NFPA 704 fire diamond

How to read it

NFPA 704 is the National Fire Protection Association's standard for marking the hazards of materials for emergency response, and NFPA's own FAQ calls its shape a “square-on-point”. Four smaller diamonds sit inside it: health in blue on the left, flammability in red at the top, instability in yellow on the right and special hazards in white at the bottom. Each coloured section holds a number from 0, a minimal hazard, to 4, a severe one. The ratings cover short-term, acute exposure in a fire, spill or similar emergency. Where several chemicals are stored together, a sign may show the highest rating in each section among all of them, so one chemical can set the health number and another the flammability number (CAMEO Chemicals, NOAA). Some safety data sheets print a product's diamond with the numbers filled in, sometimes in section 16.

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The four sections

NFPA's FAQ says the exact shades of red, blue and yellow are not regulated. The numbers may sit on a coloured background or be printed in colour on white.

Where you'll see it

The diamond is a sign for fixed sites. NFPA's FAQ lists outside buildings, on doors and on tanks, where emergency responders will see it during a spill or fire. Fire Engineering adds building exteriors near each entrance responders may use, exterior doors into chemical storage areas, chemical storage buildings and permanent chemical tanks. Riverside County, California, requires it at every entrance to a business that must file a hazardous materials business plan, at the gates of fenced property and on aboveground tanks holding 55 US gallons (208 litres) or more.

Hazardous materials in transport carry US Department of Transportation placards instead, and Fire Engineering says NFPA 704 is not used for them. The standard itself does not say when a sign is required. According to NFPA's FAQ, another code or the authority having jurisdiction, such as the local fire department, decides that; NFPA 1, Fire Code, and NFPA 400, Hazardous Materials Code, are among the codes that call for it. CAMEO Chemicals points out that a building without a diamond may still hold dangerous chemicals, since a sign can be missing or out of sight.

Look-alikes

The GHS hazard pictograms on chemical containers have the same shape: OSHA's standard defines them as a square set at a point, with a red frame around a black symbol such as the flame. They carry no numbers. The hazard categories behind them are numbered in section 2 of a safety data sheet, and those numbers run the other way: 1 is the most severe and 4 the least, where on the diamond 4 is the most severe. The NFPA and OSHA quick card says the section 2 category numbers are not to be used to fill in the diamond.

HMIS labels, from the American Coatings Association's Hazardous Materials Identification System, use the same blue, red and yellow and the same 0 to 4 scale, as stacked bars on a rectangular label. Their white bar holds a letter from A to K, or X, for personal protective equipment, where the diamond's white section holds a special hazard. Riverside County's guidance puts the difference in audience: HMIS is for the workers who handle a chemical every day, NFPA 704 for emergency responders. SUNY Geneseo's chemistry stockroom notes that the same chemical can carry different numbers in the two systems.

The Charlotte fire behind it

Fire Engineering credits the system to J.F. Morris, fire marshal of the Charlotte Fire Department in North Carolina, in 1959. Thirteen firefighters had been injured at the Charlotte Chemical Company, at a fire in a vat they took for kerosene. It held metallic sodium, which reacted violently to their efforts to put the fire out. Morris's diamond was tentatively adopted as a guide in 1960 and revised several times into today's NFPA 704.