NFPA 704 Diamond Explained
The NFPA 704 diamond is a four-color hazard marker used on buildings, tanks and storage areas. Blue is health, red is flammability, yellow is instability and white is special hazards. The first three carry a number from 0 (least hazard) to 4 (greatest hazard), so a 4 is always the worst.
The diamond is meant to be read at a glance by fire fighters and other emergency responders, from a safe distance, before they enter. NFPA 704 is the standard published by the National Fire Protection Association for the identification of the hazards of materials for emergency response.
Red is at the top, blue on the left, yellow on the right and white on the bottom. Letters shown in the diagram stand for the number or symbol that appears there.
The four boxes
The 0 to 4 scale
| Rating | General meaning |
|---|---|
| 4 | Severe or extreme hazard |
| 3 | Serious hazard |
| 2 | Moderate hazard |
| 1 | Slight hazard |
| 0 | No special hazard |
Each color has its own criteria for what a given number means, so a 2 in blue is not the same kind of hazard as a 2 in red. Details are on the health, flammability, instability and special hazards pages.
Special hazard symbols
- OX: oxidizer.
- W with a bar through it: reacts with water in an unusual or dangerous way.
- SA: simple asphyxiant gas.
Examples
Who assigns the ratings, and is it required?
NFPA 704 is a voluntary consensus standard. Fire codes and local authorities often require the diamond on buildings and tanks that hold hazardous materials. Ratings are normally assigned by the facility, sometimes with help from published ratings or the supplier. Because judgment is involved, you may see a one-point difference between two sources. The rating does not appear on GHS shipping labels, and it is not a mandatory part of the SDS, though suppliers often list it in Section 16.
Important: 4 means opposite things in NFPA and GHS
In NFPA 704, 4 is the most severe. In GHS, Category 1 is the most severe, and Category 4 is among the least severe. Never compare the numbers directly. See NFPA 704 versus GHS for a side-by-side comparison and HMIS versus NFPA for the workplace labeling system.
Related glossary terms
For hazard information in your own workplace, start with the GHS pictograms, SDS Section 2 and the chemical index.
Frequently asked questions
What do the colors on the NFPA 704 diamond mean?
Blue is health, red is flammability, yellow is instability and white is special hazards. The first three carry a number from 0 (least hazard) to 4 (greatest hazard). The white box carries a symbol such as OX, W or SA, or is left blank.
What does the NFPA 704 diamond look like?
It is a square turned on its point and divided into four smaller diamonds. Red sits at the top, blue on the left, yellow on the right and white at the bottom.
Is NFPA 704 required on chemical containers?
NFPA 704 is a voluntary consensus standard that describes how to rate and display hazards for emergency responders. Fire codes and local authorities often require it on buildings, tanks and storage areas. It does not replace GHS labels on shipped containers, which OSHA HazCom requires.
Is NFPA 4 the worst rating?
Yes. In NFPA 704 a 4 is the most severe rating and 0 the least. GHS works the other way round for hazard categories, where Category 1 is the most severe. Do not compare the numbers directly.
Where do I find the NFPA rating on an SDS?
NFPA ratings are optional on the SDS. When a supplier includes them they are usually in Section 16, and sometimes in Section 2 or 15. If none is shown, the facility can assign ratings from the SDS data using the criteria in the standard.
General reference based on a summary of NFPA 704. For authoritative criteria, consult the current edition of the standard. This page does not replace the supplier's SDS.