How to Read an NFPA 704 Diamond

In One Easy Lesson (In Four Parts)

The NFPA Diamond rating system was developed to enable first responders to a fire or similar emergency to see at a glance what hazards they might encounter while performing their duties. It didn’t take long for employers and chemical workers to realize that the Diamond was a useful tool for them as well. But it only helps if you know how to read it and to understand what it says.


I’m sure that most of you know the basics of reading the Diamond – you know that the blue square carries a Health rating, the red square carries a Flammability rating, and the yellow square carries a Chemical Instability rating. You may or may not know that the fourth square, the white one, is there in case a “Special Hazard” notification is necessary. (More on that later.)

The blue, red, and yellow squares will each have a number between 0 and 4 – the higher the number, the greater the hazard. We’ll discuss the squares individually.


Remembering that the NFPA Diamond system was developed primarily for firefighters will help you understand the Health ratings. For instance, a rating of “0” means that this material, under emergency conditions, would be no more hazardous than an ordinary combustible material. In other words, this substance may burn, but would be no more dangerous than, say, burning paper – yes, you could burn yourself with it, but you won’t be inhaling poisonous fumes.

A rating of “1” in the Health square indicates a material that, “under emergency conditions, can cause significant irritation” of lungs, skin, or eyes, or is somewhat toxic if taken orally. Isopropanol falls into this category.

A Health rating of “2” indicates a material that, “Under emergency conditions, can cause temporary incapacitation” or lasting, but not permanent, injury. Acetone and Kerosene are in this category.

A Health rating of “3” is given to a material that, “under emergency conditions, can cause serious or permanent injury”. Some examples in this category are Acetic Acid, Ammonia, and Carbon Dioxide.

Finally, the highest rating, a ”4” in the Health square, is reserved for  materials that, “under emergency conditions, can be lethal”. Hydrofluoric Acid (HF) is one of these, as is Hydrogen Sulfide.



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