Placards are used in the transportation industry to identify the contents of vessel such as a trailer, rail car, container, etc. There are several ways information of the vessel's contents are identified on the placard.
First, the color of the placard indicates in which group of hazardous material the contents reside:
RED - indicates a flammable material GREEN - indicates nonflammable substance YELLOW - indicates an oxidizer BLUE - indicates dangerous when wet WHITE - indicates inhalation hazard and poison BLACK & WHITE - indicates corrosive (acid and caustic) RED & WHITE - indicates flammable solid or
spontaneously combustible (depending on the color pattern on the placard) WHITE & YELLOW - indicates radiation or radioactive ORANGE - indicates explosives WHITE & BLACK STRIPES - indicate
miscellaneous hazardous materials
A second placard information indicator is the number in the bottom corner of the diamond.
This number refers to the hazard classes as used internationally and by the United States DOT.
There are 9 classes for hazardous materials:
Class 1 - Explosives Class 2 - Gases (flammable, nonflammable, inhalation hazard/poison, or oxygen) Class 3 - Liquids that burn (flammable and combustible liquids, based on their flashpoint) Class 4 - Flammable Solids, Spontaneously Combustible, or Dangerous when wet materials Class 5 - Oxidizers and Organic Peroxides Class 6 - Poison/Toxic Solids and Liquids, Infectious Materials Class 7 - Radioactive (three sub classes) Class 8 - Corrosives (acids and bases) Class 9 - Miscellaneous
A third indicator is the symbol in the upper corner of the diamond. A variety of symbols are used
to indicate combustion, radiation, oxidizers, compressed gas, etc...such as destruction of materials and skin
by corrosives, an explosion for flammables, or skull and cross bones to indicate poisons.
The fourth item on a placard is the four digit United Nations (UN) number used for the
hazardous material contained in the container. There are hundreds of four digit numbers used,
from 1001 (acetylene) to 9279 (hydrogen, absorbed in metal hydride). The number in some
cases is specific to a chemical and in other cases reflects a variety of hazardous materials. (For
example, 1017 is only used for chlorine, 1005 has five chemical listings, 1993 is used for eight
chemical listings and 2810 is used for 36 chemical listings.)
In some cases placards will give the real name of the chemical instead of using the four digit
number, or will describe the hazard (flammable, inhalation hazard, radioactive) and not list
the chemical name or four digit number. Placards from other countries can be found in United
States and may have different words than North American placards. It is possible to see a red
placard with a 3 in the bottom corner and the words “inflammable liquid” on it, which sounds like
the chemical may not burn, but this actually means the “chemical will burn”.
Placards are required to be posted on all four sides of a “bulk container” (rail car, truck,
intermodal container), meaning there needs to be four placards. In addition to tank cars and
intermodal, you will find hazardous materials being transported in box cars, covered hoppers,
gondolas, and on flat cars. Bulk containers with less than one placard per side (if only one placard is needed for the
chemical), are subject to a citation(s) from transportation inspection/enforcement agencies.
There are some chemicals that are required to have more than one placard on the container;
this is because they have been identified as having more than one hazard that needs to be identified. Anhydrous Hydrogen
Fluoride is required to have three different placards on each side of the “container”. A missing
placard on a container could result in a heafty fine.