The blue (left-hand) quadrant of the NFPA 704 symbol. The values are: 4 - Danger. May be fatal on short exposure. Specialized protective equipment required. 3 - Warning. Corrosive or toxic. Avoid skin contact or inhalation. 2 - Warning. May be harmful if inhaled or absorbed. 1 - Caution. May be irritating. 0 - No unusual hazard