Hazards and Symbols: 12 Pictograms & Meanings Explained

Hazards and Symbols: 12 Pictograms & Meanings Explained

Hazards and Symbols: 12 Pictograms & Meanings Explained

You uncap a solvent, spot the small red diamond, and instantly decide whether you need flame-proof gloves or a blast shield. That split-second judgment is the power of a hazard pictogram—streamlined graphics that translate dense chemical data into unmistakable warnings.

OSHA’s Globally Harmonized System (GHS) requires nine pictograms on container labels and Safety Data Sheets. Add three icons recognized worldwide—the radiation trefoil, the biohazard emblem, and the NFPA 704 diamond—and you have the twelve symbols every safety manager, lab tech, and first responder relies on. Overseen by OSHA, the UN, NFPA, NRC, and CDC, these pictograms differ from general safety signs because they identify the exact nature and severity of a hazard, not just a precaution.

Exploding bomb, flame, flame-over-circle, gas cylinder, corrosion, skull and crossbones, exclamation mark, health silhouette, environmental hazard, radiation trefoil, biohazard, NFPA 704—each tells a distinct story. Let’s examine every symbol, the dangers it flags, and the compliance steps that keep your team protected.

1. Exploding Bomb: Explosive Materials

Few symbols command instant respect like the exploding bomb. The jagged blast inside a red diamond tells you a substance can detonate with shock, heat, or friction—no second chances.

Visual Description & GHS Code

  • Icon: black burst on white field framed by red; code GHS01.
  • Minimum label size: 16 mm for most U.S. primary containers, larger for outer cartons.
  • Legacy orange “E” squares from pre-GHS EU stock may still surface in storerooms.

Hazard Classes & Risks

  • Unstable explosives
  • Self-reactive types A/B
  • Organic peroxides type A
    Potential outcomes: overpressure waves, shrapnel, secondary fires, and hearing damage.

Storage, Labeling & Response

  • Magazine or day-box storage per ATF 27 CFR 555; control temperature ≤ 54 °F and low humidity.
  • Segregate from flammables/oxidizers; post signal word “Danger” with H200–H204 statements.
  • For incidents: evacuate per ERG tables, fight fires remotely with unmanned monitors, use blast shields whenever handling large quantities.

2. Flame: Flammables & Pyrophorics

The flame pictogram is a red flag for anything that can catch fire with shocking ease. It tags everyday products like nail-polish remover and propane cylinders, but also exotic reagents that ignite on contact with air. If the icon is on the label, expect low flash points, explosive vapor clouds, or self-ignition—all nasty surprises that demand strict controls.

Visual Description & GHS Code

  • Symbol: solid black flame in a red-bordered diamond on white background
  • GHS code GHS02; mandatory size ≥ 16 mm on most primary containers
  • Used for all “Flammable,” “Pyrophoric,” “Self-Heating,” “Emits Flammable Gas,” and “Self-Reactive (C–F)” classes

Hazards & Real-World Examples

  • Flammable gases (propane, hydrogen)
  • Category 1 liquids with flash point <73 °F (acetone, diethyl ether)
  • Pyrophoric solids/liquids (tert-butyllithium, white phosphorus)
    Ignition sources include static discharge, hot work, or even air exposure, leading to flash fires or vapor explosions.

Safe Handling & Labeling

  • Ground and bond containers; store cat. 1 liquids in UL-listed Class I safety cabinets
  • Post signal word “Danger” for category 1 materials; “Warning” for cat. 2-4
  • Keep extinguishers rated Class B/C close by; use alcohol-resistant foam or CO₂—never water on metal or grease fires
  • Train staff on hot-work permits and ensure intrinsically safe tools in classified areas

3. Flame Over Circle: Oxidizers

Oxidizers don’t burn by themselves; they push everything around them to burn hotter and faster. Spot the flame over a circle and assume even a greasy rag can erupt without a spark.

Visual Description & GHS Code

  • Black flame over hollow circle in red diamond; code GHS03
  • ≥ 16 mm on primary containers; legacy yellow gas-cylinder labels still appear

Hazard Classes & Risks

  • Oxidizing gases, liquids, solids (cat. 1-3)
  • Intensify fires, spark spontaneous ignition of oils, sawdust, textiles

Storage & Emergency Tips

  • Isolate from flammables; vented metal cabinet, grease-free tools
  • Label with signal word “Danger” + H270–H272
  • Cool containers with water fog; smothering agents are useless

4. Gas Cylinder: Gases Under Pressure

A cylinder icon tells you that the container is a potential missile and, if cryogenic, a frost-bite machine. Whether it holds welding oxygen or liquid nitrogen, any loss of integrity can end with ruptures, rocketing tanks, or an oxygen-displaced workspace.

