NFPA 704 Hazmat Marking System

Most everyone involved with hazardous materials response is familiar with the U.S. Department of Transportation (DOT) placard and label system for transportation of hazardous materials. The U.S. Occupational Safety & Health Administration (OSHA) has...


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Diamonds used on the outside of buildings are generally a minimum size of 15 by 15 inches. Those used inside of the building are a minimum of 10 by 10 inches. Smaller diamonds may be found on individual containers. NFPA 704 placards are divided into four colored quadrants, or four "mini" diamonds within the larger diamond. The upper quadrant at the "12 o'clock" position is red, followed by blue at "9 o'clock" to the left, yellow at "3 o'clock" to the right and the bottom is white at the "6 o'clock" position.

Hazard Indicators

Each color designates a specific hazard. Red indicates flammability, blue health, yellow instability and white special information. Special information located in the white quadrant listed in the 704 standard includes materials that react violently or explosively with water, represented by a W with a slash through it, and OX for materials with oxidizing properties. The standard lists specific criteria for these symbols to be included on the diamond in the appendix.

Other users of the 704 system have added other symbols, which are not a part of the 704 standard and include RAD for radioactive, COR indicating corrosive, UD is unclassified detonable, 4D Class 4 detonable, 3D Class 3 detonable, and 3N non-detonable. The NFPA 704 standard is not intended to speak to the following hazardous situations:

  • Occupational exposures
  • Explosive and blasting agents, including commercial explosives
  • Chemicals whose only hazard is as a chronic health hazard
  • Teratogens, mutagens, oncogens, etiologic agents and other similar hazards

Numbers are placed within the quadrants of the 704 diamond indicating the degree of hazard posed by an individual chemical or as quoted in the standard, "according to the ease, rate, and quantity of energy release of the material in pure or commercial form." The numbers used to identify the range of hazard are from 0 to 4, with 0 indicating no particular hazard and 4 indicating the most severe hazard or most energy release.

Degrees of hazard associated with health, flammability and instability are determined by criteria outlined in the standard. Some jurisdictions may place a letter G in the quadrant with the number to indicate the presence of a compressed gas.

Health Hazards

Health hazards are ranked according to the level of toxicity and effects of exposure to response personnel. They are based on short-term, acute exposure during handling under conditions of spill, fire or similar emergencies. Short-term exposure ranges from minutes to hours. Acute exposures typically are sudden and severe and characterized by rapid absorption of the chemical that is quickly circulated through the body and damages one or more vital organs. Acute effects include severe burns, respiratory failure, coma, death or irreversible damage to a vital organ.

(The following guidelines are my effort to explain the material in NFPA 704 in terms of protection of response personnel. They are not intended to be recommendations. Materials at the scene of a hazardous materials incident should be thoroughly researched and decisions made by those on scene as to the appropriate level of protection responders should wear based upon the hazards present. Specific details of criteria used to determine hazard numbering is located in the NFPA 704 standard.)

  • 4 - Materials that can be lethal if response personnel do not wear proper chemical protective equipment. If gases or skin-absorbent gases, liquids or solids, Level A chemical protection would be necessary. Firefighter turnouts would not provide appropriate protection. Examples of Health Hazard 4 chemicals include chlorine, phosgene, hydrocyanic acid (hydrogen cyanide), hydrogen sulfide, phenol, phosphine, pentaborane and acrylonitrile (vinyl cyanide).

  • 3 - Materials that can cause serious or permanent injury. Level A chemical protection or Level B chemical protection would be appropriate depending on the physical state of the hazardous materials. Firefighter turnouts would not provide appropriate protection. Examples of Health Hazard 3 include anhydrous ammonia, acetaldehyde, acrylic acid, carbon monoxide, formic acid, pyridine, nitric acid and para xylene (p-xylene).

  • 2 - Materials that can cause temporary incapacitation or residual injury. Level B or Level C chemical protection would be appropriate for these chemicals. Firefighter turnouts would likely not provide appropriate levels of protection. Health Hazard 2 chemicals include meta and ortho xylene (m-xylene and o-xylene), toluene, styrene, ethyl formate, benzene, 1,1,1-trichloroethane and vinyl chloride.

  • 1 - Materials that can cause significant irritation. Level C chemical protection would likely be appropriate protection. Firefighter turnouts may provide some protection, particularly respiratory. Many irritants are actually solid materials and may contaminate personnel. Remember that firefighter turnouts are not classified as chemical protective clothing. Health Hazard 1 chemicals include, acetone and butane.

  • 0 - Materials that would offer no hazard beyond that of ordinary combustible materials. Firefighter turnouts would provide appropriate protection for personnel.