The nine hazard classes are those determined by the United Nations Committee of Experts and are used for all modes of transport.
Class 1 includes explosives of all kinds, such as sporting ammunition, fireworks and signal flares. Class 2 comprises compressed or
liquefied gases which may also be toxic or flammable; examples are cylinders of oxygen and refrigerated liquid nitrogen.
Class 3substances are flammable liquids including gasoline, lacquers, paint thinners, etc. Class 4 covers flammable solids, spontaneously combustible materials and materials which, when in contact with water, exit flammable gases (examples are some powdered metals,
cellulose type film and charcoal).
Class 5 covers oxidizing material, including bromates, chlorates or nitrates; this class also covers
organic peroxides which are both oxygen carriers and very combustible. Poisonous or toxic substances, such as pesticides, mercurycompounds,etc.,comprise
Class6,togetherwithinfectioussubstanceswhichmustsometimesbeshippedfordiagnosticorpreventative
purposes.
Radioactive materials are in Class 7; these are mainly radioactive isotopes needed for medical or research purposes but are
sometimes contained in manufactured articles such as heart pacemakers or smoke detectors. Corrosive substances which may be
dangerous to human tissue or which pose a hazard to the structure of an aircraft are dealt with in Class 8 (for example, caustic soda,
battery fluid, paint remover). Finally, Class 9 is a miscellaneous category for other materials which are potentially hazardous in air
transport, such as magnetized materials which could affect the aircraft's navigational systems.