2-0-1-ox
The number 4 on the NFPA 704 placard indicates the highest hazard in any of the three categories (health, fire, reactivity).
The flammable sign was standardized by the National Fire Protection Association (NFPA) in the late 1940s. The NFPA developed a system of labeling flammable materials with a red diamond symbol to alert people to the fire hazard.
Health (Blue): 1 Flammability (Red): 2 Reactivity (Yellow): 0 Special (White): None
Fire Hazard: 2, Red square Special Information: 4 Health hazard: 1 Reactivity hazard: 3
The NFPA 704 symbol for acetylene is a blue diamond with a white flame symbol on top, a red health hazard rating of 4 (extreme), a blue flammability rating of 4 (extreme), and a yellow reactivity rating of 0 (stable).
Cyclohexane does not have a specific NFPA diamond classification since it is not considered a hazardous material under the NFPA 704 standard.
Health (blue) 2 Fire (red) 0 Reactivity (yellow) 0
The NFPA 704 diamond is a ring of smaller diamonds that are blue, red, yellow and white. A number or symbol in each section indicates the relative danger.
If an NFPA 704 Fire Diamond has a 2 in the yellow section it means the reactivity of the material is such that it can have violent chemical change at high temperature or pressure, it can react violently with water, or it can form explosive mixtures with water.
The highest degree of hazard - severe hazard that a very short exposure could cause serious injury or death.
The NPFA mark is used for materials that can ignite.