Fire diamonds located on tanks and buildings indicate the level of chemical hazard located there.
The four colors are blue, red, yellow, and white. The numbers superimposed over the colors rank the severity or danger, ranging from one to four, with four being the highest rating. The blue indicates potential health effects. A four in the blue means severe and immediate health effects, including death, and a one time exposure can cause lasting health problems. The red indicates explosiveness or readiness to ignite.