Dangerous Goods are articles or substances which are capable of posing a significant risk to health, safety, property or the environment when transported by air.The International Civil Aviation Organization (ICAO) classified dangerous goods in 9 classes, which are:

CLASS 1 - EXPLOSIVES

1.1 Class 1 comprises:
1. Explosive substances (a substance which is not itself an explosive but which can form an explosive atmosphere of gas, vapour or dust is not included in class 1), except those which are too dangerous to transport or those where the predominant hazard is one appropriate to another class;
2. Explosive articles, except devices containing explosive substances in such quantity or of such a character that their inadvertent or accidental ignition or initiation during transport should not cause any effect external to the device either by projection, fire, smoke, heat or loud noise; and
3. Substances and articles not mentioned under .1 and .2, which are manufactured with a view to producing a practical, explosive or pyrotechnic effect.
Transport of explosive substances, which are unduly sensitive, or so reactive as to be subject to spontaneous reaction, is prohibited.
For the purposes of this Code, the following definitions apply:
1. Explosive substance means a solid or liquid substance (or a mixture of substances), which is in itself capable by chemical reaction of producing gas at such a temperature and pressure and at such a speed as to cause damage to the surroundings. Pyrotechnic substances are included even when they do not evolve gases.
2. Pyrotechnic substance means a substance or a mixture of substances designed to produce an effect by heat, light, sound, gas or smoke or a combination of these as the result of non-detonative self-sustaining exothermic chemical reactions.
3. Explosive article means an article containing one or more explosive substances.
4. Mass explosion means one which affects almost the entire load virtually instantaneously.
1.2 Hazard divisions: The six hazard divisions of class 1 are:
Division 1.1 Substances and articles that have a mass explosion hazard
Division 1.2 Substances and articles that have a projection hazard but not a mass explosion hazard 
Division 1.3 Substances and articles that have a fire hazard and either a minor blast hazard or a minor projection hazard or both, but not a mass explosion hazard 
This division comprises substances and articles:
1. which give rise to considerable radiant heat; or
2. which burn one after another, producing minor blast or projection effects or both.
Division 1.4 Substances and articles that present no significant hazardThis division comprises substances and articles that present only a small hazard in the event of ignition or initiation during transport. The effects are largely confined to the package and no projection of fragments of appreciable size or range is to be expected. An external fire must not cause virtually instantaneous explosion of almost the entire contents of the package.
Note: Substances and articles in this division are in compatibility group S if they are so packaged or designed that any hazardous effects arising from the accidental functioning are confined within the package unless the package has been degraded by fire, in which case all blast or projection effects are limited to the extent that they do not significantly hinder fire fighting or other emergency response efforts in the immediate vicinity of the package.
Division 1.5 Very insensitive substances that have a mass explosion hazardThis division comprises substances that have a mass explosion hazard but are so insensitive that there is very little probability of initiation or of transition from burning to detonation under normal conditions of transport.
Note: The probability of transition from burning to detonation is greater when large quantities are transported in a ship. As a consequence, the stowage provisions for explosive substances in division 1.1 and for those in division 1.5 are identical.
Division 1.6 Extremely insensitive articles that do not have a mass explosion hazardThis division comprises articles which contain only extremely insensitive detonating substances and which demonstrate a negligible probability of accidental initiation or propagation.
Note: The risk from articles of division 1.6 is limited to the explosion of a single article.

CLASS 2 - GASES

2.1 A gas is a substance which: 
1. at 50°C has a vapour pressure greater than 300 kPa; or
2. is completely gaseous at 20°C at a standard pressure of 101.3 kPa.
2.2 The transport condition of gas is described according to its physical state as:
1. Compressed gas - a gas (other than in solution) which, when packaged under pressure for transport, is entirely gaseous at 20°C;
2. Liquefied gas - a gas which, when packaged for transport, is partially liquid at 20°C;
3. Refrigerated liquefied gas - a gas which, when packaged for transport, is made partially liquid because of its low temperature; orRefrigerant means a gas used as a cooling substance in the refrigeration process, such as refrigerating machinery UN 2857 in this case..4 Gas in solution - compressed gas which, when packaged for transport, is dissolved in a solvent.
2.2.1 This class comprises compressed gases; liquefied gases; gases in solution; refrigerated liquefied gases; mixtures of gases; mixtures of one or more gases with one or more vapours or substances of other classes; articles charged with a gas; tellurium hexafluoride; aerosols.
2.3 Class subdivisionsClass 2 is subdivided further according to the primary hazard of the gas during transport, namely:
2.3.1 Class 2.1 Flammable gases
Gases which at 20°C and a standard pressure of 101.3 kPa:
1. are ignitable when in a mixture of 13% or less by volume with air; or
2.have a flammable range with air of at least 12 percentage points regardless of the lower flammable limit. Flammability should be determined by tests or calculation in accordance with methods adopted by the International Organization for Standardization (see ISO standard 10156:1996). Where insufficient data are available to use these methods, tests by a comparable method recognized by a national competent authority may be used.
Note: UN 1950 AEROSOLS and UN 2037 RECEPTACLES, SMALL, CONTAINING GAS (GAS CARTRIDGES) should be regarded as being in class 2.1 when the criteria in Special Provision 63 in 3.3.1 of IMDG Code 2000 Edition are met.
2.3.2 Class 2.2 Non-flammable, non-toxic gasesGases which are transported at a pressure not less than 280 kPa at 20°C, or as refrigerated liquids, and which:.1 are asphyxiant - gases which dilute or replace the oxygen normally in the atmosphere; or.2 are oxidizing - gases which may, generally by providing oxygen, cause or contribute to the combustion of other material more than air does; or.3 do not come under the other classes.
2.3.3 Class 2.3 Toxic gases Gases which:
1. are known to be so toxic or corrosive to humans as to pose a hazard to health; or
2. are presumed to be toxic or corrosive to humans because they have a LC50 value (as defined in 2.6.2.1 of IMDG Code 2000 Edition) equal to or less than 5,000 ml/m3 (ppm).
Note: Gases meeting the above criteria owing to their corrosivity are to be classified as toxic with a subsidiary corrosive risk.

