Chemical Weapons and Chemical Warfare Agents - CW
CW, Chemical weapons and chemical 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.
The primary groups of Chemical Agents are:
Nerve Agents, Mustard Agents, Hydrogen Cyanide, Tear Gases, Arsines, Psychotomimetic
Agents, and Toxins (Continued Below)
Protection Against Chemical Weapons
Source: A FOA Briefing Book on Chemical Weapons
There are four main cornerstones in the protection against chemical weapons, all of which
are largely dependent upon each other to provide optimum effect. These four are:
physical protection
body protection
respiratory protection
collective protection
medical protection
Even though individuals may be trained and have access to the best possible protective
equipment, there will be a performance degradation once they have started to use the
protective equipment. This is particularly noticeable in warm weather. Impermeable CW
protective suits and also to some extent permeable suits which "respire" are
very hot. During hard physical work, the surplus energy cannot be removed and therefore
the individual will rapidly become overheated and may suffer from heat collapse. This
implies a major complication for CW protection during the summer, particularly in very hot
areas such as deserts. Performance is also degraded in cooler weather.
Protective equipment is relatively clumsy, which implies that most tasks require longer to
perform than normal. Endurance decreases and when a protective mask is worn, it becomes
difficult to communicate with people in the neighbourhood.
Decontamination of Chemical warfare Agents
An introduction to methods and chemicals for decontamination
Introduction
In protection against chemical warfare agents the decontamination is an important
unavoidable part. The aim of decontamination is to rapidly and effectively render harmless
or remove poisonous substances both on personnel and equipment. High decontamination
capacity is one of the factors which may reduce the effect of an attack with CW agents. In
this way, it may act as a deterrent.
The need for decontamination should be minimized to the extent possible by contamination
avoidance and early warning. Equipment can be covered, for example, or easily
decontaminated equipment can be chosen by means of suitable design and resistant surface
cover.
Decontamination is time consuming and requires resources. Nerve agents and substances
causing injury to the skin and tissue are easily soluble in, and penetrate many different
types of material, such as paint, plastics and rubber, all of which renders
decontamination more difficult. If CW agents have penetrated sufficiently deep, then toxic
gases can be released from the material for long periods. By adding substances which
increase the viscosity of a CW agent, its persistence time and adhesive ability can be
increased. These thickened agents will thus be more difficult to decontaminate with liquid
decontaminants since they adhere to the material and are difficult to dissolve.
Good body and respiration protection is essential for the maintenance of operational
capacity for a limited period after a CW attack. If the aggressor has used persistent
substances, the unit generally must be decontaminated when regrouping or reorganizing.
The need for decontamination can only be established by means of detection. If detection
is not possible, then decontamination must be done solely on suspicion of contamination.
Decontaminants
All decontamination is based on one or more of the following principles:
to destroy CW agents by chemically modifying them (destruction),
to physically remove CW agents by absorption, washing or evaporation,
to physically screen-off the CW agent so that it causes no damage.
Most CW agents can be destroyed by means of suitable chemicals. Some chemicals are
effective against practically all types of substances. However, such chemicals may be
unsuitable for use in certain conditions since they corrode, etch or erode the surface.
Sodium hydroxide dissolved in organic solvent breaks down most substances but should not
be used in decontaminating skin other than in extreme emergencies when alternative means
are not available.
Decontaminants that have effect only against a certain group of substances can be an
alternative in favor of a substance with general effect. The condition is that they will
have a faster and better effect against the substance in question and/or a milder effect.
Examples of such substances are chloramine solutions which are often used to decontaminate
personnel. These have good effect against mustard agent and V-agents but are ineffective
against nerve agents of G-type (sarin, soman, tabun). A water solution of soda rapidly
renders nerve agents of G-type harmless but when used in connection with V-agents, it
produces a final product which is almost as toxic as the original substance. This does not
prevent V-agents being washed-off with a soda solution, provided a sufficient amount is
used. However, the final product will always be poisonous.
