NFPA 704 Colors and Numbers: What Each Quadrant Means

Last Updated: 2026-10-09

Answer Capsule: NFPA 704 diamond colors map to four hazards: blue is health, red is flammability, yellow is instability, and white is special hazards. The three colored quadrants each carry a number from 0 (no hazard) to 4 (severe), set by NFPA 704 criteria such as flash point and exposure injury. The white quadrant holds W with a line, OX or SA.

You know the diamond has four colors and some numbers. What you need is the exact meaning of a red 2 versus a red 3, or a blue 3 versus a blue 4. The fire marshal is going to ask why your storage room says what it says. "The chart said so" is not an answer that passes.

This post lays out the NFPA 704 diamond colors and numbers one table at a time, straight from the 2022 edition criteria. Each row gets a real chemical from the Print Pro AZ 50-chemical field guide so the number means something you can picture. Brent Hanke built these tables from the same criteria Print Pro AZ uses when it works out room ratings from a customer's chemical inventory.

What Do the Four NFPA 704 Colors Mean?

The four NFPA 704 colors each stand for one hazard category: blue for health, red for flammability, yellow for instability, and white for special hazards. The colors always sit in the same positions, so a responder can read the sign by flashlight without a legend.

Color	Position	Hazard	What goes in it
Blue	Left	Health	A number, 0 to 4
Red	Top	Flammability	A number, 0 to 4
Yellow	Right	Instability (older signs say reactivity)	A number, 0 to 4
White	Bottom	Special hazards	A symbol, or blank

The numbers do not add up. Each one answers its own question. A 1-3-0 sign is not a "4." It is a mild health hazard, a serious fire hazard, and a stable material. The standard behind all of this is NFPA 704, and the reading method is in the NFPA 704 diamond explained guide.

What Do the Blue Health Numbers 0 to 4 Mean?

The blue health numbers rate how badly a short exposure could injure a person. They run from 0 (no hazard beyond ordinary combustible material) to 4 (very short exposure could cause death). NFPA 704 defines each level by the type and duration of injury.

Blue	NFPA 704 criteria	Example from the field guide
4	Very short exposure could cause death or major residual injury	Chlorine gas, 4-0-0-OX
3	Short exposure could cause serious temporary or moderate residual injury	Hydrochloric acid, 3-0-0
2	Intense or continued but not chronic exposure could cause temporary incapacitation or possible residual injury	Toluene, 2-3-0
1	Exposure would cause irritation with only minor residual injury	Acetone, 1-3-0
0	No hazard beyond that of ordinary combustible material	Water, 0-0-0

The health number is the one that decides protective gear. A blue 3 or 4 means full PPE and breathing air before anyone goes in. Note that some materials, like phosphoric acid and methanol, get different health numbers from different suppliers. The SDS for your exact product and concentration is the one that counts.

What Do the Red Flammability Numbers 0 to 4 Mean?

The red flammability numbers rate how easily a material catches fire, and NFPA 704 ties them to flash point and boiling point. Flash point is the lowest temperature at which a liquid gives off enough vapor to ignite. Lower flash point, higher number.

Red	NFPA 704 criteria	Example from the field guide
4	Flash point below 73 F and boiling point below 100 F, or a flammable gas, or a material that rapidly vaporizes at normal temperature and pressure	Propane, boiling point minus 44 F
3	Flash point below 73 F with boiling point at or above 100 F, or flash point 73 F to 100 F. Ignites at normal temperatures	Gasoline, flash point about minus 45 F
2	Flash point 100 F to 200 F. Must be moderately heated to ignite	Diesel, flash point 125 F or higher
1	Flash point above 200 F. Must be preheated to burn	Motor and hydraulic oil, 0-1-0
0	Will not burn under normal fire conditions	Hydrochloric acid, 3-0-0

This table settles the gasoline versus diesel argument. Gasoline flashes at about minus 45 F, so it is a 3. Diesel flashes at 125 F or higher, so it is a 2. Both are fuels, but a match will light gasoline vapor on a cold morning and will not light diesel. Flash points for common chemicals are listed in the NIOSH Pocket Guide to Chemical Hazards.

What Do the Yellow Instability Numbers 0 to 4 Mean?

The yellow instability numbers rate whether a material can release energy on its own, through detonation, explosive decomposition or a violent reaction with water. Older signs call this quadrant reactivity. The 2022 edition calls it instability, and the numbers mean the same thing.