CLASS 3 - FLAMMABLE LIQUIDS

3.1 Class 3 includes the following substances: 
1. Flammable liquids 
2. Liquid desensitized explosives 
3.1.1 Flammable liquids are liquids, or mixtures of liquids, or liquids containing solids in solution or suspension (such as paints, varnishes, lacquers, etc., but not including substances which, on account of their other dangerous characteristics, have been included in other classes) which give off a flammable vapour at or below 61°C closed cup test (corresponding to 65.6°C open cup test), normally referred to as the flashpoint. This also includes:
1.Liquids offered for transport at temperatures at or above their flashpoint; and
2. Substances transported or offered for transport at elevated temperatures in a liquid state, which give off a flammable vapour at temperatures equal to or below the maximum transport temperature
3.1.2 However, the provisions of this Code need not apply to such liquids with a flashpoint of more than 35°C which do not sustain combustion. Liquids are considered to be unable to sustain combustion for the purposes of the Code if:
1. they have passed the suitable combustibility test (see the Sustained Combustibility Test prescribed in Part III, chapter 32.5.2 of the United Nations Manual of Test and Criteria); or
2. their fire point according to ISO 2592:1973 is greater than 100°C; or
3. they are water-miscible solutions with a water content of more than 90%, by mass.
3.1.3 Liquid desensitized explosives are explosive substances which are dissolved or suspended in water or other liquid substances, to form a homogeneous liquid mixture to suppress their explosives properties. Entries in the Dangerous Goods List for liquid desensitized explosives are: UN 1204, UN 2059, UN 3064 and UN 3343.
3.2 Hazard grouping based on flammability
Flammable liquids are grouped for packing purposes according to their flashpoint, their boiling point, and their viscosity. This table shows the relationship between two of these characteristics. 

CLASS 4 - FLAMMABLE SOLIDS; SUBSTANCES LIABLE TO SPONTANEOUS COMBUSTION; SUBSTANCES WHICH, IN CONTACT WITH WATER, EMIT FLAMMABLE GASES

4.1 In this Code, class 4 deals with substances, other than those classified as explosives, which, under conditions of transport, are readily combustible or may cause or contribute to a fire. Class 4 is subdivided as follows:
Class 4.1 Flammable solids
Solids which, under conditions encountered in transport, are readily combustible or may cause or contribute to fire through friction; self-reactive substances (solids and liquids) which are liable to undergo a strongly exothermic reaction; solid desensitized explosives which may explode if not diluted sufficiently;
Class 4.2 Substances liable to spontaneous combustion
Substances (solids and liquids) which are liable to spontaneous heating under normal conditions encountered in transport, or to heating up in contact with air, and being then liable to catch fire;
Class 4.3 Substances which, in contact with water, emit flammable gases
Substances (solids and liquids) which, by interaction with water, are liable to become spontaneously flammable or to give off flammable gases in dangerous quantities.
4.2 As referenced in this chapter, test methods and criteria, with advice on application of the tests, are given in the United Nations Manual of Tests and Criteria, for the classification of following types of substances of class 4:
1. Flammable solids (class 4.1);
2. Self-reactive substances (class 4.1);
3. Pyrophoric solids (class 4.2);
4. Pyrophoric liquids (class 4.2);
5. Self-heating substances (class 4.2); and
6.Substances which, in contact with water, emit flammable gases (class 4.3).
Test methods and criteria for self-reactive substances are given in Part II of the United Nations Manual of Tests and Criteria, and test methods and criteria for the other types of substances of class 4 are given in the United Nations Manual of Tests and Criteria, Part III, chapter 33. 

