Hazardous Substance

By Tabitha Mishra
Last updated: September 30, 2018

What Does Hazardous Substance Mean?

Hazardous substances are substances with properties that pose a physical, health, or environmental risk. This includes, among others, substances that are flammable, explosive, reactive when coming into contact with air or water, toxic, carcinogenic, or damaging to the lungs.

Due to these properties, hazardous substances must be handled with extreme care to prevent harm to individuals or the natural environment. Safety Data Sheets for all hazardous products in the workplace should be made available so all employees can refer to them to know the necessary precautions and personal protective equipment required to use them safely.

Comprehensive tables of hazardous substances can be found in 40 CFR 116.4 and 40 CFR 302.4.

Safeopedia Explains Hazardous Substance

A hazardous substance can be any item or agent – of biological, chemical, radioactive, or physical nature – that has the potential to cause harm to humans, animals, or the natural environment. This is the case whether it has properties that are hazardous on their own or only when they interact with other factors.

The handling, storage, and use of hazardous substances in the United States fall under a variety of laws and regulations administered by:

  • The Environmental Protection Agency (EPA)
  • The Occupational Safety and Health Administration (OSHA)
  • The Department of Transportation (DOT)
  • The Nuclear Regulatory Commission (NRC)

While these agencies often have regulations that cover the same materials, each works with different definitions of "hazardous substances."

The HazCom Standard

OSHA's Hazard Communication Standard (HazCom) was enacted in an effort to make chemical handling safer in the workplace. Under this standard, employers are required to inform employees of all hazardous chemicals in the workplace or on the jobsite, label chemical products with the necessary safety information, and provide training to those who are at risk of exposure.

Exposure Limits for Hazardous Substances

OSHA’s permissible exposure limits (PELs) provide a threshold for exposure to hazardous substances. Exceeding the PEL poses a known risk and must be avoided.

Many PELs are based on an 8-hour time-weighted average (TWA), meaning that it specifies a concentration of the substance that someone can be exposed to for eight hours without serious adverse effects. Other hazardous substances, however, will have short term exposure limits (STEL) that can only be considered for a brief window of time (15 minutes of exposure). And still others will have ceiling limits – levels of exposure that should never be exceeded, no matter how briefly.

While some hazardous substances have acute effects that are felt immediately after exposure or soon after exceeding permissible limits, many have chronic effects that only manifest after prolonged exposure over the course of days, months, or years.

The National Institute for Occupational Safety and Health (NIOSH) issues Recommended Exposure Limits (RELs) for the protection of workers exposed to hazardous substances. While OSHA's PELs represent the legal limit for exposure, NIOSH's RELs represent the safe threshold for exposure based on the best available science. As such, RELs tend to be stricter than PELs.


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