The environmental protection agency (EPA), under section number 3010 of the Resource Conservation and Recovery Act (RCRA) defined four things that make a waste classified as hazardous waste. Those four things are ignitability, corrosivity, reactivity, and toxicity. In general, a waste has characteristics of ignitability if it could chemically ignite by friction or other spontaneous means. A waste has the characteristics of corrosivity if, for instance, it can corrode the steel container that holds it. A waste has the characteristics of reactivity if it is generally unstable, or reacts violently with water. A waste has the characteristics of toxicity if it contains certain materials (ex: lead) above the EPA regulated concentrations in ppm.

RCRA subtitle C also contains a list of exclusions. In general, a waste is excluded if it is not defined as a solid waste, or if it does not fall in one of the four of the hazardous waste categories as described above, or if they are managed according to laws.