The disadvantage of specifically-acting decontaminants is partly that it is necessary to
know which CW agent has been used and partly that access to several different types of
decontaminating substances is required.
Decontamination methods
CW agents can be washed and rinsed away, dried up, sucked up by absorbent substances, or
removed by heat treatment. Water, with or without additives of detergents, soda, soap,
etc., can be used, as well as organic solvents such as fuel, paraffin and carburettor
spirit. Emulsified solvents in water can be used to dissolve and wash-off CW agents from
equipment.
When decontaminating by washing, consideration must be taken to the poisonous substance
remaining in the decontaminant unless the CW agent has first been destroyed. The
penetration ability of a CW agent can be enhanced when mixed with solvent. Today, there is
an international development towards chemically resistant paints and materials, which
implies that water-based methods will become more effective. However, the need for
penetrating decontamination methods will remain for many years.
When washing with water - particularly with hot water and detergent - the CW agent will
often be decomposed to some extent through hydrolysis. Detergents containing perborates
are particularly effective in destroying nerve agents. Without an addition of perborates
in the detergent, the hydrolysis products of V-agents may still remain toxic unless the pH
is sufficiently high. Mustard agent is encapsulated by the detergent and, consequently,
the hydrolysis rate decreases in comparison with clean water. However, the low solubility
of mustard agent makes it difficult to remove without the addition of detergent, but the
water used will still contain undestroyed mustard agent.
Small areas of terrain may be decontaminated by removal of the top-soil. Another
alternative is to cover the soil with chlorinated lime powder (sludge), which is a
decontaminant with general effect and which releases active chlorine. CW agents which have
penetrated into the soil, from where they release toxic vapour, are screened-off since the
gas and liquid is destroyed by the chlorinated lime.
The physical screening-off of CW agents by covering them can be done in the terrain by
spreading a layer of soil or gravel over the contaminated area. The effect will be
improved if bleaching powder is mixed into the covering material. Another example of
covering is to use special plastic foil to cover contaminated areas inside vehicles. In
this way, the personnel will be protected against transfer of liquid.
Individual Decontamination
The most important decontamination measure naturally concerns the individual. If it is
suspected that skin has been exposed to liquid CW agents, then it must be decontaminated
immediately (within a minute). All experience confirms that the most important factor is
time; the means used in decontamination are of minor importance. Good results can be
obtained with such widely differing means as talcum powder, flour, soap and water, or
special decontaminants.
In complete decontamination, clothes and personal equipment must also be decontaminated.
If clothes have been exposed to liquid contamination, then extreme care must be taken when
undressing to avoid transferring CW agents to the skin. There may be particular problems
when caring for injured since it may be necessary to remove their clothes by cutting them
off. This must be done in such a way that the patient is not further injured through skin
contact with CW agents. During subsequent treatment it is essential to ensure that the
entire patient is decontaminated to avoid the risk of exposing the medical staff to the CW
agents.
In most countries, a soldier's equipment includes means for individual decontamination,
generelly a mixture of chlorinated lime and magnesium oxide. This decontaminant works by
absorbing liquid substances and also by releasing free chlorine which has a destructive
effect on CW agents. The dry powder also has good effect on thickened agents since it
bakes together the sticky substance which makes it easier to remove. Personal
decontaminants containing chlorinated lime have, however, an irritating effect on the
skin. Consequently, comprehensive use should be followed by a bath or shower within a few
hours.
Liquid personal decontaminants are common in some countries. Sodium phenolate or sodium
cresolate in alcohol solution are used for individual decontamination of nerve agents.
Chloramines in alcohol solution, possibly with additional substances, are commonly used
against, e.g., mustard agent. Instead of liquid individual decontaminants, it is possible
to use an absorbent powder such as bentonite ("Fuller's Earth"). In the U.S.A.
the wet method formerly used was replaced by a decontaminant powder based on a mixture of
resins, which decompose CW agents, and an absorbent.
