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Table of Contents

  1. The Importance of Safety Signs
  2. Globally Harmonized System of Classification and Labeling of Chemicals
  3. Department of Transportation HAZMAT Placards
  4. Other Common Warning Signs


You can often tell warning signs from their bright colors and distinct markings, but do you know exactly what those signs were warning you about? In this article, we’re going to cover the meaning of hazardous signs, what the different hazardous waste signs mean, info about the biohazard sign, hazmat placards meanings, and even where to find more information on what safety signs and labels are required for your business.

The Importance of Safety Signs

Many of us are used to seeing signs every day, so it may seem at times that even the hazardous signs fade into the background. However, safety signs play a critical role in keeping everyday citizens and workers safe.

Especially if you work in a facility where hazardous materials or other dangers are present, you should be keenly aware of all signs that are meant to preserve your safety and be well aware of what each means. However, one study found that, on average, just over 30 percent of participants didn’t know the correct meaning of a warning sign in their workplace.

Hazardous materials come with safety data sheets that identify what is hazardous about them. These safety data sheets are comprehensive and complicated, but the warning signs are basic and simplistic. They tend to include nothing more than a pictogram, or symbol, and minimal text. If you understand the meaning of hazardous chemical information signs or other warning signs, you have a better chance of staying safe at work and anywhere that hazards are present.

So, what do all the hazardous waste symbols mean? And what about other warning symbols? Keep reading for an overview of what the different hazardous waste signs mean so you can do your part to make sure these signs keep you safe.

Globally Harmonized System of Classification and Labeling of Chemicals

globally harmonized system of classification and labeling of chemicals

The Occupational Health and Safety Administration (OSHA) recently aligned its system of labeling, known as the Hazard Communication Standard, with the Globally Harmonized System of Classification and Labeling of Chemicals (GHS), a system the United Nations developed to help identify hazardous chemicals.

  1. Health Hazard: The health hazard symbol features a silhouette of a human torso with a six-pointed shape on the person’s chest. If you see this symbol on something, it means that coming into contact with the chemical itself could cause either acute or chronic health problems. For example, this would include toxins that affect your respiratory function or are known to cause
  2. Flame: The flame symbol means that a substance presents a possible fire hazard. It could be that the substance is just flammable, or it may give off flammable gas. This would also include substances that could ignite on their own when exposed to either water or air, as well as other types of fire-related dangers.flame-placard
  3. Exclamation Mark: An exclamation point suggests urgency, which is why it’s used to label substances that would immediately cause a person harm if they came into contact with the substance. On the mild end of the spectrum, it could irritate their skin or eyes. On the more extreme end, it could be fatally toxic.exclamation-mark-placard
  4. Gas Cylinder: The gas cylinder pictogram is used to label gasses under pressure. A gas is considered under pressure if it is at 29 pounds per square inch or more. The gas could be dissolved, compressed or liquefied. You should always exercise caution around pressurized gas cylinders since a puncture or leak could cause an explosion or negative health effects.gas-cylinder-placard
  5. Corrosion: The pictogram symbolizing corrosion shows a substance being poured onto a person’s hand (on the right) and what looks like a metal pipe (on the left). In both cases, the liquid carves out a hole. As this warning sign suggests, corrosive substances can cause damage to metal and can burn skin.corrosion-placard
  6. Exploding Bomb: Explosive materials are labeled with a picture that looks like an exploding bomb. Explosives include materials that are highly unstable, self-reactive (meaning they don’t need to be exposed to air to go off) and organic peroxides. These materials are extremely dangerous.exploding-bomb-placard
  7. Flame Over Circle: Oxidizers are chemical compounds that release oxygen when they react with another substance. Oxidizers are chemicals that facilitate burning or make fires burn hotter and longer. This symbol warns that the substance inside is an oxidizer, which could cause a fire.flame-over-circle-placard
  8. Environment: This pictogram looks like an upturned fish on the shore next to a tree. If you see this sign on a chemical, it means that chemical is toxic to aquatic life. Of the nine Hazard Communication Standard/GHS signs, this is the only one that is optional, so you may not always see it on every chemical that is known to hurt fish or other aquatic life.environment-placard
  9. Skull and Crossbones: The skull and crossbones is an iconic image that most people strongly associate with the concept of toxicity or poison. But what does this symbol mean exactly? In this case, it indicates toxicity. In other words, if a person swallowed or inhaled even a small amount of the chemical, or if it got on their skin, it could prove fatal.skull-and-crossbones-placard

