There are four characteristics of hazardous waste—but that’s not the whole story.

In its simplest terms, a hazardous waste is any type of waste with properties that can cause harm to human health or the environment. In addition to the four general characteristics, hazardous waste streams are sorted into various categories and lists based on their common or intended uses.

The often-subtle distinctions can be confusing, but it’s important to educate yourself if you manage these types of waste streams for a living.

EPA Hazardous Waste Characteristics

According to the Environmental Protection Agency (EPA) in their Code of Federal Regulations (40 CFR), there are four hazardous waste characteristics:

  • Corrosivity
  • Ignitability
  • Reactivity
  • Toxicity

Certain types of waste will have more than one of the above characteristics (solvents, peroxides, and cyanide, for example), but at a regulatory level, a waste only needs one characteristic to be considered a hazardous material.


An ignitable waste (EPA waste code D001) is one that has the characteristic of ignitability. In other words, it can catch or create fire under specific conditions. If it has a flash point lower than 60 degrees Celsius (140 °F) and is capable of spontaneously combusting, it’s considered an ignitable material. The flash point is the lowest temperature at which fumes can ignite.

Examples of ignitable hazardous wastes include:

  • Cyanide waste
  • Gasoline and kerosene
  • Hydrocarbon solvents like butane and propane
  • Other assorted solvents like ethyl acetate
  • Paint booth exhaust filters
  • Petroleum-based waste oils


A corrosive material (waste code D002) is any material capable of melting or damaging metallic substances. It has a pH balance between 2 and 12.5, and it can be dangerous if stored in metal drums or barrels (as it can often eat through these containers).

Examples of corrosive wastes include:

  • Battery acid
  • Hydrochloric acid
  • Hydrogen peroxide
  • Rust removers
  • Sulfuric acid


Reactive wastes (waste code D003) are among the most dangerous because they can be unstable—e.g. causing explosions, violent reactions, or toxic fume release—even under normal conditions. Some are activated by heat, and some are even activated by water.

Examples of reactive hazardous wastes include:

  • All types of explosives
  • Certain non-flammable solvents like carbon tetrachloride
  • Concentrated bleaches
  • Lithium-sulfur batteries
  • Metallic sodium
  • Pressurized aerosol cans


Toxic waste (waste codes D004-D043) is any waste that can cause injury or death when consumed by humans or animals. Consumption, in this context, may be the result of ingestion or absorption. The EPA has specific parameters for toxic compounds, which are outlined through a laboratory procedure called the Toxicity Characteristic Leaching Procedure (TCLP) and identified in related documents.

Examples of toxic hazardous wastes include:

  • Mercury- and lead-containing substances (as well as other heavy metals)
  • Oil and gas mixtures
  • Paints
  • Pesticides
  • Solvents

Whereas ignitable, corrosive, and reactive wastes are each identified by a single EPA code, toxic materials are defined by 39 different codes. For instance, D004 is arsenic, D018 is benzene, and D028 is dichloroethane.

Listed Hazardous Wastes

In addition to each hazardous waste characteristic above, the EPA classifies hazardous waste streams on four lists, designated by the letters, F, K, P, and U. Wastes that appear on these lists are considered forms of listed hazardous waste.

F Listed Wastes

Wastes appearing on the F List are those produced from industrial and manufacturing processes. These industrial wastes span a wide range of intended uses and chemical properties, but they all fall beneath the same industry umbrella. A prime example is chlorobenzene, which doesn’t occur naturally but is made from the chlorination of benzene and used in the production of DDT.

F Listed wastes are often divided into the following seven groups:

  • Chlorinated aliphatic hydrocarbons production
  • Dioxin-bearing wastes
  • Electroplating and other metal finishing wastes
  • Multisource leachate
  • Petroleum refinery wastewater treatment sludges
  • Spent solvent wastes (including solvent mixtures)
  • Wood-preserving wastes

K Listed Wastes

K Listed wastes are those that have a specific designated purpose, such as pesticide manufacturing. So whereas F Listed wastes are noted for their origin, K Listed wastes are noted for their purpose.

