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Introduction
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. 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 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 that 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 various
contaminated surfaces.
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 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
belongings 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, such equipment includes means for
individual decontamination, generally 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 polyethyleneglycol, 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 difficulty
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-decontamination period.
"Fact Sheets on
Chemical Warfare Agents, SDE/SEARO, World Health Organization, New
Delhi, India"
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