of toxic nbc material all components of the system may be mounted on a trailer for ground transportation or a pallet for air transport which facilitates the rapid movement of systems to locations requiring the systems it will be appreciated by those familiar with the difficulty of providing a toxic free area tfa that each module of the system is a sealed unit having a floor walls and ceiling welded and or sewn together forming a sealed volume which may be connected to other modules by zipper connections having minimal leakage the important feature is that there is a flow of air through the system toward the source of contamination and that decontamination occurs principally at the downstream end of the air flow there is an over pressure maintained in the tfa which ensures that all air flow is toward the source of contamination as doors are opened and closed and that nothing is permitted into the tfa that has not been through the cca it will be noticed that the zippers 31 of fig4 which comprise the opening into the exit 11 are configured to minimize the escape of air during entry into the cca 12 by opening the zippers in the doors a limited amount the flow of air through the cca 12 can be regulated vents are also included in the end walls of the cca 12 which may be adjusted to ensure adequate flow of air through the cca 12 and to maintain an over pressure in the tfa nbc filter system providing a minimum of 300 cfm and capable of filtering and maintaining an over pressure in three inter connected units at one time up to three complete connected liner units each measuring 14 ft u00d7 24.