You walk into a lab and see a red-bordered diamond on a cabinet, a trefoil on a door, and a fan of small icons on a reagent bottle. If you cannot read them in a second or two, you are guessing. Every hazard symbol in a laboratory exists to tell you what can hurt you and what to do about it, and misreading one can mean a burn, an exposure, or an OSHA citation.
Here is the short answer. Most lab labels fall into a few families: the nine GHS pictograms for chemical hazards, plus separate symbols for biohazard, ionizing radiation, lasers, and cryogenic materials. Each one has a specific name, a specific meaning, and a standard response.
Below, you will find each symbol listed with its name, what it signals, and how to react. As a Michigan-based maker of custom safety decals and labels, we print these markings for labs every day, so we also note where durable, compliant labeling matters most. Use the list to train new staff or audit your own signage.
1. GHS chemical hazard pictograms
What the symbols look like
Every GHS pictogram is a black symbol on a white background inside a red diamond border. A label can carry several, so one reagent bottle may show three or four at once.
There are nine: exploding bomb, flame, flame over circle, gas cylinder, corrosion, skull and crossbones, exclamation mark, health hazard, and environment. OSHA's Hazard Communication Standard makes the environment pictogram optional in the US, so its absence does not mean a chemical is harmless to wildlife.
What they mean
Learn each symbol by its hazard class, not by guessing from the shape. The most common mix-up is between two similar-looking threats. The skull and crossbones means acute toxicity, while the health hazard symbol means long-term harm such as cancer or organ damage.
Skull and crossbones means immediate danger; the health hazard figure means damage that shows up later.
| Pictogram | What it signals |
|---|---|
| Exploding bomb | Explosives, self-reactives, organic peroxides |
| Flame | Flammables, pyrophorics, self-heating chemicals |
| Flame over circle | Oxidizers that intensify fires |
| Gas cylinder | Gases under pressure |
| Corrosion | Skin burns, eye damage, metal corrosion |
| Skull and crossbones | Fatal or toxic if swallowed, inhaled, or absorbed |
| Exclamation mark | Irritants, sensitizers, harmful at lower doses |
| Health hazard | Carcinogens, mutagens, reproductive toxins, organ damage |
| Environment | Toxic to aquatic life |
How to respond safely
Read the signal word (Danger or Warning) and the hazard statements, then open the Safety Data Sheet before you open the container. The pictogram tells you what to look up. The SDS tells you what to wear and how to store it.
- Flame or flame over circle: keep away from ignition sources, and store oxidizers apart from flammables.
- Corrosion: wear splash goggles, a face shield, and compatible gloves.
- Skull and crossbones: work in a fume hood and know where the nearest eyewash is.
Where you will see them
Expect them on manufacturer bottles, shipping cartons, and chemical storage cabinets. Secondary containers, such as wash bottles and beakers of stock solution, need chemical hazard labels too. Those labels take abuse from solvents and moisture, so choose chemical-resistant material that will not smear or peel.
2. Biohazard symbol
What the symbols look like
The biohazard mark is three interlocked crescents around a small circle, printed in fluorescent orange or orange-red. Dow Chemical engineers designed it in 1966 to be unlike anything else.
There is no red diamond here. OSHA's bloodborne pathogens standard lets red bags or containers substitute for the label on regulated waste.
What they mean
As a hazard symbol in a laboratory, it covers risks you cannot see. It marks material that may carry infectious agents, such as bacteria, viruses, or human blood. Labs post a biosafety level, BSL-1 to BSL-4, beside it to set the required practices.
The symbol says infectious material is present; the biosafety level says how strictly you must work.
Higher levels mean tighter access and more containment.
How to respond safely
Treat anything marked this way as infectious until proven otherwise. Wear gloves, a lab coat, and eye protection, then follow the lab's biosafety rules.
- Use a biosafety cabinet when a procedure could create aerosols.
- Put sharps in puncture-proof containers, never in bags.
- Disinfect surfaces after work and wash your hands before leaving.
Where you will see them
Expect it on incubators, freezers, sharps containers, waste bags, and lab doors. Those spots face cold and bleach wipes, so use labels rated for low temperatures and disinfectants.
Finally, post it at every entry point, so visitors and cleaning staff see it before they walk in.
3. Radiation hazard symbols
What the symbols look like
The classic radiation symbol is a three-bladed trefoil around a central dot, printed in magenta or black on a yellow background. OSHA's ionizing radiation rules call for those colors.
