Under the recommendations of the United Nations Committee of Experts on the Transport of Dangerous Goods, Explosives (Class 1) are divided into 6 Divisions as follows:

This division comprises substances and articles which have a mass explosion hazard. (A mass explosion is one which affects almost the entire load virtually instantaneously.)

This division comprises substances and articles which have a projection hazard but not a mass explosion hazard.

This division comprises substances and articles which have a fire hazard and either a minor blast hazard or a minor projection hazard, or both, but not a mass explosion hazard. Substances and articles which give rise to considerable radiant heat or which burn one after another producing minor blast or projection effects or both come into this division.

This division comprises substances and articles which present no significant hazard. They 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 of this division are in Compatibility Group S if they are so packaged or designed that any hazardous effects arising from 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.

This division comprises substances which 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 possibility of transition from burning to detonation is greater when large quantities are stored together in an enclosed space.

This 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 1 is unique in that the type of packaging frequently has a decisive effect on the hazard and therefore on the assignment to a particular division.

Explosives are assigned to one of 13 compatibility groups which, by the use of letters, identify the kinds of explosive substances and articles which are deemed to be compatible. Compatible explosives are those which can be transported together without significantly increasing either the probability of an accident or, for a given quantity, the magnitude of the effects of such an accident. The Classification Code details the possible combinations of Divisions and Compatibility groups.