J.R. S. answered • 08/22/21
Ph.D. University Professor with 10+ years Tutoring Experience
This is the labeling system used by the National Fire Protection Association.
The 3 indicates the level of health hazard and would be for chemicals that can cause temporary or moderate injury when after even a short period of exposure.
The 4 indicates the level of flammability and would be for chemicals that readily burn and have a flash point that is below normal room temperatures. These are the most dangerous chemicals.
The 2 indicates the level of instability and would be for chemicals that react violently when at elevated temperatures or pressure. Also, these chemicals may react violently when exposed to water or moisture.
The COR indicates that the chemical is corrosive (such as strong acids and bases)
