Regulatory schemes on both sides of the border (US RCRA, and the characteristic-waste criteria adopted in Canadian frameworks such as Ontario's O. Reg. 347) classify a waste as hazardous "by characteristic" if it exhibits any one of four measurable properties:
Ignitability. A liquid with a flash point below $60^{\circ}\text{C}$ ($140^{\circ}\text{F}$), a non-liquid capable of spontaneous, sustained combustion under normal handling, an ignitable compressed gas, or an oxidizer.
Corrosivity. An aqueous waste with pH $\le 2$ or pH $\ge 12.5$, or a liquid that corrodes steel at a specified rate — capable of destroying living tissue or corroding containment/transport equipment on contact.
Reactivity. Waste that is unstable and readily undergoes violent change, reacts violently or generates toxic gas with water, is capable of detonation, or is a forbidden explosive, cyanide- or sulfide-bearing waste that liberates toxic gas at low pH.
Toxicity. Waste that, when subjected to a standardized leaching test (e.g. the Toxicity Characteristic Leaching Procedure, TCLP), releases one or more regulated contaminants (heavy metals, specific organics) into the leachate above a stated concentration threshold — a proxy for the waste's potential to contaminate groundwater once landfilled.
These four tests are deliberately cheap, standardized laboratory procedures rather than full risk assessments, so a waste can be screened and classified in days rather than months; a generator only needs a positive result on ONE of the four to trigger the full cradle-to-grave hazardous-waste management obligations (manifesting, licensed transport, approved disposal). Question 3 works through exactly this logic for two specific wastes, applying the ignitability and corrosivity thresholds directly to measured properties.
