An official website of the United States government.

This is not the current EPA website. To navigate to the current EPA website, please go to This website is historical material reflecting the EPA website as it existed on January 19, 2021. This website is no longer updated and links to external websites and some internal pages may not work. More information »

Hazardous Substance Release Warning Signs

There are several ways to recognize the warning signs of a hazardous substance release. The shapes of containers are often a clue that they may be storing hazardous substances. For example, large drum barrels or reinforced (e.g., ribbed) tanker cars are often used to transport and store chemicals or hazardous wastes. The federal government has a system for labeling containers used to store or transport hazardous substances that uses colors and symbols to designate potential hazards.

Although not the preferred method, one's senses may detect hazardous substances:

  • a foul odor,
  • visible gases,
  • unusually colored flames, or
  • the increased pitch of a relief valve on a pressurized container.

However, do not assume gases and vapors are harmless because they lack odor -- odorless gases or vapors may also be extremely harmful. Other common-sense signs can warn of danger. For example, people running from or suddenly collapsing in a hazardous material area, visible signs of a leak, or gas clouds coming from a facility or vehicle all suggest the risk of a hazardous substance release. It is always best to be cautious.