Flammability rating (red)
The red section at the top of the NFPA 704 fire diamond. Its number, 0 to 4, rates how easily the material catches fire: 0 will not burn, 4 vaporizes readily at normal temperatures and burns readily.
How to read it
It is the flammability rating, at the twelve o'clock position of the NFPA 704 fire diamond. For liquids the number follows the flash point: the lower the flash point, the higher the rating. Fire Engineering calls it one of the pieces of information fire departments most want when they respond. A product's rating comes from its safety data sheet.
Also searched as: nfpa flammability rating, nfpa red, red diamond nfpa.
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 | Flash point |
|---|---|---|
| 4 | Vaporizes rapidly or completely at normal pressure and temperature, or disperses readily in air, and burns readily | Below 23 °C (73 °F) |
| 3 | Liquids and solids that can be ignited at almost any ambient temperature | Below 38 °C (100 °F) |
| 2 | Must be moderately heated, or exposed to high ambient temperatures, before it ignites | 38 to 93 °C (100 to 200 °F) |
| 1 | Must be preheated considerably before it ignites | Above 93 °C (200 °F) |
| 0 | Will not burn under typical fire conditions, including concrete, stone and sand | Does not burn |
The flash points are as the University of Texas at Dallas and Fire Engineering give them. A Department of Energy laboratory guide ties the same cut-offs to the classes of flammable and combustible liquids: class IA is a 4, IB and IC a 3, II and IIIA a 2, and IIIB a 1.
The NFPA 4 in EPA rules
The US Environmental Protection Agency uses a flammability rating of 4 to decide which flammable mixtures fall under its Risk Management Program rule. The criteria are read at standard temperature and pressure: in the EPA's answer to one question, a mixture that meets them only at raised temperature and pressure is not covered.
Look-alikes
The GHS flame pictogram marks flammable liquids on OSHA container labels. Its hazard categories are numbered the other way from the diamond: the University of San Francisco's safety office notes that under OSHA's standard 1 is the most hazardous and 4 the least.
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
- NFPA 704 Symbols, University of Texas at Dallas, Institutional Risk & Safety
- Understanding NFPA 704 Placarding Is Critical to Life Safety of First Responders, Brian Daboul, 29 January 2024, Fire Engineering
- Evaluating Hazardous Materials for NFPA 704 Diamond Ratings, WIPP Information Repository, Supplemental Information, U.S. Department of Energy, Waste Isolation Pilot Plant
- NFPA 4 Criteria, Risk Management Program (RMP) Rule, frequent questions, U.S. Environmental Protection Agency
- NFPA Hazard Diamond, University of San Francisco, Environmental Health & Safety
- Allocation of Label Elements (29 CFR 1910.1200, Appendix C), 29 CFR 1910.1200 Appendix C, U.S. Occupational Safety and Health Administration, C.4.19
Last reviewed September 30, 2026 by Rory Hansen. How we research