Traditionally, a chemical weapon (CW) is thought of as a toxic chemical loaded into a delivery system such as a munition (i.e., a complete device for exposing a population to a substance that can cause death or other injuries through its chemical action). The Chemical Weapons Convention (CWC) broadens this traditional definition significantly, for the purpose of achieving the treaty’s goal of “complete and effective prohibition of the development, production, acquisition, stockpiling, retention, transfer and use of chemical weapons, and their destruction.” (Chemical Weapons Convention, Preamble).
According to the Chemical Weapons Convention, “chemical weapons” means the following,
together or separately (Chemical Weapons Convention, Article II, Paragraph 1):
a. Toxic chemicals and their precursors, except where intended for purposes not prohibited under this Convention, as long as the types and quantities are consistent with such purposes;
b. Munitions and devices, specifically designed to cause death or other harm through the toxic properties of those toxic chemicals specified in subparagraph (a), which would be released as a result of the employment of such munitions and devices;
c. Any equipment specifically designed for use directly in connection with the employment of munitions and devices specified in subparagraph (b).
A “toxic chemical” is further defined as “any chemical which through its chemical action on life processes can cause death, temporary incapacitation or permanent harm to humans or animals. This includes all such chemicals, regardless of their origin or of their method of production, and regardless of whether they are produced in facilities, in munitions or elsewhere.” The Chemical Weapons Convention Schedules of Chemicals identify certain toxic
chemicals and precursors for application of the verification measures called for in the treaty.
These definitions are familiar to Chemical Weapons Convention National Authorities and are well suited for successful implementation of the treaty and achievement of its goals. They further address the fact that many toxic chemicals and precursors have legitimate, peaceful uses. The Chemical Weapons Convention recognises that such chemicals should not be
considered to be chemical weapon when they are (1) used for purposes not prohibited under the Chemical Weapons Convention (e.g., industrial, agricultural, research, medical, pharmaceutical, or protective purposes) and (2) are of types and quantities that would be consistent with these peaceful purposes.
However, for the objectives of the Australia Group Common Control List Handbook, a more traditional approach to chemical weapon-related terminology is taken in order to succinctly describe the potential roles of various chemicals (and equipment) in a chemical weapon
program. In the Australia Group Common Control List Handbook, a toxic chemical that could be used as a chemical weapon will be simply referred to as a chemical weapon agent; precursors to chemical weapon agents are not considered to be chemical weapon in the context of the Australia Group Common Control List Handbook, but rather chemicals that can be used to produce chemical weapon agents.
Chemical weapon agents typically are grouped into classes based upon their effect on living organisms. These biochemical effects are directly related to the structure and reactivity of the agent molecules; therefore, substances in a given agent category frequently have similar chemical structures (i.e., the same types of atoms connected in similar ways).
Description of Chemical Weapons
The general and traditional definition of a chemical weapon is a toxic chemical contained in a delivery system, such as a bomb or shell.
The Convention defines chemical weapons much more generally. The term chemical weapon is applied to any toxic chemical or its precursor that can cause death, injury, temporary incapacitation or sensory irritation through its chemical action. Munitions or other delivery devices designed to deliver chemical weapons, whether filled or unfilled, are also considered weapons themselves.
The toxic chemicals that have been used as chemical weapons, or have been developed for use as chemical weapons, can be categorised as choking, blister, blood, or nerve agents. The most well known agents are as follows: choking agents-chlorine and phosgene, blister agents (or vesicants)-mustard and lewisite, blood agents-hydrogen cyanide, nerve agents-sarin, soman, VX.
Of course some toxic chemicals, and/or their precursors, are utilised globally in industry. For example, toxic chemicals are employed as basic raw material, or as anti-neoplastic agents, which prevent the multiplication of cells, or as fumigants, herbicides or insecticides. Such chemicals are considered chemical weapons if they are produced and stockpiled in amounts that exceed requirements for those purposes that are not prohibited under the Convention.
