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Know the Code: Using the NFPA’s Fire Diamond to Assess Hazards

By Rob Chernish
Published: May 19, 2017 | Last updated: October 17, 2021 09:46:08
Key Takeaways

Knowing what the different quadrants of the Fire Diamond mean will help you assess hazards and understand the substances in your workplace.

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It's on the side of storage tanks, drums, and chemical containers. So, you've probably seen the National Fire Protection Agency's (NFPA) Fire Diamond, even if you didn't know its name.

In fact, it goes by a few different names: Fire Diamond, NFPA 704 Diamond, Hazard Diamond, Safety Square. But no matter what you call it, it's a valuable tool for communicating hazards and their severity. It is particularly helpful for first responders, who can use it to know what types of substances they're dealing with.

The Diamond, however, is only useful to people who understand the code and the information printed on its four quadrants. So, let's go over the Fire Diamond and what each part of it means.


When Is the NFPA Diamond Required?

NFPA 704 labels are required when a local, state, or federal code or regulation mandates their use. While the NFPA itself does not specify when the 704 diamond must be used, it does specify what kind of information must be included on the label.

Other widely used NFPA codes will require 704 labels for hazardous material containers, including:

  • NFPA 1 – Fire code
  • NFPA 30 – Flammable and combustible liquids code
  • NFPA 45 – Standard on fire protection for laboratories using chemicals
  • NFPA 55 – Compressed gases and cryogenic fluids code
  • NFPA 400 – Hazardous materials code

How to Read the NFPA Fire Diamond

The NFPA diamond consists of four colored quadrants, each of which displays a number or a code. Understanding each of these elements is essential to deciphering the information on the Diamond.

So, let's break it down and go over each quadrant and what they can tell you about the hazards at your jobsite.

Red Quadrant: Fire

The red quadrant indicates the flammability of the substance. It is rated on a scale from 0 to 4, with a 0 indicating that the substance cannot burn (e.g. water), while a 4 indicates that it is highly flammable (e.g. propane or acetylene).

  • 0 - Will not burn even under typical flammable conditions and when exposed to temperatures of 1,500°F for five minutes
  • 1 - Has a flashpoint of 200°F or higher and will only burn if exposed to significant heat
  • 2 - Has a flashpoint between 100°F and 200°F and requires relatively high temperatures to combust
  • 3 - Has a flashpoint between 73°F and 100°F and can ignite under most ambient conditions
  • 4 - Has a flashpoint below normal room temperature (73°F) and will readily burn

(Learn about Hazardous Material Storage Buildings and When They Are Required)

Blue Quadrant: Health

The blue quadrant represents health hazards and is also scored on a scale of 0 to 4.

A number on the lower end of the scale indicates a substance that is only likely to cause mild and temporary health effects. On the higher end are substances like sarin gas and carbon monoxide, both of which can result in death in a very short period of time.

  • 0 - No health hazard and no protection required
  • 1 - Exposure can result in mild irritation or injury and no PPE other than gloves is likely to be required
  • 2 - Intense or prolonged expose can cause temporary incapacitation or residual injury
  • 3 - Brief exposure is sufficient to produce temporary or moderate residual injury
  • 4 - Brief exposure can result in serious injury or death

(Learn more about Carbon Monoxide: The Silent Killer)


Yellow Quadrant: Reactivity

The diamond's yellow quadrant indicates the level of chemical reactivity, scored again on a scale of 0 to 4.

Substances that don't react with water, such as helium, score a zero. Nitro glycerine, on the other hand, scores a 4 since it can cause explosions at a normal temperature and pressure.

  • 0 – Very stable, will not react even in fire or when immersed in water
  • 1 – Stable under most conditions, except under significantly elevated pressures or temperature
  • 2 – May undergo violent chemical reaction under elevated pressure and temperature, and may have serious reactions when exposed to water
  • 3 – Highly unstable, may explode or detonate when exposed to heat or after ignition, and may seriously react with water or shock
  • 4 – Highly unstable and can react or detonate at normal pressure or temperatures

Visual representation of the NFPA Diamond with each quadrant labeledNFPA Diamond

White Quadrant: Additional Hazards

The white quadrant of the diamond is reserved for special codes not covered in the other parts of the diamond. Unlike those other hazards, the ones in the white quadrant are not scored numerically but indicated with an abbreviation.

Three symbols are approved by the NFPA:

  • W - Substance has a strong reaction to water and may explode, burn, or release dangerous gases if it comes into contact with it
  • OX - Violent reaction when exposed to oxygen
  • SA - Oxygen reducing or displacing gases

Other codes you may find in the white quadrant will vary between jurisdictions. These generally include:

  • COR, ACID, ALK - Strong acid or base
  • BIO - Biological hazard
  • POI - Poisonous substance
  • RA, RAD - Radioactive
  • CYL, CRYO - Cryogenic

These are usually supplemented by a larger identifying tag like a radioactive or biohazard sign.


The NFPA Diamond is an incredibly efficient safety label. It provides a wealth of information about hazardous materials at a quick glance.

If you know its system of colors and ratings, you can get a quick sense of the substances around you and the risks associated with them. So take the time to crack the code - you'll be safer for it.


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Written by Rob Chernish

A writer from Canada with firsthand experience in Oil, Gas, Mining, and environmental safety.

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