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 m 3 per person and hour. 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.