Department of Transportation HAZMAT Placards

Another set of hazardous waste symbols you may have seen are placed on vehicles transporting hazardous materials down the highway. The Department of Transportation (DOT) requires drivers to display these placards. You may see multiple pictures and numbers, but the simplest way of understanding what these signs mean is to understand the nine classes of hazardous materials they denote. Note that some classes include multiple symbols, but every sign will bear the number of its class.

    1. Explosives: Signs for explosives are orange diamond-shaped signs with a number 1. Depending on the particular type of explosive, the sign gets more specific with another number after the one, which indicates the division within the class. For example, a blasting agent is a 1.5. Some signs include an explosion symbol that resembles the bomb on the GHS sign.explosives-placard
    2. Gases: Gases get a diamond-shaped sign with a picture at the top and text below. These signs denote three types of gases: flammable, non-flammable and poisonous. You’ll see pictures on these signs that reflect the same symbols we learned about from the GHS system, including the skull and crossbones, for example, which in this case, means that a gas is poisonous and presents an inhalation hazard.gas-placard

flammable liquids can ignite easily at relatively low temperatures

    • Flammable Liquid: Class 3 does not include subdivisions, so there is just one sign for this class. It’s a red diamond with a flame and also includes the words “Flammable Liquid.” Flammable liquids, such as gasoline, for example, can ignite easily at relatively low temperatures. Specifically, a liquid is considered flammable if it has a flash point at or under 199.4 °F.flammable-liquid-placard
    • Flammable Solid, Spontaneously Combustible and Dangerous When Wet: Class 4 signs also include the flame symbol, but they include three different divisions. The red and white striped sign indicates a flammable solid. The half white, half red sign indicates that a material could spontaneously combust. A dangerous when wet sign, which is blue, indicates that a material could suddenly become flammable or emit toxic gas if exposed to water.flammable-solid-placardspontaniously-combustable-placarddangerous-when-wet-placardOxidizer and Organic Peroxide: This class includes two divisions. The yellow diamond-shaped sign features the same flame over the circle we looked at previously with the GHS pictograms, which indicates an oxidizer. An organic peroxide sign is half red, half yellow and includes the flame symbol at the top. In this case, it doesn’t just mean a substance is flammable but that it is specifically an organic peroxide.oxidizer-placard
    • Poison: Class 6 is dedicated to poisonous materials and is divided into two subcategories: toxic substances and infectious substances. Signs used to indicate a toxic substance include the skull and crossbones and may include more specific information about the particular poison. Infectious substances include a symbol you’ve probably seen in medical facilities — the biohazard sign, which looks like interlocking circles.
    • poison-placardRadioactive: Class 7 placards indicate that a truck is transporting radioactive substances. This class does not include any divisions. All signs include the symbol that’s been used since the 1940s to indicate radioactivity. This symbol is known as the trefoil. A Class 7 diamond-shaped placard may be yellow or white, but it should always include this symbol.radioactive-placard
    • Corrosive: Corrosive substances belong to Class 8. This black and white sign displays a picture that closely resembles the GHS pictogram for corrosive materials. It shows a liquid burning a hole in a metal pipe and in a person’s hand, indicating that the material could hurt people as well as metal materials.corrosive-placard
    • Miscellaneous Hazardous Materials: Class 9, the final category of DOT’s hazardous materials labeling, is reserved for miscellaneous substances that don’t fit into any of the previous eight categories but which are known to be hazardous. Signs for Class 9 have black and white stripes on the top half.misc-hazardous-materials-placard