The Convention is designed to ensure that toxic chemicals are only developed and produced for purposes unrelated to chemical weapons. Chemical technology must not be misused, and the OPCW has a mandate to monitor chemical industry to make certain that this is the case. To aid the OPCW in this task, the Convention divides toxic chemicals and precursors that could be used as chemical weapons or that could be used in the manufacture of chemical weapons into three Schedules. Schedule 1 chemicals have been used as chemical weapons in the past and/or have very few or no peaceful uses, and thus pose the most direct threat to the Convention. Schedule 2 chemicals are primarily precursors to Schedule 1 chemicals and most have some industrial uses. Schedule 3 chemicals are produced in large quantities commercially but in some cases were used as chemical warfare agents and can also serve as precursors to Schedule 1 or 2 chemicals. Production facilities of many organic chemicals termed discrete organic chemicals are also subject to declaration requirements and verification activities.
To help facilitate the destruction and verification process, chemical weapons are formally divided into three Categories. Into Category 1 fall Schedule 1 chemical agents and munitions filled with Schedule 1 agents. Category 2 covers munitions filled with other toxic chemicals and any other weaponised chemical agents-other than those in Schedule 1. Unfilled munitions and devices, and any other equipment specifically designed to aid in the deployment of chemical weapons, fall into Category 3. Destruction timelines are set by the Convention for the destruction of all three Categories of chemical weapons. 
Chemical Weapon as defined by the Chemical Weapons Convention
A common conception of a chemical weapon comprises a toxic chemical contained in a delivery system such as a bomb or artillery shell. While technically correct, a definition based on this conception would only cover a small portion of the range of things the CWC prohibits as “chemical weapons” . There are several reasons for the broad CWC definition, which, as described in Fact Sheet 2, includes munitions, precursor chemicals and equipment connected with production and use of chemical weapons. For one thing, CW components-a toxic chemical and delivery system, for example- may be stored separately, each in and of itself less than a fully developed weapon. In the case of binary munitions, a nonlethal chemical may actually be stored within a munition, only to be mixed with a second chemical inserted into the munition shortly before firing, and the toxic product disseminated upon arrival at the target.
The complexity of the chemical weapon definition needed to meet the objectives of the Convention can be seen when considering “dual-use” items and technologies. Many chemicals used widely for peaceful and commercial purposes can also be used as, or applied to the creation of, chemical weapons. To address the potential threat posed by these chemicals, the CWC definition of a chemical weapon had to be as comprehensive as possible.
At the same time, however, care had to be taken not to define chemical weapons in a way that unnecessarily hindered legitimate uses of chemicals and the economic and technological development to which such uses may lead. While providing for the prevention of production or stockpiling of chemical weapons, the definition could not result in restrictions of any State Party’s right to acquire and retain conventional weapons and their associated delivery systems nor the right to produce and use chemicals for peaceful pur-poses. The definition eventually adopted allowed for a balanced approach under which the Convention’s objectives can be met while the rights of States Parties are retained.
To preclude contravention of the treaty’s intent by separation of chemical weapons into component parts, the Convention defines each component of a chemical weapon as a chemical weapon-whether assembled or not, stored together or separately. Anything specifically designed or intended for use in direct connection with the release of a chemical agent to cause death or harm is itself a chemical weapon. Specifically, the definition is divided into three parts:
The first part of the definition states that all toxic chemicals and their precursors, except when used for purposes permitted by the CWC in specified quantities, are chemical weapons. Toxic chemicals are defined as “any chemical which through its chemical action on life processes can cause death, temporary incapacitation or permanent harm to humans or animals.” Precursors are chemicals involved in production stages for toxic chemicals. Except for very limited application for protection programmes, medical research or other permitted purposes, the production of some toxic chemicals with virtually no legitimate peaceful uses, such as sarin (GB), is banned. Determining whether genuinely dual-use chemicals are chemical weapons is more difficult. For example, chemicals such as chlorine, phosgene and hydrogen cyanide (AC)-all of which were used during World War I as chemical weapons-are also key ingredients in numerous commercial products. To make the determination, toxic dual-use chemicals are subjected tothe so-called general purpose criterion.
According to the general purpose criterion, a toxic or precursor chemical may be defined as a chemical weapon depending on its intended purpose. Put simply, a toxic or precursor chemical is defined as a chemical weapon unless it has been developed, produced, stockpiled or used for purposes not prohibited by the Convention. The definition thus includes any chemical intended for chemical weapons purposes, regardless of whether it is specifically listed in the Convention, its Annexes or the schedules of chemicals. The CWC does not, however, expressly state what “chemical weapons purposes” are. Instead, it lists those purposes that are not prohibited by the Convention. Chemicals intended for purposes other than these are considered chemical weapons.
