Example of UN Marking: 1H2 / Y1.8 / 100 / YR / USA / +AC

Code Description
UN The United Nations Coding System
1 Type of Container:
1 = Drums/Pails
2 = Barrels
3 = Jerricans
4 = Boxes
5 = Bags
6 = Composite Packagings
H Material of Construction:
A = Steel
B = Aluminum
C = Wood
D = Fibre
E = Plastic
F = Reconstituted wood
G = Fiberboard
2 Category Within Type:
1 = Closedhead
2 = Openhead
Y Packaging Group for which container was tested:
X = Packaging Group I, II, III
Y = Packaging Group II and III
Z = Packaging Group III
Packaging Group I: Great Danger - high hazard level
Packaging Group II: Medium Danger - medium hazard level
Packaging Group III: Minor Danger - low hazard level
1.8 Density or specific gravity of material packed
OR
For packaging intended for Solids (powders, pills, capsules, tablets) or that have inner packaging, this marking will indicate 100 Hydraulic pressure in kilo-pascal (kPa)
OR
For packaging intended for Solids or that have inner packaging, an "S" in

Hazard Class 1: Explosives (Class 1.1-1.6, Compatibility Groups A-L)

Hazard Class 2: Gases (Flammable, Non-Flammable, Oxygen, Toxic Gas, Inhalation Hazard)

Hazard Class 3: Flammable Liquids

Hazard Class 4: Flammable Solids (Flammable Solid, Spontaneously Combustible, Dangerous When Wet)

Hazard Class 5: Oxidizer and Organic Peroxide

Hazard Class 6: Poison/Toxic (Toxic, Poison, Infectious Substances, PG III, Inhalation Hazard)

Hazard Class 7: (Radioactive I, II, III, Fissile)

Hazard Class 8: Corrosive

Hazard Class 9: Miscellaneous

http://en.wikipedia.org/wiki/Dangerous_goods