All member countries must declare to the OPCW their activities relating to certain chemicals. The CWC contains the following three lists of chemicals of particular concern, called Schedules:

• Schedule 1 chemicals are either chemical weapons themselves or are very closely related to chemical weapons. Examples include sarin (which was used in the terrorist attacks in Japan in the 1990s)
  and mustard gas.
• Schedule 2 chemicals can be used to make chemical weapons, but can also be used for peaceful purposes in industry, although they are not produced in large quantities.
• Schedule 3 chemicals are toxic chemicals that can be used to make chemical weapons, but are also produced on a large scale to make many common products, such as oil, cement, cloth and paper.

In addition, plant sites that produce a wide range of chemicals not listed in the Schedules, which the Convention defines as “discrete organic chemicals” or DOCs, are also subject to declaration and verification. These plant sites could be capable of producing chemical weapons, and must therefore be monitored.

All such facilities dealing with Schedule 1, 2 or 3 chemicals or DOCs are liable to inspection by the OPCW. By inspecting the chemical industry, the OPCW makes an important contribution to preventing the spread of chemical weapons.

The member countries of the OPCW are also prohibited from trading in Schedule 1 and 2 chemicals with countries that are not members. By checking the international trade in all listed chemicals declared by its member countries, the OPCW works to prevent these chemicals from being used to make new chemical weapons, by either countries or individuals.