Special Hazards: NFPA Hazard Diamond

By Vince McLeod

Experienced laboratory managers know that there are four basic categories of chemicals: toxic, corrosive, flammable and reactive. However, in our chemical world there are many additional categories and subsets of these main four. We should also keep in mind that many chemicals exhibit a combination of properties and would fall into more than a single class or category. These four properties are the foundation of the NFPA hazard diamond.

At the bottom of the diamond is the white section. This section is used to denote special hazards. NFPA 704, Standard System for the Identification of the Hazards of Materials for Emergency Response,1 mentions only two approved symbols:

This denotes an oxidizer, a chemical that can greatly increase the rate of combustion or fire.

This means the substance is incompatible with water. It indicates a potential hazard with the use of water to fight a fire involving this material.

Some organizations and manufacturers use additional symbols to indicate hazards associated with the substance. One example is the Hazardous Materials Emergency Response Guidebook;2 a few of these are presented above.

This indicates that the material is an acid, a corrosive material that has a pH lower than 7.0.

This denotes an alkaline material, also called a base. These caustic materials have a pH greater than 7.0.

This denotes a material that is corrosive (it could be either an acid or a base).

This is another symbol used for corrosive.

The skull and crossbones are used to denote a poison or highly toxic material. See also: CHIP danger symbols.

The international symbol for radioactivity is used to denote radioactive hazards; radioactive materials are extremely hazardous when inhaled.

This indicates an explosive material. This symbol is somewhat redundant because explosives are easily recognized by their Instability Rating.

Vince McLeod is an American Board of Industrial Hygiene– certified industrial hygienist and the senior industrial hygienist in the University of Florida’s Environmental Health and Safety Division. He has 22 years of occupational health and safety experience at the University of Florida, and he specializes in conducting exposure assessments and health-hazard evaluations for the university’s 2,200-plus research laboratories.


  1. Standard System for the Identification of the Hazards of Materials for Emergency Response, National Fire Protection Association, Publication 704. http:// www.nfpa.org/aboutthecodes/AboutTheCodes. asp?DocNum=704
  2. Hazardous Materials Emergency Response Guidebook, U.S. Department of Transportation. Washington, D.C. 2008. http://www.fmcsa.dot.gov/safety-security/ hazmat/2004-emergency-response-guidebook.htm
Categories: Lab Health and Safety

Published In

Laboratory Etiquette Magazine Issue Cover
Laboratory Etiquette

Published: May 9, 2011

Cover Story

Laboratory Etiquette

Many lab managers still remember them from their student days—a handful of hastily stapled printouts sternly titled “Laboratory etiquette—Acceptable standards of conduct.” Those were rules to live by, and the smallest violation landed a budding laboratory scientist in front of the ticked-off chief instructor.