It is required that each laboratory or work area where chemicals are used or stored be posted with the standard NFPA placard. The system is based on a color-coded warning with blue indicating health hazard, red indicating flammability, and yellow indicating reactivity. A numerical number is assigned to each color-coded area with a range from 0 to 4, the higher the number, the more hazardous the area. The highest number within each warning category for the chemicals present is posted on the placard.