Hazardous Materials Diamond

Last updated: August 27, 2020

What Does Hazardous Materials Diamond Mean?

The Hazardous Materials Diamond is a hazard communication system used to help emergency personnel quickly identify the risks posed by hazardous materials within a given worksite. Its use is defined by the National Fire Protection Association's Standard 704, titled “NFPA 704: Standard System for the Identification of the Hazards of Materials for Emergency Response.”

It is also known as the Fire Diamond, the NFPA Diamond, and the Safety Square.

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Safeopedia Explains Hazardous Materials Diamond

The diamond is divided into four color-coded squares, each which conveys information about specific hazards present in the area. The top square is red and describes flammability hazards, the leftmost square is blue and describes health hazards, and the rightmost square is yellow and describes reactivity hazards. These squares describe risk along a numbered scale of zero (lowest risk) to four (highest risk). The bottom white square uses letter codes described as “special notice” hazards, such as the presence of oxidizing chemicals (e.g. hydrogen peroxide) that allow flammable materials to burn without an air supply.

hazardous materials diamond explainer diagram

Standards and Regulations

The use of the Hazardous Materials Diamond is not part of OSHA’s Hazard Communication Standard (HazCom), which is based on the internationally adopted Globally Harmonized System of Classification and Labelling of Chemicals. However, OSHA continues to allow the use of the NFPA Diamond for safety purposes as long as its use is consistent with the requirements of the HazCom. The purpose of OSHA’s HazCom standards is complementary to the use of the diamond, as the HazCom provides information about hazards to workers using chemical substances under normal conditions, while the NFPA Diamond provides information to emergency workers responding to an incident.

The rating system described by the NFPA is governed by a standardized system for classifying the relative risk of a material. For instance, a material’s flammability level determines what number will go in the red square of the diamond. Level 4 materials include substances that will spontaneously ignite at room temperature.

Use of the NFPA Diamond may be mandated by sub-national regulations and local ordinances such as building codes. For instance, the City of Milwaukee mandates its use in buildings containing hazardous material. The requirements of these jurisdictions may deviate outside the NFPA standard. In some jurisdictions, such as Texas, non-standard special hazard warnings such as “CRY” (for cryogenic materials) are allowed to be present in the white square.

In Texas, a building’s hazard rating indicates that a certain amount of hazardous material of a given level is present on-site (except for level 3 or 4 health hazards, which must be indicated if any quantity is present). On the other hand, in Milwaukee, a rating is applied to buildings that are simply judged as containing enough material to be considered significantly dangerous.



NFPA Diamond

HAZMAT Placards

NFPA Label

Hazard Warning Sign


HAZMAT Diamond

NFPA 704 Diamond

NFPA Placard

704 Placard

Hazardous Material Sign

Fire Diamond

Safety Square

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