In What is a Hazardous Material?, safety engineering expert James L. Unmack, P.E., C.I.H., C.S.P., describes what makes a hazardous material:

Whether a material is hazardous depends on who you ask and why. Various governmental programs have different criteria on what constitutes a hazardous substance. Most lists of hazardous materials include substances with hazardous properties such as toxic, flammable, corrosive, or reactive.

The Administrator of the U.S. Environmental Protection Agency (EPA) identifies hazardous materials as any material that is toxic, flammable, corrosive, or reactive, or otherwise listed as hazardous by the Administrator.

The Secretary of the U.S. Department of Transportation (DOT) defines hazardous material as substance or material that poses an unreasonable risk to health, safety, and property when transported in commerce, and includes hazardous substances, hazardous wastes, marine pollutants, and elevated temperature materials.

The U.S. Department of Labor, Occupational Safety and Health Administration (OSHA) identifies hazardous materials in the hazard communication standard as a substance that is carcinogenic, toxic, corrosive, flammable, unstable, or otherwise poses a significant safety or health hazard.

Consider the characteristic of flammability, or more generally, the characteristic of being capable of supporting combustion. How may this characteristic be quantified in a meaningful way? What point on the scale represents a hazardous material?