A factor common to all individual decontaminants is that they can effectively remove CW
agents on the surface of the skin. However, they have only limited ability to remove CW
agents which have become absorbed by the skin, even though very superficially. CW agents
that have penetrated into the skin therefore function as a reservoir which may further
contribute to the poisoning also after completed decontamination.
In some cases, a wet method may give a better result in decontaminating deeply penetrated
agents than a dry method. Reports from France indicate that a solution of potassium
permanganate gives effective destruction of CW agents on the surface of the skin and also
a certain penetrating effect. There are also individual decontaminants which can
simultaneously function as a protective cream for use as a prophylactic. Canada has
developed a mixture of a reactive substance (potassium 2,3-butadion monoximate) in
polyehylenglycol, which has both these properties. It can be applied to the skin either as
a cream or with a moist tissue.
Decontamination of Equipment
Immediate decontamination of personal equipment and certain other kinds of smaller
equipment is generally done with individual decontaminants. However, these substances are
only capable of decontaminating liquid CW agents covering the surface. The decontamination
is mainly done to prevent further penetration into the material and to decrease the risk
when handling the equipment.
CW agents easily penetrate different materials and into crevasses and will thus be
difficultly reached by methods only designed for superficial decontamination. When a CW
agent has penetrated into the surface, it is necessary to use some kind of
deep-penetrating method. If such a method cannot be used, then it must be realised that
the equipment cannot be used for a long period. Depending on the type of CW agent used and
prevailing weather, i.e., temperature, wind velocity and precipitation (water solubility),
the "self-decontamination" may take many days or even weeks. The absorption into
the surface and natural chemical degradation are important factors influencing the
self-econtamination period.
Example of self-decontamination times for contamination on metal surfaces and on a typical
(non-resistant) paint at +15 oC, 4 m/s and 2 mm large droplets.
____________________________________________________________
Substance
Liquid Gas
____________________________________________________________
Untreated metal surface
Soman
< 5 hr < 5 hr
Mustard agent < 20 hr < 20 hr
VX
6-8 days 6-8 days
Painted metal surface
Soman
3-4 hr 1,5 days
Mustard agent 1 day 3 days
VX
6 days 12-15 days
____________________________________________________________
Note. The times for "liquid" only indicate when the surface is free of liquid,
e.g., no liquid is transferred when touched. There is still a risk involved in contact and
inhalation through release of gas from surfaces where the CW agent has penetrated deeply.
The diffusion and evaporation rate of CW agents from material is speeded-up considerably
when heated. Other methods utilizing heat are steam or hot air which is blown against the
contaminated surface. Decontamination by boiling is also an effective method. The
advantage in comparison with heat is that hot water hydrolyzes and renders harmless many
types of CW agents. The method may be of some interest in small-scale decontamination of
rubber material, e.g., protective masks.
Decontamination of CW agents which have penetrated deeply into the surface can also be
done with decontaminants which are capable of penetrating the contaminated material. There
are different substances with varying properties. A modern decontaminant is the German
Münster emulsion which consists of calcium hypochlorite, tetrachlorethylene, emulsifier
("phase transfer" catalyst) and water. Instead of tetrachlorethylene, the more
environmentally harmless xylene is sometimes used.
In order to facilitate decontamination and decrease the risk when touched, the material
can be painted with chemical resistant paint systems, e.g., polyurethane paint. Design of
the equipment is also of major importance for ease of decontamination.
Personal Protection
During an attack with CW agents, the respiratory system must be protected against aerosols
and gases in the air at the same time as the rest of the body must be protected against
direct contact with CW agents in the form of liquid or solid particles. After the attack,
the body must be protected against contact with CW agents on the ground and on equipment.
In addition, the respiratory system must be protected against evaporating gas.
Protection for the Respiratory System
The level of protection provided by a protective mask or respirator against penetration of
biological and chemical weapons through the respiratory system depends on: advance
warning, time required to don the mask, ability of the filter to absorb the CW agent, and
degree of leakage.
