According to the NFPA, "The system is characterized by the "diamond" that is actually a "square-on-point" shape. It identifies the hazards of a material and the degree of severity of the health, flammability, and instability hazards. Hazard severity is indicated by a numerical rating that ranges from zero (0) indicating a minimal hazard, to four (4) indicating a severe hazard. The hazards are arranged spatially as follows: health at nine o'clock position, flammability at twelve o'clock position, and instability at three o'clock position. In addition to the spatial orientation that can be used to distinguish the hazards, they are also color-coded as follows: blue for health, red for flammability, and yellow for instability. The six o'clock position on the symbol represents special hazards and has a white background. The special hazards in use are W, which indicates unusual reactivity with water and is a caution about the use of water in either fire fighting or spill control response, and OX, which indicates that the material is an oxidizer."