What are dangerous goods? How are they classified?

Dangerous goods are articles or substances that are capable of posing a risk to health, safety, property or the environment when transported by air. There are many everyday items which seem harmless but can be a threat to the safety of passengers and crew when they are brought on an aircraft; hence they are often forbidden to be carried by passengers either in the aircraft cabin or their baggage. These dangerous goods are classified by International Civil Aviation Organization (ICAO) into 9 classes as follows:

Class 1 Explosives
Class 2 Gases
Class 3 Flammable liquids
Class 4 Flammable solids; substances liable to spontaneous combustion; substances in which, contact with water, emit flammable gas
Class 5 Oxidizing substances and organic peroxides
Class 6 Toxic and infectious substances
Class 7 Radioactive materials
Class 8 Corrosive substances
Class 9 Miscellaneous dangerous goods (e.g. lithium batteries) 

Please click  to review the full terms of the regulation, or refer to the "Security Control Articles" session for details."