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Collective Protection Against Chemical Weapons Source: A FOA Briefing Book on Chemical Weapons Protection against CW agents can be arranged for the individual soldier in the field by means of a protective mask and special clothing. In many cases, a group of people can use collective protection, e.g., in tents, vehicles or special shelters. People under a roof, e.g., indoors or in covered vehicles, are not only protected against CW agents in liquid form but also receive a certain degree of protection against aerosols and gases since the air turnover in such spaces is lower. The concentration increases more slowly and there is not such a hurry to don protective masks. The air supplied to shelters is purified in much the same way as in protective masks. The air is drawn through an aerosol filter and a layer of active carbon by means of a fan. Temperature is the limiting factor for the period of residence in a shelter. The more people present the faster the temperature will rise. Normally, some of this heat is removed by conductance through the walls, floor and ceiling of the shelter as well as through continuous ventilation. The capacity of the ventilation system is adapted to make the climate endurable during different times of the year and with a normal load. Ventilation with filtered air in normal individual shelters is calculated to be 1.5-3 m3 per person and hour. In more important and larger shelters, there are two ventilation systems - one for use during peace-time with a relatively high air turnover, up to 10 m3 per person and hour, and the other for use in BC-attacks with filtered air. The time that can be spent in a shelter when the ventilation system is shut down is limited by the decreasing oxygen concentration and the increasing concentration of carbon dioxide in the air. Approximate limits for survival can be placed at 15-13 per cent for oxygen and 4-6 per cent for carbon dioxide. These limits are reached almost simultaneously after ca. 6-8 hours in cases of normal occupation (each person with a floor area of 0.75 m2 and a ceiling height of 2.2 m). Bearing in mind these conditions, it is important to try to use the peace-time ventilation with high turnover of air as long as possible. Advance warning of attacks must then be given in sufficient time to enable the occupants to change to BC ventilation. Requests by personnel exposed to CW agents wishing to enter the shelter during a CW attack or later will imply a difficult problem. The people already in the shelter will be exposed to major risks if anybody attempts to pass through the gas-lock from an area exposed to persistent CW agents. If this must be done, such persons must be first decontaminated and the decontamination result checked. Collective Protection in Vehicles Permanent collective protection in tanks and other combat vehicles can, in principle, be arranged in different ways: By using sealing material in combination with ventilation by purified air. Overpressure in relation to the ambient pressure provides additional safety against inward leakage. This provides a long period of protection. The advantage of this approach is that protective masks need not be worn which is a great benefit if optical instruments, etc., must be used. A disadvantage is that there will be problems if it is necessary to get out of the vehicle into a contaminated environment. This applies particularly if it is subsequently necessary to return to the vehicle. By supplying centrally filtered air under overpressure to each individual protective mask. By means of this system, the breathing resistance in individual filters is avoided. A disadvantage is that the mobility of the soldiers is restricted because of the air hose. However, a change to individual protection is possible at any time when the hose supplying the air is disconnected. The hybrid system consists of a combination of collective overpressure and he option for supply of air via hoses to individual masks. The vehicle crew can then operate in a contaminated environment without masks until the hatch is opened, or the crew space has been penetrated by CW agents. If this occurs, the individual masks with air supply can be donned. This system links the advantages of the above-mentioned approaches. If the vehicle is not equipped with collective protection, then the only possibility remaining is to use personal protective equipment. This is not a particularly satisfactory alternative since sufficient protection can only be obtained if both a chemical warfare suit and a protective mask are worn. This leads to the physiological load being particularly discomforting, especially during summer. In addition, the protective mask used must also allow the soldier to use optical instruments. Back to the Germ Warfare page.