Other Common Warning Signs

You may see other signs warning you about a potential hazard that aren’t included in either OSHA’s or DOT’s required signage. Hopefully, you’re already familiar with road signs that indicate potential hazards, such as falling rocks or icy roads. Hazard signs show up in far more places than just on the road, though. Particularly if you work in an industrial facility or on a construction site, you may see hazardous signs that are meant to help keep you safe.

Make sure you know what each of these signs means. Here are a few common symbols you may see on these signs along with their meanings:

  • High Voltage: The high voltage sign should make you exercise extreme caution and stay out of an area completely. These signs come in a variety of configurations and may include the words “high voltage” on them. The high voltage symbol looks like a lightning bolt with an arrow on the end, pointing down. Usually, it appears on a triangular, yellow sign.high-voltage-placard
  • Slippery when Wet: There isn’t one exact symbol that is regulated by a governing body, but slippery when wet signs tend to look pretty similar. As with other general caution signs, slippery when wet signs are typically yellow with black writing. They are likely to include text, but you can always expect to see the symbol of a person who is mid-fall. If you see this sign, walk carefully so you don’t lose your footing.slippery-when-wet-placard
  • Forklifts in Use: If you work in a shipping or distribution center or any other facility where employees operate forklifts, you want to make sure you stay out of the way. This sign is typically yellow and may include the word “caution” across the top. Below that, you’ll see a rudimentary drawing of a person operating a forklift. When you see this sign, take extra care to be aware of your surroundings so you aren’t injured.forklift-in-use-placard
  • Laser Warning: The symbol for a laser looks like a sunburst with a line coming out of one side. Typically, you’ll see this symbol on a sign that is warning you that lasers are in use and you should wear protective eyewear and avoid direct exposure to the laser. You may see an eye-catching “caution,” “warning” or “danger” at the top of the sign, as well.laser-warning-placard

excessive radio frequency can cause immediate injuries

  • Radio Frequency: Exposure to excessive radio frequency can cause immediate injuries, such as shocks or burns, and could cause ongoing health complications. This is why areas where radio frequency levels are potentially unsafe are marked with a radio frequency warning sign. The symbol resembles a radio tower with lines coming off both
  • Burn Hazard: If a piece of equipment is hot enough inside to burn someone, it should feature a warning sign to let you know not to service the machine until after it has had a chance to cool down. You may see this same burn hazard symbol on other hot surfaces, as well. The symbol shows three curvy lines, to indicate heat, coming up off of a straight, horizontal line.burn-hazard-placard
  • NFPA Diamond: The National Fire Protection Agency has a system for letting emergency responders know what sorts of hazards a substance presents when there is a fire or chemical spill. This diamond includes four sections with different colors that bear their own meanings: blue means health, red means flammability, yellow means instability, and white is for special hazards. Each color includes a number from zero to four to indicate the severity of the hazard for that category. The white section includes a letter symbol to indicate whether the material is an oxidizer, is water-reactive or is a simple asphyxiant.nfpa-placard

Learn More About Hazards and Safety from HAZMAT School

hazardous chemicals online training courses

If you’re wondering what safety signs and labels are required for your business, it’s crucial to learn more about the signage itself and the materials these signs label. Signs aren’t enough to keep you safe if you work with hazardous materials. If you work with hazardous chemicals, proper training is absolutely essential so you stay safe and help keep others safe by properly labeling and handling these materials.

HAZMAT School offers training courses that cover a variety of topics related to hazardous materials, so no matter how you interact with these materials, you can be armed with the information you need to stay safe. If you have questions about our course offerings or what types of training you are required to take in order to comply with OSHA, contact us today so we can answer your questions and help you stay safe.

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