The "no water" symbol means that the hazardous substance will have an adverse reaction to contact with water including possible fire, explosion, release of toxic or corrosive fumes or liquids, release or spread of flammables, or other hazards.
The NFPA 704 diamond is a ring of smaller diamonds that are blue, red, yellow and white. A number or symbol in each section indicates the relative danger.
Health (Blue): 1 Flammability (Red): 2 Reactivity (Yellow): 0 Special (White): None
The NFPA 704 symbol is red, blue, yellow and white. Red code is "flammability" Blue code is "health" danger Yellow code is "instability" White is for "special hazards" such as "do not wet" and "oxidizer"
Health(Blue) = 2 Flammability(Red) = 0 Reactivity(Yellow) = 2 Specials(White) = OX (Oxidizing agent)
The NPFA mark is used for materials that can ignite.
The number 4 on the NFPA 704 placard indicates the highest hazard in any of the three categories (health, fire, reactivity).
NFPA 25: Standard for the Inspection, Testing, and Maintenance of Water-Based Fire Protection Systems
There are several NFPA standards that reference fire hydrant requirements, for various parameters, including NFPA 1 Fire Code and NFPA 101 Life Safety Code. You may also be interested in NFPA 291 Recommended Practice for Fire Flow Testing and Marking of Hydrants NFPA 25 Standard for the Inspection, Testing, and Maintenance of Water-Based Fire Protection Systems or NFPA 1142 Standard on Water Supplies for Suburban and Rural Fire Fighting
2-0-1-ox
0-0-0
If an NFPA 704 Fire Diamond has a 2 in the yellow section it means the reactivity of the material is such that it can have violent chemical change at high temperature or pressure, it can react violently with water, or it can form explosive mixtures with water.
NFPA 13 also possibly 13D or 13R, depending upon circumstances NFPA 25 also relates to ALL water-based fire suppression systems.