Visual Description & GHS Code

  • Solid black cylinder silhouette inside red diamond; code GHS04
  • Same size rules—≥ 16 mm on most primary labels—apply.

Hazard Types & Risks

  • Compressed, liquefied, dissolved, or refrigerated gases
  • Projectile danger, cold burns, over-pressurization, asphyxiation in confined areas

Handling & Transport Protocols

  • Store upright, chained, valve cap on; segregate empties/full
  • Use DOT-rated carts; leak-check with soapy water, never flame
  • Post “Danger—High Pressure” plus UN/ERG numbers; train staff to vent slowly and evacuate if hissing increases

5. Corrosion: Corrosive to Metals & Skin

When you see liquid eating through metal and a hand on the label, treat the contents with extreme respect. The corrosion pictogram covers chemicals capable of dissolving steel shelving, burning unprotected skin, and permanently blinding eyes—in short, some of the nastiest entries on any hazards and symbols checklist.

Visual Description & GHS Code

  • Twin test tubes dripping onto a hand and a metal bar, both etched by the fluid
  • Framed in the red GHS diamond, code GHS05
  • Must appear at least 16 mm wide on most primary containers

Hazards & Effects

  • Skin corrosion Category 1 (irreversible tissue damage within ≤ 4 hours)
  • Serious eye damage Category 1
  • Corrosive to metals ≥ 0.2 mm steel loss per year (e.g., 37 % HCl, 50 % NaOH)

PPE & First Aid

  • Don nitrile or neoprene gloves, chemical–splash goggles, face shield, and acid-resistant apron
  • Ensure an ANSI-compliant eyewash/shower within 10 seconds travel time; flush eyes or skin for 15 minutes minimum
  • Neutralize small spills with sodium bicarbonate (acids) or citric acid (bases); dilute only after reaction subsides
  • Remove contaminated clothing carefully—exothermic reactions can trap heat against skin

6. Skull and Crossbones: Severe Acute Toxicity

The skull and crossbones ranks highest on the “no-touch” scale of hazards and symbols. When this red diamond appears, even a drop, whiff, or dusting may be lethal within minutes—no chronic exposure required.

Visual Description & GHS Code

  • Black skull with crossed tibias in red diamond; code GHS06
  • Requires signal word “Danger” and pictogram size ≥ 16 mm on primary labels

Hazard Scope

  • Acute toxicity Categories 1–3 for oral, dermal, or inhalation routes
  • Examples: hydrogen cyanide, phosgene, sodium azide, nicotine base
  • Rapid onset of respiratory failure, seizures, cardiac arrest

Controls & Response

  1. Enclose processes; use ventilated glove boxes or fume hoods at ≥ 100 fpm face velocity.
  2. Stock specific antidotes—e.g., amyl nitrite for cyanide, atropine for organophosphates.
  3. Mark areas “Danger—Fatal if Inhaled/Swallowed”; keep SDS Section 4 open at stations.
  4. If exposure occurs, initiate emergency shower, call 911, and contact Poison Control (1-800-222-1222) without delay.
  5. Dispose of residues in sealed, compatible containers per RCRA P-listed waste rules.

7. Exclamation Mark: Irritant & Moderate Hazards

When the exclamation mark appears, you’re dealing with chemicals that sting, inflame, or irritate rather than outright kill.

Visual Description & GHS Code

  • Black “!” in red diamond; GHS07; ≥16 mm label width; optional when skull-and-crossbones already present.

Covered Hazards

  • Cat. 4 acute toxicity, skin/eye irritation, dermal sensitization, STOT-SE 3, ozone-layer harm under UN GHS. Think bleach fumes, mild acid cleaners too.

Minimizing Risk

  • Vent hoods, splash goggles, nitrile gloves; post “Warning—Causes irritation”; sweep small spills into sealed bags promptly for disposal.

8. Health Hazard Silhouette: Chronic & Systemic Effects

Spotting this torso-and-starburst means the danger isn’t an instant burn or explosion—it’s the kind of damage that quietly builds until cancer, lung scarring, or reproductive harm show up years later. Among the dozen hazards and symbols, this one drives the longest tail of liability.

