Health rating (blue)
The blue section on the left of the NFPA 704 fire diamond. Its number, 0 to 4, rates how harmful the material can be to people in a short exposure during a fire, spill or similar emergency; 4 means it can be lethal.
How to read it
It is the health rating, at the nine o'clock position of the NFPA 704 fire diamond. It covers acute, short-term exposure only. The NFPA and OSHA quick card says chronic health effects are not covered by NFPA 704, since acute hazards are the ones typical of emergency response; long-term hazards such as cancer appear on OSHA container labels instead. A product's rating comes from its safety data sheet, and some sheets print the diamond with the numbers filled in.
Also searched as: blue diamond nfpa, nfpa blue, nfpa health rating.
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
CAMEO Chemicals, NOAA's chemical hazard database, words each rating as what the material can do under emergency conditions.
| Rating | Under emergency conditions, the material |
|---|---|
| 4 | can be lethal |
| 3 | can cause serious or permanent injury |
| 2 | can cause temporary incapacitation or residual injury |
| 1 | can cause significant irritation |
| 0 | offers no hazard beyond that of ordinary combustible materials |
A laboratory guide in the US Department of Energy's Waste Isolation Pilot Plant library gives the toxicity figures behind the numbers. A 4 is a material with an oral LD50 of 5 mg/kg or less, or a gas or vapour with an LC50 of 1,000 ppm or less. A 0 has an oral LD50 above 2,000 mg/kg and does not irritate the skin, eyes or respiratory tract. Materials corrosive to the skin, eyes or respiratory tract are rated 3.
Look-alikes
The GHS skull and crossbones and health hazard pictograms on containers come with hazard categories numbered the other way: the University of San Francisco's safety office notes that under OSHA's Hazard Communication Standard 1 is the most hazardous and 4 the least. OSHA labels cover both acute and chronic health hazards, carcinogens among them, where the blue number is acute only. HMIS labels also have a blue health bar on a 0 to 4 scale; the NFPA 704 fire diamond page sets out how the two systems differ.
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
- Comparison of NFPA 704 and HazCom 2012 Labels (Quick Card), National Fire Protection Association and U.S. Occupational Safety and Health Administration
- NFPA 704 Guidance Document: Frequently Asked Questions (FAQ), EPO-372 (Rev 04/21), Riverside County Department of Environmental Health, Hazardous Materials Management Branch, Page 1
- Evaluating Hazardous Materials for NFPA 704 Diamond Ratings, WIPP Information Repository, Supplemental Information, U.S. Department of Energy, Waste Isolation Pilot Plant
- NFPA Hazard Diamond, University of San Francisco, Environmental Health & Safety
Last reviewed September 30, 2026 by Rory Hansen. How we research