There are 13 industries that generate K-Listed wastes:

  • Coking
  • Explosives manufacturing
  • Ink formulation
  • Inorganic pigment manufacturing
  • Inorganic chemicals manufacturing
  • Iron and steel production
  • Organic chemicals manufacturing
  • Pesticides manufacturing
  • Petroleum refining
  • Primary aluminum production
  • Secondary lead processing
  • Veterinary pharmaceuticals manufacturing
  • Wood preservation

P Listed Wastes

P Listed Wastes are designed as acute hazardous wastes. They comprise some of the most toxic wastes available, and they’re generally commercial chemical products that are discarded without being used. These products are common in the medical and pharmaceutical industries, and they may comprise packaged medicines or unused lab chemicals.

Examples of P Listed wastes include:

  • Arsenic Trioxide
  • Endrin
  • Nicotine
  • Nitric oxide
  • Physostigmine (commonly used in eye drops)
  • Sodium azide
  • Warfarin (rat poison)

U Listed Wastes

U Listed wastes are similar to P Listed wastes in the sense that they comprise unused commercial chemicals that are discarded. They’re generally less toxic than P Listed wastes and are often distinguished for being unusable (off-specification) or manufacturing chemical intermediates.

Examples of U Listed wastes include:

  • Benzene
  • Chloraseptic spray
  • DDT
  • Formaldehyde
  • Selenium sulfide
  • Vinyl chloride

Universal Waste Classifications

Universal wastes represent another subset of hazardous waste. Sometimes referred to as household hazardous wastes or dangerous goods, these are commonly consumed wastes that contain hazardous properties.

There are five common types of universal waste:

  • Aerosol cans
  • Batteries
  • Bulbs/lamps
  • Mercury-containing equipment
  • Pesticides

Universal wastes generally fall into one or more of the following nine classes:

  • Class 1: Explosives
  • Class 2: Gases
  • Class 3: Flammable Liquids
  • Class 4: Flammable Solids or Substances
  • Class 5: Oxidizing Substances and Organic Peroxides
  • Class 6: Toxic and Infectious Substances
  • Class 7: Radioactive
  • Class 8: Corrosive Substances
  • Class 9: Miscellaneous Dangerous Substances and Articles

Universal wastes should not be discarded in a standard trash can or recycling bin. These products may be dangerous if disposed of improperly. For example, certain batteries present fire hazards and contain toxic chemicals like lithium and sulfuric acid. With improper disposal, these chemicals can seep into the soil and contaminate the groundwater.

Universal waste should be set aside and discarded at an appropriate hazardous waste handling facility. Some communities offer hazardous waste pickup. In other cases, you’ll need to drop off the materials yourself.

Solid vs Liquid Waste

When classifying hazardous waste, there’s a lot of confusion between the terms “solid waste” and “liquid waste.” Only solid wastes can be considered hazardous according to federal guidelines, but the definition in this context has nothing to do with physical solidity.

For example, liquid solvents like butane and propane are considered solid waste even though they don’t have solid properties. That’s why it’s so important for solvent-based cannabis extraction companies to contract with a licensed hazardous cannabis waste management provider.

Under the Resource Conservation and Recovery Act (RCRA), the term “solid waste” is synonymous with “waste.” It’s any solid, semi-solid (sludge), or liquid substance that is abandoned, discarded, recycled in certain ways, or possessing inherently waste-like properties.

This is important to recognize because it means that liquid substances are not exempt from the restrictions surrounding solid waste. You can’t pour hazardous chemicals down the drain, and you can’t treat ignitable wastes like household garbage. Anything with hazardous properties—be it solid or liquid—is solid waste in the eyes of the law.

What to Do With Hazardous Waste

Hazardous waste regulations and protocols can vary from one county to the next, so it’s important to consult your local environmental agency. Sometimes drop-off is required at a hazardous waste facility, but in some cases you can arrange for a pickup.

In the meantime, hazardous materials should be stored in closed, labeled bins reserved specifically for that type of waste. Only compatible wastes should be mixed. For instance, never combine an ignitable waste with a reactive material, as these can make for explosive mixtures.

For commercial enterprises, the best solution is to work with a hazardous waste management company that handles both traditional and hazardous streams. They can help you to remain both safe and compliant while discarding any dangerous or regulated waste on your behalf.

If you maintain any type of hazardous waste, the important thing is to recognize it and to handle it appropriately. The consequences of not doing so can be costly, dangerous, and environmentally detrimental.

So remember: If it’s corrosive, ignitable, reactive, or toxic, always handle with care.+