CLASS 5 - OXIDIZING SUBSTANCES AND ORGANIC PEROXIDES

5. In this Code, class 5 is divided into two classes as follows: 
Class 5.1 Oxidizing substances
Substances which, while in themselves not necessarily combustible, may, generally by yielding oxygen, cause, or contribute to, the combustion of other material. Such substances may be contained in an article;
Class 5.2 Organic peroxides
Organic substances which contain the bivalent -O-O- structure and may be considered derivatives of hydrogen peroxide, where one or both of the hydrogen atoms have been replaced by organic radicals. Organic peroxides are thermally unstable substances which may undergo exothermic self-accelerating decomposition. In addition, they may have one or more of the following properties:
- be liable to explosive decomposition;
- burn rapidly;
- be sensitive to impact or friction;
- react dangerously with other substances;
- cause damage to the eyes.

CLASS 6 - TOXIC AND INFECTIOUS SUBSTANCES

6. Class 6 is subdivided into two classes as follows: 
Class 6.1 Toxic substances
These are substances liable either to cause death or serious injury or to harm human health if swallowed or inhaled, or by skin contact.
Class 6.2 Infectious substances
These are substances known or reasonably expected to contain pathogens. Pathogens are defined as micro-organisms (including bacteria, viruses, rickettsiae, parasites, fungi) or recombinant micro-organisms (hybrid or mutant), that are known or reasonably expected to cause infectious disease in animals or humans.
Note 1: However, they are not subject to the provisions of this class if they are unlikely to cause human or animal disease.
Note 2: Infectious substances are subject to the provisions of this class if they are capable of spreading disease when exposure to them occurs.

CLASS 7 - RADIOACTIVE MATERIAL

7.1 Radioactive material means any material containing radionuclides where both the activity concentration and the total activity in the consignment exceed the values. 
7.1.1 The following radioactive materials are not included in class 7 for the purposes of this Code:
(a) radioactive material that is an integral part of the means of transport;
(b) radioactive material moved within an establishment which is subject to appropriate safety regulations in force in the establishment and where the movement does not involve public roads or railways;
(c) radioactive material implanted or incorporated into a person or live animal for diagnosis or treatment;
(d) radioactive material in consumer products which have received regulatory approval, following their sale to the end user;
(e) natural material and ores containing naturally occurring radionuclides which are not intended to be processed for use of these radionuclides provided the activity concentration of the material does not exceed 10 times the values specified.
7.2 Packages and overpacks should be assigned to either category I - WHITE, II - YELLOW or III - YELLOW in accordance with the conditions specified in the table hereunder and with the following provisions:
(a) For a package or overpack, both the transport index and the surface radiation level conditions should be taken into account in determining which is the appropriate category. Where the transport index satisfies the condition for one category but the surface radiation level satisfies the condition for a different category, the package or overpack should be assigned to the higher category. For this purpose, category I - WHITE should be regarded as the lowest category.
(b) The transport index should be determined following the procedures specified.
(c) If the surface radiation level is greater than 2 mSv/h, the package or overpack should be transported under exclusive use and under the provisions as appropriate.
(d) A package transported under a special arrangement should be assigned to category III - YELLOW.(e) An overpack which contains packages transported under special arrangement should be assigned to category III - YELLOW.
Transport index Maximum radiation level at any point on external surface 
0aNot more than 0.005 mSv/h I - WHITE

CLASS 8 - CORROSIVE SUBSTANCES

8.1 Class 8 substances (corrosive substances) means substances which, by chemical action, will cause severe damage when in contact with living tissue or, in the case of leakage, will materially damage, or even destroy, other goods or the means of transport. 
8.2 Assignment of packing groups
8.2.1 Substances and preparations of class 8 are divided among the three packing groups according to their degree of hazard in transport as follows:
Packing group I: Very dangerous substances and preparations;
Packing group II: Substances and preparations presenting medium danger;
Packing group III: Substances and preparations presenting minor danger.
The packing group to which a substance has been assigned is given in the Dangerous Goods List in chapter 3.2. of IMDG Code 2000 Edition

CLASS 9 - MISCELLANEOUS DANGEROUS SUBSTANCES AND ARTICLES

9.1 Class 9 substances and articles (miscellaneous dangerous substances and articles) comprise: 
1. Substances and articles not covered by other classes which experience has shown, or may show, to be of such a dangerous character that the provisions of part A of chapter VII of SOLAS, 1974, as amended, should apply; these include substances that are transported or offered for transport at temperatures equal to. or exceeding 100°C, in a liquid state, and solids that are transported or offered for transport at temperatures equal to or exceeding 240°C; and.
2. Substances not subject to the provisions of part A in chapter VII of the aforementioned Convention, but to which the provisions of Annex III of MARPOL 73/78, as amended, apply. The properties or characteristics of each substance are given in the Dangerous Goods List in chapter 3.2 of IMDG Code 2000 Edition pertaining to the substance or article.
9.2 Assignment of packing groups to miscellaneous dangerous substances and articles
9.2.1 The substances and articles of this class have, for packing purposes, been assigned to packing group II and packing group III. The packing group to which a substance or article is assigned is given in the Dangerous Goods List in chapter 3.2. of IMDG Code 2000 Edition
9.2.2 No grouping criteria have been developed for this class. The packing groups of the substances and articles have, therefore, been assigned on the basis of assimilation with goods having similar properties and characteristics.

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