How to Read an NFPA 704 Diamond – Part 4


The white square – at the bottom of the NFPA diamond – is different from the other three squares. It doesn’t contain a number. Instead, it contains one of three “special hazard” symbols. These are hazards that cannot be defined by the ratings in the other three squares.

Materials that react violently or explosively with water earn the “water reactive” symbol, a W with a horizontal line through it:


Materials that act as oxidizers will have the “oxidizer” symbol: OX .

Simple asphyxiant gases – nitrogen, helium, neon, argon, krypton, and xenon – will have the “simple asphyxiant” symbol: SA .

If a material is both water reactive and an oxidizer, the “water reactive” symbol is to be displayed in the special hazards (white) square of the NFPA diamond, and the “oxidizer” symbol is to be displayed either directly below or adjacent to that square.


So now you know how to read an NFPA diamond!


DISCLAIMER: This article is designed to promote understanding

of the NFPA rating system. It is not a complete explanation of

the criteria involved.

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