NFPA - Yellow Diamond

The right diamond is yellow and indicates the stability of the chemical. Numbers 0 through 4 are broken down as follows:

0 - A chemical that is stable, even in the presence of fire or water.

1 - A chemical that is stable, but can become unstable at extreme temperatures or pressures.

2 - A chemical that will undergo a violent change at elevated temperatures or pressures, and those that react with water or might form an explosive mixture when in contact with water.

3 - A chemical that is capable of detonating or exploding, but requires a strong source to do so. Also, chemicals that react explosively with water or may detonate if they are severely shocked.

4 - Any chemical that is capable of detonating or exploding in normal conditions.

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