 |
|
 Protective Equipment An attack with CW agents achieves maximum effect when it is directed against an unprotected unit. However, by taking relatively simple protective measures, the injuries can be reduced considerably. In principle, it is possible to create practically complete CW protection but generally a slightly lower level is considered sufficient. If the protective level is sufficiently high, an aggressor will probably realize that a CW attack will not be cost effective. Effective CW protection requires the building-up of some kind of "barrier" around the soldier. However, the more the soldier is protected from the ambient conditions, the greater his mobility is restricted.
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:
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 ask. 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., fibber-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 fibbers where the spacing between the fibbers 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 fibbers, 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 adsorbents, 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 by heating it together with carbon dioxide or steam to 800-1000C. 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-fibber based material have higher sorption capacity than normal granulated active carbon. Use of carbon fibbers o 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 deteriorate .
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 he 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. 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 o 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 vapor 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 short-term CW protection, it is possible to use overalls made of different plastic material, e.g., the C-Cover dress.
Development of Protective Masks The historical development of military protective masks or respirators may be roughly characterized as four different generations:
Control of Air Flow in a Protective Mask The inhalation air is first purified during passage through the filter. The air that has passed through the filter is relatively dry. It is guided up over the visors in order to prevent them from misting. The flow of air then passes through the inner mask and then into the lungs. The exhaled air flows directly from the inner mask through the exhalation valve. The control of the air flow is achieved by valves. A well-functioning inhalation valve is essential for the function of the mask. It must allow air to pass in through the filter but must also prevent the exhaled air from passing out through the filter. During the inhalation phase, the exhalation valve must be fully closed and thereby prevent contaminated ambient air from entering the mask by that route. The task of the inner mask is to prevent the exhaled air from filling up the entire volume inside the mask. In this way, the moist exhaled air is prevented from passing over the visors which might cause troublesome condensation. The inner mask is usually fitted with valves to control the air flow. However, it is fully possible to design a functional inner mask without any valves.
Fitting Protective Masks A measure of the protective ability of a mask is given by the total inward leakage. This consists of the sum of the leakage in the filter, the leakage through the fit, leakage through the exhalation valve and any other leakage. Instead, the protection factor of the mask is frequently given:
The protection factor states how much lower the concentration of a pollutant in the air is inside the mask in comparison with the concentration in the ambient air. Laboratory tests with a non-hazardous test substance can easily determine protection factors up to 100 000. In the field, tear gas can be used as a test substance to obtain a rough measure of the protective ability of a mask. The sensitivity in tests with tear gas (CS) is, however, not larger than that it corresponds to a protection factor somewhere in the range between 1 000 and 10 000. Even in a modern mask with a good sealing edge, the fit will start to deteriorate already when the soldier has a 24 h-old beard stubble. The protection will deteriorate with the length of the stubble. Whole beards usually result in very poor protection.
Penetration and Permeation Two special terms are used with regard to protective clothing, penetration and permeation. Penetration implies that gases or liquids pass through seams or holes, etc. in a protective suit (non-molecular passage). Permeation implies that gases or liquids diffuse through the material, e.g., rubber, in a protective suit (molecular passage).
|
 |