These are the diamond-shaped tags you see on vehicles carrying chemicals and at chemical facilities. The standard for these tags comes from the National Fire Protection Association and are designed to provide important information to firefighters and other rescue crews in the event of a fire or other emergency.

They are divided into 4 smaller colored dimonds, as follows:

The health, flammability, and reactivity sections each have a number from 0 to 4, which represents the danger levels according to a system similar to, but not identical to, the HMIS ratings. In particular, the HMIS ratings are intended for employee safety and so the health ratings consider long-term effects, while the NFPA ratings do not.

The special code area may show a W in the case of chemicals that are highly reactive with water, or OX for the presence of oxidizing agents, or both.