Newer sealed sources may also carry the ISO 21482 symbol. It adds radiating waves, a skull, and a running figure to warn of dangerous, high-activity sources.
What they mean
The trefoil means ionizing radiation or radioactive material is present. The words beside it set the level, such as "Caution, Radiation Area" or "Danger, High Radiation Area."
The trefoil tells you radiation is present; the wording beside it tells you how restricted the space is.
Lasers and UV lamps use different signs, which the next section covers.
How to respond safely
Use time, distance, and shielding. Spend less time near the source, stay farther back, and put a barrier between you and it. This is the core of keeping exposure as low as reasonably achievable.
- Wear your dosimeter badge whenever you work with a source.
- Keep food, drink, and cosmetics out of the area.
- Survey your hands and bench with a meter before you leave.
Where you will see them
Look for trefoils on lab doors, isotope refrigerators, lead shipping containers, and waste bins, as well as on X-ray diffraction units. Any hazard symbol in a laboratory that marks a radiation area must stay legible, so replace faded labels instead of working around them.
4. Cryogenic, laser and electrical hazard symbols
What the symbols look like
Most of these signs follow ISO 7010: a yellow warning triangle with a black border and black pictogram. Laser rooms often add a rectangular text panel.
| Hazard | Pictogram |
|---|---|
| Cryogenic | Snowflake |
| Laser | Radiating beams |
| Electrical | Lightning bolt |
What they mean
The snowflake warns of extreme cold, such as liquid nitrogen, which causes cold burns on contact and can displace oxygen in small rooms. The laser sign marks a beam that can injure eyes and skin, and its label lists the class, such as Class 3B or Class 4. The lightning bolt signals shock or arc flash risk.
A yellow triangle means the danger is physical: cold, light, or current.
How to respond safely
Match your protection to the energy involved. Each hazard symbol in a laboratory in this group calls for different gear.
- Cryogenic: wear a face shield, insulated gloves, and closed shoes. Never seal a container of cryogen.
- Laser: use eyewear rated for the listed wavelength, and stay out when the warning light is on.
- Electrical: report damaged cords, keep liquids away from outlets, and follow lockout/tagout.
Where you will see them
Look for snowflakes on dewar storage areas and cryo rooms, laser signs on laser lab doors and optical tables, and lightning bolts on electrical panels and equipment covers. Keep panels clear of clutter so the sign stays visible and the panel stays reachable.
5. Safety equipment and PPE symbols
What the symbols look like
These signs use color and shape to tell you what kind of message you are reading. Under ISO 7010, each carries a white pictogram on a solid background.
| Sign | Message | Examples |
|---|---|---|
| Blue circle | Mandatory action | Goggles, gloves, lab coat |
| Green square | Safe condition | Eyewash, safety shower, first aid |
| Red square | Fire equipment | Extinguisher, fire alarm |
What they mean
Warning signs say what can hurt you. These say what to do or where help is. A blue circle is an order, not a suggestion: the gear shown is required in that area. Green signs mark emergency equipment you may need within seconds.
Blue circles tell you what to wear; green squares tell you where to run.
How to respond safely
Put on the protection shown before you enter, and check that it fits. Then learn the route to the nearest eyewash and shower now, not during an emergency. ANSI Z358.1 expects you to reach an eyewash within 10 seconds, so a blocked path is a violation.
Where you will see them
Look for blue circles on lab entrances and chemical storage rooms, and for green signs mounted above eyewash stations and showers. Flag-style signs stick out from the wall so you can spot them across the room. Every hazard symbol in a laboratory works better when a clear equipment sign sits beside it.
Keeping your lab signage clear and compliant
Every hazard symbol in a laboratory does one job: it helps you spot a risk and respond before anyone gets hurt. The families are few. GHS pictograms cover chemicals, the orange mark covers biohazards, the trefoil covers radiation, yellow triangles cover cold, light, and current, and blue and green signs show what to wear and where help is.
Knowing the symbols only helps if the labels stay readable. Faded or peeling signs put you back to guessing, and they invite citations. Walk your lab this week and replace anything damaged with materials built for your conditions, whether that means solvents, cold, or bleach.
When you are ready, order custom safety decals and labels in the size, colors, and material your lab needs. Our team can also check your labeling against OSHA and ANSI requirements and recommend durable ORAFOL materials.