Yellow	NFPA 704 criteria	Example from the field guide
4	Readily capable of detonation or explosive decomposition at normal temperature and pressure	None of the 50 common chemicals in the field guide rate a 4
3	Capable of detonation with a strong initiating source or if heated under confinement, or reacts explosively with water	Acetylene, 0-4-3
2	Undergoes violent chemical change at elevated temperature and pressure, or reacts violently with water	Concentrated sulfuric acid, 3-0-2-W
1	Normally stable but can become unstable at elevated temperatures and pressures	Sodium hydroxide, 3-0-1
0	Normally stable, even under fire exposure, and not reactive with water	Gasoline, 1-3-0

Most everyday chemicals are a yellow 0, including fuels, solvents and the common acids. Sodium hydroxide gets a 1 because it generates heat when dissolved in water. Concentrated sulfuric acid gets a 2 because it reacts exothermically with water. That is why you always add acid to water and never the reverse.

What Goes in the White Special Hazard Quadrant?

The white quadrant holds one of exactly three symbols authorized by NFPA 704, or it stays blank. There is no number in the white square.

Symbol	Meaning	Example from the field guide
W with a horizontal line through it	Reacts dangerously or unusually with water	Concentrated sulfuric acid, 3-0-2-W
OX	Oxidizer; supplies oxygen to a fire without outside air	Calcium hypochlorite pool shock, 3-0-2-OX
SA	Simple asphyxiant gas; displaces oxygen	Nitrogen, 0-0-0-SA

Callout: COR, ACID, ALK, BIO, POI and the radiation trefoil are not NFPA 704 symbols. If your facility uses them, the standard says to put them outside the diamond. A strict fire marshal can call them non-compliant inside the white square.

SA applies only to nitrogen, helium, neon, argon, krypton, xenon and liquefied carbon dioxide. What a firefighter does differently for each symbol is in the NFPA 704 special hazard symbols post.

How Do You Put the Colors and Numbers on a Sign?

You put the numbers on a sign by pulling each rating from the Safety Data Sheet and taking the highest number in each color for the room. Then you order the diamond in a size that matches the viewing distance. The facility owner or operator assigns the ratings. NFPA 704 gives the criteria, not the numbers.

Here is a call Print Pro AZ gets every month. A plant supervisor has a chemical room with a solvent, an acid and a bleach. Each SDS gives a different diamond, and the question is which one goes on the door.

The answer is none of them by itself. The door gets the highest blue, the highest red, the highest yellow and every symbol from the whole room.

For a room whose ratings may change, a blank diamond with a numbers and characters kit lets you set any rating in the field. For a fixed rating, Print Pro AZ prints the diamond in 3 to 24 inch sizes. Vinyl goes on indoor cabinets and doors, and .040 aluminum goes outdoors.

Grab the free NFPA 704 Diamond Field Guide with the download form on this page. Page 2 rates 50 common chemicals with part numbers.

Frequently Asked Questions

What do the NFPA 704 colors mean?

Blue means health, red means flammability, yellow means instability (reactivity on older signs), and white means special hazards. Each colored quadrant carries a number from 0 to 4. The white quadrant carries a symbol or stays blank.

What does a 4 mean on the NFPA diamond?

A 4 is the most severe rating in any color. Blue 4 means very short exposure could cause death or major residual injury. Red 4 means a flammable gas or a liquid with a flash point below 73 F and a boiling point below 100 F. Yellow 4 means the material can detonate at normal temperature and pressure.

Why is diesel a 2 and gasoline a 3 for flammability?

Because of flash point. NFPA 704 gives a red 3 to liquids that ignite at normal temperatures, and gasoline flashes at about minus 45 F. Diesel flashes at 125 F or higher, which lands in the 100 F to 200 F band for a red 2.

Is reactivity the same as instability on the NFPA diamond?

Yes. The yellow quadrant was called reactivity on older signs and is called instability in the current edition of NFPA 704. The 0 to 4 criteria describe the same hazards. An older sign that says reactivity does not need to be replaced for that reason alone.

Conclusion

NFPA 704 colors and numbers follow fixed rules: blue for health, red for flammability, yellow for instability, white for special hazards. Each colored quadrant is rated 0 to 4. Flash point drives the red number, exposure injury drives the blue, and detonation or water reaction drives the yellow. Only W with a line, OX and SA belong in the white square.

Getting the numbers right the first time saves you a failed fire inspection and a return trip for the marshal. Partner companies report 45%+ better first-time inspection pass rates.

Shop NFPA 704 diamond signs in any rating, or call Brent at Print Pro AZ with your SDS sheets: (602) 649-5305.

Sources

• NFPA 704, Standard System for the Identification of the Hazards of Materials for Emergency Response
• NIOSH Pocket Guide to Chemical Hazards

Brent Hanke | Print Pro AZ | (602) 649-5305 | b.hanke@printproaz.com

Brent Hanke is the founder of Print Pro AZ, supplying NEC-compliant labels to contractors across the country.