Dangerous Goods are grouped in nine classes, according to common dangers. All classes, except infectious substances (Class 6.2) and radioactive substances (Class 7), are controlled by the Dangerous Goods Act 1985.
Each class has a distinctive diamond-shaped symbol with the class number at the bottom of the diamond. These symbols appear on the labels of containers and as signs on vehicle loads. The internationally recognised symbols clearly identify the type of substance and the main danger.

Class Diamond System:

Symbol	Class	Main Danger
	1	Substance or articles used to produce explosions.(eg. gunpowder, gelignite)
	2.1	Can ignite in air on contact with a source of ignition. (eg. LPG)
	2.2	Non flammable and non toxic, but may cause suffocation. (eg. carbon dioxide, nitrogen)
	2.3	Likely to cause death or serious injury if inhaled
	3	Vapours from these liquids can ignite in air on contact with a source of ignition
	4.1	Easily ignited by external sources, such as sparks and flames. (eg. sulfur, matches)
	4.2	Likely to heat spontaneously and ignite. (eg. activated carbon, white phosphorous)
	4.3	Produce dangerous quantities of flammable or toxic gases when in contact with water. The heat from this reaction may cause these gases to spontaneously ignite.(eg. calcium hypochlorite, ammonium nitrate)
	5.1	Not necessarily combustible by themselves, but may yield oxygen which increases the risk and intensity of fire in other materials with which they come into contact. (eg. calcium hypochlorite, ammonium nitrate)
	5.2	Thermally unstable and likely to react dangerously with other substances. (eg. benzoyl, peroxide, MEKP)
	6	Likely to cause death or serious injury if swallowed, inhaled or brought into contact with skin. (eg. sodium cyanide, many pesticides)
	7	Materials or combinations of materials that emit harmful radiation. (eg. uranium, radium)
	8	Solids or liquids that can damage living tissue, and may react with many other materials. (eg. hydrochloric acid, caustic soda)
	9	Substances and articles that present a danger and not covered by other classes. (eg. dry ice, asbestos)
		Mixed Class Label (for road transport)