There are two primary types of hazardous waste, characteristic hazardous waste and listed hazardous waste.

Hazardous wastes that exhibit one or more of the following characteristics as described in 40 CFR § 261 Subpart C.

Ignitability: These wastes easily catch fire when exposed to heat. If the waste has a flash point below 140°F, it must be managed as a hazardous waste. If it is an ignitable compressed gas, it must be managed as hazardous waste. If it is an oxidizer, it must be managed as hazardous waste (40 CFR § 261.21).

Corrosivity: These waste products can damage living tissue on contact. Corrosivity is determined by properties outlined in 40 CFR § 261.22.

Reactivity: Reactive wastes are unstable, react violently or explode, and/or give off toxic gases as described fully in 40 CFR § 261.23.

Toxicity: Such wastes can cause injury or death if swallowed, inhaled, or absorbed through the skin or eyes. If the material contains any organic or inorganic chemicals in excess of the concentrations listed under 40 CFR § 261.24, it must be managed as a hazardous waste.

Hazardous wastes that appear on any of four specific lists (F-list, K-list, P-list and U-list) in 40 CFR 261 Subpart D.

F-list: Hazardous waste from non-specific sources

K-list: Hazardous waste from specific sources, typically includes wastes generated by specific industries or by specific groupings of waste generated

U-list: Unused commercial chemical products by name

P-list: Unused acutely toxic commercial chemical products by name (also called Acute Hazardous Waste)

A facility can generate wastes that belong in more than one of the above categories. Hazardous waste in the above categories are identified by hazardous waste codes. A generator must determine all the applicable hazardous waste codes that apply to each hazardous waste that it generates.

Once a facility determines the hazardous wastes that it generates, the facility must determine how much of each type a facility generates on a monthly basis, and determine its Hazardous Waste Generator Status .