NFPA Hazard Diamonds
The NFPA 704 fire diamond (or hazmat diamond) is described in NFPA Standard 704, maintained by the National Fire Protection Association. The system identifies four key hazards (health (blue), flammability (red), instability (yellow), and special (white)) and their degree of severity. Hazard severity is rated numerically, ranging from 0 (minimal) to 4 (severe).
The hazard diamond is useful because it allows emergency personnel to quickly and easily identify the risks posed by hazardous materials and is useful to determine what, if any, special equipment should be used, procedures followed, or precautions taken during an emergency response. (Summarized & more information here.)
Want to make your own customizable hazard diamond? Click here. Why does this feature exist? So people can make easily identifiable hazard diamonds for any chemical they have on hand.