A basic component of the general purpose criterion is the principle of consistency. A toxic chemical held by a State Party and in agreement with this principle will not only be produced, stockpiled or used for a legitimate purpose, but also will be of a type and quantity appropriate for that purpose.
The second part of the Convention’s definition of a chemical weapon includes any munitions or devices specifically designed to inflict harm or cause death through the release of toxic chemicals. Among these could be mortars, artillery shells, missiles, bombs, mines or spray tanks. In order to be defined as a chemical weapon, however, the items in question would have had to have been designed and built with the intent to release any of the toxic chemicals in the first part of the definition.
Thirdly and lastly, any equipment specifically designed for use “directly in connection” with employment of the munitions and devices of the second part of the definition are identified as chemical weapons. As with the second part, the principle of specificity applies. Thus, only that equipment specifically designed to be used with munitions and devices or toxic chemicals and their precursors falls under the chemical weapons definition.
One other definition of relevance is that of riot control agents (RCAs), the use of which as a method of warfare is prohibited by the CWC. A riot control agent is defined as being “any chemical not listed in a schedule which can produce rapidly in humans sensory irritation or disabling physical effects which disappear within a short time following termination or exposure” .
Regarding herbicides, the prohibition of their use as a method of warfare is recognised in the CWC Preamble. However, herbicides are not defined specifically in the Convention and there are no specific declaration or destruction requirements related to them. This does not preclude application of the general purpose criterion to chemicals traditionally considered as herbicides. In other words, if the intended purpose of a toxic chemical is prohibited by the Chemical Weapons Convention, the chemical shall be considered a chemical weapon.
Also deserving of mention are toxins – toxic chemicals produced by living organisms. Although also considered to be biological weapons, toxins are addressed by the CWC. The development, production and stockpiling of toxins for purposes of warfare are prohibited under the Biological and Toxin Weapons Convention (BTWC). Parties to that treaty that possess toxin weapons agree to destroy them. However, inasmuch as toxins are chemicals themselves and can have chemical weapons applications, they are automatically covered by the definitions listed above for chemical weapons and toxic chemicals. (Two toxins, ricin and saxitoxin, are in fact explicitly listed in Schedule 1.) This is due to the fact that a large number of toxins can be synthesised in laboratories without resorting to the organisms that produce them in nature. Moreover, a number of toxins are also synthetic dual-use chemicals, meaning that under the CWC, at least, amounts needed for legitimate activities are permitted.
Several unresolved issues remain regarding the definition of chemical weapons. One has to do with the status of old chemical weapons. Old chemical weapons fall into two categories: 1) chemical weapons produced before 1925 and 2) chemical weapons produced between 1925 and 1946 “that have deteriorated to such an extent that they can no longer be used as chemical weapons.” Old chemical weapons of the first category may be “destroyed or disposed of” as toxic waste in accordance with the relevant State Party’s national laws after the OPCW Secretariat has confirmed that they were indeed produced before 1925. Those weapons that fall into the second category of old chemical weapons are to be destroyed in accordance with the same conditions as other chemical weapons, though the time limits and the order of destruction can be changed, subject to approval by the Executive Council. Guidelines for determining whether weapons in this category have deteriorated enough to be unusable, however, have yet to be decided, though efforts to do so are ongoing. Categorisation of such weapons therefore remains problematic. 
1. Information published in the Chemical Weapons Convention website.
Hierarchical Display of Chemical weapon
Concept of Chemical weapon
Characteristics of Chemical weapon
Translation of Chemical weapon
- Spanish: Arma química
- French: Arme chimique
- German: Chemische Waffe
- Italian: Arma chimica
- Portuguese: Arma química
- Polish: Broń chemiczna
Thesaurus of Chemical weapon
International Relations > Defence > Military equipment > Weapon of mass destruction > Chemical weapon
Environment > Deterioration of the environment > Degradation of the environment > Defoliation > Chemical weapon