Hazard Symbols on NFPA 704 Symbol and Number Meaning Example Blue - 0 Does not pose a health hazard. No precautions are necessary. water Blue - 1 Exposure may cause irritation and minor residual injury. acetone Blue - 2 Intense or continued non-chronic exposure may result in incapacitation or or residual injury. ethyl ether Blue - 3 Brief exposure may cause serious temporary or moderate residual injury. chlorine gas Blue - 4 Very brief exposure may cause death or major residual injury. sarin, carbon monoxide Red - 0 Will not burn. carbon dioxide Red - 1 Must be heated in order to ignite. Flash point exceeds 90°C or 200°F mineral oil Red - 2 Moderate heat or relatively high ambient temperature is required for ignition. Flash point between 38°C or 100°F and 93°C or 200°F diesel fuel Red - 3 Liquids or solids that readily ignite at most ambient temperature conditions. Liquids have a flash point below 23°C (73°F) and boiling point at or above 38°C (100°F) or flash point between 23°C (73°F) and 38°C (100°F) gasoline Red - 4 Rapidly or completely vaporizes at normal temperature and pressure or readily disperses in air and readily burns. Flash point below 23°C (73°F) hydrogen, propane Yellow - 0 Normally stable even when exposed to fire; not reactive with water. helium Yellow - 1 Normally stable, but may become unstable elevated temperature and pressure. propene Yellow - 2 Changes violently at elevated temperature and pressure or reacts violently with water or forms explosive mixtures with water. sodium, phosphorus Yellow - 3 May detonate or undergo explosive decomposition under the action of a strong initiator or reacts explosively with water or detonates under severe shock. ammonium nitrate, chlorine trifluoride Yellow - 4 Readily undergoes explosive decomposition or detonates at normal temperature and pressure. TNT, nitroglycerine White - OX oxidizer hydrogen peroxide, ammonium nitrate White - W Reacts with water in a dangerous or unusual way. sulfuric acid, sodium White - SA simple asphyxiant gas Only: nitrogen, helium, neon, argon, krypton, xenon