Instability rating (yellow)
The yellow section on the right of the NFPA 704 fire diamond. Its number, 0 to 4, rates how readily the material can release energy by itself, through violent chemical change, explosive decomposition or detonation: 0 is stable even in a fire, 4 can detonate at normal temperature and pressure.
How to read it
It is the instability rating, at the three o'clock position of the NFPA 704 fire diamond, and older charts and some safety guides call it reactivity. Both 3 and 4 mark a material that can detonate or decompose explosively. The difference, in CAMEO Chemicals' wording, is that a 3 needs a strong initiating source or heating under confinement, while a 4 can go off at normal temperatures and pressures. A product's rating comes from its safety data sheet.
Also searched as: nfpa instability rating, nfpa reactivity rating, nfpa yellow.
These explain what a rating on the diamond means. For handling, storage and first aid, refer to the product’s label and safety data sheet.
What 0 to 4 mean
| Rating | CAMEO Chemicals' description |
|---|---|
| 4 | Readily capable of detonation, explosive decomposition or explosive reaction at normal temperatures and pressures |
| 3 | Capable of detonation, explosive decomposition or explosive reaction, but needs a strong initiating source or heating under confinement |
| 2 | Readily undergoes violent chemical change at elevated temperatures and pressures |
| 1 | Normally stable, but can become unstable at elevated temperatures and pressures |
| 0 | Normally stable, even under fire conditions |
Instability, formerly reactivity
Older editions of NFPA 704 called the yellow section reactivity. The University of Florida's chart of the 1996 edition labels it reactivity and stability, and SUNY Geneseo's summary of the 1990 edition says reactivity. CAMEO Chemicals and the Department of Homeland Security's Center for Domestic Preparedness use instability, while the University of Texas at Dallas's campus guide still says reactivity.
The wording changed along with the name. In the 1996 chart the yellow numbers also covered reactions with water: a 2 included materials that may react violently with water or form potentially explosive mixtures with it. CAMEO's current descriptions rate how stable a material is in itself, and a violent reaction with water is marked separately, with the W in the white section.
Look-alikes
OSHA container labels list physical hazards as separate classes, such as explosives, reactives and oxidizers, each with its own pictogram; explosives take the exploding bomb. The NFPA and OSHA quick card notes that the diamond instead splits fire and instability into two numbers. HMIS labels have a yellow bar on a 0 to 4 scale that SUNY Geneseo describes as reactivity.
More NFPA 704 fire diamond
Browse symbols drawn with diamonds or letters and numbers.
Sources
- NFPA Diamond (CAMEO Chemicals help), NOAA Office of Response and Restoration
- Hazardous Material Code Identification (NFPA 704, 1996 Edition), University of Florida Environmental Health & Safety
- Hazard Labeling System, SUNY Geneseo, Chemistry Stockroom, Section 1
- NFPA 704 Symbols, University of Texas at Dallas, Institutional Risk & Safety
- Hazardous Materials Facility Markings, AWR-358 course, Center for Domestic Preparedness, U.S. Department of Homeland Security
- Comparison of NFPA 704 and HazCom 2012 Labels (Quick Card), National Fire Protection Association and U.S. Occupational Safety and Health Administration
- Allocation of Label Elements (29 CFR 1910.1200, Appendix C), 29 CFR 1910.1200 Appendix C, U.S. Occupational Safety and Health Administration, C.4.14
- NFPA Hazard Diamond, University of San Francisco, Environmental Health & Safety
Last reviewed September 30, 2026 by Rory Hansen. How we research