CW agents may reach the people on the ground already 5-10 seconds after an attack. The
agents may either be in the form of liquid droplets affecting the skin or clothing, or as
a cloud of gas or aerosol. Already a few breaths from such a cloud may supply an injurious
or lethal dose. In cases of surprise attacks, it is therefore of vital importance to
rapidly don the protective mask so that it fits tightly against the face.
The best protection against surprise attacks is obtained by continuously carrying some
kind of respiratory protection. A protective mask to be used for long periods must be
comfortable. A solution tested in some countries is a facelet, a semi-protective mask
which is supposed to be more comfortable to wear but does not provide as good protection
as a normal protective mask.
However, experience has shown that the facelet is not a good alternative and,
consequently, efforts are made to make the conventional protective mask as comfortable as
possible to wear. This can be achieved partly by making a broad and flexible sealing edge
and also by reducing the physiological load in the mask.
In modern protective masks, the inhalation resistance has been reduced by decreasing the
air resistance in the filter. Exhalation resistance is reduced by means of a carefully
adjusted outlet valve with a large flow area. Protective masks are designed so as to
reduce the dead space.
Other characteristics of the new generation of protective masks are a large field of
vision and very small leakage, which in turn implies high protection. Despite this, a
small proportion of the wearers will still receive insufficient protection either because
of diverging face shape or inability to don the mask in the best way. This proportion can
be reduced by better training and education but cannot be entirely eliminated.
A device for speech communication is included in all of the new masks. The earlier
solution, a speech membrane, is now being replaced by a speech horn, which is easier to
manufacture. A speech horn also gives largely the same effect as a speech membrane. New
material for the filter canisters, e.g., fibre-reinforced plastic, gives them better
resistance to external influence.
New technical solutions to the problem of combining protective mask and glasses are
available, which permit correction of visual defects without degrading the protection.
A protective mask must be capable of adaptation to different face shapes and is therefore
manufactured in an elastic material. Modern masks are almost always made of some kind of
rubber material. If high demands are placed on a good protective ability to permeation of
CW agents, it often results in the choice of halogenated butyl rubber.
A demand frequently placed today on a protective mask is that it can be worn for at least
24 hours. The mask must then also permit the intake of liquids.
The filter in a protective mask consists of two parts; an aerosol filter and a gas filter.
The aerosol filter is built up of a layer of glass fibres where the spacing between the
fibres is large in relation to the size of the particles to be filtered. Consequently, an
aerosol filter of this kind does not work by screening or filtering off the particles. The
particles are removed mainly when they collide with the fibres, to which they adhere. If
it is a volatile substance that adheres, it may subsequently evaporate from the aerosol
filter. Consequently, it is important to design a filter whereby the gas filter component
is located after the aerosol filter.
The gas filter component of the protective filter consists of active carbon. Recently
other adsorbants, e.g., different synthetic polymers and zeolites have been tested but
none has proved as widely applicable as active carbon. Neither have any other absorbents
been found to have higher uptake ability for CW agents than active carbon.
Active carbon is produced by heat-treating different organic materials. A number of
commonly-used materials are peat, coconut shell and coal. The material is activated
byheating it together with carbon dioxide or steam to 800-1000 degrees Centigrade. The
carbon so obtained contains numerous pores and cavities and under magnification looks
rather like a face sponge. Active carbon of the type used in protective masks has a total
area of 1 000 -1 500 m2 per gram.
By selecting different starting materials and conducting the activation in different ways,
the active carbon obtained has different degrees of pore distribution. Carbon with large
pores is the most suitable for cleaning water, whereas carbon with small pores is better
for removing gas. Pore distribution and pore size are also important for the carbon's
ability to absorb water. The particle size distribution is also important and particularly
for properties such as air resistance and the protective ability against different gases.
Certain low-molecular CW agents such as hydrogen cyanide and cyanogen chloride are poorly
absorbed by active carbon. In order to improve protection against these substances, the
carbon is impregnated with metallic salts of copper, chromium and sometimes also silver.
Further impregnation with organic substances also occurs, the most common additive being
triethylendiamine (TEDA).
