Chemical Warfare Agents
An overview of chemicals defined as chemical
weapons
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.
