NFPA 704

First "tentatively adopted as a guide" in 1960,[1] and revised several times since then, it defines the "Safety Square" or "Fire Diamond" which is used to quickly and easily identify the risks posed by hazardous materials.

This helps determine what, if any, special equipment should be used, procedures followed, or precautions taken during the initial stages of an emergency response.

The crew tried to suppress the fire, which resulted in the vat exploding due to metallic sodium being stored in the kerosene.

In this case, sodium was able to react with water to release hydrogen gas and large amounts of heat, which has the potential to explode.

Fire Marshal J. F. Morris developed the diamond shaped placard as a marking system to indicate when a building contained hazardous materials, with their levels of flammability, reactivity and health effects.

NFPA 704 four-colored diamond Health 4: Very short exposure could cause death or major residual injury. E.g. VX gas Flammability 4: Will rapidly or completely vaporize at normal atmospheric pressure and temperature, or is readily dispersed in air and will burn readily. Flash point below 23 °C (73 °F). E.g. propane Instability 4: Readily capable of detonation or explosive decomposition at normal temperatures and pressures. E.g. nitroglycerin Special hazard W: Reacts with water in an unusual or dangerous manner. E.g. sodium, sulfuric acid
NFPA 704 safety squares on containers of ethyl alcohol and acetone .
Standard System for the Identification of the Hazards of Materials for Emergency Response
NFPA 704 placard of hydrofluosilicic acid . Notably, it is using the nonstandard COR sign.