Decontamination of Chemical Warfare Agents
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Decontamination of Chemical Warfare Agents
An introduction to methods and chemicals for decontamination
Decontamination of equipment
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
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
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, e.g., if the unit has
passed on the fringe of a contaminated area.
All decontamination is based on one or more of the following
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
Decontaminants that have effect only against a certain group of
substances can be an alternative in favour 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.
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, e.g., first-aid stations or gun sites, 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.
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
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
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
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
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 h < 5 h
Mustard agent < 20 h < 20 h
VX 6-8 days 6-8 days
Painted metal surface
Soman 3-4 h 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. The Swedish
decontamination tent is heated with a mixture of hot exhaust gases
and air from a small jet-pulse engine. The tent is used for
decontamination of lighter articles, e.g., personal equipment. The
decontamination container used by the civil defence forces is a
development of the tent and heated with heat-exchanged hot air
from a diesel burner.
The temperature in the tent is kept at about 130 oC and in the
container at 80-130 oC, depending on the type of material to be
decontaminated. Decontamination time varies between two and five
hours depending on the temperature.
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 Mnster emulsion which consists of
calcium hypochlorite, tetrachlorethylene, emulsifier ("phase
transfer" catalyst) and water. Instead of tetrachlorethylene, the more
environmentally harmless xylene is sometimes used.
Decontamination of vehicles and other large objects sometimes is
done with steam and suspension and/or emulsion systems. A
German company has developed special equipment, C8-DADS
(Direct Application Decontamination System), with which the
emulsion is prepared and then dispersed onto the vehicle or the
Generally, it is an advantage to give the material an initial flushing
with water before the chemical solution is added. A Swedish
development of this approach is ongoing, where the intention is to
spray water on, e.g., a vehicle which passes through a flushing arch.
The flushing arch has several jets which are supplied with water
from a powerful pump. Another type of equipment which can use
water from lakes, etc., has been developed by a Norwegian firm.
This is used for both flushing with cold and hot water/steam and
also as a field shower.
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.