oxidizers. Oxidizers don’t necessarily burn on their own, but they release oxygen or other reactive elements that intensify fires or cause other materials to ignite. Both oxidizing gases, liquids, and solids carry this pictogram.
Gas Cylinder
A symbol shaped like a pressurized tank warns that the container holds gas under pressure. This includes compressed gases, liquefied gases, refrigerated liquefied gases, and dissolved gases. The danger is that a damaged container can rupture violently, and refrigerated gases can cause severe cold burns.
Corrosion
The corrosion pictogram shows material being eaten away on a surface and a hand. It represents chemicals that destroy metal on contact and also cause severe skin burns or serious eye damage. This dual meaning is important: the same symbol warns about damage to both your body and your equipment.
Health Hazard Pictograms
Skull and Crossbones
This is the classic poison symbol, reserved for substances with high acute toxicity, meaning they can kill or cause serious harm from a single exposure. The threshold for earning this label is precise. A substance gets the skull and crossbones if its lethal dose is 300 mg/kg of body weight or less when swallowed, or 1,000 mg/kg or less through skin contact. For inhaled gases, the cutoff is 2,500 parts per million or less. In practical terms, these are chemicals where even a small accidental exposure could be fatal.
Exclamation Mark
The exclamation mark covers a broad category of lower-level but still meaningful hazards. It appears on products that cause skin irritation, serious eye irritation, or allergic skin reactions. It also covers substances that are harmful (but not immediately fatal) if swallowed, inhaled, or absorbed through skin. Narcotic effects like drowsiness or dizziness, respiratory tract irritation, and hazards not otherwise classified also fall under this symbol. Think of it as the “caution” level, one step below the skull and crossbones.
Health Hazard (Silhouette)
This pictogram shows a human figure with a starburst on the chest, and it represents some of the most serious long-term health risks. Chemicals carrying this symbol may cause cancer, genetic mutations, or reproductive harm including damage to fertility or the unborn child. It also covers respiratory sensitization (chemicals that can trigger asthma or breathing difficulties after inhalation), organ damage from single or repeated exposure, and aspiration toxicity, where swallowing a liquid causes it to enter the lungs and potentially be fatal.
The range here is wide. A chemical labeled with this pictogram might be a suspected carcinogen, or it might cause organ damage through prolonged workplace exposure. The specific risk is always spelled out in the hazard statement text printed alongside the pictogram on the label.
Environment
The ninth GHS pictogram shows a dead tree and dead fish, representing chemicals that are toxic to aquatic life. This covers both acute aquatic toxicity (kills organisms quickly) and chronic aquatic toxicity (causes long-term damage to water ecosystems). Unlike the other eight pictograms, OSHA does not require the environment pictogram on workplace labels in the United States, though it appears on labels in many other countries and on safety data sheets.
Transport Hazard Placards
When chemicals move by truck, rail, or ship, a different but overlapping system applies. The U.S. Department of Transportation uses nine classes of hazardous materials, displayed as diamond-shaped placards on vehicles. These cover explosives, gases, flammable liquids, flammable solids, oxidizers and organic peroxides, toxic and poison inhalation hazards, radioactive materials, corrosives, and miscellaneous dangerous goods.
The transport placards look different from GHS labels. They use color coding (red for flammable, yellow for oxidizers, white for toxic) and include a four-digit UN identification number so emergency responders can quickly identify the exact material involved in a spill or accident. GHS labels, by contrast, are designed for workers and consumers handling products in a warehouse, lab, or home.
Radiation and Biohazard Symbols
Two other widely recognized hazard symbols fall outside the GHS system entirely.
The radiation trefoil, three blade-shaped segments arranged around a central dot, is the international symbol for ionizing radiation. It appears in magenta or black on a yellow background wherever radioactive materials are handled or radiation-producing equipment is used. In 2007, the International Organization for Standardization and the International Atomic Energy Agency introduced a supplementary symbol (ISO 21482) for the most dangerous radiation sources, those capable of causing death or serious injury. This newer symbol adds a skull, running figure, and red background to the traditional trefoil and is placed directly on devices like industrial radiography units and cancer treatment machines as a clear warning not to dismantle the equipment or approach the source.
The biohazard symbol, three interlocking crescents forming a circular pattern, warns of biological agents that pose a risk to human health. You’ll see it on containers holding infectious materials, in laboratories working with pathogens, and on medical waste bins. It is defined by a separate standard and is not part of the GHS or DOT systems.
How To Read a Label With Multiple Pictograms
Many chemicals carry two or more pictograms at once. A strong acid, for example, might display both the corrosion symbol (for skin burns) and the exclamation mark (for eye irritation at lower concentrations). A solvent could carry the flame, the exclamation mark, and the health hazard silhouette if it is flammable, irritating to skin, and suspected of causing organ damage over time.
When pictograms overlap in severity, the more serious one takes priority on the label. A chemical that is both acutely toxic (skull and crossbones) and an irritant (exclamation mark) will display the skull and crossbones, since that already communicates the greater danger. The exclamation mark would be redundant and is dropped.
The pictograms are just the first layer. Every GHS label also includes a signal word (“Danger” for more severe hazards, “Warning” for less severe ones), specific hazard statements explaining the risk in plain language, and precautionary statements telling you how to store, handle, and respond to exposure. The pictogram gets your attention. The text tells you exactly what you’re dealing with.