Visual Description & GHS Code

  • Black human outline with radiating “burst” on chest, inside red diamond
  • GHS code GHS08; minimum 16 mm on primary containers
  • Signal word varies by category, but “Danger” is common for carcinogens and mutagens

Long-Term Risks

  • Carcinogenicity (e.g., benzene, formaldehyde)
  • Germ-cell mutagenicity
  • Reproductive toxicity and endocrine disruption
  • Respiratory sensitization (isocyanates)
  • Specific Target Organ Toxicity—Repeated Exposure (STOT-RE)
  • Aspiration hazards such as mineral oils entering lungs

Employer Duties

  • Maintain exposures below OSHA PELs and ACGIH TLVs; implement engineering controls first
  • Provide medical surveillance for regulated carcinogens; retain records 30 years under 29 CFR 1910.1020
  • Ensure Section 11 & 12 data on SDS are up-to-date and accessible
  • Train workers annually; label secondary containers and process vessels clearly
  • Document hazard assessments and keep a written compliance plan for auditors and insurers

9. Environment: Aquatic Toxicity

A dead tree next to a belly-up fish is a blunt reminder that one mishandled drum can poison streams at parts-per-billion concentrations.

Visual Description & GHS Code

  • Black tree and fish on white field, framed in red diamond; code GHS09
  • Mandatory on EU labels, voluntary but advisable under OSHA HCS

Hazards & Substances

  • Acute Cat. 1 or Chronic Cat. 1–4 aquatic toxicity
  • Usual suspects: copper sulfate, pyrethroid pesticides, mercury salts, diesel fuel, detergent surfactants

Mitigation

  • Store containers on spill pallets with 110 % secondary containment
  • Plug or cover floor drains during transfers; keep absorbent socks and drain protectors nearby
  • Follow EPA SPCC plans and dispose via RCRA-hazardous waste streams, never down the sink

10. Ionizing Radiation Trefoil: Radiation Sources

Seeing the trefoil means invisible ionizing rays are present and ordinary PPE won’t cut it.

Visual Description & Regulatory Context

Magenta or black trefoil on yellow; ≥1-in diameter per ANSI Z535. Regulated by NRC 10 CFR 20 and OSHA 1910.1096.

Radiation Types & Health Effects

Sources emit alpha, beta, gamma, X-ray, or neutron energy. High doses burn; chronic doses raise cancer odds—no taste, smell, or sight clues.

Controls & Signage

Follow ALARA—time, distance, shielding. Wear badge dosimeters above 10 % annual limit. Mark >5 mrem/hr zones with “Caution—Radiation Area” labels.

11. Biohazard: Infectious Materials

The biohazard emblem flags pathogens that sicken people—anything from Hepatitis B in blood to SARS-CoV-2 aerosols. Unlike chemicals, living hazards replicate, so quick isolation matters.

Visual Description & Standard

Orange-red trefoil on fluorescent orange background per OSHA 1910.1030; also cited in CDC/NIH BMBL and DOT biohazard labeling standards.

Hazards & Transmission

Includes bloodborne viruses, prions, bacterial cultures, and sharps; spread by needle-sticks, aerosol inhalation, mucous contact, or ingestion.

Containment & Decontamination

Employ BSL-rated controls—Class II cabinets, sealed rotors, negative pressure. Autoclave waste at 121 °C/15 psi; wipe surfaces with 1:10 bleach within minutes.

12. NFPA 704 Diamond: Multi-Hazard Quick Reference

The NFPA 704 diamond condenses multiple chemical dangers into a single, color-coded square visible from the street. Fire crews scan this emblem to decide hose streams, respirators, or full hazmat entry before they ever crack a drum.

Layout & Coding

  • Blue (health), red (fire), yellow (reactivity), white (special).
  • Numbers 0 – 4 rank severity; 0 is minimal, 4 is lethal.
  • White quadrant carries alerts such as W (water-reactive) or OX (oxidizer).

Reading & Application

Front gates, tank farms, and lab doors—post the diamond where first responders can see it from 100 ft.

Complement to GHS Labels

Use GHS pictograms on containers; NFPA outside—never let severity numbers and H-phrases contradict each other.

13. Final Safety Pictogram Checklist

Before you print the next label or open a new drum, run through this quick-fire list:

  1. Exploding Bomb – explosives
  2. Flame – flammables & pyrophorics
  3. Flame-Over-Circle – oxidizers
  4. Gas Cylinder – gases under pressure
  5. Corrosion – skin/metal corrosion
  6. Skull & Crossbones – severe acute toxicity
  7. Exclamation Mark – irritants & moderate hazards
  8. Health Silhouette – chronic/systemic effects
  9. Environment – aquatic toxicity
  10. Radiation Trefoil – ionizing radiation
  11. Biohazard – infectious materials
  12. NFPA 704 Diamond – multi-hazard snapshot

Check every label for a red diamond (or correct color scheme), minimum 16 mm width, legible signal word, and placement that isn’t hidden by tape or valves. Proper pictograms satisfy OSHA/GHS, speed emergency response, and—most importantly—keep people safe. Need compliant decals or a second opinion on your layout? Visit Safety Decals for custom labels and field-tested consulting.