By: Expert No. 8901, P.E., C.I.H., C.S.P.
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?

Organizations such as the National Fire Protection Association and the American Society for Testing Materials have developed standard methods to test and criteria for labeling combustible materials. A flammable material is considered more hazardous than a combustible material. To simplify the quantification, solids, liquids, and gases are addressed separately. The flammability of a gas is easily described by the minimum concentration needed to support combustion, expressed as the lower flammability limit (LFL) or the lower explosive limit (LEL). The flammability of a liquid is measured by the flash point (FP), the minimum temperature at which the vapors, above the surface of the liquid, form an explosive mixture. The flammability of solids is much more complex and is usually addressed on a case by case basis.

How a material is presented may strongly affect its hazard. Generally, the more finely divided the material, the greater the hazard. Solids and liquids reduced to particle size less than 5 micrometers mean aerodynamic diameter can be much more hazardous to health because of their ability to penetrate the lung. In the air, such finely divided particles can present an explosion hazard even when the solid material is not considered flammable. Consider powdered iron and other powdered metals that are used in fireworks that burn brightly and add color.

The National Fire Protection Association (NFPA) classifies flammable and combustible liquids according to their flash points. Class I flammable liquids have the lowest flash point and are the most dangerous to handle. Class III combustible liquids have the highest flash points and are the most difficult to ignite. The Cal/OSHA program distinguishes between Class IA, IB, and IC flammable liquids, and Class II, IIIA, and IIIB combustible liquids, based on flash point and boiling point. For OSHA, flammable liquids have a flash point of 100˚F or less. DOT must consider the inside of a sun-baked trailer and flammable liquids have a flash point of 140˚F or less.

The various regulatory agencies each define flammable, toxic, corrosive and reactive in a way to protect people and environment that their legislative mandate dictates. The result is a material that may be ignitable to EPA and may not be flammable to OSHA. A material that may be corrosive to OSHA, may not be corrosive to DOT and another material may be corrosive to DOT and not to OSHA. For example, citric acid applied to the skin for up to 4 hours will cause injury to the skin and be considered corrosive by OSHA, but since it does not corrode steel, would not be considered corrosive by DOT. Conversely, the saline solution used for intravenous injection will corrode steel and be considered corrosive by DOT standards, yet is considered harmless by OSHA.

The Clean Air Act Amendments of 1990 introduce another term, highly hazardous chemicals. In response to the chemical release disaster in Bhopal, India, Congress has requested the EPA and OSHA to address the unintentional release of highly hazardous substances in their regulations. Congress listed 100 highly hazardous substances and directed the agencies to continue adding to the list.

Litigation often turns on a definition in law. A case where the release of toxic substances caused injury to persons down wind from the point of release hinges on the definition of highly hazardous substances and the requirements in law for employers who use highly hazardous substances. If the materials and processes used by the industrial facility meet the definition of acutely hazardous, extremely hazardous, or highly hazardous, the specific requirements in OSHA and EPA regulations must be met by the facility and breach of duties to the community become the basis for litigation.

Expert No. 8901, PE, CIH, CSP is a Licensed Safety Engineer, Certified Industrial Hygienist and Certified Safety Professional with more than 30 years experience in accident investigation systems in industrial facilities, exposure assessment strategies, reconstructing exposures, Cal/OSHA, industrial and environmental hygiene. He has thorough knowledge of federal and state environmental and worker health and safety regulations and has managed numerous programs to evaluate and ensure compliance with these regulations. He has taught at UCLA and at Cal State – Dominguez Hills.

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