photo courtesy of International Civil Defence Organisation
decontamination of CW

Chemical Warfare (CW) Attack & Decontamination



chemical warfare decontamination

The aim of decontamination is to rapidly and effectively render harmless, or remove, poisonous substances on both personnel and equipment. The capacity to decontaminate both equipment and personnel is one of the factors that may reduce the effectiveness of an attack with CW agents. In this way, it may act as a deterrent. The need for decontamination should be minimized by taking preventative measure and early warning of a CW attack is a vital part of defence against the use of these weapons. Military and industrial equipment can be covered, for example, or equipment that is designed to be easily decontaminated can be chosen as a preference to other equipment. These factors have to be considered because decontamination is time–consuming and requires resources.

Nerve agents and substances causing injury to the skin and tissue are easily soluble and penetrate many different types of material, such as, paint, plastics and rubber. This makes decontamination more difficult. If CW agents have penetrated sufficiently deep, then toxic gases can be released from these materials for long periods of time. CW agents are made more effective as weapons by adding substances that increase their viscosity; this increases their persistence–time and makes them more adhesive. These thickened agents will thus be more difficult to decontaminate with liquid decontaminants since they adhere to the material and are difficult to dissolve. CW agents can also be difficult to detect. If these agents are suspected and detection equipment is not available, then everything has to be decontaminated.

Decontaminants

All decontamination is based on one or more of the following principles:
  1. To destroy CW agents by chemically modifying them (destruction);

  2. physically to remove CW agents by absorption, washing or evaporation;

  3. physically to 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. For example, sodium hydroxide dissolved in organic solvent breaks down most substances but should not be used for decontaminating skin (other than in extreme emergencies when there is no other alternative).

Chloramine solutions are often used to decontaminate personnel. These are effective 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 if these agents are used in connection with V–agents, a water solution of soda produces a final product that is almost as toxic as the original nerve agents are.  This does not prevent V–agents being washed–off with a soda solution, provided a sufficient amount is used, however, the used decontaminant will always be poisonous.

To use a specific decontaminant it is necessary to know exactly what CW agent has been deployed. If using a specific decontaminant, rather than general, decontaminants, a large stock of different contaminants has to be on hand, along with the means for accurate detection of the CW agent or agents used.

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 given to the poisonous substance remaining in the decontaminant unless the CW agent has first been destroyed. There is a risk that the penetration ability of a CW agent can be enhanced when mixed with solvent. Today, there is an international development towards the use of water–based decontamination methods, 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 topsoil. Another alternative is to cover the soil with chlorinated lime powder (sludge), which is a decontaminant with general effect releasing active chlorine. CW agents that have penetrated into the soil and are releasing toxic vapour are screened off since the toxic 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.

Individual Decontamination

decontaminating
Decontamination of the individual is most important. 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 being scrubbed over the body.

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 the 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 body of the patient is decontaminated to avoid the risk of exposing the medical staff to the CW agents.

In most countries, individual decontamination is carried out by using a mixture of chlorinated lime and magnesium oxide. This decontaminant works by absorbing liquid substances and also by releasing free chlorine that 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 so decontamination 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 and an absorbent, which decompose CW agents.

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 that have become absorbed by the skin, even though very superficially. CW agents that have penetrated into the skin therefore function as a reservoir that may further contribute to the poisoning that can continue even after completed decontamination.

In some cases, a wet method, rather than a dry method, may give a better result in decontaminating deeply penetrating agents. Reports from France indicate that a solution of potassium permanganate gives effective destruction of CW agents on the surface of the skin and also has a certain penetrating effect. There are also individual decontaminants that 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. 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 realized 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), this "self–decontamination" may take many days or even weeks.



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