The National Fire Protection Agency, or NFPA, uses these signs to indicate hazardous materials stored in an unknown building. Listen in to learn how the signs work -- and how they help firefighters -- in this podcast from HowStuffWorks.com.
Learn more about your ad-choices at https://www.iheartpodcastnetwork.com

BrainStuff Classics: Why Are Some Americans Cancelling Columbus Day?
07:16

American Versus British English: What Are Biscuits, Muffins, and Pudding?
09:51

How Do Sunspots Work?
14:22