Certain types of carbon-fibre based material have higher sorption capacity than normal
granulated active carbon. Use of carbon fibres of this kind in a gas filter offers
advantages such as lower pressure drop, smaller volume and lower weight.
The degree of leakage in modern filters is maximally 0.001 per cent and, in extreme cases,
the filter provides protection against at least 10 but probably up to 100 attacks before
CW agents start to leak through. If the protective mask is used in a non-contaminated
atmosphere the filter will gradually become loaded since it absorbs moisture and pollution
from the air. Long-term use or unsuitable storage may lead to the protective ability
against certain CW agents becoming deteriorated.
Protection Against CW Agents in Liquid Form
A direct CW attack not only results in gases and aerosols but also droplets of liquid
which penetrate the body through the skin. Consequently, respiratory protection is
insufficient and this must be complemented with body protection. The amount of substance
absorbed by the skin is determined by the following factors: CW agent, the period elapsing
before decontamination, the efficiency of the decontaminant, the size of the contaminated
area and the type of clothing.
A condition for high levels of survival after a direct attack with CW agents in liquid
form is either that the entire body surface can rapidly be protected by some kind of
cover, or that protection is incorporated in the uniform of the soldiers or clothing of
civilians.
Protection by covering serves two purposes: it is mainly designed to prevent droplets
falling on bare skin but it is also designed to reduce the need of subsequent
decontamination of personal equipment.
Body Protection
The oldest types of protective clothing against CW agents consists of rubber
clothing which, together with gloves and boots, cover the entire body apart from that
protected by the mask. Clothing of this kind is usually characterized as impermeable. This
not only refers to the fact that CW agents cannot pass through the material but also the
fact that perspiration released from the skin is also prevented from passing out.
Consequently, to wear clothing of this kind for longer periods may be extremely
uncomfortable and in hot climates the period during which protective clothing of this kind
can be worn will be very short.
In order to reduce the heat load, permeable clothing has been designed where a layer of
finely distributed active carbon, either bound in polyurethane foam or as particles of
carbon, is bound between two layers of textile. A layer of this kind consisting of active
carbon permits water vapour released from the body to pass through. The active carbon
absorbs CW agents and thereby prevents them from passing through to the skin. This layer
of carbon is never used alone but is combined with different textiles.
A CW combat suit is an example of clothing made of permeable material. It is often
designed in the same way as a battle dress. The largest difference is that inside the
impregnated outer material there is a layer of active carbon on a suitable carrier. The CW
combat suit can be used instead of a battle dress or as an overall placed over the
uniform. An alternative is to use inner clothing with a layer of carbon which is worn
underneath the normal uniform. It is impossible to conduct warfare for longer periods
outdoors in CW environment without having access to CW combat suits.
Impermeable suits will also in the future be used in severely contaminated environments,
e.g., during decontamination. The heat load can be reduced by ventilating the clothing
with fans. However, this solution is too vulnerable to be used for soldiers in combat.
In order to achieve shortterm CW protection, it is possible to use overalls made of
different plastic material, e.g., the C-Cover dress.
Development of Protective Masks - CW Masks - Gas Masks
The historical development of military protective masks or respirators may be
roughly characterized as four different generations:
1. The First World War. The first primitive masks were quickly developed after the initial
use of CW agents during the First World War. The illustration shows an American mask from
1918. The basic frame of the mask is made of leather.
2. The Second World War. The protective capability was greatly improved during the period
between the wars when natural rubber was used to make the basic frame of the mask. The
elastic rubber material allowed the mask to better adapt itself to different shaped faces.
3. After the Second World War and up to about 1980. In about 1950, there was a more
general trend to equip the mask with an inner mask. This must be regarded as a technical
break-through. The inner mask solved the problem with misting of the visors also in low
winter temperatures.
4. The current generation of protective masks. During the 1980's and 1990's, protective
masks were improved in many ways, as regards for example comfort, fit and the intake of
liquids. It might therefore be justified to regard them as the fourth generation of
protective masks.