The hazard symbol on a beaker tells you what kind of danger the chemical inside poses, whether that’s a burn risk, a fire risk, a poison risk, or something else. These red-bordered diamond-shaped symbols are part of the Globally Harmonized System (GHS), an international standard used on chemical labels in labs, classrooms, and workplaces worldwide. There are nine pictograms in total, and each one communicates a specific type of hazard at a glance.
The Nine GHS Hazard Symbols
Every GHS pictogram is a black symbol inside a white diamond with a red border. If you see one on a beaker, bottle, or container label, here’s what each one means:
- Corrosion (liquid pouring onto a hand and surface): The chemical can burn skin, cause serious eye damage, or eat through metals. This is one of the most common symbols you’ll encounter on lab beakers. It applies to strong acids and bases, generally those with a pH below 4 or above 9.
- Flame: The substance is flammable. It can catch fire easily, sometimes at temperatures well below room temperature. This covers flammable liquids, solids, gases, and chemicals that release flammable gas on contact with water.
- Skull and crossbones: The chemical can cause death or severe harm from a single exposure or short-term contact. This signals acute toxicity through swallowing, skin absorption, or inhalation.
- Health hazard (a silhouette of a person with a starburst on the chest): The substance poses longer-term health risks. These include cancer, reproductive harm, respiratory sensitization, organ damage from repeated exposure, or genetic damage. This symbol flags chronic dangers rather than immediate ones.
- Exclamation mark: A lower-level warning. The chemical may irritate skin or eyes, cause allergic skin reactions, or be harmful (but not fatal) if swallowed or inhaled. It also covers substances with narcotic effects like drowsiness or dizziness.
- Flame over circle: The substance is an oxidizer. It doesn’t burn on its own but supplies oxygen that makes other materials ignite more easily or burn more intensely. This is distinct from the plain flame symbol.
- Exploding bomb: The chemical is explosive or self-reactive and can detonate under certain conditions like heat, shock, or friction.
- Gas cylinder: The container holds gas under pressure. If damaged or heated, it can rupture or explode. Some compressed gases are also cold enough to cause frostbite.
- Environment (a dead tree and fish): The chemical is toxic to aquatic life. This symbol is not always required on workplace labels but appears on many chemical containers, particularly for substances that persist in water systems.
How to Read the Full Label
The pictogram is only one piece of the label. GHS labels also include a signal word, either “Danger” or “Warning.” Danger indicates the more severe hazards within a given category, while Warning covers less severe ones. If a chemical qualifies for both, only Danger appears on the label. A single container can display multiple pictograms if the substance poses more than one type of hazard.
Below the signal word, you’ll find hazard statements that spell out the specific risks in plain language, things like “causes severe skin burns and eye damage” or “may cause cancer.” There are also precautionary statements describing safe handling, storage, and what to do after exposure. Together, these elements give you a much more complete picture than the pictogram alone.
Corrosion: The Most Common Beaker Symbol
If you searched this question because you saw a symbol showing liquid dripping onto a hand or a surface and destroying it, you’re looking at the corrosion pictogram. It’s the one people encounter most often on lab glassware because so many common lab chemicals are corrosive: hydrochloric acid, sulfuric acid, sodium hydroxide, and concentrated ammonia, to name a few.
Corrosive chemicals can cause irreversible damage to skin and eyes on contact, sometimes within minutes. They also attack certain metals, which is why some corrosive substances carry additional warnings about damaging equipment. When handling anything with this symbol, you need chemical-resistant gloves, safety goggles (not just glasses), and a lab coat at minimum. Splashes should be flushed immediately with large amounts of water.
Health Hazard vs. Skull and Crossbones
These two symbols confuse people because both relate to poisoning, but they describe very different timelines. The skull and crossbones means a single dose or brief exposure could kill you or cause serious immediate harm. The health hazard silhouette, by contrast, warns about damage that builds up over time or results from a specific biological mechanism like cancer or genetic mutation.
A chemical with the skull and crossbones demands extreme caution during any handling. A chemical with the health hazard symbol may seem less immediately dangerous, but it requires careful long-term precautions like proper ventilation, respiratory protection, and strict limits on how often and how long you’re exposed.
Flame vs. Flame Over Circle
These two are easy to mix up, but they describe opposite roles in a fire. The plain flame means the substance itself is fuel: it can ignite. Flammable liquids are classified by their flash point, the lowest temperature at which they produce enough vapor to catch fire. The most dangerous (Category 1) have flash points below 23°C (73°F) and boil below 35°C (95°F), meaning they can ignite at room temperature and evaporate quickly. Category 4 flammable liquids, the least severe, have flash points between 60°C and 93°C and only become hazardous near heat sources.
The flame over circle means the substance is an oxidizer. It provides oxygen to a fire rather than acting as fuel. Oxidizers make fires hotter, harder to extinguish, and more likely to start in the first place. Keeping oxidizers separated from flammable materials is one of the most basic rules in any lab.
GHS vs. the NFPA Diamond
You might also see a different system in some labs: the NFPA 704 diamond, a large square rotated 45 degrees and divided into four colored sections (blue for health, red for flammability, yellow for instability, and white for special hazards). Each colored section contains a number from 0 to 4, with 4 being the most hazardous.
Here’s where it gets confusing. The GHS system also uses numbered categories, but its scale runs in the opposite direction: Category 1 is the most severe and Category 4 is the least severe. These two numbering systems are not interchangeable. You should never use GHS category numbers to fill in an NFPA diamond or vice versa. The NFPA diamond is typically used on building exteriors and storage areas to help emergency responders, while GHS labels appear on individual chemical containers.
What to Do When You See a Symbol
The pictogram tells you the type of hazard, but for specific protective measures, look at the full label and the chemical’s Safety Data Sheet (SDS). Every hazardous chemical in a workplace or school lab is required to have an SDS available. Section 2 of the SDS lists all the hazard classifications, and Section 8 describes exactly what protective equipment you need.
As a general rule, any chemical with a hazard pictogram calls for eye protection and gloves at minimum. Corrosives and acute toxins demand chemical-splash goggles and resistant gloves rather than standard latex. Flammables should be kept away from open flames and heat sources. Substances with the health hazard symbol often require a fume hood or respiratory protection to prevent inhalation. If a container has multiple pictograms, follow the precautions for all of them.