NFPA 704 Health Hazard (Blue)
The blue quadrant of the NFPA 704 diamond is the health rating. It runs from 0 (no hazard beyond ordinary combustible material) to 4 (a very short exposure could cause death or major lasting injury) and describes how dangerous a material is to a person during an emergency such as a fire or spill.
Where it sits: the blue quadrant on the left of the diamond.
Sample diamond for illustration only. The blue box is the one this page explains.
How to read it
The health rating is built for emergency responders. It looks at the acute effects of a single, short exposure, whether by breathing, skin contact, eye contact or swallowing, under fire or spill conditions. It also considers the hazards of the material as it burns or decomposes, not just the product as sold.
That focus matters when you read it. A material can have a low blue number and still be a serious long-term hazard. Chronic effects such as cancer, reproductive harm or organ damage from repeated low-level exposure are not what the blue number is measuring. For those you need the GHS health hazard classes and the exposure limits on the SDS.
The rating is assigned by the facility or by a qualified person using the criteria in the standard, usually with toxicity data (such as LD50 and LC50 values), irritation and corrosivity data, and professional judgment. Because the standard describes severity in terms of effects and the treatment responders can expect to give, two sources can legitimately rate the same product a point apart. Treat a published number as a starting point.
What each rating means
| Rating | Description | Meaning |
|---|---|---|
| 4 | Deadly | A very short exposure could cause death or major residual injury, even if prompt medical treatment is given. |
| 3 | Extreme danger | A short exposure could cause serious temporary or moderate residual injury. |
| 2 | Hazardous | Intense or continued exposure, but not chronic exposure, could cause temporary incapacitation or possible residual injury unless medical treatment is given quickly. |
| 1 | Slightly hazardous | Exposure would cause irritation, with only minor residual injury even if no treatment is given. |
| 0 | Normal material | Exposure under fire conditions would offer no hazard beyond that of ordinary combustible material. |
Paraphrased summary of the NFPA 704 criteria. Check the current edition of NFPA 704 for the authoritative text; ratings for specific products come from the supplier or the facility.
Points to remember
- Responders normally need full protective clothing and respiratory protection for materials rated 3 or 4. The diamond tells them that before they get close.
- The blue number is not an exposure limit and it cannot be converted to a PEL, TLV or GHS category.
- NFPA 704 numbers run the opposite way to GHS categories. See NFPA 704 versus GHS.
Where to find the information on an SDS
Section 2 gives the GHS health classifications and hazard statements, and Section 11 gives the toxicological data used to judge severity. Some SDSs also list an NFPA or HMIS health number in Section 16. See SDS Section 2 and Section 16 for optional NFPA and HMIS ratings.
Related GHS pages
- GHS hazard classes (acute toxicity, corrosion, irritation, sensitization)
- GHS pictograms
- Browse chemical SDS pages
Frequently asked questions
What does the blue number on an NFPA diamond mean?
The blue number is the health hazard rating from 0 to 4. It describes how severe the acute health effects of a short exposure would be in an emergency, with 4 being the most severe and 0 meaning no hazard beyond ordinary combustible material.
Does NFPA 704 health include cancer or long-term effects?
No. The blue rating is about acute effects from a single short exposure in a fire or spill. Chronic effects such as cancer or organ damage from repeated exposure are shown by GHS classifications and exposure limits, not by the NFPA health number.
Is a health rating of 4 the same as GHS Category 4?
No. In NFPA 704, 4 is the most severe rating. In GHS, Category 1 is the most severe and Category 4 is among the least severe within a hazard class. Never compare the numbers directly.