NFPA 704 fire diamond
The coloured diamond on buildings and tanks that tells firefighters how hazardous a material is, section by section.
The NFPA diamond is the hazard sign set out in NFPA 704, the National Fire Protection Association’s standard for identifying the hazards of materials for emergency response. It is a square on its point divided into four smaller diamonds: health in blue on the left, flammability in red at the top, instability in yellow on the right and special hazards in white at the bottom. Each coloured section holds a number from 0, a minimal hazard, to 4, a severe one. NFPA’s FAQ says the ratings cover short-term, acute exposure in a fire, spill or similar emergency, and that the sign is there to alert emergency response personnel. There is a page for each section and for each symbol that can go in the white section.
The diamond names the class of hazard and how severe it is in an emergency. A chemical’s own hazard classification is in section 2 of its safety data sheet, and the NFPA and OSHA quick card comparing the two systems notes that some safety data sheets also print the diamond with the numbers filled in.
What 0 to 4 mean in each section
CAMEO Chemicals, NOAA’s chemical hazard database, publishes the wording for each number. Shortened, it reads:
| Rating | Health (blue), under emergency conditions | Flammability (red) | Instability (yellow) |
|---|---|---|---|
| 4 | Can be lethal | Vaporizes rapidly or completely at normal pressure and temperature, or disperses readily in air, and burns readily | Readily capable of detonation, explosive decomposition or explosive reaction at normal temperatures and pressures |
| 3 | Can cause serious or permanent injury | Liquids and solids that can be ignited at almost any ambient temperature | Capable of detonation or explosive reaction, but needs a strong initiating source or heating under confinement |
| 2 | Can cause temporary incapacitation or residual injury | Must be moderately heated, or exposed to relatively high ambient temperatures, before it ignites | Readily undergoes violent chemical change at elevated temperatures and pressures |
| 1 | Can cause significant irritation | Must be preheated before it ignites | Normally stable, but can become unstable at elevated temperatures and pressures |
| 0 | No hazard beyond that of ordinary combustible materials | Will not burn under typical fire conditions, like concrete, stone and sand | Normally stable, even under fire conditions |
The University of Texas at Dallas ties the flammability numbers to flash points: below 23 °C (73 °F) for a 4, below 38 °C (100 °F) for a 3, below 93 °C (200 °F) for a 2, and above 93 °C for a 1.
The white section: W, OX and SA
The white section has no number. A Department of Homeland Security training course says it is either blank or holds an abbreviation or symbol for a specific hazard. The three in NFPA’s FAQ are W with a line through it, which CAMEO Chemicals defines as materials that react violently or explosively with water; OX, for materials with oxidizing properties; and SA, for a simple asphyxiant gas, which Fire Engineering says acts by displacing oxygen.
Facilities use other letters too, and sources disagree about them. Riverside County’s environmental health department calls W, OX and SA the only symbols the standard recognizes, and lists COR, ACID and ALK as non-standard symbols in wide use. The Homeland Security course, citing the 2007 edition, counts ACID, ALK and COR among seven authorized symbols. The University of Texas at Dallas shows further extensions to the standard, among them the radiation symbol and the biohazard symbol drawn in the white section.
The diamond beside GHS pictograms and HMIS labels
A GHS pictogram on a chemical label has the same outline, a square set at a point, but it puts a black hazard symbol in a red frame and carries no number. The hazard categories behind it are numbered in section 2 of the safety data sheet, where 1 is the most severe and 4 the least, the reverse of the diamond. The NFPA and OSHA quick card says those category numbers are not to be used to fill in a diamond. The GHS also has pictograms for two of the diamond’s hazards: Great Britain’s Health and Safety Executive lists the flame for flammable and the flame over circle for oxidising.
HMIS labels, from the American Coatings Association’s Hazardous Materials Identification System, put their ratings in stacked bars. Their fourth, white bar holds a letter from A to K, or X, for personal protective equipment, where the diamond’s white section holds a special hazard. SUNY Geneseo’s chemistry stockroom notes that the same chemical can be rated differently in the two systems.
Where the diamond is posted
NFPA’s FAQ lists outside buildings, on doors and on tanks, where emergency responders will see it during a spill or fire. The standard doesn’t say when a building needs one: another code, or the authority having jurisdiction such as the local fire department, decides that. Where several chemicals are kept together, CAMEO Chemicals says a diamond may give the overall hazard of the location, showing the highest value in each section for any chemical there. Hazardous materials in transport carry Department of Transportation placards instead, and Fire Engineering says NFPA 704 is not used for them.
Where the diamond came from
Fire Engineering credits the diamond to J.F. Morris, fire marshal of Charlotte, North Carolina, who created it in 1959 after thirteen firefighters were injured at the Charlotte Chemical Company, at a fire in a vat they took for kerosene. The vat held metallic sodium, which reacted violently to their efforts to put the fire out. Morris’s answer was a diamond divided into four smaller diamonds, colour-coded by hazard, and it was tentatively adopted as a guide in 1960.
Sources
- Frequently Asked Questions on NFPA 704, National Fire Protection Association, published by the Cambridge Fire Department (Massachusetts), Questions 1, 2, 3, 4 and 5
- NFPA Diamond (CAMEO Chemicals help), NOAA Office of Response and Restoration
- Comparison of NFPA 704 and HazCom 2012 Labels (Quick Card), National Fire Protection Association and U.S. Occupational Safety and Health Administration
- 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
- NFPA 704 Guidance Document: Frequently Asked Questions (FAQ), EPO-372 (Rev 04/21), Riverside County Department of Environmental Health, Hazardous Materials Management Branch, Page 2
- Understanding NFPA 704 Placarding Is Critical to Life Safety of First Responders, Brian Daboul, 29 January 2024, Fire Engineering
- Allocation of Label Elements (29 CFR 1910.1200, Appendix C), 29 CFR 1910.1200 Appendix C, U.S. Occupational Safety and Health Administration, C.2.3.1
- Hazard pictograms (symbols), GB CLP, Health and Safety Executive (Great Britain)
- Hazard Labeling System, SUNY Geneseo, Chemistry Stockroom, Sections 2–3
- Other Industrial Labeling Systems: ACA/NPCA HMIS and NFPA 704, Society for Chemical Hazard Communication
Last reviewed September 30, 2026 by Rory Hansen. How we research