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Table of Contents

  1. The Importance of Safety Signs
  2. What Makes a Material Hazardous?
  3. Regulating Hazardous Waste Symbols
  4. Globally Harmonized System of Classification and Labeling of Chemicals
  5. Department of Transportation HAZMAT Placards
  6. Other Common Warning Signs

You can often tell warning signs from their bright colors and distinct markings, but do you know what those signs warned you about? In this article, we will cover the meaning of hazardous cargo 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 cargo signs fade into the background. However, safety signs play a critical role in keeping everyday citizens and workers safe.

You should be aware of all signs meant to preserve your safety and know what each means, especially if you work in a facility with hazardous materials or other dangers.

Hazardous materials come with safety data sheets identifying what is hazardous. 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 wherever hazards are present.

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

What Makes a Material Hazardous?

The Environmental Protection Agency (EPA) uses numerous standards to make it easier to determine whether or not a material is hazardous. These standards help determine whether something should include a hazardous waste sign. The EPA standards used to determine if a material is hazardous include:

  • Ignitability: Materials are ignitable if they can cause fires in specific conditions or spontaneously burst into flame. Ignitable materials usually have a flash point lower than 140 degrees Fahrenheit (60 degrees Celsius). Different examples of ignitable materials include solvents and oils.
  • Corrosivity: Materials are considered corrosive if they are an acid with a pH lower or equal to 2 or a base with a pH more than or equal to 12.5. These materials are capable of causing corrosive damage to barrels, storage tanks and other metal containers. One example of corrosive hazardous waste is battery acid.
  • Reactivity: Reactive materials are considered unstable under normal circumstances. Reactive materials can be dangerous because they can cause toxic fumes, explosions and harmful vapors under heat or in water. Explosives and lithium batteries are commonly identified as reactive materials.
  • Toxicity: Materials are considered toxic waste when they cause physical harm when absorbed through the skin or ingested. Commonly known toxic wastes include lead and mercury. These materials are marked with toxic waste signs to let individuals know of the risks to their health, which could be fatal.

These hazardous materials pose a danger to public health and safety, which is why they must be marked with a hazardous waste sign. These signs help individuals know how to operate around these materials to prevent injury or property damage.

regulating hazardous waste symbols

Regulating Hazardous Waste Symbols

The EPA requires that hazardous materials are properly marked with the correct symbols when their characteristics are identified. These labels must be placed on any containers that contain hazardous waste. However, hazardous waste signs don’t always include symbols since they’re not required by the EPA, except in cases of bio-waste.

Toxic waste signs that include symbols are easier to identify quickly rather than using text alone. Symbols are commonly used to communicate information effectively, helping individuals identify hazardous materials and preventing physical damage to people and property.

While the EPA doesn’t require hazardous waste signs to include labels, they’re strongly recommended. The Department of Transportation (DOT) also regulates the transportation of these materials and requires materials to be marked with specific designs on placards.

The Occupational Safety and Health Administration (OSHA) also requires chemicals to be adequately labeled in the workplace to protect employees using Globally Harmonized System (GHS) labels. However, this system doesn’t apply to hazardous waste since these are regulated by the EPA.


Globally Harmonized System of Classification and Labeling of Chemicals

globally harmonized system of classification and labeling of chemicals

Hazardous signs and meanings have evolved since they were first used to indicate poison in the 1800s. More hazardous materials have been identified since then, and labeling these materials prevents harm to the public.

OSHA has aligned its system of labeling, known as the Hazard Communication Standard, with the GHS, a system the United Nations developed to help identify hazardous chemicals. The symbols include:

  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 hazmat symbol mean exactly? In this case, it is a symbol for hazardous materials that 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 or DOT requires drivers to display these placards. You may see multiple pictures and numbers, but to understand these signs is to understand the nine classes of hazardous materials they denote. Note that some classes include numerous symbols, but every sign will bear its class number.

    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, indicating the class division. For example, a blasting agent is a 1.5. Some signs include an explosion hazmat 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. The flammable liquid sign is a red diamond with a flame and also includes the words “Flammable Liquid.” Flammable liquids like 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
    • Class 4 signs also include the flame symbol with 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 and infectious substances. Signs to indicate a toxic substance include the skull and crossbones and may include more specific information about the 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 used since 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 isn’t included in the required signage of OSHA or DOT. 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. 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: A governing body doesn’t regulate one same symbol, but slippery when wet signs often 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. The symbol shows three curvy lines to indicate heat coming off 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

learn more about hazards and safety from hazmat school

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 hazmat shipping 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 training you are required to take to comply with OSHA, contact us today so we can answer your questions and help you stay safe.

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