NFPA 704 Diamond Information: Yellow Segment
Yellow region - Reactivity
The yellow region of the RTK diamon indicates reactivity and may contain either a 0, 1, 2, 3 or 4. These numbers indicate the level of explosion, detonation or reaction risk, and can be interpreted as follows:
- 4 Readily capable of detonation or explosive decomposition at normal temperatures and pressures (e.g., nitroglycerin).
- 3 Capable of detonation or explosive decomposition but requires a strong initiating source, must be heated under confinement before initiation, reacts explosively with water, or will detonate if severely shocked (e.g., fluorine).
- 2 Undergoes violent chemical change at elevated temperatures and pressures, reacts violently with water, or may form explosive mixtures with water (e.g., phosphorus).
- 1 Normally stable, but can become unstable at elevated temperatures and pressures (e.g., calcium).
- 0 Normally stable, even under fire exposure conditions, and is not reactive with water (e.g., helium).