drawing of the NFPA diamond
Figure 2-2, NFPA 704 System
The bottom quadrant is white, and contains information about any special hazards that may apply. There are three possible codes for the bottom quarter of the NFPA symbol:
  • OXY means this material is an oxidizer. It can easily release oxygen to create or worsen a fire or explosion hazard.
  • The symbol W indicates a material that reacts with water to release a gas that is either flammable or hazardous to health. See Figure 2-2.
  • If the material is radioactive, the usual tri-blade “propeller” symbol for radioactivity will appear.
Radioactive

It is important to remember that the system is chemical-specific. No chemical identification system can accurately assess the synergistic effects of one chemical combining with another, or the possible effects of combining unknown amounts of several chemicals.

The Department of Transportation (DOT), in cooperation with the United Nations, has devised an international classification system, which tags hazardous materials in transit with color-coded, symbolic warning placards.