Chemical Warfare Agents

An overview of chemicals defined as chemical weapons


Main Groups


What is a Chemical Warfare Agent?

A United Nations report from 1969 defines chemical warfare agents as " ... chemical substances, whether gaseous, liquid or solid, which might be employed because of their direct toxic effects on man, animals and plants ... ".

The Chemical Weapons Convention defines chemical weapons as including not only toxic chemicals but also ammunition and equipment for their dispersal. Toxic chemicals are stated to be " ... any chemical which, through its chemical effect on living processes, may cause death, temporary loss of performance, or permanent injury to people and animals". Plants are not mentioned in this context.

Toxins, i.e., poisons produced by living organisms and their synthetic equivalents, are classed as chemical warfare agents if they are used for military purposes. However, they have a special position since they are covered by the Biological and Toxin Weapons Convention of 1972. This convention bans the development, production and stockpiling of such substances not required for peaceful purposes.

Today, thousands of poisonous substances are known but only a few are considered suitable for chemical warfare. About 70 different chemicals have been used or stockpiled as CW agents during the 20th century. Today, only a few of these are considered of interest owing to a number of demands that must be placed on a substance if it is to be of use as a CW agent.

  • A presumptive agent must not only be highly toxic but also "suitably highly toxic" so that it is not too difficult to handle.
  • The substance must be capable of being stored for long periods in containers without degradation and without corroding the packaging material.
  • It must be relatively resistant to atmospheric water and oxygen so that it does not lose effect when dispersed.
  • It must also withstand the heat developed when dispersed.


"War Gases" are Seldom Gases

CW agents are frequently called war gases and a war where CW agents are used is usually called a gas war. These incorrect terms are a result of history. During the First World War use was made of chlorine and phosgene which are gases at room temperature and normal atmospheric pressure. The CW agents used today are only exceptionally gases. Normally they are liquids or solids. However, a certain amount of the substance is always in volatile form (the amount depending on how rapidly the substance evaporates) and the gas concentration may become poisonous. Both solid substances and liquids can also be dispersed in the air in atomized form, so-called aerosols. An aerosol can penetrate the body through the respiratory organs in the same way as a gas.

Some CW agents can also penetrate the skin. This mainly concerns liquids but in some cases also gases and aerosols. Solid substances penetrate the skin slowly unless they happen to be mixed with a suitable solvent.


Effects on Vegetation

Flowers and leaves of some plants may change colour if they are exposed to droplets of a CW agent in an attack. Light or matt spots may occur as well as brown discoloration, particularly on leaves. Entire trees, or parts of them, may also get brown discoloration in situations of strong exposure. The discoloration often arises within a few minutes but may also occur after some days.


Classification

CW agents can be classified in many different ways. There are, for example, volatile substances, which mainly contaminate the air, or persistent substances, which are involatile and therefore mainly cover surfaces.

CW agents mainly used against people may also be divided into lethal and incapacitating cathegories. A substance is classified as incapacitating if less than 1/100 of the lethal dose causes incapacitation, e.g., through nausea or visual problems. The limit between lethal and incapacitating substances is not absolute but refers to a statistical average. In comparison, it may be mentioned that the ratio for the nerve agents between the incapacitating and lethal dose is approximately 1/10. Chemical warfare agents are generally also classified according to their effect on the organism.

In order to achieve good ground coverage when dispersed from a high altitude with persistent CW agents the dispersed droplets must be sufficiently large to ensure that they fall within the target area and do not get transported elsewhere by the wind. This can be achieved by dissolving polymers (e.g., polystyrene or rubber products) in the CW agent to make the product highly-viscous or thickened. The result will be that the persistence time and adhesive ability increase which thus complicates decontamination.

Although it may appear that a CW agent can be "custom-made" for a certain purpose, this is not the case. Instead, there is always some uncertainty about the persistence time, the dispersal and the effect.


These Military Chemicals are Not Considered to be Chemical Weapons

Incendiary agents such as napalm and phosphorus are not considered to be CW agents since they achieve their effect mainly through thermal energy. Certain types of smoke screen may be poisonous in extremely high concentrations but, nonetheless, smoke ammunition is not classed as a chemical weapon since the poisonous effect is not the reason for their use. Plants, microorganisms, algae, etc. which produce toxins are not classed as chemical weapons even if the produced toxins belong to that class. Pathogenic microorganisms, mainly viruses and bacteria, are classed as biological weapons.